Christel Gervais

Christian Bonhomme

Danielle Laurencin
email: danielle.laurencin@umontpellier.fr

Recent directions in the

come

Introduction

Calcium phosphates are widely studied in the field of biomaterials. [START_REF] Dorozhkin | Calcium orthophosphates (CaPO4): occurrence and properties[END_REF][START_REF] Elliott | Structure and Chemistry of the Apatites and Other Calcium Orthophosphates[END_REF][START_REF] Legeros | Calcium phosphate biomaterials: an update[END_REF][START_REF] Verron | Calcium phosphate biomaterials as bone drug delivery systems: a review[END_REF][START_REF] Dorozhkin | Functionalized calcium orthophosphates (CaPO4) and their biomedical applications[END_REF][START_REF] Dorozhkin | Bioceramics calcium orthophosphates[END_REF][START_REF] O'neill | Critical review: Injectability of calcium phosphate pastes and cements[END_REF] The main interest for these compounds originates from the fact that bone and teeth contain a calcium phosphate phase generally referred to as biological carbonated apatite. [START_REF] Elliott | Structure and Chemistry of the Apatites and Other Calcium Orthophosphates[END_REF] While the first studies on calcium phosphates appear to date back to the 18th century, [START_REF] Dorozhkin | Calcium orthophosphates and man: a historical perspective from the 1770s to 1940[END_REF] numerous investigations have since been performed, crossing disciplines such as chemistry, biology and medicine. Indeed, the biocompatibility of calcium phosphate phases together with their capacity to host a wide variety of substituents make them highly attractive not only for bone and dental repair (as ceramic coatings on implants or as biocements), but also for applications as drug delivery systems or contrast agents for MRI.

From a chemist's perspective, calcium phosphates can come under a many different chemical compositions. [START_REF] Elliott | Structure and Chemistry of the Apatites and Other Calcium Orthophosphates[END_REF][START_REF] Dorozhkin | Bioceramics calcium orthophosphates[END_REF] First, the phosphate ions can vary in terms of degree of condensation and protonation state (Figure 1). Orthophosphates (PO4 3-) are the most frequent. These anions can be (i) fully deprotonated, as in stoichiometric hydroxyapatite (HA, Ca10(PO4)6(OH)2) and β-tricalcium phosphate (Ca3(PO4)2, β-TCP), (ii) protonated once, as in brushite CaHPO4.2H2O and monetite CaHPO4, or (iii) protonated twice, as in monocalcium phosphate monohydrate (MCPM, Ca(H2PO4)2.H2O). More condensed phosphate ions include pyrophosphates (P2O7 4-, as in α-Ca2P2O7), metaphosphates and polyphosphates (with ~ 2 P-O-P bonds per phosphorous, as in γ-Ca(PO3)2), as well as ultraphosphates (with ~ 3 P-O-P bonds per phosphorous, as in Ca2P6O17). While some calcium phosphate phases are anhydrous, others are hydrated. The Ca-pyrophosphate phases Ca2P2O7.nH2O are a very good example of this, as mono, di, tri, and tetrahydrate phases have been reported, in addition to the anhydrous polymorphs. [START_REF] Gras | Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7•H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates[END_REF][START_REF] Gras | Crystallisation of a highly metastable hydrated calcium pyrophosphate phase[END_REF][START_REF] Gras | Synthesis and Characterisation of Hydrated Calcium Pyrophosphate Phases of Biological Interest[END_REF][START_REF] Slater | Enhanced stability and local structure in biologically relevant amorphous materials containing pyrophosphate[END_REF] In addition to the structural complexity, synthetic and natural calcium phosphate phases can exhibit very different crystallinities, and several amorphous phases have also been described.

Moreover, the degree of crystallinity/order can significantly vary within one mineral particle (e.g. from surface to bulk). They also frequently contain traces of other ions as substituents within their structures (e.g. CO3 2-, F -, SiO4 4-, Na + , Mg 2+ …). Last but not least, a large proportion of these biomaterials also have an organic component (biopolymers, peptides…), which mainly consists of collagen in the case of native bone. In relation to this, many investigations have focused on the study of the structure of bone mineral itself, and in finding synthetic models capable of mimicking some of its structural features. These have included carbonate-substituted nanocrystalline hydroxyapatite and octacalcium phosphate phases.

In view of gaining deeper insight into the structure of bone, and preparing calcium phosphatebased biomaterials with optimal properties, much effort has been made in the development of advanced characterization tools, capable of providing information on their structure at different scales.

