Andrea Dodero

Guy Schlatter

Anne Hebraud

Silvia Vicini

Maila Castellano
email: a.castellano@unige.itguy.schlatter@unistra.fr

Anne Hébraud

Polymer-free cyclodextrin and natural polymer-cyclodextrin electrospun nanofibers: A comprehensive review on current applications and future perspectives

Keywords:

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Electrospinning is a simple, versatile, and cost-effective technique that allows the fabrication of polymeric nano-and microfibers starting from a polymer solution or polymer melt (J. Xue et al., 2019). Demonstrated in 1934 by A. Formhals [START_REF] Anton | Process and apparatus for preparing artificial threads[END_REF], electrospinning started to gain considerable interest from the 2000s

and it is nowadays one of the most employed fiber-forming approaches for several purposes [START_REF] Ahmed | A review on electrospinning for membrane fabrication: Challenges and applications[END_REF]Dodero, Alloisio, Castellano, et al., 2020;Dodero, Brunengo, Castellano, et al., 2020;Dodero, Vicini, Lova, et al., 2020;[START_REF] Tebyetekerwa | What Is Next for Electrospinning?[END_REF][START_REF] Thenmozhi | Electrospun nanofibers: New generation materials for advanced applications[END_REF]. Among others, electrospun nanofibers can be efficiently used to encapsulate a great variety of molecules, such as drugs, bioactive compounds and nanoparticles [START_REF] Castellano | Electrospun composite mats of alginate with embedded silver nanoparticles[END_REF][START_REF] Figueiredo | Design of 3D multi-layered electrospun membranes embedding iron-based layered double hydroxide for drug storage and control of sustained release[END_REF][START_REF] Quirós | Bioactive Applications for Electrospun Fibers[END_REF][START_REF] Torres-Giner | A review on electrospun polymer nanostructures as advanced bioactive platforms[END_REF][START_REF] Wen | Electrospinning: A novel nanoencapsulation approach for bioactive compounds[END_REF]. In this sense, cyclodextrins (CDs) offer the chance to obtain functionalized nanofibers with high encapsulation efficiency, enhanced thermal stability, water-solubility, and bioavailability of the encapsulated molecules [START_REF] Costoya | Electrospun fibers of cyclodextrins and poly(cyclodextrins)[END_REF][START_REF] Muthu Kumar | A comprehensive review of electrospun nanofibers: Food and packaging perspective[END_REF]Topuz & Uyar, 2019). However, cyclodextrin-functionalized nanofibers remain a barely explored research field and, to the best of our knowledge, no commercial products currently exist besides an increasing number of original research work has being recently published. To this regard, Costoya et al. [START_REF] Costoya | Electrospun fibers of cyclodextrins and poly(cyclodextrins)[END_REF] recently reviewed the fabrication of cyclodextrin functional nanofibers, whereas Topuz et al. (Topuz & Uyar, 2019) and [START_REF] Vidal | Electrospinning and cyclodextrin inclusion complexes: An emerging technological combination for developing novel active food packaging materials[END_REF] focused the attention on their pharmaceutical and food packaging applications, respectively. By way of example, Figure 1 reports the number of publications per year in the last two decades (i.e., 2000-2020) concerning electrospinning (Figure 1a), functionalized nanofibrous membranes (Figure 1b), cyclodextrins (Figure 1c) and cyclodextrin-functionalized nanofibrous membranes (Figure 1d). Among the great variety of commercial polymers that can be electrospun, naturally occurring materials represent an attractive alternative to synthetic ones [START_REF] Ding | Electrospun polymer biomaterials[END_REF][START_REF] Soares | Electrospinning and electrospray of bio-based and natural polymers for biomaterials development[END_REF]. Indeed, biopolymers, such as polysaccharides and proteins, can be used to fabricate nanofibers with superior biocompatibility, biodegradability, and lower environmental impact compared to industrially derived materials. Nonetheless, their processing is usually more difficult and it requires a series of experimental precautions [START_REF] Bertasa | Agar gel strength: A correlation study between chemical composition and rheological properties[END_REF][START_REF] Ding | Electrospun polymer biomaterials[END_REF][START_REF] Dodero | Alginate-based hydrogels prepared via ionic gelation: An experimental design approach to predict the crosslinking degree[END_REF][START_REF] Kakoria | A Review on Biopolymer-Based Fibers via Electrospinning and Solution Blowing and Their Applications[END_REF][START_REF] Mendes | Electrospinning of food proteins and polysaccharides[END_REF][START_REF] Noruzi | Electrospun nanofibres in agriculture and the food industry: a review[END_REF]. A schematic representation of the most common natural biomaterial-based electrospun mats and their applications is reported in Figure 2. With these premises, aiming to highlight the importance of developing environmentally benign materials, this review aims to provide a comprehensive summary of the recent advances in the preparation of either polymer-free cyclodextrin-based nanofibers, polycyclodextrin-based nanofibers, or natural polymer-based (i.e., polysaccharides and proteins) nanofibers functionalized with cyclodextrins. To this end, after a brief introduction concerning cyclodextrins first and electrospinning then, a critical and complete overview of the current literature is presented and discussed. Finally, a short consideration about the future trends and possibilities is reported together with a conclusion paragraph.

Cyclodextrins

Structure and Properties

Cyclodextrins consist of cyclic oligosaccharides of glucopyranose assuming the structure of a hollow truncated cone (Figure 3b) [START_REF] Sá Couto | Cyclodextrins[END_REF]. The inner cavity of this three-dimensional structure is partially hydrophobic owing to the -CH and -CH2 carbons and ether oxygens, whereas the exterior surface is hydrophilic due to the high number of hydroxyl groups [START_REF] Szejtli | Introduction and general overview of cyclodextrin chemistry[END_REF]. Although several types of CDs exist, the most common ones consist of 6, 7, and 8 glucopyranose units and are named CDs,CDs, andCDs, respectively, with their structure and main properties reported in Figure 3a-c (Del [START_REF] Valle | Cyclodextrins and their uses: A review[END_REF][START_REF] Jansook | Cyclodextrins: structure, physicochemical properties and pharmaceutical applications[END_REF][START_REF] Kurkov | Cyclodextrins[END_REF]. Schematics of inclusion complex formation with blue and green objects representing cyclodextrins (i.e., host molecules) and small molecules (i.e., guest molecules). For example, inclusion complexes with a molar ratio 1:1 have been prepared between CDs and racecadotril [START_REF] Semalty | Cyclodextrin Inclusion Complex of Racecadotril: Effect of Drug-β-Cyclodextrin Ratio and the Method of Complexation[END_REF], with a molar ratio 1:2 between CDs and naproxen [START_REF] Grandelli | Inclusion complex formation of βcyclodextrin and Naproxen: A study on exothermic complex formation by differential scanning calorimetry[END_REF], with a molar ratio of 2:1 between CDs and carvacrol [START_REF] Bethanis | Structural study of the inclusion compounds of thymol, carvacrol and eugenol in β-cyclodextrin by X-ray crystallography[END_REF], and with a molar ratio 2:2 between CDs and linalool [START_REF] Ceborska | Structural investigation of the β-cyclodextrin complexes with linalool and isopinocampheol -Influence of monoterpenes cyclicity on the host-guest stoichiometry[END_REF].

Native CDs are highly crystalline and are known to adopt a cage structure with a herringbone arrangement [START_REF] Saenger | Structures of the common cyclodextrins and their larger analogues -beyond the doughnut[END_REF]. Typically, they present a low solubility that depends on their size, with CDs being the less soluble ones [START_REF] Szejtli | Introduction and general overview of cyclodextrin chemistry[END_REF]. In order to overcome this processing limitation, CDs have been chemically modified to enhance their water solubility mostly by causing a considerable loss of crystallization.

Among others, the most studied are randomly methylated-CDs (MCDs), 2-hydroxypropyl-CDs (HPCDs) and 2-hydroxypropyl-CDs (HPCDs) [START_REF] Crini | Review: A history of cyclodextrins[END_REF][START_REF] Landy | Remediation technologies using cyclodextrins: An overview[END_REF]. Remarkably, an interesting feature of native and modified CDs is represented by their capability to undergo crosslinking/polymerization reactions leading to water-insoluble cyclodextrin-based polymers (polyCDs)

with tailor-made properties [START_REF] Blanchemain | Polyester vascular prostheses coated with a cyclodextrin polymer and activated with antibiotics: Cytotoxicity and microbiological evaluation[END_REF][START_REF] Crini | Review: A history of cyclodextrins[END_REF][START_REF] Morin-Crini | Environmental applications of water-insoluble β-cyclodextrinepichlorohydrin polymers[END_REF][START_REF] Sherje | Cyclodextrin-based nanosponges: A critical review[END_REF].

Cyclodextrin Inclusion Complexes

Cyclodextrins are nowadays applied in many industrial sectors (Q. Liu et al., 2020a;[START_REF] Matencio | Applications of cyclodextrins in food science. A review[END_REF][START_REF] Wankar | Recent Advances in Host-Guest Self-Assembled Cyclodextrin Carriers: Implications for Responsive Drug Delivery and Biomedical Engineering[END_REF][START_REF] Zhang | Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions[END_REF]. The main reason for CDs success is related to their unique ability to form non-covalent host-guest complexes with a variety of small molecules via inclusion in their hydrophobic cavity (G. [START_REF] Chen | Cyclodextrin-based inclusion complexation bridging supramolecular chemistry and macromolecular self-assembly[END_REF][START_REF] Folch-Cano | Inclusion and Functionalization of Polymers with Cyclodextrins: Current Applications and Future Prospects[END_REF][START_REF] Mura | Analytical techniques for characterization of cyclodextrin complexes in the solid state: A review[END_REF]. Depending on both the type of cyclodextrins and hydrophobic molecules, as well as on the formulation conditions, the complexation can occur between a host and a guest molecule, a host and two guest molecules, or two hosts and a guest molecule as represented in Figure 3d (Frömming & Szejtli, 1994;[START_REF] Kim | Preference prediction for the stable inclusion complexes between cyclodextrins and monocyclic insoluble chemicals based on Monte Carlo docking simulations[END_REF][START_REF] Li | Cyclodextrins and Their Applications in Analytical Chemistry[END_REF][START_REF] Mohanty | Host-guest complexation of neutral red with macrocyclic host molecules: Contrasting pKa shifts and binding affinities for cucurbit[]uril and βcyclodextrin[END_REF][START_REF] Song | Inclusion complexation, encapsulation interaction and inclusion number in cyclodextrin chemistry[END_REF]. Cyclodextrin inclusion complexes (CD-ICs) are commonly exploited to protect those molecules that are sensitive to light, oxygen, heat, and chemical reactions, as well as to increase the water solubility of hydrophobic compounds and to preserve highly volatile fragrances/flavours. By way of examples, CD-ICs have been widely proposed in food and beverage products [START_REF] Dos Santos | Novel trends in cyclodextrins encapsulation. Applications in food science[END_REF][START_REF] Fenyvesi | Cyclodextrins in Food Technology and Human Nutrition: Benefits and Limitations[END_REF], in the pharmaceutical and [START_REF] Jansook | Cyclodextrins: structure, physicochemical properties and pharmaceutical applications[END_REF] cosmetic fields [START_REF] Crini | Cyclodextrins, from molecules to applications[END_REF], in the textile industry [START_REF] Narayanan | Efficient wound odor removal by βcyclodextrin functionalized poly (ε-caprolactone) nanofibers[END_REF][START_REF] Singh | Sustainable cyclodextrin in textile applications[END_REF], and in developing filtering materials [START_REF] Fenyvesi | Removal of hazardous micropollutants from treated wastewater using cyclodextrin bead polymer -A pilot demonstration case[END_REF][START_REF] Liu | Novel cyclodextrin-based adsorbents for removing pollutants from wastewater: A critical review[END_REF].

Electrospinning and its Use as Encapsulation Technique

The electrospinning (ES) technique consists of the application of a high voltage to a polymer solution, or a polymer melt, that is usually extruded from a spinneret at a constant rate. Owing to the presence of free surface charges, the polymeric droplet exiting the spinneret takes the shape of a cone (i.e., Taylor cone) and, when the repulsive electrostatic forces overcome the liquid surface tension, a continuous jet erupts from the spinneret tip. Hence, solid nano-or microfibers are obtained and generally collected in a pseudo-random manner on a grounded collector [START_REF] Lukáš | Physical principles of electrospinning (Electrospinning as a nano-scale technology of the twenty-first century)[END_REF]. The stability of the polymer jet and the related fiber morphology depend on the spinning system properties, processing parameters and environmental conditions [START_REF] Amiraliyan | Effects of some electrospinning parameters on morphology of natural silk-based nanofibers[END_REF][START_REF] Ismail | A mathematical model to predict the effect of electrospinning processing parameters on the morphological characteristic of nano-fibrous web and associated filtration efficiency[END_REF][START_REF] Thompson | Effects of parameters on nanofiber diameter determined from electrospinning model[END_REF]. In this sense, electrospinning represents an easy, versatile, and industrially scalable approach to prepare fibers with tailored properties [START_REF] Kannan | Electrospinning-commercial applications, challenges and opportunities[END_REF][START_REF] Xue | Electrospinning and electrospun nanofibers: Methods, materials, and applications[END_REF][START_REF] Yu | Recent Advances in Needleless Electrospinning of Ultrathin Fibers: From Academia to Industrial Production[END_REF].

