Maella Severino-Freire

Aude Maza

Paul Kuentz

Yannis Duffourd

Laurence Fiavre

Edith Brazet

Nicolas Chassaing

Eliane Mery-Lemarche

Pierre Vabres

Juliette Mazereeuw-Hautier

Maëlla Severino-Freire

Severe gynaecological involvement in Proteus Syndrome

Keywords: Proteus Syndrome, gynaecological involvement, AKT1 mutation

INTRODUCTION

Proteus Syndrome (PS) is a rare sporadic overgrowth syndrome, initially described in 1979 by Cohen and Hayden as a newly recognised hamartomatous syndrome [START_REF] Cohen | A newly recognized hamartomatous syndrome Birth Defects Orig[END_REF] and by [START_REF] Wiedemann | The proteus syndrome. Partial gigantism of the hands and/or feet, nevi, hemihypertrophy[END_REF][START_REF] Wiedemann | The proteus syndrome. Partial gigantism of the hands and/or feet, nevi, hemihypertrophy[END_REF]. Approximately 200 cases have been reported, with an estimated prevalence between 1:1,000,000 and 1:10,000,000 [Biesecker and Sapp, 2012]. In 2011, [START_REF] Lindhurst | A mosaic activating mutation in AKT1 associated with the Proteus syndrome[END_REF] demonstrated that PS is caused by a post-zygotic activating LRG_721t1 (AKT1) mutation (NM_001014432.1:c.49G>A ; NP_001014432.1:p.(Glu17Lys)), supposed to be lethal in a non-mosaic state. This gene encodes the AKT1 kinase, a key enzyme for activating the PI3K-AKT pathway involved in cell growth, proliferation, apoptosis and angiogenesis. This mutation has been identified in more than 90% of patients meeting PS diagnostic criteria. An absence of mutation in PS patients may be explained either by a mutation in another gene unknown to date, or inadequate tissue sampling for genetic testing [START_REF] Lindhurst | A mosaic activating mutation in AKT1 associated with the Proteus syndrome[END_REF].

PS becomes apparent in early infancy (between 6 and 18 months of age) and then rapidly progresses in childhood. After adolescence, it appears to stabilise or progress less rapidly [START_REF] Valéra | Proteus syndrome: Report of a case with AKT1 mutation in a dental cyst[END_REF][START_REF] Marsh | Rapamycin treatment for a child with germline PTEN mutation[END_REF]. It is characterised by the excessive and asymmetric overgrowth of soft tissues, skin and bones. Clinical diagnostic criteria for PS were established in 1999 by Biesecker et al [START_REF] Biesecker | Proteus syndrome: diagnostic criteria, differential diagnosis, and patient evaluation[END_REF]. Plantar cerebriform connective tissue nevus is considered a pathognomonic lesion [Biesecker and Sapp, 2012]. Patients may also present with a range of tumours (most commonly ovarian cystadenomas, parotid monomorphic adenomas, and meningiomas) [Biesecker and Sapp, 2012;[START_REF] Cohen | Proteus syndrome review: molecular, clinical, and pathologic features[END_REF], pulmonary abnormalities (bullous lung disease), and a striking predisposition to deep vein thrombosis and pulmonary embolism [Biesecker and Sapp, 2012]. This latter complication, together with infections of the central nervous system, results in substantial morbidity and early mortality [START_REF] Cohen | Causes of premature death in Proteus syndrome[END_REF] in PS sufferers. Men and women seem to be equally affected. In women, gynaecological involvement may contribute as reported by Turner et al [START_REF] Turner | Reassessment of the Proteus syndrome literature: application of diagnostic criteria to published cases[END_REF]. Here, we report on a novel case of PS with an AKT1 mutation and with severe gynaecological involvement.

CLINICAL REPORT

A 26-year-old female patient, born to unrelated, healthy parents, was referred to our department for evaluation of an overgrowth syndrome. At the age of 6, she had developed progressive overgrowth and deformity of the right knee, right hip, left thumb and left first toe.

X-rays of the first toe showed upper and lower retrocalcaneal ossified enthesopathy. She also had debilitating scoliosis. At the age of 16, she developed a cerebriform connective tissue nevus on her left foot, associated with subcutaneous hypertrophy and bone abnormalities (Xray images not available), resulting in an impaired gait. Debulking of this connective tissue nevus was performed at 18 years, but the lesion rapidly relapsed and was still present upon her first visit to our department (Fig 1).

Deep targeted next-generation sequencing of the AKT1 gene on an Illumina MiSeq® was performed on peripheral blood leukocytes and connective tissue skin from the left foot.

The missense heterozygous post-zygotic mutation p.(Glu17Lys) was identified on skin DNA in 6% of alleles, with a mean coverage of 4228X. In contrast, the mutation was not detected from blood leukocytes. She had suffered from severe and recurrent metrorrhagia since the age of 25, which had never been investigated. Blood analysis (CBC and chemistry including prothrombin, APTT and fibrinogen) was unremarkable except for microcytic anaemia. Pelvic magnetic resonance imaging showed a massive microcystic tumour of the uterine cervix, extending into the uterus. She also had 2 extensive cysts (5 and 10cm in diameter) on the left ovary (Fig. 2 a-b). A diagnostic hysteroscopy showed a very irregular mass of approximately 10cm. The biopsies performed during the diagnosis were reassuring.

Vascular Doppler ultrasonography of the leg revealed deep vein thrombosis in the left calf. Enoxaparin sodium was initiated, but resulted in increased metrorrhagia, requiring iterative blood transfusions. Low dose oral rapamycin (1mg/d) was initiated, but it was discontinued 45 days later, due to life-threatening metrorrhagia. A complete hysterectomy with left adnexectomy was performed. A histological examination of the surgical specimens revealed an ovarian serous cystadenoma, atypical endocervical hyperplastic glandular polyps, and endometrial hyperplastic polyps without atypia (Fig. 2 c-d). Deep targeted NGS of AKT1 on DNA from FFPE gynaecological tissue was performed, but no mutation was detected due to poor DNA quality.

DISCUSSION

Our patient demonstrated 3 specific diagnostic criteria for PS -cerebriform connective tissue nevus, asymmetric and disproportionate overgrowth -specific tumours with ovarian cystadenoma -, and carried the p.(Glu17Lys) AKT1 mutation in the affected skin.

Although PS was clinically diagnosed, its link with metrorrhagia and the pelvic tumour was not recognised for several months. This may be due to the fact that gynaecological involvement in PS is not well known. However, life-threatening gynaecological involvement in our patient was the principal symptom of Proteus Syndrome, requiring a hysterectomy although she was young and had never had children.