In this context, solid state NMR has played a significant role, [START_REF] Duer | The contribution of solid-state NMR spectroscopy to understanding biomineralization: Atomic and molecular structure of bone[END_REF][START_REF] Mroue | Solid-state NMR spectroscopy: the magic wand to view bone at nanoscopic resolution[END_REF] with the first studies dating back to the 1960s (to the best of our knowledge). [START_REF] Bhatnagar | of calcium and strontium hydroxyapatites[END_REF] Most of the early magic angle spinning (MAS) NMR work concerned 1 H and 31 P NMR analyses, [START_REF] Rothwell | High-resolution variable-temperature phosphorus-31 NMR of solid calcium phosphates[END_REF][START_REF] Yesinowski | Hydrogen environments in calcium phosphates: proton MAS NMR at high spinning speeds[END_REF][START_REF] Beshah | Solid state carbon-13 and proton NMR studies of carbonate-containing calcium phosphates and enamel[END_REF] as both of these spin-1/2 isotopes have a very good receptivity (Table 1). [START_REF] Kolodziejski | Solid-state NMR studies of bone[END_REF][START_REF] Pourpoint | Calcium phosphates and hydroxyapatite: solid-state NMR experiments and first-principles calculations[END_REF][START_REF] Pourpoint | High-resolution solid state NMR experiments for the characterization of calcium phosphate biomaterials and biominerals[END_REF] One of the highlights of these investigations was the study by Ackermann et al in 2003, who provided direct evidence of the presence of apatite-like hydroxyl groups in bone mineral using 2D 1 H-31 P HETCOR (heteronuclear correlation) experiments. [START_REF] Cho | Detection of hydroxyl ions in bone mineral by solid-state NMR spectroscopy[END_REF] Other important landmarks subsequently followed between 2005 and 2010, including the 13 C{ 31 P} REDOR (Rotational Echo Double Resonance) studies initiated by Duer et al to elucidate the organic-mineral interface of bone, [START_REF] Jaeger | Investigation of the Nature of the Protein-Mineral Interface in Bone by Solid-State NMR[END_REF][START_REF] Wise | The Organic-Mineral Interface in Bone Is Predominantly Polysaccharide[END_REF] the first 2D NMR studies of substituted apatites aiming at locating precisely the position of ionic substituents, [START_REF] Mason | Solid-State NMR Study of the Role of H and Na in AB-Type Carbonate Hydroxylapatite[END_REF][START_REF] Gomes | Thorough analysis of silicon substitution in biphasic calcium phosphate bioceramics: A multitechnique study[END_REF][START_REF] Laurencin | Probing the calcium and sodium local environment in bones and teeth using multinuclear solid state NMR and X-ray absorption spectroscopy[END_REF] and the first complete natural-abundance 43 Ca MAS NMR experiments of synthetic calcium phosphates and bone. [START_REF] Laurencin | Probing the calcium and sodium local environment in bones and teeth using multinuclear solid state NMR and X-ray absorption spectroscopy[END_REF][START_REF] Laurencin | Natural abundance 43Ca solid-state NMR characterization of hydroxyapatite: identification of the two calcium sites[END_REF][START_REF] Gervais | New perspectives on calcium environments in inorganic materials containing calcium-oxygen bonds: A combined computational-experimental 43Ca NMR approach[END_REF] In the latter case, the main challenge was due to the very poor receptivity of calcium-43, which has a natural abundance of only 0.14% and a very low resonance frequency (Table 1). [START_REF] Laurencin | Development of 43Ca solid state NMR spectroscopy as a probe of local structure in inorganic and molecular materials[END_REF] Since 2010, materials chemists have continued to explore new frontiers to use NMR for gaining even deeper insight into these systems, by taking advantage of the progress made by the NMR community in terms of instrumentation, pulse sequence development, and data interpretation (using combined experimental-computational approaches). While some of these new achievements have been described in recent reviews, [START_REF] Duer | The contribution of solid-state NMR spectroscopy to understanding biomineralization: Atomic and molecular structure of bone[END_REF][START_REF] Mroue | Solid-state NMR spectroscopy: the magic wand to view bone at nanoscopic resolution[END_REF][START_REF] Bonhomme | Recent NMR developments applied to organic-inorganic materials[END_REF] the purpose of this manuscript is to highlight a selection of results and trends which have emerged over the past 5 years, to show what level of insight they are likely to lead to in the future. The focus will first be set on studies relative to synthetic calcium phosphate biomaterials, before focussing on natural bone and dental tissues.

Isotope

Synthetic calcium phosphates and related biomaterials

Crystalline phases

As crystalline calcium phosphates are most frequently isolated as powders which are unsuitable for single-crystal X-ray diffraction, it is no surprise that approaches based on NMRcrystallography [START_REF] Bryce | NMR crystallography: structure and properties of materials from solid-state nuclear magnetic resonance observables[END_REF][START_REF] Taulelle | Fundamental principles of NMR crystallography[END_REF][START_REF] Martineau | NMR crystallography: Applications to inorganic materials[END_REF][START_REF] Ashbrook | Combining solid-state NMR spectroscopy with first-principles calculations -a guide to NMR crystallography[END_REF][START_REF] Harris | NMR Crystallography[END_REF][START_REF] Mayen | Advances in the synthesis and structure of α-canaphite: a multitool and multiscale study[END_REF] are increasingly being used to help establish the details of their structure and local dynamics. In such investigations, high resolution NMR analyses are combined to powder X-ray and neutron diffraction data, and often complemented by ab initio calculations of NMR parameters (in the so-called « SMARTER crystallography » strategy), [START_REF] Martineau | SMARTER crystallography of the fluorinated inorganic-organic compound Zn3Al2F12[END_REF] in order to refine the atomic positions. Over the past 5 years, these approaches have clearly enabled to gain deeper insight into the bulk structure of monetite, [START_REF] Yu | The Monetite Structure Probed by Advanced Solid-State NMR Experimentation at Fast Magic-Angle Spinning[END_REF][START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF] hydrated calcium pyrophosphates, [START_REF] Gras | From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective[END_REF] and carbonated hydroxyapatite [START_REF] Leroy | Hydroxyapatites: Key Structural Questions and Answers from Dynamic Nuclear Polarization[END_REF], as detailed below.

Concerning monetite (CaHPO4), the main progress made concerns the higher resolution achieved in the 1 H, 31 P and 43 Ca NMR analyses, allowing a better assignment of the NMR resonances.

On one hand, using fast-MAS 2), and a tentative assignment was subsequently proposed on the basis of DFT calculations [START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF] (performed using the Gauge Including Projector Augmented Wave (GIPAW) approach). [START_REF] Pickard | All-electron magnetic response with pseudopotentials: NMR chemical shifts[END_REF][START_REF] Bonhomme | First-Principles Calculation of NMR Parameters Using the Gauge Including Projector Augmented Wave Method: A Chemist's Point of View[END_REF][START_REF] Charpentier | The PAW/GIPAW approach for computing NMR parameters: A new dimension added to NMR study of solids[END_REF] Figure 2. 43 Ca MAS NMR spectra of a monetite phase (enriched in 43 Ca), recorded at 20.0 and 35.2 T, showing the significant gain in resolution achieved in the latter case. The fits are shown below each spectrum (dashed green and purple lines). The local environments of calcium are represented above the spectra (Ca in green, O in red, H in white) ; these can be split into two sub-groups on the basis of the ultra-high field NMR experiments and GIPAW-DFT calculations of 43 Ca NMR parameters (the colours used for the two dashed boxes around the Ca-environments match those of the corresponding fits). [START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF] Adapted from Ref. [START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF] with permission from The Royal Society of Chemistry.