During the past decades, both synthetic and naturally derived polymers have been electrospun. Synthetic polymers are usually easier to electrospun and allow good reproducibility and superior mechanical performances. Additionally, by using hydrophobic materials, water-resistant mats able to maintain their peculiar structure in contact with aqueous media can be easily obtained without the need for post-production treatments. However, such materials usually require the use of organic hazardous solvents to be processed thereby representing a substantial environmental and health threat. Conversely, the electrospinning of naturally occurring polymers is starting to be broadly investigated as a less impacting and "greener" alternative. Indeed, besides the fact that they can be processed via eco-friendly solvents (e.g., water, slightly acid mixtures, etc), natural biopolymers can be often extracted from food and agricultural wastes hence endowing the interesting possibility to develop circular economy products [START_REF] Ding | Electrospun polymer biomaterials[END_REF][START_REF] Kakoria | A Review on Biopolymer-Based Fibers via Electrospinning and Solution Blowing and Their Applications[END_REF][START_REF] Mendes | Electrospinning of food proteins and polysaccharides[END_REF][START_REF] Noruzi | Electrospun nanofibres in agriculture and the food industry: a review[END_REF][START_REF] Schiffman | A review: Electrospinning of biopolymer nanofibers and their applications[END_REF]. Moreover, such materials are usually biocompatible, weakly immunogenic, biodegradable, and digestible, and present other peculiar properties that make them extremely promising for the fabrication of biomedical and pharmaceutical products, as well as for food packaging and biosensor applications (Dodero, Lova, Vicini, Castellano, et al., 2020;[START_REF] Galiano | Advances in biopolymer-based membrane preparation and applications[END_REF]. Nevertheless, natural polymers present drawbacks such as poor reproducibility, mechanical properties and thermal resistance, and usually require a post-processing crosslinking reaction to exhibit appropriate stability and performances. Hence, it is not surprising that the electrospinning of such materials is considerably harder compared to synthetic polymers [START_REF] Valencia | Self-Assembled Carbohydrate Polymers for Food Applications: A Review[END_REF][START_REF] Yi | Natural polysaccharides experience physiochemical and functional changes during preparation: A review[END_REF].

With these premises, it is not surprising that electrospinning is nowadays widely used to prepare nanofibrous membranes for a broad range of purposes. For example, electrospun mats find several uses as biomedical and pharmaceutical devices [START_REF] Cheng | Biomedical application and controlled drug release of electrospun fibrous materials[END_REF][START_REF] Miguel | Electrospun polymeric nanofibres as wound dressings: A review[END_REF], in filter materials (D. [START_REF] Lv | Green Electrospun Nanofibers and Their Application in Air Filtration[END_REF][START_REF] Snowdon | Electrospun filtration membranes for environmental remediation[END_REF], in the packaging sector [START_REF] Muthu Kumar | A comprehensive review of electrospun nanofibers: Food and packaging perspective[END_REF]C. Zhang et al., 2020), but also for energy-related applications (J. [START_REF] Wang | Progress of electrospray and electrospinning in energy applications[END_REF], sensors and biosensors [START_REF] Han | Fabrication of nanofibrous sensors by electrospinning[END_REF][START_REF] Rozemarie Manea | Sensors from Electrospun Nanostructures[END_REF], and textile products [START_REF] Mirjalili | Review for application of electrospinning and electrospun nanofibers technology in textile industry[END_REF]. Additionally, electrospinning has proved to be a promising encapsulation technique with several advantages compared to the common industrial approaches, such as spray-drying and solvent evaporation [START_REF] Becerril | Encapsulation Systems for Antimicrobial Food Packaging Components: An Update[END_REF][START_REF] Celli | Bioactive Encapsulated Powders for Functional Foods-a Review of Methods and Current Limitations[END_REF][START_REF] Kumar | Encapsulation of bioactive compounds using nanoemulsions[END_REF][START_REF] Shishir | Advances in micro and nano-encapsulation of bioactive compounds using biopolymer and lipid-based transporters[END_REF]. Specifically, apart from its versatility, the key advantage of electrospinning as an encapsulation technique consists of the absence of heat, which is fundamental to preserve the structure and properties of the entrapped molecules. However, most of the drugs and bioactive compounds of major interest are characterized either by low water solubility, poor thermal stability or a highly volatile nature. Hence, to overcome such limitations and improve the efficiency of electrospinning as an encapsulation technique, the use of cyclodextrins to obtain functionalized nanofibers has recently gained increasing relevance.

Polymer-free Electrospun Cyclodextrinbased Membranes

One of the main requirements to obtain defect-free homogenous nanofibers via electrospinning technique is the presence of sufficient intermolecular interactions in the working solutions (or melts). In polymer-based systems, these are usually provided by chain entanglement [START_REF] Mendes | Electrospinning of food proteins and polysaccharides[END_REF][START_REF] Wang | Impact of Entanglement Density on Solution Electrospinning: A Phenomenological Model for Fiber Diameter[END_REF]. On the contrary, the electrospinning of low molecular weight molecules is quite a challenge because of the complete lack of entanglements. Hence, only a few can be electrospun alone. Among others, owing to their unique self-assembling behaviour, pure phospholipids [START_REF] Mckee | Phospholipid nonwoven electrospun membranes[END_REF], surfactants [START_REF] Cashion | Gemini surfactant electrospun membranes[END_REF], tannic acid [START_REF] Allais | Polymer-free electrospinning of tannic acid and cross-linking in water for hybrid supramolecular nanofibres[END_REF], and cyclodextrins [START_REF] Celebioglu | Cyclodextrin nanofibers by electrospinning[END_REF]) can be used to prepare polymer-free nanofibers. In this sense, thanks to their unique physical-chemical properties, polymer-free cyclodextrin nanofibers have gained huge interest in recent years. However, their proficient usage in industrial applications remains a challenge and further studies are required to obtain products with effective large-scale applicability [START_REF] Costoya | Electrospun fibers of cyclodextrins and poly(cyclodextrins)[END_REF]Topuz & Uyar, 2019, 2020). In the following, a detailed summary (see Table 1) of the current state-of-the-art is provided by reviewing both proofs of concept and applicative reports. [START_REF] Aytac | Electrospinning of cyclodextrin/linalool-inclusion complex nanofibers: Fast-dissolving nanofibrous web with prolonged release and antibacterial activity[END_REF] Citral --- [START_REF] Aytac | Efficient encapsulation of citral in fast-dissolving polymer-free electrospun nanofibers of cyclodextrin inclusion complexes: High thermal stability, longer shelf-life, and enhanced water solubility of citral[END_REF] Eugenol --- (Celebioglu, Yildiz, et al., 2018b) Thymol --- [START_REF] Celebioglu | Thymol/cyclodextrin inclusion complex nanofibrous webs: Enhanced water solubility, high thermal stability and antioxidant property of thymol[END_REF] Air filter materials CDs ---Water -DMSO [START_REF] Celebioglu | Electrospun gamma-cyclodextrin (γ-CD) nanofibers for the entrapment of volatile organic compounds[END_REF] HPCDs ---Water -DMF [START_REF] Celebioglu | Molecular entrapment of volatile organic compounds (VOCs) by electrospun cyclodextrin nanofibers[END_REF] HPCDs ---Water -DMF [START_REF] Celebioglu | Molecular entrapment of volatile organic compounds (VOCs) by electrospun cyclodextrin nanofibers[END_REF] Reducing agents for nanoparticle synthesis HPCDs Au-NPs Water -DMF (Celebioglu & Uyar, 2013c) Ag-NPs Water -DMF (Celebioglu, Topuz, Yildiz, et al., 2019b) Pd-NPs Water -DMF (Celebioglu, Topuz, & Uyar, 2019a) Sacrificial templates for ceramic hollow nanofibers HPCDs ---DMF [START_REF] Celebioglu | Water-soluble non-polymeric electrospun cyclodextrin nanofiber template for the synthesis of metal oxide tubes by atomic layer deposition[END_REF] MCDs ---DMF [START_REF] Celebioglu | Water-soluble non-polymeric electrospun cyclodextrin nanofiber template for the synthesis of metal oxide tubes by atomic layer deposition[END_REF] Water purification

PolyHPCDs

------ (Celebioglu et al., 2017) Poly-benzoxazine DFM [START_REF] Dogan | Crosslinked PolyCyclodextrin/PolyBenzoxazine electrospun microfibers for selective removal of methylene blue from an aqueous system[END_REF] ------ (Celebioglu, Topuz, Yildiz, et al., 2019a) ---Water -NaOH (Celebioglu, Topuz, & Uyar, 2019b) Peracetylated CDs ---DMF (Topuz et al., 2020)

Implantable scaffolds PolyHPCDs

Triclosan --- [START_REF] Hamsici | Bioactive peptide functionalized aligned cyclodextrin nanofibers for neurite outgrowth[END_REF] Azobenzene Water -NaOH [START_REF] Heydari | Encapsulation and Controlled Release of Vitamin B2 Using Peracetyl-β-Cyclodextrin Polymer-Based Electrospun Nanofiber Scaffold[END_REF]

Fundamental Studies

The first report concerning polymer-free cyclodextrin electrospun nanofibers can be attributed to the group of Uyar ten years ago, which investigated the electrospinning of methyl--cyclodextrins using water or dimethylformamide (DMF) as solvents with a concentration ranging from 50 wt% to 61 wt% (i.e., 100-160 w/v%) [START_REF] Celebioglu | Cyclodextrin nanofibers by electrospinning[END_REF]. A few years later, the same authors extended their studies to three other CD derivatives (i.e., HPCDs, HPCDs and MCDs) in different solvents [START_REF] Celebioglu | Electrospinning of nanofibers from non-polymeric systems: Polymer-free nanofibers from cyclodextrin derivatives[END_REF].

Similarly to polymer-based systems, the results revealed that CD electrospinning is mainly governed by the solution viscosity, bound water, and conductivity. Comparable findings were also reported by Manasco et al. [START_REF] Manasco | Cyclodextrin fibers via polymer-free electrospinning[END_REF], who investigated the possibility to prepare HPCD-based nanofibers (Figure 4a-g) by using aqueous solutions with a concentration in the range of 10-70 wt%. In another work, [START_REF] Zhang | Correlation of polymer-like solution behaviors with electrospun fiber formation of hydroxypropyl-β-cyclodextrin and the adsorption study on the fiber[END_REF] evaluated the influence of HPCD concentration on the electrospinning process in DMF. By studying the solution viscosity concentration dependence and the concentration regimes, the authors supposed that HPCDs behave in DMF as neutral polymers in good solvents nevertheless much higher scaling factors were observed compared to the predicted ones [START_REF] Colby | Structure and linear viscoelasticity of flexible polymer solutions: comparison of polyelectrolyte and neutral polymer solutions[END_REF]. Such results were explained by considering the HPCD tendency to self-aggregate similarly to wormlike micelles [START_REF] Cashion | Gemini surfactant electrospun membranes[END_REF]Dodero, Vicini, Alloisio, et al., 2020;[START_REF] Rubinstein | Dynamics of entangled solutions of associating polymers[END_REF]. Celebioglu et al. (Celebioglu & Uyar, 2013a) also reported on the electrospinning of native CDs and CDs from aqueous solutions in the concentration range 55-61 wt% (i.e., 120-160 w/v%). As for their derivatives, the concentration of native cyclodextrin solutions was found to play a fundamental role in conditioning the nanofiber morphology. Interestingly, besides the fact that native CDs are highly crystalline, the authors proved that the resultant CD nanofibers were completely amorphous probably due to the fast solvent evaporation rate. Yet, Ahn et al. [START_REF] Ahn | Preparation of β-cyclodextrin fiber using electrospinning[END_REF] presented the preparation of native CD nanofibers by using an ionic liquid and DMF as solvents and a concentration between 10 wt% and 60 wt%.

Only recently, Celebioglu et al. [START_REF] Celebioglu | Electrospinning of cyclodextrins: hydroxypropyl-alpha-cyclodextrin nanofibers[END_REF]) investigated the possibility to prepare nanofibrous membranes by using highly concentrated (i.e., 61-71 wt% or 160-240 w/v%) hydroxypropyl-αCDs (HPCDs) solutions. Noticeably, the authors also considered industrially relevant aspects by using distilled water, tap water and salty water for preparing the nanofibrous membranes. Furthermore, the effect on the electrospinning process of solution storage over 8 days was investigated due to the tendency of CDs to form aggregates, despite no significant changes were observed neither in the viscosity of the solutions nor in terms of electrospun fiber morphology.

Applicative Studies

The previously discussed pioneering works demonstrated the possibility to fabricate polymer-free cyclodextrin nanofibers straightforwardly by using different types of CDs and solvents, thereby anticipating the development of a broad number of applicative products.

Drug and Bioactive Compound Delivery Systems with Enhanced Release Performances

The ability of CDs to increase the water solubility of several hydrophobic molecules, as well as their thermal resistance, light stability, and bioavailability, has led to the development of polymer-free nanofibers with enhanced drug delivery capabilities hence allowing the development of a new generation of biomedical and pharmaceutical devices.

Encapsulation of Hydrophobic Drugs

Celebioglu et al. (Celebioglu, Umu, et al., 2014;[START_REF] Celebioglu | Electrospinning of polymer-free nanofibers from cyclodextrin inclusion complexes[END_REF] first prepared HPCD-ICstriclosan and HPCD-ICs-triclosan (TCL) electrospun membranes via the electrospinning of polymer-free aqueous solutions achieving defect-free homogeneous nanofibers, with similar morphological results obtained with poly(lactic acid)-based nanofibers in the work of [START_REF] Kayaci | Antibacterial electrospun poly(lactic acid) (PLA) nanofibrous webs incorporating triclosan/cyclodextrin inclusion complexes[END_REF]. The authors investigated the CD-ICs-TCL formation to select the optimal compound concentration to obtain homogeneous nanofibers while avoiding the presence of free triclosan molecules. Both HPCD-ICs-TCL and HPCD-ICs-TCL nanofibers were tested against E. Coli and S. Aureus bacteria showing enhanced and prolonged antibacterial properties compared to uncomplexed triclosan powder. Remarkably, Chen et al. (M. [START_REF] Chen | Electrospun UV-responsive supramolecular nanofibers from a cyclodextrin-azobenzene inclusion complex[END_REF] reported on the preparation of UV-responsive nanofibers consisting of the inclusion complexes between HPCDs and azobenzene (AAB) molecules. By investigating the effect of UV light in different phases of the electrospinning process, the authors were able to prove the responsive properties of the prepared mats which were pointed out to be extremely promising for the development of stimulicontrolled drug delivery systems.