Among 13 reported cases of gynaecological involvement in PS, all were diagnosed at a young age, with 11 patients under 20 years of age (range: 7 months to 30 years). Various clinical symptoms have been reported, including metrorrhagia, and premature puberty. The nature of gynaecological lesions and their size have rarely been precisely reported. They include ovarian serous cystadenomas (4 cases) [START_REF] Cohen | Proteus syndrome: Clinical evidence for somatic mosaicism and selective review[END_REF][START_REF] Skovby | Compromise of the spinal canal in Proteus syndrome[END_REF]Cohen, 2002;[START_REF] Gordon | Neoplasms in proteus syndrome[END_REF], ovarian cysts (3 cases) [Koussef, 1986;[START_REF] Maassen | Proteus-syndrome[END_REF][START_REF] Bouzas | Ophthalmologic examination in the diagnosis of Proteus syndrome[END_REF], uterine leiomyomas [START_REF] Maassen | Proteus-syndrome[END_REF], endometrial carcinoma (1 case) [START_REF] Cohen | Overgrowth syndromes: an update[END_REF], bilateral paraovarian villoglandular endometrioid cystadenomatous tumours of borderline malignancy with neoplastic perineal implant (1 case) [START_REF] Raju | Genital tract tumors in Proteus syndrome: report of a case of bilateral paraovarian endometrioid cystic tumors of borderline malignancy and review of the literature[END_REF], juvenile granulosa cell tumours (1 case) [START_REF] Ezzeldin | Precocious puberty in a female with Proteus Syndrome[END_REF], ovarian dermoid cysts and paratubal cysts (1 case) [START_REF] Hong | Unilateral ovarian dermoid cyst accompanied by an ipsilateral paratubal cyst in a girl with Proteus Syndrome discovered by laparoscopic surgery[END_REF], endometrioid paraovarian borderline cystic tumours (1 case) [START_REF] Vasquez | Endometrioid Paraovarian Borderline Cystic Tumor in an Infant with Proteus Syndrome[END_REF] and Müllerian papilloma associated with ovarian serous cystadenoma (1 case) [START_REF] Smrkolj | Müllerian papilloma in a patient with Proteus syndrome: case report and review of the literature[END_REF]. The most common and specific gynaecological lesion reported in PS is ovarian serous cystadenoma. It has therefore been included among specific diagnostic criteria for PS. To our knowledge, the atypical endocervical hyperplastic glandular polyps and endometrial hyperplastic polyps without atypia reported in our patient have not previously been reported. In contrast, such lesions are common in otherwise healthy women, and are a risk factor for endometrial carcinoma.

The p.(Glu17Lys) AKT1 mutation could not be detected from the gynaecological surgical specimen due to poor DNA quality. The absence of mutation in the samples studied can also result from low mutation levels in tumour specimens, as suggested by [START_REF] Lindhurst | AKT1 gene mutation levels are correlated with the type of dermatologic lesions in patients with Proteus syndrome[END_REF], or non-uniform distribution of mutant cells throughout the lesion, with studied samples from an area with low-level mosaicism. Overgrowth has also been found to be poorly correlated with bulk tissue mutation levels [START_REF] Doucet | Lack of mutation-histopathology correlation in a patient with Proteus syndrome[END_REF].

Gynaecological lesions often require surgery (ranging from tumour excision to radical surgery depending on their severity). As an alternative to surgery, our decision to treat with rapamycin was based on its inhibition of the PI3KA-AKT1-mTOR pathway. It had previously been reported as effective on pelvic masses in a 9-month-old male with PTEN hamartoma tumour syndrome, harbouring a germline PTEN (c.507delC; p.(Ser170Valfs*13)) [START_REF] Marsh | Rapamycin treatment for a child with germline PTEN mutation[END_REF]. In our case, efficacy could not be assessed because of early withdrawal. Other drugs targeting the PI3KA-AKT1-mTOR pathway in overgrowth syndromes are currently under evaluation.

In conclusion, clinicians must be aware that female patients suffering from PS necessitate a thorough evaluation in case of gynaecological symptoms. By reporting on a novel case of PS with gynaecological involvement, we wish to raise awareness on rare yet potentially severe manifestations of this rare and severe genetic mosaic syndrome.

subcutaneous tumors, macrocephaly or other skull anomalies and possible accelerated growth and visceral affection. Eur. J. Pediatr. 140,5-12.

Keys:

Fig. 1: Cerebriform connective tissue nevus on the left foot, causing an increase in the size of the foot.

Fig. 2 :

 2 Fig. 2: a and b: Pelvis magnetic resonance imaging (T2). a: Voluminous mixed formation (6 x

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


S Shehayeb

X Deschanels

J Lautru

L Ghannam

M Odorico

I Karamé

G Toquer

Thin polymeric CuO film from EPD designed for low temperature photothermal absorbers

Keywords: Nanoparticles, Electrophoretic deposition, selective tandem materials, Selective solar absorbers CuO, PEI

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

In order to limit the use of fossil fuels, the production of hot water by using tandem photothermal collectors is in growing importance. The efficiency of the absorber is determined by its high optical selectivity by having a high absorptance α (i.e. low reflectance) over the spectral range of solar emission (0.5-2.5 µm) and a low emittance ԑ (i.e. high reflectance) in the mid and far infrared region (2.5-20 µm). These two properties can be achieved by forming tandem absorber composed of highly absorbing UV-VIS and NIR layer deposited on a highly IR reflecting metallic substrate. The absorption of the upper layer could be a result of the intrinsic properties of the material (e.g. black paint) or due to texturing created by the processing technique that shift the absorption edge toward higher wavelengths [START_REF] Katzen | Thin films of silica-carbon nanocomposites for selective solar absorbers[END_REF]. In the 20 th century, selective surfaces of absorber/ reflector tandems were metal-oxide and sulfide layers coated onto various metals. Metal oxides of Copper, Chromium, Zinc and Nickel were generally used. These layers have showed high selectivity (α/ԑ) by having α>0.9 and a low ԑ. Non-selective layers like black paints have high α (>0.9) and very high ԑ (>0.9).

In this context, copper oxides present interesting optical properties (i.e. intrinsic selectivity) for the design of photothermal absorbers [START_REF] Amri | Developments in the synthesis of flat plate solar selective absorber materials via sol-gel methods: A review[END_REF]. It has already been obtained by several processes including reactive sputtering [START_REF] Karlsson | Optical properties and spectral selectivity of copper oxide on stainless steel[END_REF], chemical vapor deposition (CVD) [START_REF] Maruyama | Copper oxide thin films prepared by chemical vapor deposition from copper dipivaloylmethanate[END_REF], chemical conversion [START_REF] Richharia | Surface analysis of a black copper selective coating Solar[END_REF], thermal oxidization [START_REF] Musa | Production of cuprous oxide, a solar cell material, by thermal oxidation and a study of its physical and electrical properties[END_REF] [START_REF] Jayatissa | Fabrication of cuprous and cupric oxide thin films by heat treatment[END_REF], chemical conversion [START_REF] Xiao | A facile process to prepare copper oxide thin films as solar selective absorbers[END_REF], cathodic arc deposition [START_REF] Marquez | Properties of cupric oxide coatings prepared by cathodic arc deposition[END_REF] and DC co-sputtering of Cu and Al [START_REF] Sathiaraj | Solar selective properties of copper-aluminium composite films[END_REF]. The increase of the selectivity is induced by optical trapping of energy or wavelength discrimination by surface roughening and/or even with the formation of dendritic structure. Such structures absorb efficiently high energy solar radiation from multiple absorption and reflection, and in the thermal infrared region the wavelengths of the radiation are now much larger than the dendrite spacing, while the emittance in the IR spectral region is rather unaffected since the relevant wavelengths are much larger than the dendrite, and consequently the surface appears at this scale fairly smooth [START_REF] Granqvist | Solar energy materials[END_REF] [START_REF] Lampert | Coatings for enhanced photothermal energy collection Solar Energy Materials[END_REF].