Crystalline calcium pyrophosphates Ca2P2O7.nH2O (n = 0, 1, 2, 4) were extensively investigated by Gras et al, using high resolution 1 H, 31 P and 43 Ca NMR experiments and GIPAW-DFT calculations. [START_REF] Gras | From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective[END_REF] For each phase, 1 H MAS NMR spectra were recorded at 14.1 T using DUMBO homonuclear decoupling, [START_REF] Sakellariou | Homonuclear dipolar decoupling in solidstate NMR using continuous phase modulation[END_REF] 31 P MAS NMR spectra were recorded at 14.1 T using different spinning speeds in order to extract the chemical shift anisotropy (CSA) parameters δCSA and ηCSA, and natural-abundance 43 Ca MAS NMR spectra were recorded at two fields (14.1 and 20.0 T) in order to extract the quadrupolar parameters CQ and ηQ. The overlap between some of the resonances and similarity between their NMR parameters were found to be a challenge for identifying the different sites. GIPAW-DFT calculations were thus performed using as starting points the published crystallographic structures, and optimising either H atom positions only, or all atomic positions. This allowed not only the 31 P and 43 Ca NMR resonances of each phase to be assigned, but also the quality of the starting crystallographic data to be evaluated. The case of the monoclinic Ca2P2O7.2H2O phase was in this context particularly interesting, because the two 31 P resonances could only be safely attributed after relaxation of H atom positions: this was the only way to have a consistent agreement between experimental and calculated δiso, δCSA and ηCSA parameters. The 1 H NMR analyses were also of interest, as the differences between experimental and calculated parameters were observed, which were interpreted as an indication of the presence of dynamics within the crystal structures. This point is currently being further investigated. Overall, this investigation clearly underscores the importance of combining high resolution NMR analyses to GIPAW-DFT calculations when studying hydrated calcium phosphates for which the position and dynamics of water molecules can have a significant impact on the spectra.

While most biological apatites are known to be carbonated, the actual position of carbonate ions within the hydroxyapatite structure has been the subject of much discussion. Indeed, although these are known to be able to substitute for both hydroxyl groups (« A-type » substitution) and phosphates (« B-type » substitution), the question of order/disorder related to carbonate substitution, and the possible clustering of carbonate ions within the apatite lattice had long remained unanswered. [START_REF] Fleet | Carbonated Hydroxyapatite: Materials, Synthesis, and Applications[END_REF] Using Dynamic Nuclear Polarization (DNP), Bonhomme and co-workers were able to provide the very first direct evidence of carbonate clustering within synthetic carbonated nanocrystalline apatites. [START_REF] Leroy | Hydroxyapatites: Key Structural Questions and Answers from Dynamic Nuclear Polarization[END_REF] By combining 2D 31 P → 13 C CP-HETCOR and 13 C double-quantum-singlequantum (DQ-SQ) MAS NMR experiments at 9.4 T, enhanced by indirect DNP using 1 H 31 P and 1 H 13 C CP transfers, respectively (Figure 3), it was possible to conclude on the presence of clustering of the carbonates, with a majority of clustered B/B substitutions, a minority of A/B substitutions, and only a small fraction of isolated B sites. Such analyses were only made possible thanks to the significant gain in sensitivity achieved using DNP, and appear as a major step forward to the study of carbonate substitutions within apatites, as the level of information achieved here could not have been extracted 13 C DQ-SQ MAS NMR spectrum, together with some of the 1D 13 C NMR slices (noted i) to iv)). Adapted with permission from Ref. [START_REF] Leroy | Hydroxyapatites: Key Structural Questions and Answers from Dynamic Nuclear Polarization[END_REF]. Copyright 2017 American Chemical Society.

Amorphous phases

In parallel to the investigations on crystalline calcium phosphates, amorphous phases have also been the subject of active research, in relation with the increased evidence of their importance within mineralized tissues, and the need to understand their formation and possible evolution into more Amorphous calcium pyrophosphates have attracted the attention of several research groups, in view of : (i) trying to understand the formation of pathological calcifications composed of calcium pyrophosphates in the joints (a disease called « pseudo-gout »), [START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF][START_REF] Gras | From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective[END_REF] or (ii) developing novel classes of phosphate-based biomaterials for bone substitution and regeneration. [START_REF] Mayen | A soft-chemistry approach to the synthesis of amorphous calcium ortho/pyrophosphate biomaterials of tunable composition[END_REF][START_REF] Soulie | Development of a new family of monolithic calcium (pyro)phosphate glasses by soft chemistry[END_REF][START_REF] Yu | Advanced solidstate 1H/31P NMR characterization of pyrophosphate-doped calcium phosphate cements for biomedical applications: The structural role of pyrophosphate[END_REF] Concerning the first point, precipitated amorphous phases of general formula Ca2P2O7.nH2O (n ~ 4) were characterized by 1 H, 31 P and 43 Ca MAS NMR, and their spectra compared to those related to crystalline phases. [START_REF] Gras | From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective[END_REF] Differences in the 1 H and 43 Ca NMR spectra were observed depending on the precipitation procedure (i.e. with or without control or not of the pH), while 31 P MAS NMR spectra were essentially the same. This clearly demonstrates the importance of performing multinuclear NMR characterizations (including challenging nuclei like 43 Ca) when studying these amorphous materials. From a more materials perspective, it was concluded that the H-bond network of the water molecules within these amorphous phases depends on the synthetic protocol. Structural models were subsequently proposed, using a computational approach based on Monte Carlo (MC) simulations, structural relaxation using Ab Initio Molecular Dynamics (AIMD), and geometry optimization using DFT calculations. [START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF] For each model, GIPAW-DFT calculations of NMR parameters were then performed. Calculated 43 Ca MAS NMR spectra were compared to experimental ones, which had been recorded at natural abundance at 35.2 T in less than 4 hours (Figure 4a). Although the range of calculated 43 Ca NMR isotropic shifts was found to be overall consistent with the experimental data, discrepancies remained between experimental and calculated values, which may be due to dynamics of the water molecules within these systems (as also pointed out in section 2.1 when discussing the corresponding crystalline phases). [START_REF] Gras | From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective[END_REF] Figure 4. a/ Natural abundance 43 Ca MAS NMR spectrum of a precipitated amorphous Capyrophosphate, recorded at 35.2 T, and comparison with DFT-calculated isotropic shifts of structural models of the material (as illustrated above in the insert). Adapted from Ref. [START_REF] Bonhomme | Pushing the limits of sensitivity and resolution for natural abundance 43Ca NMR using ultra-high magnetic field (35.2 T)[END_REF] with permission from The Royal Society of Chemistry. b/ 2D 31 P DQ-SQ MAS NMR spectrum of an amorphous mixed ortho/pyrophosphate biomaterial, recorded at 16.4 T (using SPC5 recoupling and 1 H 31 P CP transfer to create the initial 31 P magnetization), showing clearly the proximity of ortho and pyrophosphate units (dashed red boxes). Adapted from Ref. [START_REF] Mayen | A soft-chemistry approach to the synthesis of amorphous calcium ortho/pyrophosphate biomaterials of tunable composition[END_REF] with permission from Elsevier.