Encapsulation of Volatile Bioactive Substances

Polymer-free cyclodextrin nanofibers can also be efficiently exploited to avoid the rapid evaporation of highly volatile compounds. For example, Aytac et al. (Aytac, Yildiz, Kayaci-Senirmak, San Keskin, Tekinay, et al., 2016) prepared HPCD, HPCD, or MCD geraniol inclusion complex nanofibrous mats. The authors proved the capability to encapsulate a higher amount of geraniol in pure CD nanofibers (11 wt%) compared to polymeric membranes (5 wt%). After both short-term temperature and long-term open-air release studies, MCD-based nanofibers showed the slowest release of geraniol. Moreover, along with strong antibacterial activities, CD-ICs-geraniol mats also displayed efficient antioxidant properties. Yet, Celebioglu et al. [START_REF] Celebioglu | Encapsulation of camphor in cyclodextrin inclusion complex nanofibers via polymer-free electrospinning: enhanced water solubility, high temperature stability, and slow release of camphor[END_REF] prepared HPCD-ICs-and HPCD-ICs-camphor nanofibers from highly concentrated aqueous solutions obtaining thermally stable and manageable membranes, with HPCD-ICscamphor nanofibers showing a slow release of the compound.

Fast-dissolving Nanofibers for the Rapid Compound Administration in Food or Pharmaceutical Products

Polymer-free cyclodextrin nanofibers are highly soluble in water if not subjected to a crosslinking reaction (see Section 5), but such drawback has been efficiently turned into a benefit by exploiting the fast-dissolving nature of these systems for the rapid administration of drugs and bioactive compounds in both food and pharmaceutical products [START_REF] Balusamy | Progress in the design and development of "fast-dissolving" electrospun nanofibers based drug delivery systems -A systematic review[END_REF]. Owing to their capability to form stable inclusion complexes, cyclodextrins can indeed considerably increase the water-solubility of a wide variety of guest hydrophobic drugs and volatile molecules that can consequently be rapidly released when in contact with a high moisture environment, human saliva or biological fluids [START_REF] Cheirsilp | Inclusion complex formation of cyclodextrin with its guest and their applications[END_REF][START_REF] Mura | Analytical techniques for characterization of cyclodextrin complexes in the solid state: A review[END_REF].

Encapsulation for the Fast-dissolution of Hydrophobic Substances

The encapsulation of a hydrophobic drug within polymer-free cyclodextrin membranes has been first demonstrated by [START_REF] Vigh | Polymer-free and polyvinylpirrolidone-based electrospun solid dosage forms for drug dissolution enhancement[END_REF]. The authors reported on polymer-free HPCD nanofibers encapsulating spironolactone which were able to completely release the encapsulated drug within a minute, therefore being promising for the rapid oral administration of highly lipophilic compounds. Shortly after, Balogh et al. [START_REF] Balogh | Electroblowing and electrospinning of fibrous diclofenac sodium-cyclodextrin complex-based reconstitution injection[END_REF] investigated the possibility to prepare fast-dissolving HPCD nanofibers containing diclofenac sodium (DCF), a poorly soluble and highly crystalline drug, to avoid the common issues related to its injection delivery methods. Remarkably, the authors implemented the common electrospinning set-up with high-speed blowing air (i.e., electroblowing) able to enhance both productivity rate and fiber morphology. Above all, HPCD-ICs-DCF nanofibers were completely amorphous and displayed a high solubility in water hence representing a promising alternative to reconstitution injections.

Starting from these preliminary studies, great efforts have been done in preparing fast-dissolving cyclodextrin electrospun nanofibers encapsulating a variety of hydrophobic molecules. For instance, Celebioglu et al. (Celebioglu & Uyar, 2017) reported on the electrospinning of HPCD inclusion complexes with vitamin E, which consists of a long hydrophobic chain. The authors were able to load and preserve around the 13 wt% of vitamin E in the prepared mats observing only a small loss of the compound during the electrospinning process. The mats showed a fast-dissolving nature and strong antioxidant activities, which were even maintained after UV-irradiation and 3-year storage proving the stability of the formed complexes.

Relatedly, [START_REF] Yildiz | Polymer-free electrospun nanofibers from sulfobutyl ether7-beta-cyclodextrin (SBE7-β-CD) inclusion complex with sulfisoxazole: Fast-dissolving and enhanced water-solubility of sulfisoxazole[END_REF] developed first a nanofibrous solid inclusion complex between sulfobutylether-β-cyclodextrins (SEBCDs) and sulfisoxazole, and then HPCD-ICs-and SBECD-ICs-paracetamol nanofibrous membranes (Zehra Irem Yildiz & Uyar, 2019). The authors demonstrated that the crystalline nature of paracetamol was completely lost owing to the complexation with CDs, thus increasing its water solubility, bioavailability and thermal stability. Recently, Celebioglu et al. (Celebioglu & Uyar, 2019a, 2019b, 2019c, 2020c, 2020d, 2020e) reported on several types of polymer-free cyclodextrin nanofibers encapsulating hydrophobic drugs showing a fast-dissolving nature. For example, the authors demonstrated the possibility to form stable HPCD-ICs-and HPCD-ICs--lipoic acid nanofibrous membranes. Owing to the absence of crystallinity, the prepared mats displayed a fast-dissolving nature both in water and artificial saliva, and they were characterized by good mechanical resistance. Similarly, the authors prepared free-standing and flexible HPCD-ICs-ibuprofen nanofibers achieving the complete inclusion of the drug within the host molecules and a much higher loading concentration compared to PVA/CD-ICs-ibuprofen nanofibers investigated in the same work. Again, metronidazole, a poorly watersoluble drug widely used in pharmaceutical formulations, was encapsulated in polymer-free HPCD nanofibers via the electrospinning of highly concentrated aqueous solutions. Lately, the authors also reported on the preparation of nanofibrous membranes consisting of the inclusion complex between HPCDs or HPCDs and curcumin with a remarkable 100% encapsulation efficiency. Specifically, HPCD-ICscurcumin nanofibers displayed a much higher water solubility and were almost instantaneously dissolved once in contact with water or artificial saliva. Moreover, the authors were able to prove the enhanced antioxidant properties of the prepared mats compared to pristine curcumin, with similar results reported by Aytac et al. (Aytac & Uyar, 2017). In an analogous study, the authors prepared electrospun HPCD-ICshydrocortisone nanofibers to enhance the water solubility and the bioavailability of the drug obtaining selfstanding and flexible defect-free mats able to completely preserve the drug during the electrospinning process. Additionally, the authors investigated the preparation of nanofibrous mats consisting of the inclusion complex between ferulic acid (FA) and HPCDs or HPCDs. Despite both systems allowed to reach a compound content of 11 wt%, HPCD-ICs-ferulic acid were found to be much more stable thereby making it possible to obtain amorphous nanofibers with enhanced thermal stability and fast-dissolving nature.

Lately, Gao et al. [START_REF] Gao | Encapsulation of thiabendazole in hydroxypropyl-βcyclodextrin nanofibers via polymer-free electrospinning and its characterization[END_REF] prepared HPCD-ICs-thiabendazole (TBZ) nanofibrous mats to exploit the compound antifungal properties, which are usually limited by its poor solubility. Interestingly, owing to the fast-dissolving nature of the mats, the antifungal properties of the compound were considerably enhanced thereby indicating the possibility to use such systems as a novel pesticide formulation. Yet, Celebioglu et al. (Celebioglu & Uyar, 2020a) demonstrated the possibility to prepare HPCD-ICs-and HPCD-ICs-vitamin A acetate nanofibers with self-standing and fast-dissolving nature. In detail, the nanofibers were prepared with a loading concentration of around 5 wt% with the complexation between the HPCDs and the bioactive compound ensuring the fast dissolution both in water and artificial saliva media. Only recently, Celebioglu et al. [START_REF] Celebioglu | Electrospun formulation of acyclovir/cyclodextrin nanofibers for fastdissolving antiviral drug delivery[END_REF]) also reported on polymer-free HPCD-ICs-acyclovir nanofibers. In particular, by using PVP-acyclovir nanofibrous mats as a control sample, the authors proved the greater encapsulation efficiency of the hydrophobic compound within the membranes in the presence of the inclusion complexes.

Additionally, Topuz et al. [START_REF] Topuz | Fast-dissolving antibacterial nanofibers of cyclodextrin/antibiotic inclusion complexes for oral drug delivery[END_REF]) also developed polymer-free HPCD nanofibers with high antibiotic loadings through the electrospinning of cyclodextrin-antibiotic inclusion complexes from water, and the resultant fast-dissolving fibers demonstrated high antibacterial activity towards Gram-negative bacteria.

Remarkably, the possibility to prepare polymer-free cyclodextrin nanofibers at an industrial scale has also been explored, despite only a few works are reported in the literature. In this regard, Vass et al. (Vass et al., 2019) investigated the use of a high-speed electrospinning (HSES) setup to process an aqueous solution of SBECD-ICs-voriconazole (VOR). The authors were able to achieve an outstanding production rate of 300 mL/h (i.e., 240 g/h of solid material) under ambient conditions and the grounded fibrous powder showed to be rapidly dissolvable in water with similar results to Vfend  (i.e., reference commercial pharmaceutical product containing VOR), consequently demonstrating the capability of the proposed approach to fulfil the requirements of the pharmaceutical industry. More recently, the authors also reported on the high-speed electrospinning of HPCD nanofibers containing -galactosidase, which is a protein-type drug widely used in pharmaceutical formulations, that were subsequently grounded and converted in tablets for oral assumption with -galactosidase found to maintain its activity over a period of 6 months [START_REF] Vass | Continuous drying of a protein-type drug using scaled-up fiber formation with HP-β-CD matrix resulting in a directly compressible powder for tableting[END_REF].

Similarly, Kiss et al. [START_REF] Kiss | A solid doxycycline HP-β-CD formulation for reconstitution (i.v. bolus) prepared by scaled-up electrospinning[END_REF] developed a solid HPCD-ICs-doxycycline (DOX) intravenous formulation using high-speed electrospinning with a production rate of 80 g/h (i.e., solid material). The authors proved that the explored inclusion complex allowed the preparation of a DOX formulation with a concentration 7 times higher than the commercially available ones, hence suggesting HSES as an alternative to freeze-drying technique.

Encapsulation for the Fast-dissolution of Volatile Substances

Another important advantage of polymer-free cyclodextrin nanofibers is their ability to encapsulate highly volatile compounds hence preserving their bioactivity over a long period while ensuring their fast administration when required. For example, Celebioglu et al. [START_REF] Celebioglu | Polymer-free nanofibers from vanillin/cyclodextrin inclusion complexes: High thermal stability, enhanced solubility and antioxidant property[END_REF] prepared polymer-free electrospun mats by using the inclusion complexes between vanillin and HPCDs, HPCDs, and MCDs in water, DMF or DMA. The authors demonstrated that MCDs were more stably linked to vanillin leading to a higher encapsulation efficiency (up to ~12 wt%). Remarkably, compared to pure PVA and PVA/CD-ICs-vanillin nanofibers [START_REF] Kayaci | Encapsulation of vanillin/cyclodextrin inclusion complex in electrospun polyvinyl alcohol (PVA) nanowebs: Prolonged shelf-life and high temperature stability of vanillin[END_REF], the proposed CD-based mats could encapsulate a considerably higher amount of vanillin and showed strong antioxidant activities, high thermal stability and the possibility to tune their dissolving behaviour. Similarly, Aytac et al. [START_REF] Aytac | Electrospinning of cyclodextrin/linalool-inclusion complex nanofibers: Fast-dissolving nanofibrous web with prolonged release and antibacterial activity[END_REF][START_REF] Aytac | Fast-Dissolving, Prolonged Release, and Antibacterial Cyclodextrin/Limonene-Inclusion Complex Nanofibrous Webs via Polymer-Free Electrospinning[END_REF] proposed the preparation of polymer-free HPCD-, HPCD-, and MCD-based nanofibrous mats encapsulating the highly volatile limonene or linalool compounds. In both cases, the authors proved MCD nanofibers to be the most efficient in terms of encapsulation capability. Remarkably, short-term (i.e., 3h) and long-term (i.e., 100 days) release studies demonstrated the stability of the encapsulated compounds within the nanofibrous mats, which showed strong antibacterial activities against both Gram-positive and Gram-negative bacteria, as well as good manageability and fast-dissolving character in water or high humidity environment. In another study, the authors reported on the encapsulation of citral within HPCD-, HPCD-and MCD-based nanofibers obtaining an 80% encapsulation efficiency and the capability to preserve half of the volatile compound after 15 days, as well as increasing both its thermal stability and water solubility [START_REF] Aytac | Efficient encapsulation of citral in fast-dissolving polymer-free electrospun nanofibers of cyclodextrin inclusion complexes: High thermal stability, longer shelf-life, and enhanced water solubility of citral[END_REF].