In this work, from an electrophoretic deposition (EPD) based on dispersed CuO nanoparticles, we have attempted to adjust the coating thickness and structure, having a favorable surface in order to optimize the optical efficiency. Compared to the above used methods, electrophoretic deposition (EPD) is fairly rapid and economic. It is based on a two-step deposition process. In the first step (electrophoresis), charged particles suspended in a suitable medium are forced to migrate upon the application of an electric field. In the second step (deposition), particles form a coherent deposit on the electrode to which they are attracted. The required coating is obtained while operating at room temperature compared to CVD and PVD techniques (cathodic arc deposition and DC sputtering) where high processing temperature is required. Compared to chemical, thermal conversion and dip coating methods, there is not some thermochemical post deposition steps with EPD, and then the bulk properties of the starting material are conserved. By EPD, the content, density and the homogeneity of the coating are expected to be tuned by varying process and suspension parameters. Although, EPD coating is concentration dependent, an initial suspension concentration as low as 0.05 wt% is sufficient in order to form a coating. This makes EPD economic compared to the other wet deposition techniques. Up to now several studies have reported successful CuO dispersion [START_REF] Fedele | Experimental stability analysis of different water-based nanofluids[END_REF] using catechol derivatives (such as Tiron) [START_REF] Guedes | A study on the aqueous dispersion mechanism of CuO powders using Tiron[END_REF], Poly(vinyl alcohol) [START_REF] Mallakpour | Poly(vinyl alcohol) Chains Grafted onto the Surface of Copper Oxide Nanoparticles: Application in Synthesis and Characterization of Novel Optically Active and Thermally Stable Nanocomposites Based on Poly(amide-imide) Containing N-trimellitylimido-L-valine Linkage[END_REF], PEG [START_REF] Kulkarni | Effect of temperature on rheological properties of copper oxide nanoparticles dispersed in propylene glycol and water mixture[END_REF] in water.

Nevertheless, none of these was dedicated to a charged suspension of CuO suitable for EPD or for the study of the stabilization of CuO nano-powder. The strategy of coating or grafting polymer to the surface of nanoparticles is often used to avoid their aggregation by inducing surface-surface repulsion [START_REF] Laucournet | Coagulation method of aqueous concentrated alumina suspensions by thermal decomposition of hydroxyaluminum diacetate[END_REF] [START_REF] Pagnoux | Suspension systems for coagulation processing[END_REF]. Polyethyleneimine (PEI) is a cationic dispersant widely used in different sizes and structures for the preparation of stable suspensions of Ti nanoparticles [START_REF] Fedele | Experimental stability analysis of different water-based nanofluids[END_REF], Ti3SiC2 [START_REF] Mishra | pH localization: a case study during electrophoretic deposition of ternary MAX phase carbide-Ti3SiC2[END_REF], TiN [START_REF] Mendoza | Improvement of TiN nanoparticles EPD inducing steric stabilization in non-aqueous suspensions[END_REF], BaTiO3 [START_REF] Zarbov | Methodology for selection of charging agents for electrophoretic deposition of ceramic particles[END_REF], ZnO [START_REF] Verde | Electrophoretic Deposition of Transparent ZnO Thin Films from Highly Stabilized Colloidal Suspensions[END_REF]. The amine groups complex the surface of the metal oxide through dative bonds while the other free amine groups are pH sensitive and readily adsorb protons in aqueous solution which in turn should affects the mechanism of stabilization resulting mainly in electro-steric stabilization of CuO nanoparticles [START_REF] Wen | A facile, sensitive, and rapid spectrophotometric method for copper(II) ion detection in aqueous media using polyethyleneimine[END_REF] [START_REF] Jia | Spectrometry recognition of polyethyleneimine towards heavy metal ions[END_REF]. In addition, PEI also plays the role of binder in the final film by avoiding crack formation during the drying process.

We also investigate the stabilization of CuO in water by using PEI in order to form CuO thin films by EPD. Firstly, the suspension parameters are adjusted by varying the concentration of the polymer and then the pH of the suspension. Secondly, the EPD processing parameters (applied electric field and deposition time) were adjusted in order to control the structure (density, roughness, thickness) and consequently the optical efficiency of the deposit. This colloidal route offers the advantage of the formation of the CuO film from a bottom-up approach controlling the roughness and the structure of the film.

Experimental section

2.1. Preparation of the CuO/PEI suspension Suspensions of 0.88 wt % PEI (MW~2000 g mol -1 , 50 wt % in H2O, from Sigma Aldrich) in distilled water, were stirred for 30 mins then few drops of 1.5M HNO3 were used to attain the wished pH. Then 0.05 wt% of CuO nanoparticles (<50nm, Sigma Aldrich) were added to each suspension and left to stir for 2 days.

Characterization of the CuO/PEI suspension

In order to follow the stabilization nanoparticles by PEI at different pH, the charge of the suspended nanoparticles was determined via the electrophoretic mobility measured by laser Doppler velocimetry (zetasizerNanoZS, Malvern). The zetasizer uses electrophoresis to determine the electrophoretic mobility which is simply related to zeta potential through the Henry equation by using the Smolukowski model.

Besides, the stabilization of nanoparticles was also studied by atomic force microscopy (AFM), the suspension of 0.05 wt% CuO was diluted 100 folds, and a drop was placed on a freshly cleaved "Mica" disc for each pH. Mica substrates provide a flat and even surface for high resolution AFM.

EPD procedure

Electrophoretic experiments are conducted in potentiostatic conditions using a VersaSTAT 4 potentiostat controlled by the Versastudio software (Princeton Applied Research®), based on three connection electrodes: the working electrode (WE) at 1 cm from the counter electrode (CE) and the reference (RE) electrode (Ag/AgCl filled with 3M KCl solution 0.2 V/SHE), placed in between. The WE and the CE received as platinum coated silicon wafers discs (from Sil'tronix®), were cut into 15x20 mm² rectangles. The EPD instrument supplies absolute compliance voltage of 12 V at full rated current. The software yields electrochemical cell features (current, resistance, time, apparent applied potential difference). Before each EPD experiment, both WE, CE and RE were dipped in the PEI/CuO suspension prepared. After EPD, the working electrode was then removed and dipped 2 times in a beaker containing water and then in one containing ethanol. Finally, the deposit was left to dry vertically, in a closed box, for two days at room temperature before further analysis.

Spectral reflectance characterization

Low temperature tandem solar absorbers are characterized by solar absorptance (α), thermal emittance (ε) and efficiency (η). The α value of a surface may be defined as the weighted fraction (by total power density) of the absorbed radiation to that incident on the surface, given by:

∫ ∫ - = 5 . 2 28 . 0 5 . 2 28 . 0 ) ( )] ( 1 )[ ( λ λ λ λ λ α d I d R I solar solar (Equation 1)
Where R(λ) is the spectral reflectance of the surface and Isolar(λ) is the normal spectral irradiance, defined by the ISO standard 9845-1 (1992) for air mass (AM) 1.5. The equation 4 completely describes the collection ability of the material over a given wavelength range, without any consideration given to the losses due to thermal emittance, hence the lower and the upper limit of the integration are that of the solar spectrum between 0.28 and 2.5 μm, respectively. The ε value of a surface is defined from the weighted fraction (by total power density) of the emitted radiation at a particular temperature to the spectral Planck radiation, ρ (λ) at the same temperature than the surface and established as:

∫ ∫ - = 16 5 . 2 16 5 . 2 ) , ( )] ( 1 )[ , ( λ λ λ λ λ ε d T I d R T I blackbody blackbody (Equation 2)
The simplified heat balance of a solar collector combines α and ε by the following expression:

Q = S . . E -S . . σ T -T -S . H. T -T (Equation 3)
Where Qu is the useful energy, Sc the collector's surface (m 2 ), Sa the absorber surface (m 2 ), H the thermal losses coefficient by conduction and convection (W. m -2 . K -1 ), Es the solar radiation flux W. m -2 , σ the Stefan-Boltzmann constant (W. m -2 . K -4 ), Ta the temperature of the absorber (K), T0 the temperature of the environment (K). If one considers only the optical losses, i.e. the heat losses by conduction and convection are neglected, an efficiency η of the collector is defined having the following expression: 4)

η = - σ T -T (Equation
Where X = , the factor of concentration is considered equal to 1 (being exposed to direct solar radiation). At a fixed operation temperature, this measure probes the efficiency of the absorber. Thus, one can conclude that it increases by the increasing of α value or by the diminishing of ε value. Ideal cases are obtained when α approaches 1 and ε approaches 0.