Another important family of amorphous phases involving both ortho-and pyrophosphate anions are the monolithic glass-like materials which have been developed by Soulié, Combes and coworkers, [START_REF] Mayen | A soft-chemistry approach to the synthesis of amorphous calcium ortho/pyrophosphate biomaterials of tunable composition[END_REF][START_REF] Soulie | Development of a new family of monolithic calcium (pyro)phosphate glasses by soft chemistry[END_REF] as a means to propose alternatives to silicate bioactive glasses. The idea behind the synthesis of these materials is that by controlling the ortho/pyrophosphate ratio it should be possible to tune the kinetics of biomaterial degradation and bone mineral formation in vivo. These materials are of high complexity, as they contain a variety of anions (ortho and pyrophosphates, which can be protonated or not), a variety of cations (Ca 2+ as well as Na + or K + , depending on the pyrophosphate precursor used in the synthesis), and water molecules. Hence, many questions deserved to be answered, regarding (i) the ortho/pyrophosphate ratio in the isolated material (in comparison to the one used in the starting solution), (ii) the relative protonation of ortho and pyrophosphate anions, and (iii) the possible segregation between ortho and pyrophosphate species within the precipitated material. To address these questions, a variety of different NMR experiments were used, which included (i) 31 P INADEQUATE analyses (Incredible Natural Abundance DoublE QUAntum Transfer Experiment), as some overlap between the 31 P ortho and pyrophosphate resonances can occur), (ii) 31 P{ 1 H} HETCOR studies at short contact time, which revealed that the orthophosphates are mainly protonated, and (iii) 31 P DQ-SQ analyses (using SPC5 recoupling and 1 H 31 P CP transfer to create the initial 31 P magnetization), which confirmed the intimate mixing of both anions (Figure 4b). [START_REF] Mayen | A soft-chemistry approach to the synthesis of amorphous calcium ortho/pyrophosphate biomaterials of tunable composition[END_REF] Such information is currently being used, in conjunction with additional high resolution 43 Ca and 23 Na data, and pair distribution function (PDF) analyses, to construct computational models of the materials.

Concerning amorphous calcium orthophosphates (ACPs), several recent investigations have also been reported. [START_REF] Bussola Tovani | Formation of stable strontium-rich amorphous calcium phosphate: Possible effects on bone mineral[END_REF][START_REF] Von Euw | Amorphous surface layer versus transient amorphous precursor phase in bone -A case study investigated by solid-state NMR spectroscopy[END_REF][START_REF] Yang | Novel gallium-doped amorphous calcium phosphate nanoparticles: Preparation, application and structure study[END_REF][START_REF] Chen | Characterization of the crystallization pathway of calcium phosphate in liposomes[END_REF][START_REF] Wang | Water-mediated structuring of bone apatite[END_REF] One important study by the group of Azaïs, Nassif and co-workers, is the NMR analysis performed in view of deciphering between two representations of bone mineral : (i) nanoparticles formed of an apatitic crystalline core surrounded by an ACP-like surface layer; and/or (ii) phase-separated particles of ACP and apatite. To distinguish both cases, a series of solid-state NMR analyses were carried out on ACP, synthetic biomimetic apatites, and physical mixtures of apatite and ACP, and spectra were compared to those of sheep bone mineral. NMR experiments consisted of (i) a double cross polarization (CP) 1 H  31 P  1 H pulse sequence, in order to select the 1 H resonances belonging to calcium phosphate environments, followed by (ii) a 1 H spin diffusion experiment (EXchange SpectroscopY, EXSY) in order to look into the relative proximity of the different calcium phosphate domains. [START_REF] Von Euw | Amorphous surface layer versus transient amorphous precursor phase in bone -A case study investigated by solid-state NMR spectroscopy[END_REF] These NMR analyses were able to provide unambiguous evidence that bone mineral particles have a core-shell organisation, with a crystalline apatitic core, surrounded by an ACP coating. Such information is particularly important, considering the complexity of bone mineral and the ongoing discussions regarding its structure and formation.

Calcium phosphate surfaces & interfaces

In addition to investigating the bulk structure of crystalline and amorphous calcium phosphate phases, a number of NMR studies have also concerned characterizing the surface of these particles, and how they can interact at the interface with organic functions (such as those found in bone) or other inorganic materials (such as bioactive glasses).

While experiments such as those described just above can provide evidence of an interface between the crystalline and amorphous calcium phosphate components in biomimetic apatites and bone, [START_REF] Von Euw | Amorphous surface layer versus transient amorphous precursor phase in bone -A case study investigated by solid-state NMR spectroscopy[END_REF] the obvious next step is to determine what ionic environments are present at the surface of the particles. This was actually one of the goals of the DNP studies recently reported by Lee et al. [START_REF] Lee | Interfacial Ca2+ environments in nanocrystalline apatites revealed by dynamic nuclear polarization enhanced 43Ca NMR spectroscopy[END_REF] Thanks to the significant gain in sensitivity provided by DNP, it was possible to identify not only surface carbonate ions (Figure 5a), but also surface calcium sites (Figure 5b). The latter result is all the more noteworthy when considering the challenges related to performing 2D 1 H- 43 Ca HETCOR analyses at natural abundance (0.14 %), due to the unfavorable NMR properties of calcium-43 (Table 1). The study of organic-mineral interfaces in synthetic hybrid materials involving a calciumphosphate component has also been the subject of active research. While some of the recent studies have been performed in order to establish the structure of apatite-based drug formulations and composite bioceramics for bone repair, [START_REF] Pizzoccaro | Adsorption of benzoxaboroles on hydroxyapatite phases[END_REF][START_REF] Brouillet | Biomimetic apatite-based composite materials obtained by spark plasma sintering (SPS): physicochemical and mechanical characterizations[END_REF] others were carried out to further investigate the a/ b/ structure of bone (by looking at octacalcium phosphate derived phases, [START_REF] Li | Solid state NMR -An indispensable tool in organicinorganic biocomposite characterization; refining the structure of octacalcium phosphate composites with the linear metabolic di-acids succinate and adipate[END_REF][START_REF] Davies | Citrate bridges between mineral platelets in bone[END_REF] or at the adsorption of non-collagenous bone proteins like osteocalcin on hydroxyapatite [START_REF] Iline-Vul | How does osteocalcin lacking γ-glutamic groups affect biomimetic apatite formation and what can we say about its structure in mineral-bound form?[END_REF]), or to help understand how ACPs can be stabilized in presence of proteins. [START_REF] De Sa Peixoto | How High Concentrations of Proteins Stabilize the Amorphous State of Calcium Orthophosphate: A Solid-State Nuclear Magnetic Resonance (NMR) Study of the Casein Case[END_REF] In the latter case, Gésan-Guiziou and co-workers looked at the structure of ACPs in presence of high concentrations of casein (used as a model phosphorylated protein). Using a combination of static and MAS 1 H and 31 P NMR experiments, the signatures of bound and free phosphoserine moieties were distinguished, and evidence of the interaction of non-phosphorylated amino acids with the amorphous mineral surface was obtained from a series of 2D 1 H-31 P HETCOR experiments. Moreover, measurements were also performed at higher temperatures (45°C), demonstrating how highly concentrated casein continues to stabilize the ACP particles.