Comparably, fast-dissolving polymer-free HPCD-ICs-and HPCD-ICs-carvacrol nanofibers with potential applications as food or oral care products were reported by [START_REF] Yildiz | Fast-dissolving carvacrol/cyclodextrin inclusion complex electrospun fibers with enhanced thermal stability, water solubility, and antioxidant activity[END_REF]. Besides the high encapsulation efficiency, the carvacrol complexation enhanced its thermal stability and antioxidant properties for up to three years. In a similar study, the authors explored the preparation of polymer-free CD-ICs-menthol nanofibers by using highly concentrated HPCD-IC and HPCD-IC aqueous solutions (Zehra Irem Yildiz et al., 2018). The stable complexation of menthol, a volatile substance with strong antibacterial properties widely used in several applications, led to an increase of the compound solubility and thermal stability while allowing to obtain homogenous and smooth nanofibers with good flexibility and a fastdissolving character. The developed mats endorsed to encapsulate a much higher amount of menthol, which was also stable over a long period, compared to polystyrene (PS)/CD-ICs-menthol (Uyar, Hacaloglu, et al., 2009) and polymethylmethacrylate (PMMA)/CD-ICs-menthol [START_REF] Uyar | Electrospinning of functional poly(methyl methacrylate) nanofibers containing cyclodextrin-menthol inclusion complexes[END_REF] nanofibers. Also, Celebioglu et al. (Celebioglu, Yildiz, et al., 2018a) prepared HPCD-ICs-and HPCD-ICs-based electrospun mats containing cineole or p-cymene. HPCD-based nanofibers were able to encapsulate a greater amount of cineole, whereas p-cymene was better preserved by the HPCD-based ones. However, both mats improved the compound thermal stability consequently representing potential products in food and oral care applications. Yet, the authors investigated the preparation of free-standing nanofibrous mats obtained via the electrospinning of HPCD-ICs-, HPCD-ICs-, and MCD-ICs-eugenol or thymol (THY) systems (Celebioglu, Yildiz, et al., 2018b[START_REF] Celebioglu | Thymol/cyclodextrin inclusion complex nanofibrous webs: Enhanced water solubility, high thermal stability and antioxidant property of thymol[END_REF]. The complex formation within the nanofibers allowed to reach an encapsulation efficiency considerably higher compared to analogous PVA/CDs-ICs-eugenol nanofibers [START_REF] Kayaci | Enhanced thermal stability of eugenol by cyclodextrin inclusion complex encapsulated in electrospun polymeric nanofibers[END_REF]. Additionally, owing to their fast-dissolving nature, CD-ICs-eugenol and CD-ICs-thymol nanofibers showed much stronger antioxidant properties compared to the pure compounds. In another work, cinnamaldehyde was successfully encapsulated in self-standing HPCD-and HPCD-based nanofibers by [START_REF] Yildiz | Molecular Encapsulation of Cinnamaldehyde within Cyclodextrin Inclusion Complex Electrospun Nanofibers: Fast-Dissolution, Enhanced Water Solubility, High Temperature Stability, and Antibacterial Activity of Cinnamaldehyde[END_REF]. Bead-free and homogeneous nanofibers were obtained with considerably higher efficiency in preserving the volatile cinnamaldehyde compared to analogous PLA-based nanofibers (Y. [START_REF] Liu | Fabrication of electrospun polylactic acid/Cinnamaldehyde/β-cyclodextrin fibers as an antimicrobialwound dressing[END_REF]. Moreover, owing to their fast-dissolving nature, the prepared mats displayed strong antibacterial properties against E. Coli representing a new potential class of materials for applications in both the food, biomedical and pharmaceutical industries.

Encapsulation of Living Bacteria

Keskin et al. [START_REF] San Keskin | Encapsulation of living bacteria in electrospun cyclodextrin ultrathin fibers for bioremediation of heavy metals and reactive dye from wastewater[END_REF] demonstrated the possibility to encapsulate living bacteria within electrospun HPCD-based nanofibers to increase their availability for wastewater bioremediation applications. Despite the encapsulation efficiency was not particularly high, a sufficient amount of bacteria was preserved during the preparation process with the cell viability maintained for 7 days. Remarkably, the used bacteria retained their bioactivity and were proved able to remove Ni(II), Cr(VI) and a commercial reactive dye from aqueous solutions. Such findings indicated the proposed approach as a faster and simpler alternative to the lyophilization procedure commonly applied to preserve organisms for strain collections and applications in dye removal products.

Applications in Air and Water Filtration

The capability of cyclodextrins and their derivatives to form stable non-covalent inclusion complexes with a variety of molecules makes them extremely interesting for the removal of several pollutants from the environment. Furthermore, nanofibrous electrospun membranes represent a class of materials with superior adsorption capabilities owing to their unique structure, which allows exploiting a higher surface of interaction between the adsorbent and the adsorbate. With these premises, in the past decade, intensive research has been carried out to develop efficient filter materials based on polymer-free cyclodextrin nanofibers aiming to maximize the adsorption capability. Celebioglu et al. [START_REF] Celebioglu | Electrospun gamma-cyclodextrin (γ-CD) nanofibers for the entrapment of volatile organic compounds[END_REF] first reported on the electrospinning of pristine CDs in dimethyl sulfoxide (DMSO) aqueous solutions to be used for the entrapment of volatile organic compounds (VOCs). The obtained electrospun mats were completely amorphous and presented, above all, a surface area three times higher than their powder form according to BET analysis. Aniline and toluene volatile organic compounds were used to test the adsorption ability of CD nanofibers that showed a marked complexation capability compared to CD powder. Similarly, the authors also investigated the possibility to use HPCD-and HPCD-based nanofibers as filter materials [START_REF] Celebioglu | Molecular entrapment of volatile organic compounds (VOCs) by electrospun cyclodextrin nanofibers[END_REF]. Polymer-free electrospinning of CDs was carried out in water and DMF obtaining defect-free mats with a considerably higher surface area with respect to CD powders. DMA characterization was employed to demonstrate the good mechanical properties and integrity of the obtained mats, which were indicated as potentially foldable materials to be inserted in air filter modules. Recently, Topuz et al. (Topuz et al., 2020) reported on hydrophobic water-insoluble nanofibers obtained from the polymer-free electrospinning of peracetylated -cyclodextrins. Native CDs were first modified and subsequently electrospun by using a DMF solution, whose minimum concentration to obtain defect-free nanofibers was 64 wt% (i.e., 180 w/v). The peracetylation procedure drastically boosted the thermal stability and the hydrophobicity of the obtained nanofibers, which were indeed being proved to maintain their nanofibrous structure in water for 24h.

Other Applications

Despite the capability to form inclusion complexes that remains one of the most interesting and exploited properties of cyclodextrins, other promising applications have been considered as well. For example, their use for the easy synthesis of metal nanoparticles have been also investigated [START_REF] He | Recent progress in the synthesis, structural diversity and emerging applications of cyclodextrin-based metal-organic frameworks[END_REF][START_REF] Prochowicz | Metal complexes based on native cyclodextrins: Synthesis and structural diversity[END_REF][START_REF] Prochowicz | Interactions of Native Cyclodextrins with Metal Ions and Inorganic Nanoparticles: Fertile Landscape for Chemistry and Materials Science[END_REF]. CDs can indeed directly act as reducing agents for metal ions without the need for toxic chemicals or severe processing conditions, hence allowing the development of environmentally benign materials with unique features and a wide range of possible applications [START_REF] Celebioglu | One-step synthesis of size-tunable Ag nanoparticles incorporated in electrospun PVA/cyclodextrin nanofibers[END_REF]Shan Wang, Bai, Li, & Zhang, 2012;Shan Wang, Bai, Li, Zhang, et al., 2012). Celebioglu et al. (Celebioglu & Uyar, 2013c) first proposed the one-step in-situ synthesis of gold nanoparticles (Au-NPs) via the electrospinning of HPCD solutions containing an appropriate salt precursor. The authors exploited the capability of CDs to act as reducing and stabilizing agents, as well as fibrous matrix supporting material, to synthesize Au-NPs directly during the electrospinning process. Subsequently, the authors reported on the preparation of HPCD nanofibers containing in-situ synthesized silver nanoparticles (Ag-NPs) produced by a single-step electrospinning process (Celebioglu, Topuz, Yildiz, et al., 2019b). The authors observed that DMF solution led to thinner nanofibers compared to water, besides an increase of the mean diameter was observed for both solvents by increasing the amount of loaded Ag salt precursor, as similarly reported by Chae et al. [START_REF] Chae | Synthesis and antibacterial performance of sizetunable silver nanoparticles with electrospun nanofiber composites[END_REF]. TEM images revealed that Ag-NPs having a size between 2 and 5 nm were successfully embedded within the nanofibers, with their dimension being a function of the precursor amount and solvent type. Owing to the nanoparticle presence, the prepared nanofibers showed strong antibacterial

properties against E. Coli and S. Aureus bacteria over a period of 24h, thus being suitable also for biomedical and food packaging applications. Yet, the authors proposed HPCD nanofibers loaded with palladium nanoparticles (Pd-NPs) (Celebioglu, Topuz, & Uyar, 2019a). Cyclodextrin solutions in water and DMF containing an appropriate precursor were electrospun leading to bead-free nanofibers. Pd-NPs were homogeneously distributed within the nanofibers and showed a dimension ranging from 3 up to 5 nm that increased with the precursor loading concentration and was bigger for DMF compared to water. Moreover, HPCD/Pd-NP nanofibers showed strong catalytic performances being able to reduce p-nitrophenol (PNP)

in few minutes into p-aminophenol (PAP), thus showing great potentialities for the development of products for catalytic applications.

Cyclodextrin-based nanofibers, owing to their fast-dissolving character in water, can be even employed as sacrificial templates for the development of hollow nanofibers. To this purpose, Celebioglu et al. [START_REF] Celebioglu | Water-soluble non-polymeric electrospun cyclodextrin nanofiber template for the synthesis of metal oxide tubes by atomic layer deposition[END_REF] reported on polymer-free cyclodextrin nanofibers (i.e., HPCDs and MCDs) as a sacrificial pattern for the preparation of metal oxide nanotubes via atomic layer deposition (ALD). The authors proved the possibility to deposit a layer of aluminium oxide (Al2O3) or zinc oxide (ZnO) on the nanofiber surface to obtain a core-shell structure, subsequently removing the cyclodextrin core by a simple washing process in water. The presence of -OH groups was found to promote the smooth and homogeneous deposition as shown by SEM images, whereas TEM analysis indicated that Al2O3 and ZnO maintained an amorphous and highly crystalline nature with wurtzite structure. Despite such an approach remains at a preliminary stage, the obtained findings indicated that the use of water-soluble CD nanofibers could lead to the simple and cost-effective preparation of metal oxide nanotubes with possible energy storage applications [START_REF] Yun | Structure and electrochemical properties of highly conductive and porous carbon nanofiber derived from inclusion complex of cyclodextrin-phenylsilane[END_REF].

Water-insoluble Crosslinked Polycyclodextrin Nanofibers

The high surface area of cyclodextrin-based electrospun mats and their unique inclusion complexation capability make such systems very promising for wastewater purification applications, as well as for implantable biomedical devices. However, as broadly discussed in the previous Section, their high solubility and fast-dissolving features in aqueous environments represent a limitation to their proficient use for such applications. Therefore, the development of crosslinked cyclodextrin-based systems has started to be explored in the viewpoint to fabricate insoluble and highly performing systems. However, as summarized in Table 1, only a few studies are reported in the literature and further research are needed to investigate eventual toxicity issues related to the crosslinking reaction. Figure 5 depicts some of the most commonly employed crosslinking approaches for cyclodextrins.

Water Purification Applications of polyCD Nanofibers

Celebioglu et al. (Celebioglu et al., 2017) first demonstrated the possibility to prepare crosslinked electrospun poly-cyclodextrin nanofibers as highly efficient molecular filter materials. By using butanetetracarboxylic acid (BTCA) as crosslinker (Figure 5a), the authors avoided the fast dissolution of the prepared polyHPCD nanofibers while maintaining their high hydrophilicity. In particular, polyHPCD nanofibers were characterized by a good affinity with methylene blue (MB) having an extremely high adsorption capacity at dye concentration well above the acceptable limits, showing improved performances compared to an acetate cellulose commercial filter and similar polyacrylonitrile (PAN)/CD nanofibers (W. [START_REF] Zhang | Highly porous cyclodextrin functionalized nanofibrous membrane by acid etching[END_REF]. Moreover, the authors were able to prove both their reusability via a simple, fast, and cost-effective washing cycle and their applicability in a real water filtration apparatus. Similarly, Dogan et al. [START_REF] Dogan | Crosslinked PolyCyclodextrin/PolyBenzoxazine electrospun microfibers for selective removal of methylene blue from an aqueous system[END_REF] reported on polyHPCD/poly-benzoxazine (polyBA-a) nanofibers as potential dye adsorbents by using citric acid (CTR) as crosslinker and activating the crosslinking reaction via a simple thermal treatment (Figure 5c). The authors proved that the crosslinked mats were able to withstand several washing cycles with both water and organic solvents showing enhanced thermal stability, hence representing promising products for filtration applications. Noticeably, the obtained mats were tested against a mixture of methylene blue and methyl orange (MO) dyes exhibiting a strong selectivity towards MB being able to nearly completely remove the dye in a period of 6h. Yet, Celebioglu et al. (Celebioglu, Topuz, Yildiz, et al., 2019a) evaluated the possibility to use the polyHPCD nanofibers crosslinked with BTCA as filter materials for the removal of several polycyclic aromatic hydrocarbons (PHAs) and heavy metals from water obtaining interesting equilibrium adsorption capabilities and the ability to reduce to half the contaminant amount in only 20 minutes. Interestingly, the proposed mats could be recycled four times by a simple treatment with acetonitrile or with a nitric acid solution without showing changes in their morphology and adsorption capability. Also, the authors recently reported on water-insoluble polyHPCD nanofibers obtained by using epichlorohydrin (ECH) as crosslinker agent (Figure 5b) (Celebioglu, Topuz, & Uyar, 2019b). The rheological investigation of HPCD/ECH aqueous solutions showed that the reaction partially initiated prior to the electrospinning, despite a post-preparation thermal treatment was the main responsible for the process.