Energy Dispersive X-Ray spectroscopy

The determination of thin film thickness and density are established by using Energy Dispersive X-Ray (EDX) coupled with X-film® software. Conventional measurements are performed at varying incident electron energy (in the 5-30 keV range) which allows the variation of the depth of penetration into the material resulting in different k-ratios. These k-ratios are processed with the help of thin-film analysis software (i.e. X-film®) which determines the density and thickness by fitting the predictions of an X-Ray emission model to the measured kratios. The obtained expression from the software is in the form of "ρz (mg cm -2 )". Then from the measured experimental value of thickness z (μm) obtained via SEM cross-section observations, the density ρ (g cm -3 ) is finally determined.

Results and Discussion

Colloidal Suspension

The PEI used in these experiments is a highly branched polyamine, composed of primary, secondary and tertiary amines achieving their cationicity through their protonation from the surrounding medium. However, primary amine groups which are the chain terminating units are At pH=9 stronger dative bonds are formed between the surface of Cu 2+ and the amine groups.

The slight protonation results in inter-repulsion between of the protonated amine groups in the polymer chain. CuO nanoparticles surrounded by polymer are expected to be found in the suspension at pH=9 while at pH=3 individual protonated polymers will more probably exist and deposit alone during cathodic EPD.

Electrophoretic deposition (EPD)

Thickness of the coating

The yield of EPD depends directly on the charge of the suspended NPs. Thus, the thickness of the deposit obtained should be proportional to ζ value. From the SEM cross-section micrographs of the deposits obtained at different pH, the thickness is measured between 1358±33 nm for deposits obtained at pH=11 up to 1627±44 nm for deposits obtained at pH=3 (see Fig. 3).

A linear relationship between pH and thickness of the deposit is observed here and the deposit thickness increases with decreasing pH and increasing ζ. Electrolysis reactions usually affect the morphology of the deposit by the formation of gas bubbles, during EPD, leading to the incorporation of empty holes/spaces into the final coating [START_REF] Ammam | Electrophoretic deposition under modulated electric fields: a review[END_REF]. As H + ions increase in solution, H2 gas formation increases at the cathode and thus more bubble are incorporated as holes in the deposit. This activity could be observed in the SEM micrograph of the coating obtained at pH =3 (see Fig. 4). For pH=9, we found that the deposit obtained is more homogeneous and no empty gas holes/spaces are present, compared to pH=3.

At pH=11, the deposition of large agglomerates is observed, which is expected, since the nanoparticles are not sufficiently charged having the lowest ζ value (6.3 ± 0.2 mV). Thus, large charged agglomerates migrate to form the deposit, resulting in reduced homogeneity and uniformity.

Density of the coatings

Fig. 5 shows the calculated density (ρtheo) based on the estimated volume percentage (%V) of PEI in the deposit obtained from the total organic carbon (TOC) at different pH, compared with the experimental density (ρX-film). For the same applied electric field of 2V cm -1 and deposition time of 120 min, the %V of polymer present in the deposit obtained decreases with the pH from 32 % at pH=3 down to ~20% at pH=11. However, the calculated density of the film increases with the pH reaching its highest value at pH=9 being 5.41 g cm -3 . These values are calculated by considering bulk density ρ and volume fraction of the polymer and that of the CuO (e.g. at pH=9: ρ(theoretical)= ρCuO x VCuO + ρPEI x VPEI= (6.3x0.83 + 1.08x0.17) = 5.41g cm -3 ).

The real/experimental density of the deposits from X-film is 5.02 and 5.90 g cm -3 for pH=3 and pH=9, respectively. Both experimental and theoretical density values are close in magnitude. The slightly higher value obtained with X-film is expected, since the presence of Cu metal (ρ=8.96g cm -3 ) is not quantified and only the density of CuO is taken into account which is lower than that of Cu. Thus, a general lowering in the calculated density value is expected. As a result, the density of CuO coatings obtained for E=2V cm -1 at pH=9 is much higher than 5 g cm -3 . The EPD process at this pH showed homogeneous and bubble free deposits compared to those obtained at pH=3. As a result, the suspension conditions were fixed at pH=9 and the applied electric field and deposition time were varied.

Effect of the applied electric field

In order to study the effect of applied electric field (E), the deposition time was fixed at 120 minutes and E was varied between 1 and 5V cm -1 .

Since EPD is a kinetic phenomenon, the accumulation rate of the particles around the electrode could influence their packing behavior. As a result, the choice of the applied electric field could be critical for EPD affecting the morphology of the deposits [START_REF] Shehayeb | Spectrally selective coatings obtained from electrophoretic deposition of CuO nanoparticles[END_REF]. High electric fields create turbulence around the deposition electrode due to the increased gas bubbles formation altering the morphology of deposit formed. Fig. 6 shows the top view SEM micrographs of deposits obtained. The size of the agglomerate increases with the increasing applied electric field varying between 50-200 nm for 2V cm -1 , ~500 nm for 3V cm -1 and 500-1000 nm for 4V cm -1 and 1000-2000 nm for 5V cm -1 . For 5V cm -1 , the obtained deposit has low adherence to the substrate due to the increased formation of gas bubbles, which prevents further deposition and causes the detachment of the formed deposit (see Fig. 6). As a conclusion, at lower electric fields as 2 V cm -1 deposits are formed from individual nanoparticles deposition, but with increasing the applied electric field nanoparticles are forced to migrate so fast without finding the right place to deposit and form close-packed structure. Fig. 7 shows the SEM micrographs of the obtained deposits in cross section view accompanied by the measured thickness and top-view (to analyze the morphology). The deposit thickness increases linearly with the applied electric field between E= 2 and 4V cm -1 , for higher electric field the thickness of the deposit saturated for a value of ~2600 nm. For E 1V cm -1 , no deposit was observed at the cathode. The origin of this could be due to the fact that 1V cm -1 is not sufficient to form the first layer of CuO. For the slightly higher E=1.5V cm -1 , an irregular deposit of 108±11 nm thickness is deposited which also lies outside of the linear fit. This shows that an applied electric field E 2V cm -1 is required to allow the deposition phenomenon. While for E= 5 V cm -1 saturation is attained since as E increases, the deposition process is accelerated thus higher thickness is obtained in a shorter time increasing the resistance of the deposit preventing further deposition. As a result, 2V cm -1 is the optimum applied electric field in order to obtain a homogeneous and dense deposit possessing low surface roughness and high substrate adherence.