Inorganic-inorganic interfaces involving a calcium phosphate component have also been [69] The latter study underscores the interest of developing methodologies to analyze some of the more challenging isotopes, like oxygen-17 (Table 1), which despite their unfavourable NMR properties are likely to provide valuable information.

Natural calcium phosphate phases

Considerations on sample preparation for NMR and DNP analyses

While the NMR study of synthetic calcium phosphates is relatively straightforward in terms of sample preparation, as these can generally easily be reduced to a powdered form and packed inside rotors, analyzing biological tissues raises a number of questions. First, the grinding of bone and teeth can be problematic, because (i) the grinding conditions can lead to changes in the organic and mineral components, or in the way in which they are associated to each other, [START_REF] Zhu | Time-Resolved Dehydration-Induced Structural Changes in an Intact Bovine Cortical Bone Revealed by Solid-State NMR Spectroscopy[END_REF][START_REF] Rai | Dehydration-induced structural changes in the collagen-hydroxyapatite interface in bone by high-resolution solid-state NMR spectroscopy[END_REF][START_REF] Nikel | NMR Investigation of the Role of Osteocalcin and Osteopontin at the Organic-Inorganic Interface in Bone[END_REF] (ii) the grinding leads to a loss of integrity of the sample, thereby preventing further analyses to be performed on it (e.g. mechanical studies), which can be a problem if the sample is « precious », as is the case for bone and dental tissues coming from genetically engineered or « isotopically-enriched » animals, [START_REF] Nikel | NMR Investigation of the Role of Osteocalcin and Osteopontin at the Organic-Inorganic Interface in Bone[END_REF] and (iii) the grinding provides an average information of the structure, which could potentially have been morefinely described by characterizing smaller fractions of the material, as recently demonstrated by Yon, Fayon and co-workers. [START_REF] Yon | Solid-state 31P and 1H chemical MR micro-imaging of hard tissues and biomaterials with magic angle spinning at very high magnetic field[END_REF] Hence, although the majority of initial solid state NMR investigations on bone and dental tissues concerned ground samples, several groups have proposed approaches to perform MAS experiments on intact ones. [START_REF] Zhu | Time-Resolved Dehydration-Induced Structural Changes in an Intact Bovine Cortical Bone Revealed by Solid-State NMR Spectroscopy[END_REF][START_REF] Rai | Dehydration-induced structural changes in the collagen-hydroxyapatite interface in bone by high-resolution solid-state NMR spectroscopy[END_REF][START_REF] Nikel | NMR Investigation of the Role of Osteocalcin and Osteopontin at the Organic-Inorganic Interface in Bone[END_REF][START_REF] Yon | Solid-state 31P and 1H chemical MR micro-imaging of hard tissues and biomaterials with magic angle spinning at very high magnetic field[END_REF][START_REF] Nikel | Solid State NMR Investigation of Intact Human Bone Quality: Balancing Issues and Insight into the Structure at the Organic-Mineral Interface[END_REF][START_REF] Kaflak | The solid-state proton NMR study of bone using a dipolar filter: apatite hydroxyl content versus animal age[END_REF][START_REF] Chow | Proline provides site-specific flexibility for in vivo collagen[END_REF] The second issue regarding biological samples is that they need to remain hydrated to preserve their functional (and hence structural) properties. Indeed, it has been shown that bone dehydration can lead to changes in the NMR spectra, [START_REF] Zhu | Time-Resolved Dehydration-Induced Structural Changes in an Intact Bovine Cortical Bone Revealed by Solid-State NMR Spectroscopy[END_REF][START_REF] Rai | Dehydration-induced structural changes in the collagen-hydroxyapatite interface in bone by high-resolution solid-state NMR spectroscopy[END_REF][START_REF] Wang | The predominant role of collagen in the nucleation, growth, structure and orientation of bone apatite[END_REF] meaning that strategies aiming at keeping the samples hydrated are to be privileged. [START_REF] Nikel | NMR Investigation of the Role of Osteocalcin and Osteopontin at the Organic-Inorganic Interface in Bone[END_REF][START_REF] Wang | The predominant role of collagen in the nucleation, growth, structure and orientation of bone apatite[END_REF] The question of sample preparation has recently been re-opened with the popularization of dynamic nuclear polarization, as DNP is now also starting to be used for studying bone tissue and other biominerals. In this case, the need to impregnate the sample by a radical solution raises the question of the choice of the radical/solvent couple, the goal being to avoid (or minimize) any structural changes within the biological sample. When looking at the few studies reported so far, most bone sample preparations involved an AMUPol biradical solution in H2O/D2O, [START_REF] Azais | Structural description of surfaces and interfaces in biominerals by DNP SENS[END_REF][START_REF] Singh | Direct Evidence of Imino Acid-Aromatic Interactions in Native Collagen Protein by DNP-Enhanced Solid-State NMR Spectroscopy[END_REF][START_REF] Goldberga | Detection of nucleic acids and other low abundance components in native bone and osteosarcoma extracellular matrix by isotope enrichment and DNP-enhanced NMR[END_REF] leading to 13 C DNPenhancement factors between ~ 20 and 60 (Figure 6). It is worth noting that these impregnation procedures differed slightly in terms of AMUPol concentration (between 12 and 20 mM), D2O/H2O ratio, duration of the impregnation, and size of the bone particles studied. Another preliminary DNP study of mice teeth was also reported, in which glycerol was added to the DNP-juice. [START_REF] Lee | Interfacial Ca2+ environments in nanocrystalline apatites revealed by dynamic nuclear polarization enhanced 43Ca NMR spectroscopy[END_REF] More importantly, it is worth noting that a broadening as well as shifts in some of the NMR resonances were observed on the DNP spectra (in comparison to conventional NMR analyses) ; this was ascribed to the lower temperatures used in the DNP analyses (but without verifying this point by performing a conventional 1 H  13 C CPMAS NMR analysis at 100 K). [START_REF] Azais | Structural description of surfaces and interfaces in biominerals by DNP SENS[END_REF][START_REF] Singh | Direct Evidence of Imino Acid-Aromatic Interactions in Native Collagen Protein by DNP-Enhanced Solid-State NMR Spectroscopy[END_REF] Moreover, differences in DNP enhancements were also noticed for the mineral and organic components of bone (with stronger enhancements for the organic fraction, as shown in Figures 6b-c) ; [START_REF] Azais | Structural description of surfaces and interfaces in biominerals by DNP SENS[END_REF] this implies that future optimizations of the impregnating conditions may also depend on the type of structural information which is sought.