The obtained polyHPCD nanofibers were proved to be highly hydrophilic, nearly completely amorphous, with enhanced thermal stability, and were above all able to maintain their structure after the immersion in water and several organic solvents. The authors investigated the scavenging ability of the crosslinked nanofibers against phenolphthalein and phenanthrene in their aqueous solutions proving that the prepared nanofibers showed enhanced adsorption capabilities compared to polyHPCD powder and analogous poly(ethylene terephthalate) (PET)/CD nanofibers [START_REF] Kayaci | Surface modification of electrospun polyester nanofibers with cyclodextrin polymer for the removal of phenanthrene from aqueous solution[END_REF].

Biomedical Applications of polyCD Nanofibers

Hamsici et al. [START_REF] Hamsici | Bioactive peptide functionalized aligned cyclodextrin nanofibers for neurite outgrowth[END_REF] proposed water-insoluble HPCD aligned nanofibers functionalized with bioactive peptides as implantable scaffolds for peripheral nerve regeneration. The highly aligned nanofibers were first prepared and crosslinked via BTCA before being functionalized with IKVAV or KK peptides with a simple impregnation procedure. PolyHPCD-ICs-peptide nanofibers did not show toxicity issues and provided the optimal environment to promote cell adhesion, differentiation and proliferation.

Specifically, the peptide presence on the nanofiber surface was found to guide the differentiation to PC-12 cells compared to unfunctionalized membranes, whereas the aligned topological arrangement was proven to help the formation of longer neurites compared to the randomly structured samples. In another work, Heydari et al. [START_REF] Heydari | Encapsulation and Controlled Release of Vitamin B2 Using Peracetyl-β-Cyclodextrin Polymer-Based Electrospun Nanofiber Scaffold[END_REF] prepared hydrophobic peracetyl-CD nanofibers loaded with vitamin B2 (VB2) by the electrospinning of an acetone/DMF solution. HPCDs were subjected to crosslinking and peracetylation reactions before being electrospun together with VB2 leading to bead-free homogeneous nanofibers. PolyHPCD-ICs-VB2 nanofiber release kinetic was studied in simulated gastric and intestinal conditions showing an initial burst release followed by a sustained slow release for 16h. Compared to HPCD-ICs-VB2 powder, the prepared mats displayed a considerably slower and more controlled release of vitamin B2, thus representing an important advancement in the development of a new class of controlled drug delivery systems.

Electrospun Membranes Made of Natural Polymers Functionalized with Cyclodextrins and Their Inclusion Complexes

Together with polymer-free CDs and polyCDs nanofibers, electrospun mats containing cyclodextrins have also been prepared from both native CDs and their derivatives in combination with a broad variety of carrier polymers able to provide a good spinnability and very specific properties of the mats depending on the targeted application [START_REF] Costoya | Electrospun fibers of cyclodextrins and poly(cyclodextrins)[END_REF]Topuz & Uyar, 2019). The use of CDs to functionalize nanofibers offers a wide number of advantages and represents a more and more investigated research field owing to the wide range of possibilities of the obtained products. The ability of CDs to complex hydrophobic compounds and volatile molecules represents the opportunity to enhance their encapsulation efficiency, stability, solubility and bioavailability, as well as provide them with controlled release kinetics. For example, such materials can be used as implantable scaffolds enriched with growth factors and vitamins, pharmaceutical formulations containing poorly soluble drugs, highly performing filters for wastewater and volatile organic compounds, and active food packaging materials with antibacterial and antioxidant properties [START_REF] Alvarez-Lorenzo | Cyclodextrins as versatile building blocks for regenerative medicine[END_REF][START_REF] Celebioglu | Molecular entrapment of volatile organic compounds (VOCs) by electrospun cyclodextrin nanofibers[END_REF][START_REF] Hall Barrientos | Fabrication and characterisation of drug-loaded electrospun polymeric nanofibers for controlled release in hernia repair[END_REF][START_REF] Lin | Antibacterial poly(ethylene oxide) electrospun nanofibers containing cinnamon essential oil/beta-cyclodextrin proteoliposomes[END_REF][START_REF] Moyers-Montoya | Polycaprolactone/Amino-β-Cyclodextrin Inclusion Complex Prepared by an Electrospinning Technique[END_REF][START_REF] Wen | Fabrication of electrospun polylactic acid nanofilm incorporating cinnamon essential oil/β-cyclodextrin inclusion complex for antimicrobial packaging[END_REF]. Several approaches are reported in the literature to prepare cyclodextrin-functionalized electrospun nanofibers with some of them schematically illustrated in Figure 6. The simplest one consists of adding to a proper polymer solution the CDs or the CD-ICs of interest, with the latter usually prepared by precipitation or freeze-drying methods [START_REF] Beachley | Polymer nanofibrous structures: Fabrication, biofunctionalization, and cell interactions[END_REF][START_REF] Meinel | Electrospun matrices for localized drug delivery: Current technologies and selected biomedical applications[END_REF]. A faster alternative, which is however less applied owing to the difficulty in accurately control the guest molecule loading concentration, consists of the direct mixing of all the components (i.e., polymer, cyclodextrins, drug or bioactive compound, etc.) [START_REF] Narayanan | Functional nanofibers containing cyclodextrins[END_REF]. Another possibility is represented by the electrospinning of a polymer-cyclodextrins mixture with the a posteriori loading of the guest molecules of interest usually via a solution impregnation method [START_REF] Séon-Lutz | Electrospinning in water and in situ crosslinking of hyaluronic acid / cyclodextrin nanofibers: Towards wound dressing with controlled drug release[END_REF]). Yet, polymer nanofibers can be functionalized by grafting their surface with CDs or CD-ICs via a chemical reaction, therefore obtaining a high surface reactivity [START_REF] Wu | Polydopamine-assisted attachment of βcyclodextrin on porous electrospun fibers for water purification under highly basic condition[END_REF][START_REF] Yuan | Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution[END_REF]. Similarly, CDs and their derivatives can be directly employed as a crosslinker for the polymer chains, thus acting as stabilizing agents and reducing the nanofiber solubility [START_REF] Boas | Electrospinning polyelectrolyte complexes: PH-responsive fibers[END_REF][START_REF] Li | Ultra-fine polyelectrolyte fibers from electrospinning of poly(acrylic acid)[END_REF]. Alternatively, CDs and their complexes can be completely embedded within the nanofibers by employing a coaxial set-up producing core-shell nanofibers [START_REF] Chou | Current strategies for sustaining drug release from electrospun nanofibers[END_REF]. Finally, it should be kept in mind that CDs and CD-ICs, when mixed with a polymer in a liquid solvent, can thread along the polymer chains forming polypseudorotaxanes.

These can assemble in supramolecular structures where the interactions between CDs play a fundamental role in conditioning the spinning solution properties [START_REF] Uyar | Electrospinning of cyclodextrin-pseudopolyrotaxane nanofibers[END_REF] and bring grafting sites for nanofiber post-functionalization (M. [START_REF] Oster | The study of the pseudo-polyrotaxane architecture as a route for mild surface functionalization by click chemistry of poly(ε-caprolactone)-based electrospun fibers[END_REF][START_REF] Oster | Starpseudopolyrotaxane organized in nanoplatelets for poly(ε-caprolactone)-based nanofi brous scaffolds with enhanced surface reactivity[END_REF]. To date, both synthetic and natural polymer-based nanofibers have been functionalized with cyclodextrins and their derivatives with their advantages and disadvantages. Along with the fact that most natural polymers can be processed in green solvents under mild working conditions, their main advantages are enhanced biocompatibility, biodegradability and the possibility to be obtained from agricultural and food wastes with the development of green and circular economy products. Thereby, it is much likely that natural polymer-based electrospun membranes functionalized with cyclodextrins will soon represent a new class of environmentally friendly materials with potential applicability in a wide range of markets. In the next two subsections, the current literature about polysaccharide-and protein-based functionalized electrospun membranes is critically discussed by highlighting the recent advances.

Electrospun Polysaccharide -Cyclodextrin Based Membranes

Polysaccharides are a family of natural polymers consisting of multiple saccharide units linked together through glycosidic linkages and possess a wide variety of unique properties which make them extremely interesting from an industrial point of view [START_REF] Cazón | Polysaccharide-based films and coatings for food packaging: A review[END_REF]Dodero, Lova, Vicini, Castellano, et al., 2020;Y. Yu et al., 2018). Most polysaccharides can be easily and cheaply recovered from natural sources such as plants, microbes, and animals, with their use being especially profitable when they are by-products of other processes (Dodero, Vicini, & Castellano, 2020;[START_REF] Hamed | Industrial applications of crustacean by-products (chitin, chitosan, and chitooligosaccharides): A review[END_REF][START_REF] Sila | Watersoluble polysaccharides from agro-industrial by-products: Functional and biological properties[END_REF]. Compared to other natural polymers, polysaccharides are usually more stable and not irreversibly denatured upon heating and can consequently be used as an effective shell to confer enhanced temperature stability to a variety of bioactive compounds. Moreover, polysaccharides show a broad range of interesting properties such as biocompatibility, low toxicity, mucoadhesive behaviour, biodegradability, and ease of functionalization, hence being nowadays widely employed in several industrial fields (Öner et al., 2016). Regardless of their advantages, the electrospinning of polysaccharides remains a challenge due to their tendency to form strong hydrogen bonds that lead to high viscous solutions or even gels, the small number of entanglements formed between the polymer chains, the high solution surface tension, and the poor water stability of the obtained mats (Dodero, Vicini, et al., 2019;[START_REF] Mendes | Electrospinning of food proteins and polysaccharides[END_REF]. For example, Dodero et al. reported on the preparation of sodium alginate (SA) (Dodero, Alloisio, Vicini, & Castellano, 2020;[START_REF] Dodero | Effect of sodium alginate molecular structure on electrospun membrane cell adhesion[END_REF][START_REF] Dodero | Alginate-Based Electrospun Membranes Containing ZnO Nanoparticles as Potential Wound Healing Patches: Biological, Mechanical, and Physicochemical Characterization[END_REF] and chitosan (CH) [START_REF] Dodero | Chitosan-based electrospun membranes: effects of solution viscosity, coagulant and crosslinker[END_REF][START_REF] Dodero | Effect of Crosslinking Type on the Physical-Chemical Properties and Biocompatibility of Chitosan-Based Electrospun Membranes[END_REF] crosslinked electrospun membranes by using poly(ethylene oxide) (PEO) as a co-spinning agent, which was then removed by a simple postelectrospinning washing cycle. In another work, Séon-Lutz et al. [START_REF] Séon-Lutz | Electrospinning in water and in situ crosslinking of hyaluronic acid / cyclodextrin nanofibers: Towards wound dressing with controlled drug release[END_REF] proposed the electrospinning of hyaluronic acid (HA)/PVA solutions being able to decrease the co-spinning agent concentration compared to other similar works reported in the literature (J. [START_REF] Li | Electrospinning of Hyaluronic Acid (HA) and HA/Gelatin Blends[END_REF], whereas Vicini et al. [START_REF] Vicini | Alginate and alginate/hyaluronic acid membranes generated by electrospinning in wet conditions: Relationship between solution viscosity and spinnability[END_REF] used a bath collector electrospinning to obtain crosslinked composite alginate/hyaluronic acid/PEO membranes. Similarly, Ge et al. [START_REF] Ge | Immobilization of glucose oxidase in electrospun nanofibrous membranes for food preservation[END_REF] and [START_REF] Huang | Preparation and characterization of stable chitosan nanofibrous membrane for lipase immobilization[END_REF] reported on chitosan/PVA electrospun membranes for the encapsulation of bioactive compounds, whereas pullulan (PUL)/PVA nanofibers with UV-resistant properties were obtained by Qian et al. [START_REF] Qian | Incorporation of Rutin in Electrospun Pullulan/PVA Nanofibers for Novel UV-Resistant Properties[END_REF]. Compared to pure polysaccharide nanofibrous membranes, cyclodextrin-functionalized polysaccharide nanofibers offer several advantages that will be deeply discussed in this section with a complete and up-to-date summary of the literature reported in Table 2. Chitosan (CH) is a polysaccharide derived from the partial deacetylation of chitin, the second most abundant biopolymer in nature after cellulose and widely present in the exoskeleton of shellfish and fungi organisms.