Effect of the deposition time

To study of the evolution of the deposit thickness, as a function of deposition time, the applied electric field was fixed at 2V cm -1 and the deposition time was varied between 5, 10, 15, 30, 45, 60, 90, 120 and 180 min for the same suspension, Fig. 8 represents this evolution. In accordance with Hamaker equation, the deposit thickness increases linearly with deposition time between 5 and 30 min and then deviates from linearity after 30 min. However, the deviation from linearity is expected since the deposit formed with time creates a resisting layer that decreases the conductivity of the substrates preventing further linear deposition. Thus, for the linear part (5 and 30 mins), Hamaker equation could be used to calculate the effective density (ρe) of the deposit [START_REF] Shehayeb | Spectrally selective coatings obtained from electrophoretic deposition of CuO nanoparticles[END_REF]. The ρe value is found to be 5.8g cm -3 , which is comparable with that obtained from X-film and TOC.

Spectral efficiency

In Fig. 9, the calculated spectral features (α, ε, and η) of the EPD deposits obtained at different applied electric fields are represented. At 1V cm -1 nothing deposited at the electrode while increasing E slightly allowed the slight deposition of CuO and the α and ԑ values varied from that of the substrate. Increasing E to 2, 3, and 4V cm -1 , increased α and ԑ to 0.88-0.02, 0.86-0.01 and 0.8-0.03 respectively. As a result, the applied electric field increase doesn't enhance the α value, rather it is decreased for E = 2, 3 and 4V cm -1 . While for E= 5V cm -1 , α and ԑ attain the highest values of 0.95 and 0.44 resulting in a tandem absorber of low efficiency due to the high calculated ԑ. We point out that the deposits obtained at E=2V cm -1 present the highest efficiency of ~0.9.

Characterization of the deposit

In order to determine the composition of the deposit, we performed a conventional Ɵ/2Ɵ XRD scan, Grazing incidence XRD (GIXRD) and XPS on the CuO/PEI deposit on Pt Si wafer obtained at E=2V cm -1 and deposition time of 120 minutes from the suspensions prepared at pH=9.

X-ray diffraction study

Two intense peaks were obtained at 2Ɵ of 39.9 and 69.4. These peaks correspond to the peaks of the substrate. Upon deposition of CuO/PEI film, a slight shift in these peaks was observed and two new peaks appeared at 43.3° and 50.5°. These peaks were identified as Cu (111) and Cu (200) corresponding to face-centered cubic Copper (see Fig. 11). Knowing that the main peaks corresponding to CuO, are located at 35.4° and 38.68° [START_REF] Maruyama | Copper oxide thin films prepared by chemical vapor deposition from copper dipivaloylmethanate[END_REF], could be masked by the substrate, we performed a 2Ɵ scan at a fixed grazing angle of incidence below the critical angle (Ɵc) of the substrate.

Then for the GIXRD analysis, incidence angle Ɵi is fixed to a value slightly above the critical angle of the material. In Fig. 12, the obtained GIXRD scan of the Pt Si wafer substrate shows a small hump at 39.9 o corresponding to that of Pt and a strong peak at 69 o corresponding to Si. Pt peak is observed more clearly when the Ɵi reaches 1 o . While in Fig. 13 As a conclusion, the appearance of Cu(0) peaks in the XRD spectrum and the unresolved hump at ~36° suggests that part of the CuO NPs surface have been reduced. This mechanism is reported in literature by electrochemical reduction which could occur to bulk CuO nanoparticles or CuO films under cathodic applied electric field especially in alkaline conditions at 874 mV vs SCE [28] [29]. This reduction potential is equivalent to 913 mV for Ag/AgCl (3.5M KCl), which is inferior to the electric filed used for this study and then this scenario is plausible in our case.

X-ray photoelectron spectroscopy (XPS)

In order to identify the surface composition, the resulting CuO/PEI deposits are analyzed by XPS technique which analyzes the extreme surface (10-20 nm) (see Fig. 13). The peaks in the Cu2p scan corresponds to the core level Cu2p1/2 and Cu2p3/2 transitions of Cu. The binding energy (BE) at 932.5 eV corresponds to Cu(I) while the peak at 934.1 and shakeup satellites correspond to Cu(II). However, the peaks of Cu(I) and Cu (0) in Cu2p scan are very close and the difference is around 0.2 eV. Thus, a CuLMM scan is performed to differentiate these two peaks since the difference will be higher. The peak observed at 916.7 corresponds to Cu(I) and that at 918.5 corresponds to Cu(0). Moreover, the O1s peak at 530.5 eV corresponds to Oxygen bonded to Cu (MO) while that at 532 could correspond to C-O bonds (adventitious carbon). The peaks obtained in the C1s spectra corresponding to 284.9, 286.2, 288.6 eV, respectively proves the presence of adventitious carbon since the sample is dried in air. As a result, the data obtained from XPS, which analyzes only the extreme surface (20 nm) shows that the surface of CuO nanoparticles is reduced into Cu2O or Cu(0) due to the release of H2 gas formed at the cathode as a result of electrolysis of water.

Conclusion

A cathodic EPD of CuO nanoparticles (size of 25±5 nm) stabilized by PEI has been yield a dense and crack-free coating displaying high optical efficiency. For this, the EPD processing parameters (applied electric field, deposition time) are adjusted in order to control the structure (density, roughness, thickness) and consequently the optical efficiency of the deposit. The colloidal route offers the advantage of the formation of the CuO film from a bottom-up approach controlling the features of the film. Best selective low temperature tandem materials, having a high density (≈5.9g cm -3 for pH=9) and obtained during 120 mins at E=2V cm -1 , provide an efficiency closed to 0.9 which is prominent to be used as solar selective absorbers.

  the most basic and reactive. The ionization pH range of low MW branched PEI used is between pH=2-10[START_REF] Zarbov | Methodology for selection of charging agents for electrophoretic deposition of ceramic particles[END_REF].In a first step before EPD process, to study the effect of pH at the zeta potential value (ζ (mV)), 0.05 wt % of CuO were added to 0.88 wt % PEI at pH working range of 3, 6, 9, and 11.The addition of CuO to PEI solution resulted in blue solution which has UV-VIS absorption band maxima at ~270 nm and ~640 nm showing the formation of dative bond or a complex between surface Cu 2+ of CuO nanoparticles and amine groups of PEI[START_REF] Wen | A facile, sensitive, and rapid spectrophotometric method for copper(II) ion detection in aqueous media using polyethyleneimine[END_REF] [24].The corresponding ζ of CuO/PEI system as a function of pH are presented in Fig. 1. The measured ζ of PEI is positive for the whole pH range studied (3-11). The magnitude of the ζ increases with decreasing pH ranging between ~4 and 22 mV. Upon the addition of CuO, the ζ shifts to higher positive values varying between 5 mV for pH=11 and 35 mV for pH=3. This proves that the PEI is well adsorbed on the surface of CuO and repulsive forces are dominating. The low values obtained at pH=11 are due to the fact that PEI is not enough protonated. At pH=9, the corresponding ζ (24 mV) proves a build-up of charge and the existence of a dative bond. At pH=3 the highest ζ (+35 mV) is obtained. This shows that the interaction between PEI and CuO is due to the dative bonds formed between Cu(II) surfaces and the amino groups of PEI resulting in surface complexation of CuO. While the other free amino groups play the role of charging agents which explain the increase of ζ with decreasing pH.

Figure 1 : 8 Figure 2 :

 182 Figure 1: ζ (mV) of CuO/PEI (0.05 wt % CuO/ 0.88 wt% PEI) suspension as a function of pH.

Figure 3 :

 3 Figure 3: SEM cross-sections (a) of CuO/PEI deposits at pH= 3, 6, 9 and 11 for E=2V cm -1 and t=120 min and corresponding measured thickness versus pH (b).