Advances in NMR and DNP analyses of bone structure

Regarding bone mineral, although many 1 H and/or 31 P MAS NMR analyses have already been reported, recent investigations focussed more specifically on (i) demonstrating the « core-shell » structure of bone mineral (made of a crystalline HA core surrounded by a hydrated ACP layer, as mentioned previously in section 2.2), [START_REF] Von Euw | Amorphous surface layer versus transient amorphous precursor phase in bone -A case study investigated by solid-state NMR spectroscopy[END_REF] and (ii) determining the location and concentration in HPO4 2- anions. In the latter case, one of the key questions was to determine if HPO4 31 P NMR analyses, the thickness of the ACP layer could be estimated to ~0.8 nm. [START_REF] Von Euw | Bone mineral: new insights into its chemical composition[END_REF] In itself, the latter study constitutes one of the most thorough analyses of bone mineral reported so far.

Concerning the organic component of bone, the most significant advances over the past few years have been made possible thanks to the work of Duer and co-workers on the preparation of isotopically-enriched mice bone tissues (by feeding the animal with 13 C, 15 N labeled Celtone powder), [START_REF] Wong | Preparation of highly and generally enriched mammalian tissues for solid state NMR[END_REF][START_REF] Chow | NMR Spectroscopy of Native and in Vitro Tissues Implicates PolyADP Ribose in Biomineralization[END_REF] and the development of in-vitro protocols for producing enriched extracellular matrix collagen from osteoblasts. [START_REF] Chow | NMR Spectroscopy of Native and in Vitro Tissues Implicates PolyADP Ribose in Biomineralization[END_REF][START_REF] Goldberga | Collagen Structure-Function Relationships from Solid-State NMR Spectroscopy[END_REF] Thanks to the significant gain in sensitivity achieved by these isotopic labeling procedures, [START_REF] Wong | Preparation of highly and generally enriched mammalian tissues for solid state NMR[END_REF] it has become possible to use high resolution 13 C and 15 N NMR (e.g.

2D 13 C-13 C DQ-SQ, and DARR-assisted 15 N- 13 C correlations) to highlight a number of major features concerning the organic component of bone and the development of the tissue. These include (i) the potential importance of poly-ADP-ribose in the extacellular matrix for developing bone, which is likely to play a role in calcification, [START_REF] Chow | NMR Spectroscopy of Native and in Vitro Tissues Implicates PolyADP Ribose in Biomineralization[END_REF][START_REF] Muller | Poly(ADP-Ribose) Links the DNA Damage Response and Biomineralization[END_REF] (ii) the detection in native intact bone of nucleic acids and other low-abundant components (like cholines from phospholipid headgroups, as well as histidinyl and hydroxylysyl groups), [START_REF] Goldberga | Detection of nucleic acids and other low abundance components in native bone and osteosarcoma extracellular matrix by isotope enrichment and DNP-enhanced NMR[END_REF] and (iii) the in-depth study of collagen structure and flexibility. [START_REF] Chow | Proline provides site-specific flexibility for in vivo collagen[END_REF] Organic-mineral interfaces in bone have also been the focus of much attention. On one hand, the potential role of small molecular ions like citrate, acting as bridges between bone mineral platelets, was highlighted. [START_REF] Davies | Citrate bridges between mineral platelets in bone[END_REF][START_REF] Hu | Strongly bound citrate stabilizes the apatite nanocrystals in bone[END_REF] On the other hand, using DNP, it was shown that a full set of 13 C{ 31 P} REDOR dephasing curves could be recorded on a sheep bone sample in just 11 hours (instead of several weeks in absence of DNP), and this allowed estimating the distance of citrate carbon atoms from the mineral surface. [START_REF] Azais | Structural description of surfaces and interfaces in biominerals by DNP SENS[END_REF] In the latter case, based on these dephasing curves, it was suggested that only two out of three carboxylate functions attach to the mineral surface. This level of information is particularly important in relation to the different computational modeling studies of the organic/mineral interface.

Solid state NMR and high field MAS MRI of teeth

Regarding dental tissues, the extensive investigations performed recently by Balan, Gervais and co-workers on a collection of teeth remains collected from Mio-Pliocene deposits in Kenya are worth mentioning. Indeed, by analyzing a series of fossil tooth enamel samples by different techniques, including 19 F MAS NMR, the distinct signature of a « defect » fluoride environment could be identified. [START_REF] Yi | Probing atomic scale transformation of fossil dental enamel using Fourier transform infrared and nuclear magnetic resonance spectroscopy: A case study from the Tugen Hills (Rift Gregory, Kenya)[END_REF] Using 19 F double quantum-single quantum (DQ-SQ) MAS NMR (using the SPIP sequence:

SPin-locked symmetry-based double-quantum homonuclear dIPolar recoupling) and 13 C{ 19 F} frequency-selective REDOR experiments, as well as ab initio DFT calculations of NMR parameters, this environment could be unambiguously identified as fluoride ions in close vicinity to carbonate substituents within the apatite lattice. [START_REF] Yi | A carbonate-fluoride defect model for carbonate-rich fluorapatite[END_REF] It was suggested that such spectroscopic signatures can serve as tracers of the structure evolution of bioapatite during fossilization, and they were subsequently used to analyze fossilized bone samples from different geographic origin. [START_REF] Aufort | Assessing bone transformation in late Miocene and Plio-Pleistocene deposits of Kenya and South Africa[END_REF] As a final example, the research work recently reported by Yon, Fayon and co-workers is worth highlighting, as it brings the study on mineralized tissues a major step forward. [START_REF] Yon | Solid-state 31P and 1H chemical MR micro-imaging of hard tissues and biomaterials with magic angle spinning at very high magnetic field[END_REF] In this case, the key idea was to perform the ex vivo micro-imaging of an intact mouse tooth, under magic angle spinning conditions at 17.6 T, using 1 H and 31 P NMR analyses (Figure 7). By spinning the intact tooth at a moderate speed (10 kHz), it was possible to avoid potential undesirable effects due to centrifugal forces, while keeping benefit of MAS. By performing the analyses at very high magnetic field (17.6 T) and using rotating pulsed field gradients, 31 P 2D slice-selected and 3D solid-state images could be obtained, with very good signal-to-noise and spatial resolution (approaching ~ 100 µm in some cases).