Owing to its unique properties and wide availability, chitosan has been recognized as one of the most promising materials of the future to substitute synthetic polymers [START_REF] Riaz Rajoka | Chitosan and its derivatives: synthesis, biotechnological applications, and future challenges[END_REF]. The first study concerning chitosan nanofibers functionalized with cyclodextrins can be attributed to Norouzi et al. [START_REF] Norouzi | Electrospinning of βcyclodextrine grafted chitosan[END_REF] who reported on chitosan/PVA electrospun membranes grafted with -cyclodextrins for the efficient dye removal from effluents. After a crosslinking procedure carried out with glutaraldehyde vapours, the prepared samples were able to retain their nanofibrous structure for a long time during which they showed a surprisingly high uptake capacity. Similarly, Bazhban et al. [START_REF] Bazhban | Electrospinning of cyclodextrin functionalized chitosan/PVA nanofibers as a drug delivery system[END_REF] prepared chitosan/PVA electrospun membranes grafted with carboxymethyl--cyclodextrins (CMCDs) as drug delivery systems demonstrating a slower release compared to the correspondent polymer films. Subsequently, Burns et al. [START_REF] Burns | Cyclodextrin facilitated electrospun chitosan nanofibers[END_REF] tried to understand the effect of HPCDs on the electrospinning process of chitosan solutions in acetic acid (AA) and trifluoroacetic acid (TFA). The authors observed a strong improvement in the processability of CH solutions enriched with HPCDs with more homogeneous nanofibers obtained by increasing the cyclodextrin concentration as shown in Figure 7a-d. [START_REF] Burns | Cyclodextrin facilitated electrospun chitosan nanofibers[END_REF], it was suggested that the enhanced processability of chitosan solutions was likewise related to the formation of a ternary complex between CH, HPCDs, and TFA with the solvent molecules acting as bridges, as schematically depicted in Figure 7e. By Raman imaging, the authors were able to prove the absence of direct interactions between chitosan and cyclodextrins opening the way to the development of new supramolecular structures. Along with these preliminary studies, Ouerghemmi et al. [START_REF] Ouerghemmi | Triclosan loaded electrospun nanofibers based on a cyclodextrin polymer and chitosan polyelectrolyte complex[END_REF] prepared chitosan electrospun membranes containing the inclusion complexes between polyHPCDs and triclosan. Compared to pristine HPCDs, polyHPCDs provided a higher encapsulation capability and led to the formation of a polyelectrolyte complex with chitosan enhancing the water-resistance to the nanofibers. With respect to chitosan nanofibers functionalized with HPCD-ICs-TCL or free TCL, CH/polyHPCD-ICs-TCL mats showed a slower release over a longer period both at pH = 7.4 and pH = 5.5 conditions. Moreover, the authors proved that the mats were embedded with strong antibacterial activities remarkably higher in terms of growth inhibition zone compared to those of similar synthetic products [START_REF] Kayaci | Antibacterial electrospun poly(lactic acid) (PLA) nanofibrous webs incorporating triclosan/cyclodextrin inclusion complexes[END_REF][START_REF] Tonelli | Nanostructuring and functionalizing polymers with cyclodextrins[END_REF], thus making them suitable candidates for both biomedical and food packaging applications. Yet, Munhuweyi et al. [START_REF] Munhuweyi | Physical and antifungal properties of β-cyclodextrin microcapsules and nanofibre films containing cinnamon and oregano essential oils[END_REF] reported on the encapsulation of cinnamon and oregano essential oils in CH/PVA nanofibers embedding CDs. Owing to the great encapsulation efficiency, which was much higher compared to PLA-, PVA-, and PCL-based nanofibers containing cinnamon oil [START_REF] Amiri | Poly(ε-caprolactone) electrospun nanofibers containing cinnamon essential oil nanocapsules: A promising technique for controlled release and high solubility[END_REF][START_REF] Pan | Development of polyvinyl alcohol/β-cyclodextrin antimicrobial nanofibers for fresh mushroom packaging[END_REF][START_REF] Wen | Fabrication of electrospun polylactic acid nanofilm incorporating cinnamon essential oil/β-cyclodextrin inclusion complex for antimicrobial packaging[END_REF]Wen, Zhu, Wu, et al., 2016), the proposed CH/PVA/CD-ICs-cinnamon mats showed particularly marked antibacterial properties against Botrytis sp.

bacteria, hence representing interesting materials especially for food packaging applications. Recently, Kersani et al. [START_REF] Kersani | Stent coating by electrospinning with chitosan/poly-cyclodextrin based nanofibers loaded with simvastatin for restenosis prevention[END_REF] developed a bare-metal stent for angioplasty covered by an electrospun layer of chitosan/polyHPCD-ICs-simvastatin (SV) drug as an efficient tool for restenosis prevention represented in Figure 7a. Compared to the nanofibers loaded with free SV or embedding HPCD-ICs-SV, the use of polyHPCDs highly improved the drug loading efficiency leading to a much more prolonged and controlled release from the mats. Additionally, the release of simvastatin was found to be tuneable by simply changing the sample thickness or the initial loading concentration indicating the possibility to accurately personalize the system depending on the patient requirements.

Pullulan (PUL) is a water-soluble extracellular polysaccharide obtained from fermentation processes and exploited in the manufacturing of edible films, as well as in several biomedical and pharmaceutical oral care applications [START_REF] Prajapati | Pullulan: An exopolysaccharide and its various applications[END_REF]. In this regard, Fuenmayor et al. [START_REF] Fuenmayor | Encapsulation of R-(+)-limonene in edible electrospun nanofibers[END_REF] developed edible nanofibrous membranes by single-step electrospinning of a pullulan/CD aqueous solution containing R-(+)-limonene, which was found to be stable over a long time with its release occurring only at high water activity values (aW) hence making the prepared mats suitable for fresh food packaging products. Similarly, [START_REF] Mascheroni | Encapsulation of volatiles in nanofibrous polysaccharide membranes for humidity-triggered release[END_REF] investigated the encapsulation of the volatile compound perillaldehyde, an aroma largely employed in the food industry, within a pullulan electrospun matrix containing CDs. No evident losses of the aroma compound were observed over several months at ambient conditions with the release occurring exclusively for aw > 0.9. Lately, Celebioglu et al. [START_REF] Celebioglu | Electrohydrodynamic encapsulation of eugenol-cyclodextrin complexes in pullulan nanofibers[END_REF] reported on pullulan nanofibers embedding CD-ICs-eugenol able to almost preserve the volatile compound with an encapsulation efficiency of 93%, which was considerably higher with respect to pullulan/eugenol nanofibers (i.e., 23%). Moreover, the complexation increased the thermal stability of eugenol, whereas its antioxidant properties were substantially enhanced and remained unvaried over a period of 3 months.

Cellulose acetate (CA) is one of the most important derivatives of cellulose and it is widely employed as a film base for photography, vapour sensors, optical materials, and to produce synthetic fibers for textile applications owing to its renewable source, biodegradability, non-toxicity and low cost [START_REF] Candido | Synthesis of cellulose acetate and carboxymethylcellulose from sugarcane straw[END_REF][START_REF] Lova | Advances in Functional Solution Processed Planar 1D Photonic Crystals[END_REF][START_REF] Lova | Flory-Huggins Photonic Sensors for the Optical Assessment of Molecular Diffusion Coefficients in Polymers[END_REF][START_REF] Ummartyotin | A critical review on cellulose: From fundamental to an approach on sensor technology[END_REF]. [START_REF] Li | Preparation and antimicrobial activity of β-cyclodextrin derivative copolymers/cellulose acetate nanofibers[END_REF] prepared CA nanofibrous membranes embedding CD inclusion complexes with an ad hoc synthesized Nhalamine copolymer as promising candidates for biomedical and food packaging applications with strong biocidal properties against both Gram-positive and Gram-negative bacteria. Aiming to the efficient removal of bacteria from drinking water, Nthunya et al. [START_REF] Nthunya | Greener Approach to Prepare Electrospun Antibacterial β[END_REF] investigated the possibility to prepare cellulose acetate/-cyclodextrin membranes embedding in-situ synthesized metal nanoparticles. Ag/Fe nanoparticles were here prepared via a green UV photoreduction process under ambient conditions and enriched the mats with strong antibacterial properties against several bacteria strains thus making them a valid alternative for water purification purposes. More recently, Ghorani et al. [START_REF] Ghorani | Assembly of odour adsorbent nanofilters by incorporating cyclodextrin molecules into electrospun cellulose acetate webs[END_REF] developed CA nanofibers embedding CDs as odour adsorbent filter materials by selecting acetone:DMF

(2:1) as the most appropriate solvent system to obtain a considerably high production rate suitable for industrial applications. Above all, the proficiency of the prepared mats to adsorb hexanal molecules, which are a marker for oil and fat oxidation, suggested their suitability for filtration purposes. While the previously mentioned works consist in the direct electrospinning of CA/CD solutions, a different approach was first proposed by [START_REF] Celebioglu | Cyclodextrin-grafted electrospun cellulose acetate nanofibers via "click" reaction for removal of phenanthrene[END_REF] who reported on cellulose acetate nanofibers grafted with CDs via a simple "click" reaction carried out to avoid leaking issues. The grafted membranes were tested as potential molecular filters for water purification purposes showing greater adsorption capability in removing phenanthrene compared to the pristine CA nanofibers, as well as respect to comparable PET/CD nanofibers [START_REF] Kayaci | Surface modification of electrospun polyester nanofibers with cyclodextrin polymer for the removal of phenanthrene from aqueous solution[END_REF]. Similarly, Yuan et al. [START_REF] Yuan | Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution[END_REF] investigated the possibility to use regenerated cellulose (RC) nanofibers functionalized with CDs,CDs orCDs via physical mixing or grafting reaction for the removal of toluene residues from wastewater. Each type of CD led to homogenous nanofibers with the grafting approach enriching the mats with considerably higher adsorption capability compared to the works of [START_REF] Kayaci | Electrospun nylon 6,6 nanofibers functionalized with cyclodextrins for removal of toluene vapor[END_REF] and Uyar et al. [START_REF] Uyar | Cyclodextrin functionalized poly(methyl methacrylate) (PMMA) electrospun nanofibers for organic vapors waste treatment[END_REF]). Yet, [START_REF] Chen | Hierarchical porous nanofibers containing thymol/beta-cyclodextrin: Physico-chemical characterization and potential biomedical applications[END_REF] reported on the development of hierarchical CA nanofibers embedding the inclusion complex between CDs and thymol. The proposed membranes showed a prolonged release resulting in marked antibacterial properties, mechanical properties suitable for wound dressing applications, and excellent cytocompatibility. Lately, [START_REF] Lv | Rapid elimination of trace bisphenol pollutants with porous β-cyclodextrin modified cellulose nanofibrous membrane in water: adsorption behavior and mechanism[END_REF] prepared -cyclodextrin cellulose acetate nanofibers for the removal of bisphenol pollutants from water. The authors first modified native CDs with tetrafluoroterephthalonitrile (TF) by a simple chemical treatment before grafting them onto the CA mats to enhance the pollutant adsorption efficiency. The obtained products showed a highly porous morphology, a stable crystal structure, and excellent thermal stability, as well as the abundance of surface functional groups. Noticeably, the authors demonstrated the capability of the proposed nanofibers to efficiently act as adsorbent materials in a broad range of conditions for several cycles indicating their suitability for practical applications.

Hydroxypropyl cellulose (HPC) is another cellulose derivative showing good solubility in both water and organic solvents and mainly used as an excipient, lubricant and ophthalmic protectant owing to its thermoand pH-responsive properties [START_REF] Qiu | Smart" Materials Based on Cellulose: A Review of the Preparations, Properties, and Applications[END_REF][START_REF] Yang | Self-assembled cellulose materials for biomedicine: A review[END_REF]. In this regard, Aytac et al. [START_REF] Aytac | Sulfisoxazole/cyclodextrin inclusion complex incorporated in electrospun hydroxypropyl cellulose nanofibers as drug delivery system[END_REF] presented the preparation of HPC nanofibers functionalized with the inclusion complex between hydroxypropyl--cyclodextrin and sulfisoxazole (SFS) for drug delivery applications by developing sandwich-like multilayer materials. Compared to nanofibers containing the free drug, HPC/HPCD-ICs-SFS mats showed a considerably higher release most likely owing to the enhanced incorporation of SFS through inclusion complexation.

Almond gum (ALG) is a natural gum copiously exuded from the trunk, branches, and fruits of Prunus amygdalus trees after mechanical injury and/or infection by microorganisms. Almond gum represents an important waste product in several developing countries and, owing to its antibacterial and antioxidant activities, could be successfully employed as a green alternative to several synthetic materials [START_REF] Bouaziz | Biological properties of watersoluble polysaccharides and hemicelluloses from almond gum[END_REF]. The release mechanism of curcumin from almond gum/PVA/CD-ICs-curcumin electrospun membranes in simulated saliva and gastrointestinal conditions was investigated by Rezaei et al. [START_REF] Rezaei | Evaluation of Release Kinetics and Mechanisms of Curcumin and Curcumin-β-Cyclodextrin Inclusion Complex Incorporated in Electrospun Almond Gum/PVA Nanofibers in Simulated Saliva and Simulated Gastrointestinal Conditions[END_REF]. Compared to the nanofibers loaded with free curcumin, the presence of CD-curcumin ICs allowed to reach a much higher compound encapsulation efficiency (i.e., > 90%) and enriched the membranes with a greater and faster release, thus proving the possibility to use almond gum-based composite nanofibers as efficient drug delivery systems.

Hyaluronic acid (HA) is an anionic polysaccharide present in several human tissues with unique physicalchemical properties and a wide range of important biological functions, including cell signalling, wound reparation, tissue regeneration, morphogenesis, matrix organization and pathobiology [START_REF] Dodero | A microrheological and rheological study of biopolymers solutions: Hyaluronic acid[END_REF][START_REF] Fallacara | Hyaluronic acid in the third millennium[END_REF]. [START_REF] Séon-Lutz | Electrospinning in water and in situ crosslinking of hyaluronic acid / cyclodextrin nanofibers: Towards wound dressing with controlled drug release[END_REF] reported on the preparation of HA-PVA membranes functionalized with HPCDs for wound dressing applications using only water as solvent.