Figure 4 :

 4 Figure 4: Top-view SEM micrographs of EPD deposit of CuO/PEI obtained at pH=3. Holes generated from electrolysis reaction are shown in red.

Figure 5 :

 5 Figure 5: Variation of deposit density and %V of PEI as a function of pH

Figure 6 :

 6 Figure 6: Top-view SEM micrographs of the obtained deposits for applied electric fields (1.5, 2, 3, 4, 5V cm -1 ).

Figure 7 :

 7 Figure 7: (right) SEM cross section micrographs of the effect of applied electric field. (left) Average measured thickness as a function of applied electric field (t=120 min).

Figure 8 :

 8 Figure 8: SEM cross section of the EPD deposits (right) and average measured thickness as a function of deposition time (5-180 min) (left).

Figure 9 :

 9 Figure 9: Measured thickness and spectral features of the obtained deposits at 1, 1.5, 2, 3, 4, 5V cm -1 for deposition time of 120 min.

Fig. 10

 10 Fig.10shows the average measured thickness (nm) and the calculated spectral efficiency as a function of deposition time (min). As expected, the deposition yield increases with deposition time. Upon EPD for 5 min, α value of the tandem absorber was 0.60. Then, with the deposition time increase, α value of 0.87 was reached for a deposition time of 120 min. On the other hand, the calculated emittance of CuO tandems varies between 0.01 and 0.09 for a deposition time varying between 5 and 120 min. Despite the formation of CuO thin film on the Pt Si wafer, the tandem absorbers still possess a low emittance and high absorptance. Thus, these tandem solar absorbers possess high efficiency (η). The highest efficiency of 0.84 is obtained for a deposition time of 120 mins and average measured thickness of 1240 ± 25 nm.

Figure 10 :

 10 Figure 10: Calculated α, ԑ and η and measured deposit thickness as a function of deposition time (min).

,

  The scan of the deposit having a thickness of ~ 1500 nm is observed at Ɵi=0.4 o , a small hump between 35 o and 40 o which could correspond to CuO or Cu2O planes and an intense peak at 44 o and 52 o corresponding to Cu are also observed. Varying the angle of incidence has resulted in varying the intensity of the peak which increased as we penetrated the deposit.

Figure 12 :

 12 Figure 12 : GIXRD scans of (right) of Pt Si wafer and (left) of CuO/PEI EPD deposit (E=2 V.cm -1 , t=120 mins).

Figure 13 :

 13 Figure 13: Cu2p, CuLMM, and O1s and C1s XPS spectra of CuO/PEI EPD deposit.Combing the XRD, GIXRD and the XPS data we have concluded that CuO, Cu2O and Cu coexist together in the deposit. This was also observed by the total reflectance spectra of the deposits, which showed a shift in the expected absorption edge of CuO. Compared to other reported work Cu has the least absorption in the UV-VIS-NIR region, while Cu2O and CuO have higher absorption. Cu2O has a better absorption in the UV-VIS while CuO absorbs better in the NIR region and a hybrid of CuO and Cu2O results in an absorption and absorption edge intermediate between the two. As a mechanism we propose that CuO is reduced by electrochemical reduction at the cathode forming a hybrid composite of Cu, CuO, and Cu2O[START_REF] Wan | Electrochemical formation and reduction of copper oxide nanostructures in alkaline media[END_REF].

  Ɵ/2Ɵ scan of XRD spectra of Pt Si wafer and CuO/PEI deposit.

		6000			Substrate					Pt Si wafer
	Intensity (cps)	1000 2000 3000 4000 5000							Substrate	CuO/PEI deposit
		0
		12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88
		40
	Intensity (cps)	20			Cu (111)
						Cu (200)
		0
		32	36	40	44	48	52	56	60	64	68	72
						2θ (degrees)
	Figure 11:

Acknowledgement

The authors would like to thank the University of Montpellier and the Lebanese National council for Scientific research (CNRS-L) for the co-joint funding of the project and the attribution of PhD's fellowship. The authors are grateful to Alban Jonchère (ICSM) for his help during the reflectance measurements.


Dr Jean Xavier
email: jean.xavier@aphp.fr

Hakim Guedjou

Salvatore Anzalone

Sofiane Boucenna

Emmanuel Guigon

Mohamed Chetouani

David Cohen

Toward a motor signature in autism: studies from human-machine interaction Vers une signature motrice dans l'autisme: études en interaction homme-machine

Keywords: Motor dimension, autism spectrum disorder, motor control, postural control, postural and motor variability, movement smoothness

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.

Résumé

Contexte: Le trouble du spectre de l'autisme (TSA) est un groupe hétérogène de troubles neurodéveloppementaux dont les principaux symptômes sont des troubles des interactions sociales, des intérêts restreints et des stéréotypies. Bien qu'ils ne soient pas des symptômes cardinaux en tant que tels, les troubles moteurs sont des aspects fondamentaux des TSA. On trouve des troubles de contrôle postural et moteur que nous avons étudiés en utilisant des modélisations computationnelles et la robotique développementale à travers des paradigmes d'interaction hommemachine. Méthode: Tout d'abord, dans un ensemble d'études impliquant une imitation postural homme-robot, nous avons exploré l'impact de 3 groupes différents de partenaires (y compris un groupe d'enfants atteints de TSA) sur l'apprentissage par imitation du robot. Deuxièmement, en utilisant une tâche écologique, une imitation motrice en temps réel avec un avatar funambule, nous avons étudié la synchronisation interpersonnelle, la coordination motrice et le contrôle moteur pendant la tâche chez des enfants atteints de TSA (n = 29), des enfants typiques (n = 39) et des enfants avec un trouble des acquisitions motrices (n = 17, TAC). Résultats: À partir des expériences en interaction homme robot, nous avons démontré que la signature motrice au niveau des groupes et des individus avait une influence clé sur l'apprentissage par l'imitation, la reconnaissance de la posture et la reconnaissance de l'identité. A partir du paradigme d'imitation motrice plus dynamique avec un avatar funambule, nous avons trouvé que la synchronisation interpersonnelle, la coordination motrice et le contrôle moteur étaient plus altérés et beaucoup plus variable chez les enfants atteints de TSA que chez les enfants typiques et les enfants atteints de TAC. L'ensemble de ces résultats confirme les particularités motrices des enfants atteints de TSA, malgré l'exécution adéquate des tâches d'imitation. Discussion: Les études de l'interaction homme-machine appuient l'idée d'une signature comportementale chez les enfants atteints de TSA. Cependant, plusieurs problèmes doivent être approfondis. Cette signature comportementale est-elle motrice par essence ? Est-il possible de s'assurer que ces particularités se produisent dans toutes les tâches motrices (par exemple, la posture, le mouvement volontaire) ? Cette signature motrice pourrait-elle être considérée comme spécifique à l'autisme, notamment par rapport au TAC qui présente également de faibles capacités de coordination motrice? Nous suggérons que plus de travaux comparant les deux conditions devraient être mis en oeuvre, y compris l'analyse de la cinématique et de la fluidité du mouvement avec une qualité de mesure suffisante pour permettre des analyses spectrales.

Mots clé:

Dimension motrice, trouble du spectre autistique, contrôle moteur, contrôle postural, variabilité motrice et posturale, fluidité du mouvement.