Moreover, it was shown that several solid-state NMR sequences could be used in these conditions to achieve additional contrast in the images, such as CP MAS for 31 P imaging of the different mineral components (Figure 7b), or frequency-selective 1 H spin-echos for the chemically-selective imaging of either the organic component of the tooth by looking at aliphatic species, or the more mineralized zones by looking at the apatitic hydroxyl groups (Figures 7c-d). In the latter case, a spatial resolution close to 100 µm could be achieved. On a more general perspective, such high-field MAS MRI approaches are highly promising for the ex vivo imaging of mineralized tissues, as they can provide a more complete picture of both their structure and chemical composition. Indeed, they could also allow following the hard tissue modifications which can be caused by different diseases. Moreover, they could be used for studying the osteointegration of bone or dental implants from both spatial and chemical points of view, and thereby be highly complementary to other approaches described so far.

[92] identifying the presence of yet-undetected minor organic species (e.g. nucleic acids), and determining the distance and binding geometry of small molecular ions like citrate at the surface of mineral particles. Moreover, by comparing NMR signatures of the natural materials to those of synthetically derived models, including in vitro cultured tissues, it has been possible to obtain important information on the inorganic and organic components, and to rule out previously proposed models concerning bone structure and formation.

While most investigations still concern 1 H, 31 P and 13 C NMR analyses, due to their more favorable NMR properties, 43 Ca NMR is now increasingly being used. Indeed, recent NMR and DNP studies show how calcium-43 is a good target to help refine the description of the surface-structure of synthetic apatites, and of the bulk-structure of (amorphous) calcium phosphates. Oxygen-17, however, has more rarely been studied, despite the high level of information that 17 O NMR can provide. [START_REF] Pourpoint | Calcium phosphates and hydroxyapatite: solid-state NMR experiments and first-principles calculations[END_REF][START_REF] Wu | Solid-State 17O NMR Spectroscopy of Organic and Biological Molecules[END_REF][START_REF] Wu | Solid-State 17O NMR studies of organic and biological molecules: Recent advances and future directions[END_REF][START_REF] Ashbrook | Oxygen-17 NMR of Inorganic Materials[END_REF] Indeed, only a few investigations have looked into the 17 O NMR study of enriched model calciumphosphates and related bioglasses, [START_REF] Pourpoint | High-resolution solid state NMR experiments for the characterization of calcium phosphate biomaterials and biominerals[END_REF][START_REF] Davies | Citrate bridges between mineral platelets in bone[END_REF][START_REF] Lin | A multinuclear solid state NMR spectroscopic study of the structural evolution of disordered calcium silicate sol-gel biomaterials[END_REF][START_REF] Wu | High-resolution oxygen-17 NMR spectroscopy of solids by multiple-quantum magic-angle-spinning[END_REF][START_REF] Chen | Direct 17O Isotopic Labeling of Oxides Using Mechanochemistry[END_REF] and only one analysis of a bone sample has been reported, though the sensitivity was quite low. [START_REF] Davies | Citrate bridges between mineral platelets in bone[END_REF] With the current development of novel 17 O-labeling schemes based on mechanochemistry [START_REF] Chen | Direct 17O-isotopic labeling of oxides using mechanochemistry[END_REF][START_REF] Metro | Unleashing the Potential of 17O NMR Spectroscopy Using Mechanochemistry[END_REF] and of 17 O DNP, [START_REF] Brownbill | Oxygen-17 dynamic nuclear polarisation enhanced solid-state NMR spectroscopy at 18.8 T[END_REF][START_REF] Blanc | Dynamic Nuclear Polarization Enhanced Natural Abundance 17O Spectroscopy[END_REF] it can be expected that a much larger number of analyses on this nucleus will be performed in the future for these materials, including to help better understand the role played by one of the key components of bone, namely water. This is a point we are currently looking into.

Figure 1 .

 1 Figure 1. Molecular structure of different types of phosphate anions, and examples of calcium orthoand pyro-phosphate crystal structures. .

Figure 3 .

 3 Figure 3. a/ Transmission Electron Microscopy (TEM) of a synthetic carbonated nanocrystalline apatite (enriched in 13 C) ; b/ 2D DNP-enhanced 31 P → 13 C DNP CP-HETCOR MAS NMR spectrum ; c/ 2D DNPenhanced13 C DQ-SQ MAS NMR spectrum, together with some of the 1D 13 C NMR slices (noted i) to iv)). Adapted with permission from Ref.[START_REF] Leroy | Hydroxyapatites: Key Structural Questions and Answers from Dynamic Nuclear Polarization[END_REF]. Copyright 2017 American Chemical Society.

  forms. Amorphous calcium phosphates represent a real challenge in terms of structural characterization, due to the lack of long range order and significant distribution in local environments around the different ions. Advanced solid state NMR analyses have been shown to be particularly valuable in this context, as illustrated below in a selection of recent investigations.

Figure 5 .

 5 Figure 5. DNP studies of nanocrystalline apatite at 9.4 T and 100 K. a/ 1 H-13 C HETCOR spectrum with associated 13 C skyline projection (top). b/ 1 H-43 Ca HETCOR spectrum with associated 43 Ca (top) and 1 H (right) skyline projections (in blue), and the DNP-enhanced 1 H Hahn-echo MAS NMR spectrum (in purple). Reproduced with permission from Ref. [62] (Copyright © 2017, Springer Nature).