The membranes were thereafter crosslinked with a carbodiimide and N-hydroxysuccinimide ensuring thus a completely green process of fabrication. The authors proved that the use of HPCDs stabilized the electrospinning process owing to their capability to establish intermolecular interactions with HA and PVA, thus allowing to noticeably reduce the minimum concentration of co-spinning agent (i.e., PVA). More importantly, naproxen (NAP) drug was a posteriori encapsulated within the prepared nanofibers and presented a sustained release over several days.

Dandelion (DP) is an -type polysaccharide extracted from the roots of a perennial herbaceous plant and currently employed in several food products owing to its antitumor, antioxidant, and anti-complement properties [START_REF] Guo | Physicochemical, Structural, and Biological Properties of Polysaccharides from Dandelion[END_REF]. [START_REF] Cui | Preparation and antibacterial activity of Litsea cubeba essential oil/dandelion polysaccharide nanofiber[END_REF] reported on the preparation of nanofibrous dandelion-based membranes embedding CD-ICs-Litsea cubeba essential oil (LCEO) as efficient antibacterial agents. The structure of the mats was improved thanks to the addition of the CD complexes in the spinning solutions owing to the interactions between the components. Interestingly, a sustained release of the encapsulated LCEO was observed over several days resulting in marked antibacterial properties, therefore making the prepared nanofibers suitable to be used for both biomedical and food packaging purposes.

Electrospun Protein -Cyclodextrin Based Membranes

Proteins are biomacromolecules composed of long amino acid chains with an important role in several body functions such as DNA replication, metabolic reactions, stimuli responses, and moieties transportation, as well as in cell viability. Proteins are biocompatible, biodegradable, easily accustomed in the human body, and with interesting isoelectric properties that allow them to interact with a wide variety of molecules [START_REF] Muiznieks | Biomechanical Design of Elastic Protein Biomaterials: A Balance of Protein Structure and Conformational Disorder[END_REF][START_REF] Wang | Protein Secondary Structure Prediction Using Deep Convolutional Neural Fields[END_REF][START_REF] Weisel | Fibrin formation, structure and properties[END_REF]. Owing to such properties, it is not surprising that protein-based electrospun membranes are gaining increasing interest for several applications, especially in the food packaging and biomedical industries. However, proteins are known to be infamously difficult to be electrospun because of their complex secondary and ternary structures, with globular properties having too few interactions to form a sufficient number of entanglements [START_REF] Babitha | Electrospun protein nanofibers in healthcare: A review[END_REF][START_REF] Defrates | Protein-Based Fiber Materials in Medicine: A Review[END_REF][START_REF] Ding | Electrospun polymer biomaterials[END_REF][START_REF] Kakoria | A Review on Biopolymer-Based Fibers via Electrospinning and Solution Blowing and Their Applications[END_REF][START_REF] Zhong | Electrospinning of foodgrade nanofibres from whey protein[END_REF].

Protein-based nanofibrous membranes functionalized with cyclodextrins represent an emerging and interesting class of novel materials with the possibility to couple the outstanding properties of both components. However, their investigation remains to an initial stage with only a small number of publications reported in the literature as summarized in Table 3. Soy protein isolate (SPI) is the most refined protein obtained from soybean with several applications in food-related products due to its great abundance and high availability as by-products from industries [START_REF] Rani | A Review on Material and Antimicrobial Properties of Soy Protein Isolate Film[END_REF][START_REF] Tian | Fabrication, properties and applications of soy-protein-based materials: A review[END_REF]. SPI was the first protein employed to prepare protein-based electrospun nanofibers functionalized with cyclodextrins by Vega-Lugo et al. [START_REF] Vega-Lugo | Controlled release of allyl isothiocyanate using soy protein and poly(lactic acid) electrospun fibers[END_REF], who reported on SPI nanofibers encapsulating allyl isothiocyanate compound (AITC) by using CDs as complexation agents and PEO as a co-spinning agent. Beyond the possibility to tune the nanofiber structure by simple changing the mixture composition, AITC release kinetics from the composite nanofibers strongly depended on the environment relative humidity. Specifically, no compound loss was observed at 0% RH, whereas a sustained release for 20h was detected at 75% RH comparably to the results showed by Aytac et al.

concerning PVA/CD-ICs-AITC membranes [START_REF] Aytac | Release and antibacterial activity of allyl isothiocyanate/β-cyclodextrin complex encapsulated in electrospun nanofibers[END_REF].

Zein (ZN) is a clear, odourless, tasteless, water-insoluble and edible prolamin protein derived from corn and broadly employed in several commercial products ranging from the textile fiber market to the food industry [START_REF] Kasaai | Zein and Zein-Based Nanoparticles for Food Packaging Applications: A Global View[END_REF][START_REF] Turasan | Advances in Understanding the Molecular Structures and Functionalities of Biodegradable Zein-Based Materials Using Spectroscopic Techniques: A Review[END_REF][START_REF] Zhang | Design, fabrication and biomedical applications of zein-based nano/micro-carrier systems[END_REF]. strong growth reduction and the possibility to use the obtained mats for applications in the food packaging.

More recently, Aytac et al. [START_REF] Aytac | Antioxidant electrospun zein nanofibrous web encapsulating quercetin/cyclodextrin inclusion complex[END_REF] reported on electrospun zein/CD-ICs-quercetin nanofibers as quick and efficient antioxidant materials, with the encapsulated quercetin showing enhanced thermal stability and water solubility compared to its free form. Similarly, [START_REF] Wang | Characterization and bacteriostatic effects of β-cyclodextrin/quercetin inclusion compound nanofilms prepared by electrospinning[END_REF] prepared homogenous and free-standing zein nanofibers embedding CD-ICs-quercetin. The encapsulation of the bioactive compound was proved to improve its availability, release time, and thermal stability.

Consequently, the obtained mats showed strong antibacterial properties against both E. Coli and S. Aureus bacteria, thus resulting in promising materials for future active food packaging products.

Silk fibroin (SF) is an insoluble protein largely produced by the larvae of Bombyx mori and numerous other insects. SF has assumed an increasing interest in biomedical applications owing to its biocompatibility, low immunogenicity, mechanical properties, and ability to remodel in response to the biological environment [START_REF] Koh | Advancing the frontiers of silk fibroin protein-based materials for futuristic electronics and clinical wound-healing (Invited review)[END_REF][START_REF] Qi | A Review of Structure Construction of Silk Fibroin Biomaterials from Single Structures to Multi-Level Structures[END_REF]. With this premises, [START_REF] Liu | Tamoxifen-loaded silk fibroin electrospun fibers[END_REF] demonstrated the possibility to prepare regenerated silk fibroin (RSF) nanofibers embedding HPCD-ICs-tamoxifen (TAM) as potential drug delivery systems by using a simple aqueous mixture. The complex addition strongly increased the spinnability of RSF solutions leading to thinner and more homogenous nanofibers as shown in Figure 8, whereas the encapsulated drug was slowly released over 3 weeks making RSF cyclodextrin-functionalized nanofibers promising products as transdermal drug delivery systems. Gelatin (GL) is a largely available protein obtained from animal products and broadly employed in manufacturing to prepare foods, cosmetics and medicines owing to its gelling properties and ability to improve product elasticity, consistency and stability [START_REF] Hosseini | A state-of-the-art review on the elaboration of fish gelatin as bioactive packaging: Special emphasis on nanotechnology-based approaches[END_REF][START_REF] Karayannakidis | Fish Processing By-Products as a Potential Source of Gelatin: A Review[END_REF]. The use of gelatin/-cyclodextrins nanofibers for the removal of dyes from wastewater was proposed by Chen et al. [START_REF] Chen | Environmentally friendly gelatin/βcyclodextrin composite fiber adsorbents for the efficient removal of dyes from wastewater[END_REF]. The authors developed a crosslinking approach with glutaraldehyde vapour both to stabilize the nanofibers and permanently grafting the cyclodextrins to the polymer chains avoiding leaking issues. Remarkably, the prepared mats showed promising adsorption capability towards methylene blue in different experimental conditions and several other common dyes, being above all characterized by good recyclability and reusability, therefore representing cost-effective and promising products for the efficient purification of wastewater. Yet, Aytac et al. [START_REF] Aytac | Fast-dissolving electrospun gelatin nanofibers encapsulating ciprofloxacin/cyclodextrin inclusion complex[END_REF] investigated the use of gelatin nanofibers loaded with HPCD and ciprofloxacin (CIP) complexes as fastdissolving drug delivery systems. The authors were able to prove that the bead-free nanofibers encapsulating HPCD-ICs-CIP showed to be more rapidly dissolved compared to gelatin/CIP nanofibers, thus pointing out the capability of HPCDs in increasing the sample wettability and opening the way to the preparation of a broad variety of drug delivery systems able to quickly release high drug dosages. Additionally, Zhou et al. [START_REF] Zhou | Active packaging based on swim bladder gelatin/galangal root oil nanofibers: Preparation, properties and antibacterial application[END_REF] investigated the preparation of gelatin-based nanofibers containing the inclusion complex between CDs and galangal root oil (GRO). By using different gelatin sources, the authors evaluated how the composition of the protein amino acids affected the electrospinning process. Remarkably, gelatin/CD-ICs-GRO showed marked antibacterial properties against E Coli, as well as excellent mechanical and thermal properties, thus being suitable as food packaging materials. Lately, Kadam et al. [START_REF] Kadam | Gelatin/β-Cyclodextrin Bio-Nanofibers as respiratory filter media for filtration of aerosols and volatile organic compounds at low air resistance[END_REF] reported on the preparation of gelatin/CDs nanofibers to be used as filter materials. In particular, the possibility to easily control the fiber dimension and the mat porosity, coupled with the cyclodextrin inclusion complex capabilities, allowed the prepared materials to show filtration efficiency towards both solid/liquid particles and VOCs.

Gliadin (GD) is a prolamin protein largely present in wheat, as well as in other cereals, with a wide range of interesting applications [START_REF] Jia | Physicochemical and structural characteristics of the Venn components of wheat gliadin[END_REF][START_REF] Urade | Gliadins from wheat grain: an overview, from primary structure to nanostructures of aggregates[END_REF]. [START_REF] Sharif | Active food packaging coatings based on hybrid electrospun gliadin nanofibers containing ferulic acid/hydroxypropyl-beta-cyclodextrin inclusion complexes[END_REF] reported on the encapsulation of HPCD-ICs-ferulic acid within gliadin electrospun nanofibers. The complexation phenomenon allowed to increase both the thermal and photostability of FA thus preserving its antioxidant properties. Noticeably, compared to the GL nanofibers containing free FA, gliadin/HPCD-ICs-FA mats showed a superior and faster release of the bioactive compound in artificial media simulating different food or biological conditions.

Hordein (HD), likewise gliadin, is a prolamin protein present in barley and other cereals and mainly used for food applications (X. [START_REF] Huang | Proposal for C-Hordein as Reference Material in Gluten Quantification[END_REF]. [START_REF] Guan | Adsorption of Cu(II) ion by a novel hordein electrospun nanofiber modified by β-cyclodextrin[END_REF] proposed hordein nanofibrous membranes embedding N,N'-methylene bisacrylamide (MBA) molecules and grafted with CDs for the adsorption of copper ions. The uptake properties of the prepared mats were evaluated at different pH and temperature conditions with the hordein/CD-ICs-MBA nanofibers showing higher adsorption capability both compared to hordein/MBA and hordein electrospun mats. Additionally, the authors were able to prove the recyclability of the obtained mats via a humble and cost-effective washing procedure hence demonstrating their efficient use for the treatment of wastewater.

Conclusions and Future Perspectives

Nowadays, electrospinning is worldwide recognized as a simple, flexible, and cost-effective technique for the preparation of nano-and microfibers with applicability in almost any research field and it has become, in the last decade, one of the most promising approaches to improve human quality of life via the production of tailored-made products for biomedical, food, energy harvesting, textile and environmental purposes. In this sense, cyclodextrins may play a very important role and their use in combination with electrospinning has aroused growing interest. Specifically, in most cases, the objective is to prepare polymer-free cyclodextrin nanofibers able to efficiently encapsulate bioactive compounds and accurately control their release. Indeed, the outstanding capability of cyclodextrins to form non-covalent stable complexes with small molecules (e.g., hydrophobic and/or volatile compounds) allows to considerably increase their solubility, stability, and availability, hence leading to a superior encapsulation efficiency that was previously unreachable. However, a variety of innovative applications are recently being evaluated for electrospun nanofibers made of (or containing) cyclodextrins and their derivatives, also creditable to the fact that their preparation allows avoiding the intensive use of toxic solvents and/or hazardous chemicals. For instance, cyclodextrin-based nanofibers can be employed as reducing agents for the in-situ synthesis of metal nanoparticles, as sacrificial templates for the development of conductive hollow structures, as implantable scaffolds for tissue regeneration purposes, as well as to develop high performing filtering materials and food packaging products with antibacterial and antioxidant properties.

Additionally, combining the complexation capability of cyclodextrins with naturally occurring biopolymers appears to be the optimal format for the development of mats with unique and tuneable features. For instance, besides biocompatibility and greater biological response, biodegradability and digestibility, the greatest advantage of natural biopolymers is that they can be processed by using water or poorly toxic organic solvents making them extremely interesting from an industrial point of view. Moreover, the continuous advances in the extraction of materials from natural waste sources may lead in the future to the development of environmentally friendly electrospun products in view of a green circular economy. However, the development of these strategies remains at an initial stage and further studies are required since, at present, the electrospinning of natural biopolymers requires appropriate additives to facilitate the processing, as well as post-processing treatments to increase the mat stability and mechanical performances without affecting the intrinsic biocompatibility. Noticeably, it is noteworthy that cyclodextrins have been demonstrated able to enhance the spinnability of biopolymer-based formulations due to the tendency to create supramolecular structures with the biopolymers, thus reducing, or even eliminating, the amount of required synthetic cospinning agents. Nevertheless, despite the considerable advances recently made at the laboratory scale, the industrial implementation of natural polymer electrospinning has been scarcely explored and remains a great challenge especially in terms of production rate.