Introduction

Autism spectrum disorders (ASD) is a neurodevelopmental syndrome staring before age 3 years. Core symptoms include deficit in social interaction and restricted pattern of interests and stereotypies. Motor dysfunction is not included in the cardinal symptoms of ASD [START_REF] Xavier | Autism spectrum disorders: An historical synthesis and a multidimensional assessment toward a tailored therapeutic program[END_REF]. However, patients with ASD have sensorimotor disorders [START_REF] Jansiewicz | Motor Signs Distinguish Children with High Functioning Autism and Asperger's Syndrome from Controls[END_REF][START_REF] Haswell | Representation of internal models of action in the autistic brain[END_REF][START_REF] Fournier | Motor Coordination in Autism Spectrum Disorders: A Synthesis and Meta-Analysis[END_REF], impaired performance in skilled motor tasks and gestures [START_REF] Anzulewicz | Toward the Autism Motor Signature: Gesture patterns during smart tablet gameplay identify children with autism[END_REF][START_REF] Mostofsky | Developmental dyspraxia is not limited to imitation in children with autism spectrum disorders[END_REF][START_REF] Rogers | Imitation and pantomime in high-functioning adolescents with autism spectrum disorders[END_REF] and difficulties with imitation [START_REF] Rogers | Imitation and the social mind -Autism and Typical development[END_REF][START_REF] Vivanti | Imitation in autism spectrum disorders[END_REF], impairments in motor control [START_REF] Schmitz | Motor control and children with autism: deficit of anticipatory function?[END_REF], and difficulties in motor synchronization [START_REF] Fitzpatrick | Dynamical methods for evaluating the timedependent unfolding of social coordination in children with autism[END_REF][START_REF] Fitzpatrick | Impairments of Social Motor Synchrony Evident in Autism Spectrum Disorder[END_REF]. These disorders in movement are also associated with postural control disabilities [START_REF] Fournier | Motor Coordination in Autism Spectrum Disorders: A Synthesis and Meta-Analysis[END_REF][START_REF] Cook | From movement kinematics to social cognition: the case of autism[END_REF]. Children with ASD exhibit impaired postural control and meaningful variability in posture [START_REF] Cook | Atypical basic movement kinematics in autism spectrum conditions[END_REF][START_REF] Kohen-Raz | Postural control in children with autism[END_REF][START_REF] Vernazza-Martin | Goal Directed Locomotion and Balance Control in Autistic Children[END_REF][START_REF] Gepner | Postural effects of motion vision in young autistic children[END_REF][START_REF] Gepner | Brief Report: Postural Reactivity to Fast Visual Motion Differentiates Autistic from Children with Asperger Syndrome[END_REF][START_REF] Calhoun | Gait patterns in children with autism[END_REF][START_REF] Rinehart | Gait function in newly diagnosed children with autism: Cerebellar and basal ganglia related motor disorder[END_REF][START_REF] Rinehart | An examination of movement kinematics in young people with high-functioning autism and Asperger's disorder: Further evidence for a motor planning deficit[END_REF][START_REF] Chang | Visual tasks and postural sway in children with and without autism spectrum disorders[END_REF][START_REF] Minshew | Underdevelopment of the postural control system in autism[END_REF][START_REF] Molloy | Postural stability in children with autism spectrum disorder[END_REF][START_REF] Weimer | Motor impairment in Asperger syndrome: evidence for a deficit in proprioception[END_REF].

In typical developing (TD) children, motor control starts at birth. Infants develop skills through a coupling between their sensory and motor systems. They use sensory information to modify motor behaviors and learn from their experiences [START_REF] Dusing | Postural variability and sensorimotor development in infancy[END_REF]. An essential property of movement is its inherent variability. The stochastic patterns of minute fluctuations in motor trajectories, named sub-movements [START_REF] Bernstein | The coordination and regulation of movement[END_REF] or motor noise [START_REF] Torres | Autism: the micro-movement perspective[END_REF], contribute to the development of motor control [START_REF] Thelen | Grounded in the World: Developmental Origins of the Embodied Mind[END_REF].

Development of motor control requires forming an internal model of action that accurately predicts the sensory consequences of motor commands [START_REF] Krakauer | Towards a computational neuropsychology of action[END_REF]. Internal models of motor control are neural representations of the external world used to predict and adjust movements [START_REF] Ito | control of mental activities by internal models in the cerebellum[END_REF][START_REF] Kawato | Internal models for motor control and trajectory planning[END_REF], allowing coordination with an interaction partner and a fine exploration of the environment. Formation of internal models of action which are critical to the development of social, communicative, and motor coordination behaviors, rely on the coupling between action (motor commands) and perception (sensory feedback) which includes proprioceptive sensory information of kinesthetic order [START_REF] Izawa | Motor learning relies on integrated sensory inputs in ADHD, but over-selectively on proprioception in autism spectrum conditions[END_REF].

Torres et al. [START_REF] Torres | Autism: the micro-movement perspective[END_REF] showed disrupted patterns of proprioceptive sensory feedback in ASD using a pointing motor task and computational analysis of movement kinematics. They found a disruption in the maturation of proprioception, accompanied by behavioral variability in motor control. Across development, they found the persistence of micro-movements in adolescents and young adults with ASD that were underlined by a random (unpredictable) and noisy proprioceptive input. Besides this unique study exploring the role of proprioception and motor control in ASD, a striking observation is the relative high frequency of Ehlers-Danlos syndrome (EDS) in autism [START_REF] Takei | High-functioning autistic disorder with Ehlers-Danlos syndrome[END_REF]. Proprioceptive impairment is one of the core characteristics of EDS [START_REF] Scheper | The association between muscle strength and activity limitations in patients with the hypermobility type of Ehlers-Danlos syndrome: the impact of proprioception[END_REF][START_REF] Rombaut | Joint position sense and vibratory perception sense in patients with Ehlers-Danlos syndrome type III (hypermobility type)[END_REF], a group of genetic connective tissue disorders. However, the association between autism, proprioceptive impairments and the maintenance of micro-movements across development remains to be explored.

Objectives

In the present paper, we focus on the exploration of the motor dimension in patients with ASD through human-machine interaction and summarize a set of studies that we performed to explore human-machine motor imitation. We use computational modeling and developmental robotics involving human-machine interaction, through several paradigms, according to the idea that the structure of social interaction at both behavioral and neural levels is modified by individuals' social/motor traits [START_REF] Yun | Interpersonal body and neural synchronization as a marker of implicit social interaction[END_REF][START_REF] Walters | The influence of subjects' personality traits on personal spatial zones in a human-robot interaction experiment[END_REF]. First, we describe 3 studies that explored the impact of 3 different groups of partners (including a group of children with ASD) on robot learning by imitation. We evidenced that motor signature at both groups' and individuals' levels had a key influence on imitation learning, posture and identity recognition. Taken together these studies confirmed the motor peculiarities of children with ASD despite imitation tasks were adequately performed. Second, we summarize another study using a more dynamic motor imitation paradigm with a tightrope walker (TW) avatar.

In this study, we find that interpersonal synchronization, motor coordination and motor control were more impaired in children with ASD compared to both TD children and children with Developmental Coordination Disorder (DCD), meaning that there may be a specific motor signature in ASD.