  looked into. In particular, the formation of hydroxyapatite-like phases at the surface of bioactive glasses upon immersion in simulated body fluids (SBF) has been the subject of much attention, in view of optimizing the synthesis of biomaterials for bone regeneration. In this context, several recent studies underscore how solid state NMR can be used as a qualitative and/or quantitative technique for understanding the reactivity of a variety of bioglasses, prepared according to different synthetic procedures (melt-quench or sol-gel syntheses), and displaying different chemical compositions (« CaO-SiO2 », « CaO-SiO2-P2O5 », and « Na2O-CaO-SiO2-P2O5 » families).[START_REF] Lin | A multinuclear solid state NMR spectroscopic study of the structural evolution of disordered calcium silicate sol-gel biomaterials[END_REF][START_REF] Yu | Quantitative composition-bioactivity relationships of phosphosilicate glasses: Bearings from the phosphorus content and network polymerization[END_REF][START_REF] Mathew | Proton Environments in Biomimetic Calcium Phosphates Formed from Mesoporous Bioactive CaO-SiO2-P2O5 Glasses in Vitro: Insights from Solid-State NMR[END_REF][START_REF] Turdean-Ionescu | Surface Reactions of Mesoporous Bioactive Glasses Monitored by Solid-State NMR: Concentration Effects in Simulated Body Fluid[END_REF] For example, Edén and coworkers demonstrated how 1 H MAS NMR spectra edited by 1 H 31 P CP transfer are more sensitive than powder X-ray diffraction and than simple 31 P MAS NMR experiments for detecting the beginning of apatite formation at the surface of the materials.[START_REF] Mathew | Proton Environments in Biomimetic Calcium Phosphates Formed from Mesoporous Bioactive CaO-SiO2-P2O5 Glasses in Vitro: Insights from Solid-State NMR[END_REF] Moreover, by performing NMR analyses on model17 O-labeled CaO-SiO2 glasses, Smith and co-workers showed how the quick release of calcium from the bulk-glass structure (which promotes the subsequent precipitation of hydroxyapatite) can be made evident by the loss of the17 O NMR resonance of non-bridging oxygens.

Figure 6 .

 6 Figure 6. a/ Schematic representation of the DNP approach used in the study of bone. b/ 1 H-31 P and c/ 1 H-13 C DNP enhanced CPMAS NMR spectra of sheep bone. Adapted with permission from Ref. [81] (Copyright © 2019 Elsevier Inc.).

Figure 7 .

 7 Figure 7. a/ 3D micro-computed tomography (µ-CT) image of a mouse tooth (the white arrows indicate the location of the pulp channels). b/ 3D 1 H  31 P CP MAS MR image of tooth mineral (experimental duration of 69 h), c-d/ 3D 1 H MAS MR chemically selective images of the (c) OH -hydroxyl groups of apatite and (d) aliphatic species in the organic part of mouse tooth sample (experimental duration of 18 h). All micro-imaging NMR analyses were performed under magic angle spinning (10 kHz spinning frequency) at very high magnetic field (17.6 T), with the tooth sample introduced in the rotor as shown below the MRI images. Adapted with permission from Ref. [76] (Copyright © 2017 Springer Nature).4. Outlook

Table 1 .

 1 NMR properties of the main isotopes present in calcium phosphates.

		Nuclear	Natural	Quadrupolar	Larmor frequency	Receptivity
		spin	abundance	moment Q	at 14.1 T	(rel. to 13 C)
			(%)	(fm 2 )[32, 33]	(MHz)
	1 H	1/2	99.98	/	600.1	5.87 × 10 3
	31 P	1/2	100	/	242.9	3.91 × 10 2
	17 O	5/2	0.04	-2.56	81.3	6.5 × 10 -2
	43 Ca	7/2	0.14	-4.44	40.4	5.1 × 10 -2

  2-anions were present inside the HA lattice or within the amorphous surface layer.[84] Using 1 H 31 P 1 H double CP MAS NMR experiments and studying the 1 H-detected CP dynamics (in comparison to model synthetic phases like monetite, octacalcium-phosphate and a biomimetic carbonated HA), Azaïs et al demonstrated that the protonated phosphates reside within the hydrated ACP layer. Moreover, thanks to additional quantitative

Acknowledgement

Funding from the ANR, under contract # ANR-16-CE19-0013 (PyVerres) is gratefully acknowledged.


Estuarine marshes restoration

Estuarine marshes restoration through 'depolderisation': ecological, social and economical perspectives on the Ile Nouvelle case study (Gironde estuary, France)

General context

o Coastal and estuarine marshes have been intensively dyked in Europe, with > 15,000 km 2 of polders a . o Climate change scenarios forecast an elevated risk of marine submersion and flood hazards. o The cost of dykes management in such hazardous environment justifies an increasing interest towards nature-based (NB) solutions. o The restoration of natural flood expansion zones is one of those NB solutions retaining some managers interest. o Such restoration can also promote marsh ecological functionalities, that serve many other regulation and cultural services for human societies. Evaluate the benefits of alternative estuarine wetland restoration scenarios h

  stable isotopes (δ 13 C, δ 15 N, δ 34 S) References and notes a: Goeldner-Gianella L, 2007. Dépoldériser en Europe occidentale. Annales de Géographie 339-360. b: Lechêne A, 2017. Trajectoire de restauration des marais intertidaux: réponse du nekton à la dépoldérisation dans l'estuaire de la Gironde. PhD thesis, University of Bordeaux, 357 pp. c: Salles D, Gassiat A, Coynel A, Laffaille P, Pereau JC, Valette P, 2012, Adaptation to hydrological regime shifts (flood and low flow) in the Garonne-Gironde river-estuarine environment. Potentialities, testing and governance of adaptation options. 1 rst International Conference of Integrative Sciences for Research and Action for Large Rivers, Lyon, 26-28/06/2012, d: Gassiat A, Lechêne A, Lafon V, Deldreve V, Kervella S, Salles D, Sottolichio A, 2016, La dépoldérisation de l'île Nouvelle, trajectoires écologiques et sociétales d'une opération de renaturation, REVER7: journées atelier 2016 du Réseau d'Echanges et de Valorisation en Ecologie de la Restauration, 19-20/01/2016, Bordeaux. e: Haines-Young R, Potschin M, 2010, The links between biodiversity, ecosystem services and human well being? Chap.6 in D Raffaelli, C Frid (eds.) Ecosystems Ecology, a New Synthesis. Cambridge University Press, Cambridge, pp 110-139, f: Haines-Young R, Potschin M, 2018, Common International Classification of Ecosystem Services (CICES) V5.1; Guidance on the Application of the Revised Structure: www,cices.eu g: Campagne C, Roche P, 2018, May the matrix be with you! Guidelines for the application of expert-based matrix approach for ecosystem services assessment and mapping, One Ecosystem 3when tackling the issue of climate change related risks (focus on flood and marine submersion risks; the Ile Nouvelle as a policy window or new model to promote wetland renaturation…) c …to a broader context, considering contrasted socio-economical and cultural frameworks, and the diversity of water exchange regulation regimes applied in estuarine and littoral marshes in France and Europe Laure Carassou 1* , Tina Rambonilaza 2 , Anne Gassiat 2 , Denis Salles 2 , Alain Lechêne 3 1: Irstea EABX (laure.carassou@irstea.fr); 2: Irstea ETBX; 3: Ministère de la Transition Ecologique et Solidaire Source : Dossier de presse « Bienvenue sur l


Arnaud Bourdin

Indirect treatment comparison of asthma biologics fraught with methodology issues