In conclusion, in order to ensure the efficient translation between laboratory prototypes and commercial products, workability studies are mandatory to verify the effective applicability of cyclodextrin-based electrospun membranes for the proposed applications and more research-industry collaborations are indispensable to lower the cost and improve the industrialization of such materials.

Conflict of Competing Interest

None.

Cu

Figure 1 .

 1 Figure 1. Annual trend of publications regarding (a) electrospinning, (b) functionalization of electrospun nanofibers, (c) cyclodextrins, and (d) cyclodextrin-functionalized electrospun nanofibers. Insets represent the cumulative number of publications. Data has been retrieved from Scopus database.

Figure 2 .

 2 Figure 2. (a) Schematic of natural biopolymer-based electrospun membranes depending on the source materials and (b) pie chart representing their main applications according to the Scopus database.

Figure 3 .

 3 Figure 3. (a) Chemical structure of the most common CDs. (b) Three-dimensional conformation taken by CDs. (c) Summary of the main physical properties of CDs depending on the glucose unit number. (d)

Figure 4 .

 4 Figure 4. (a) Effect of HPCD concentration on the conductivity, bound water and viscosity of aqueous solutions. SEM micrographs of electrospun HPCD solutions of (b) 50 wt%, (c) 60 wt%, (d) 65 wt%, (e) and 70 wt%. TEM micrographs showing fibers electrospun from a 65 wt% solution at (f) 200000X and (g) 400000X magnifications. Reproduced with permission from Manasco et al., 2012. © The Royal Society of Chemistry 2012.

Figure 5 .

 5 Figure 5. Schematics of different crosslinking strategies of the cyclodextrin nanofibers. The crosslinking agents are added to the CD solution prior to electrospinning and a curing step initiate the reaction in the final membrane. Reaction of CDs with (a) 1,2,3,4-butanetetracarboxylic acid (BTCA) (reproduced with permission from Celebioglu et al., 2017. © The Author(s) 2017), (b) epichlorohydrin (ECH) (reproduced with permission from Celebioglu, Topuz, & Uyar, 2019b. © 2018 American Chemical Society), and (c) citric acid (CTR) and benzoxazine (BA-a) monomers (reproduced with permission from Dogan et al., 2019. © 2019 Elsevier Ltd.

Figure 6 .

 6 Figure 6. Schematics of preparation methods for cyclodextrin-functionalized nanofibers. (a) Electrospinning of polymer/CD-ICs solutions, (b) electrospinning of polymer/CDs/active compound solutions, (c) CD/CD-ICs grafted or CD/CD-ICs crosslinked nanofibers, (d) coaxial electrospinning of CD/CD-ICs core functionalized nanofibers, and (e) pseudopolyrotaxanes structures.

Figure 7 .

 7 Figure 7. Fiber morphology of chitosan-based electrospun mats with an increasing HPCD content: (a) 0 wt%, (b) 30 wt%, (c) 40 wt%, and (d) 50 wt%. Reproduced with permission from Burns et al., 2015. © The Royal Society of Chemistry 2015. (e) Schematic illustration of CH/HPCD electrospun nanofiber composition. Reproduced with permission from C. Xue & Wilson, 2019. (f) Macroscopic and microscopic images of Nitinol stent covered with CH/polyHPCD-ICs-simvastatin nanofibers before (g, i, k) and after crimping (h, j, l). Reproduced with permission from Kersani et al., 2020. © 2020 Elsevier B.V.

Figure 8 .

 8 Figure 8. SEM micrographs of (a) as-spun RSF nanofibers, (b) RSF nanofibers after ethanol spraying treatment, (c) RSF nanofibers after acetone immersion treatment, (d) as-spun RSF/HPβCD-ICs-TAM nanofibers, (e) RSF/HPβCD-ICs-TAM nanofibers after ethanol spraying treatment, (f) RSF/HPβCDs-ICs-TAM nanofibers after acetone immersion treatment. Reproduced with permission from W. Liu et al., 2016. © 2016 Elsevier B.V.

Drug and bioactive compound delivery systems

			sodium Acyclovir	---	(Celebioglu & Uyar, 2021) Kusku, et al., 2016)
	Application	Cyclodextrin	compounds Paracetamol Chloramphenicol Encapsulated Vitamin E Kanamycin Linalool	Solvent ------Water -EtOH ------	(Zehra Irem Yildiz & Uyar, 2019) (Topuz et al., 2021) Ref. (Celebioglu & Uyar, 2017) (Topuz et al., 2021)
		MCDs	---α-lipoic acid Gentamicin	Water, DMF, DMAc, Urea ------	(Celebioglu & Uyar, 2010, 2012) (Celebioglu & Uyar, 2019a) (Topuz et al., 2021)
		HPCDs	---Ibuprofen Ampicillin	Water, DMF, Urea ------	(Manasco et al., 2012; W. Zhang et al., 2012) (Celebioglu & Uyar, 2019b) (Topuz et al., 2021)
		HPCDs	---Metronidazole Sulfisoxazole	Water, DMF, DMAc, Urea ------	(Celebioglu & Uyar, 2012) (Celebioglu & Uyar, 2019c) (Zehra Irem Yildiz et al., 2017)
	Fundamental studies	αCDs SEBCDs	---Curcumin Paracetamol Hydrocortisone Voriconazole	------Water, DMF, DMAc, DMSO, water -NaOH ------	(Celebioglu & Uyar, 2020c) (Zehra Irem Yildiz & Uyar, 2019) (Celebioglu & Uyar, 2013a) (Celebioglu & Uyar, 2020d) (Vass et al., 2019)
		CDs	---Ferulic acid α-lipoic acid -galactosidase Curcumin	------Water, DMF, DMAc, DMSO, water -NaOH, ionic liquids ------	(Celebioglu & Uyar, 2020e) (Celebioglu & Uyar, 2019a) (Ahn et al., 2013; Celebioglu & Uyar, 2013a) (Vass et al., 2020) (Celebioglu & Uyar, 2020c)
		HPαCDs	---Doxycycline Ferulic acid	Water, tap water, salty water ------	(Celebioglu & Uyar, 2020b) (Kiss et al., 2020) (Celebioglu & Uyar, 2020e)
			Triclosan Thiabendazole Vanillin Azobenzene Vitamin-A acetate Limonene	---Water, DMF, DMAc ------------	(Gao et al., 2020) (Celebioglu, Yildiz, et al., 2018b) (Celebioglu, Umu, et al., 2014; Celebioglu & Uyar, 2011) (M. Chen et al., 2013) (Celebioglu & Uyar, 2020a) (Aytac, Yildiz, Kayaci-Senirmak, San Keskin, Kusku, et al., 2016)
		HPCDs HPCDs	Geraniol Vanillin Linalool Camphor Limonene Citral Carvacrol	Water, DMF, DMAc ------------------	(Celebioglu, Kayaci-Senirmak, et al., 2016) (Aytac, Yildiz, et al., 2017) (Aytac, Yildiz, Kayaci-Senirmak, San Keskin, Tekinay, et al., 2016) (Celebioglu, Aytac, et al., 2018) (Aytac, Celebioglu, et al., 2018) (Aytac, Yildiz, Kayaci-Senirmak, San Keskin, Kusku, et al., 2016) (Zehra I. Yildiz et al., 2018)
			Triclosan Linalool Menthol Citral Cineole	---------------	(Aytac, Yildiz, et al., 2017) (Zehra Irem Yildiz et al., 2018) (Celebioglu, Umu, et al., 2014; Celebioglu & Uyar, 2011) (Aytac, Celebioglu, et al., 2018) (Celebioglu, Yildiz, et al., 2018a)
		HPCDs	Geraniol Carvacrol p-cymene Menthol Eugenol	---------------	(Zehra I. Yildiz et al., 2018) (Celebioglu, Yildiz, et al., 2018a) (Aytac, Yildiz, Kayaci-Senirmak, San Keskin, Tekinay, et al., 2016) (Zehra Irem Yildiz et al., 2018) (Celebioglu, Yildiz, et al., 2018b)
			Camphor Cineole Thymol	---------	(Celebioglu, Aytac, et al., 2018) (Celebioglu, Yildiz, et al., 2018a) (Celebioglu, Yildiz, et al., 2018c)
	Fast-dissolving nanofibers for the rapid compound administration	MCDs HPCDs MCDs	Geraniol p-cymene Cinnamaldehyde Spironolactone Eugenol Thymol Vitamin-A acetate Diclofenac Cinnamaldehyde Vanillin Living bacteria Limonene	---------EtOH ---------EtOH ---Water, DMF, DMAc Water -skim milk ---	(Celebioglu, Yildiz, et al., 2018a) (Zehra I. Yildiz et al., 2019) (Aytac, Yildiz, Kayaci-Senirmak, San Keskin, Tekinay, et al., 2016) (Vigh et al., 2013) (Celebioglu, Yildiz, et al., 2018b) (Celebioglu, Yildiz, et al., 2018c) (Celebioglu & Uyar, 2020a) (Balogh et al., 2015) (Celebioglu, Kayaci-Senirmak, et al., 2016) (Zehra I. Yildiz et al., 2019) (San Keskin et al., 2018) (Aytac, Yildiz, Kayaci-Senirmak, San Keskin,
			13

Table 2 .

 2 Comprehensive summary of polysaccharide-based electrospun membranes functionalized with CDs or CD-ICs and their main applications.

	617
	Polysaccharide	Cyclodextrins	Encapsulated bioactive molecules	Application	Ref.
			---	Cyclodextrin grafted nanofibers for effluent dye removal	(Norouzi et al., 2012)
		CDs	Cinnamon and oregano essential oils	Nanofibrous membranes with strong antibacterial properties for biomedical and food packaging applications	(Munhuweyi et al., 2018)
		CMCDs	Salicylic acid	Cyclodextrin grafted nanofibers as drug delivery systems with tuneable release kinetics	(Bazhban et al., 2013)
	Chitosan	HPCDs	---	Fundamental study of the effect of CDs on chitosan solution spinnability	(Burns et al., 2015; C. Xue & Wilson, 2019)
		Poly-HPCDs	Triclosan	Biomedical and food packaging products with improved water stability, tenable release kinetics and antibacterial properties	(Ouerghemmi et al., 2016)
			Simvastatin	Angioplasty bare metal stent covering layer for restenosis prevention	(Kersani et al., 2020)
		CDs	Limonene, Perillaldehyde	Edible food packaging products with antibacterial properties, high stability and humidity triggered release behaviour	(Fuenmayor et al., 2013; Mascheroni et al., 2013)
	Pullulan	CDs	Eugenol	Biomedical and food packaging products with enhanced release and antioxidant properties	(Celebioglu & Uyar, 2020f)
			N-halamine copolymers	Biomedical and food packaging products with biocidal properties	(R. Li et al., 2014)
			Ag/Fe-NPs	Filter materials embedding in-situ synthesized metal nanoparticles for wastewater purification	(Nthunya et al., 2017)
			---	Odour adsorbent filter materials for oil and fat derived volatile compounds	(Ghorani et al., 2019)
	Cellulose acetate	CDs	---	Cyclodextrin grafted nanofibers for the removal of phenanthrene	(Celebioglu, Demirci, et al., 2014)
			---	Cyclodextrin grafted nanofibers as filter materials for toluene in wastewater	(Yuan et al., 2017)
			Tetrafluoroterephthalonitrile	Cyclodextrin grafted nanofibers for the removal of bisphenol pollutants	(Y. Lv et al., 2021)

  Owing to the abovementioned finding and keeping in mind cyclodextrin complexation capability, the authors indicated that these nanofibrous mats are promising products for biomedical and food packaging applications. Subsequently, Aytac et al.[START_REF] Aytac | Antibacterial electrospun zein nanofibrous web encapsulating thymol/cyclodextrin-inclusion complex for food packaging[END_REF] prepared zein nanofibers functionalized with the inclusion complexes between -cyclodextrins and thymol, which were able to provide a high encapsulation capability leading to enhanced stability and release kinetic. Moreover, by testing the antibacterial properties toward E. Coli and S. Aureus bacteria in meat simulated storage conditions at T = 4 °C, the prepared mats were suggested as promising antibacterial food packaging materials. Similar work was reported by Antunes et al.[START_REF] Dias Antunes | Antimicrobial electrospun ultrafine fibers from zein containing eucalyptus essential oil/cyclodextrin inclusion complex[END_REF], who proposed the encapsulation of -

Kayaci et al. (Kayaci & Uyar, 2012a)

first reported on a fundamental study regarding the preparation of zein nanofibers encapsulating different amount of CDs,CDs, orCDs. Comparably to what was reported by other research groups for polysaccharides, the addition of CDs noticeably improved the spinnability of pristine zein solutions leading to bead-free nanofibers, with only a slight morphological dependence on the cyclodextrin type, and enhanced thermal stability.

cyclodextrin-eucalyptus essential oil complexes in zein electrospun nanofibers by using aqueous ethanol (EtOH) eco-friendly mixture as solvent. SEM images proved the good homogeneity of the obtained nanofibers, which contained around 24% of the formed inclusion complexes. Moreover, the antibacterial properties were tested against S. aureus and Listeria monocytogenes (L. monocytogenes) bacteria showing a

Polycyclodextrins.29

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-forprofit sectors.

Abbreviations