Human-robot posture imitation studies from a robotlearning-centered perspective

In this set of studies, imitation is defined as the process by which an individual learns behavioral characteristics from a teacher (i.e., an interactive partner or model). These experiments involve a human-robot learning paradigm. Based on a sensorimotor architecture using artificial neural networks (NN) that enables learning by imitation, identity recognition and posture recognition, Nao is a "naive" robotic system that uses perceptual-motor coupling of what it does to what it sees. Involved in an imitation game with participants asked to imitate 5 different postures we added a dedicated NN. In addition, based on a first exploratory study where we showed that the number of neurons needed to learn in the VF-NN was a good metric of learning complexity and variability of posture imitation of the partners [START_REF] Boucenna | Learning of social signatures through imitation game between a robot and a human partner[END_REF], we coupled the VF-NN with a novelty detector (ND, a self-evaluation mechanism that allows Nao to recognize a new partner i.e., to detect novelty in the visual sensations) allowing the robot to achieve the recognition of participant identity in the Identity Recognition NN (IR-NN). This coupling of the number of neuron needed to learn in the VF-NN and the ND allowed the robot to recognize the participants after the learning phase, above chance levels when presented through a picture [START_REF] Boucenna | Cognitive developmental robotics: How robots learn to recognize individuals from imitating children with autism and other agents[END_REF]. In summary, inspired by the function of social identity carried by imitation [START_REF] Meltzoff | Early imitation within a functional framework: the importance of person identity, movement and development[END_REF][START_REF] Meltzoff | Imitation, memory, and the representation of persons[END_REF], they explored whether imitation learning during robot-human interaction allows the development of the robot's ability to recognize a human partner that is reencountered at a subsequent time. After a period of mutual imitation with the human partner, the robot was able to integrate the social signatures of actions (postures or facial expressions when they changed the robotic platform from Nao to Kismet) of the participants, and spontaneously develop the ability to recognize them. Finally, we also showed that posture recognition was achievable using a similar testing that the one used for identity recognition and that posture recognition was lower in children with ASD [START_REF] Guedjou | The influence of individual social traits on robot learning in a human-robot interaction[END_REF]. In figures 2B, 2C, and 2D, we further explored how learning was modulated by the number of neurons available for the system (an estimation of the cognitive complexity of learning), by time and by the novelty detector threshold.

When we modified off-line the learning-time (from two seconds to 50 seconds), and evaluated posture recognition score for each partner and for each group we found that the robot learned by imitation more easily with adults compare to both children groups, thus indicating a developmental age effect. Additionally, the robot has more difficulties (i.e., more neurons are recruited in VF-NN) during learning by imitation with children with ASD (figure 2B). This is likely due to their highly variable movements.

Similarly, when we modified off-line the learning-time and explored posture recognition score for each partner and for each group we found that, for each participant, the longer was the interaction the better was his/her posture recognition score. This result was also found in the group analysis. Furthermore, in terms of posture recognition scores, unlike for TD group for which the increase of recruited neurons compensates the difference with adults, for children with ASD posture recognition scores remained significantly lower than that of the two other groups (Figure 2C).

Finally, in the first study, the number of neurons needed to learn recognition in IR-NN was fixed to one per participant and the novelty detector threshold was also fixed [START_REF] Boucenna | Cognitive developmental robotics: How robots learn to recognize individuals from imitating children with autism and other agents[END_REF]. In a last exploration, we studied how changes in parameters influenced robot's learning [START_REF] Guedjou | The influence of individual social traits on robot learning in a human-robot interaction[END_REF]. In figure 2D, we simulated a variation of the threshold parameter controlling the novelty detection sensitivity. The partners' identities in each group were learned sequentially. To ease the comparison, we kept the same amount of subjects (N=11) in each group and randomly discarded 4 TD children and 4 children with ASD. We show the effect on identity recognition scores (2D-top) and on the number of neurons recruited (2D-down) for the 3 groups. At any tested threshold, identity recognition scores of adult partners were higher compared to those of TD children, which were higher to the recognition scores of children with ASD. Considering the recruitments of neurons in IR-NN, we found that (i) the threshold needed to perform best identity recognition for both children groups was below than the threshold for adults, respectively (figure 2D-top); and (ii) for almost all the tried threshold intervals, the system recruited more neurons while learning from children with ASD compared to TD children and from TD children compared to adults (figure 2D-down). To achieve the identity recognition task and reach score higher than 85%, the architecture needed 12 neurons for adults, 15 neurons for TD children and more than 30 for children with ASD [START_REF] Guedjou | The influence of individual social traits on robot learning in a human-robot interaction[END_REF].

All together, these different results show that participants with ASD have a higher variability in terms of posture realization and, for the robot, a higher complexity of the visual input when it is learning by imitation with children with ASD compared to other partners (adults or TD children). This is revealed by the higher number of neurons needed to learn to capture this variability. It seems that the robot is able to detect subtle instabilities in ASD children's posture (i.e., in the spatial and temporal micro-stability) that were undetected by a therapist in a clinical setting [START_REF] Boucenna | Learning of social signatures through imitation game between a robot and a human partner[END_REF]. These results motivate further exploration of ASD motor signature.

Interpersonal synchronization and motor dynamics during human-avatar motor imitation

Behavioral imitation is common in children with autism spectrum disorder (ASD) despite frequent motor coordination impairments. Impairments in imitation abilities have been also described in other neurodevelopmental disorders such as developmental coordination disorder (DCD). Children with DCD display motor incoordination and visual spatial processing deficits [START_REF] Mazeau | Troubles neurovisuels et praxiques : un élément déterminant du pronostic à long terme[END_REF] which may affect their imitation abilities [START_REF] Green | A pilot study of psychopathology in Developmental Coordination Disorder[END_REF][START_REF] Werner | Neural Correlates of Developmental Coordination Disorder: The Mirror Neuron System Hypothesis[END_REF]. How motricity impacts imitation during long lasting semi-ecological conditions has not been carefully investigated. In Xavier et al. [START_REF] Xavier | Interpersonal synchronization, motor coordination and control are impaired during a dynamic imitation task in children with autism spectrum disorder[END_REF] experiment, we explore behavioral imitation abilities in terms of interpersonal synchronization, motor coordination and control by means of an interaction paradigm using a TW avatar. To get a better understanding of imitation difficulties in children with ASD, we explore the potential alteration of the development of behavioral imitation abilities in children with ASD in comparison with DCD children and TD control children. ASD and DCD have in common motor and visual spatial difficulties. Therefore, comparing these two pathological groups offered the opportunity to disentangle the contribution of visualspatial and motor coordination impairments in motor imitation difficulties. For this study, we recruited 85 children and adolescents (39 controls with typical development, TD; 29 patients with ASD; 17 patients with DCD), aged 6 to 20 years who participated to a behavioral paradigm.

Participants, standing and moving in front of the TW avatar, interacted with it standing and moving as well. During the protocol, we measure automatically and continuously avatar's and participant's heads and bars from RGB sensor recording to assess participants' behavioral imitation (see figure 3).

In this experiment, we find that interpersonal synchronization (as evidenced by the synchrony between the participant's and the tightrope walker's bars) and motor coordination (as evidenced by the synchrony between the participant's bar and its own head axis) increased with age and were more impaired in patients with ASD compared to both TD children and children with DCD. Also, motor control as evidenced by the movement angle standard deviations of participants' bar and head were significantly larger in ASD compared to both TD children and children with DCD [START_REF] Xavier | Interpersonal synchronization, motor coordination and control are impaired during a dynamic imitation task in children with autism spectrum disorder[END_REF].

In sum, behavioral imitation abilities during an ecological interaction with a TW avatar show subtle impairment in children with ASD as compared to TD children or children with DCD, both in terms of interpersonal synchrony, motor coordination and control. These results question how motricity matures in terms of motor control and proprioception in children with ASD. Exploring motor control from a developmental point of view through a dynamic process like imitation poses significant pragmatic challenges for researchers and clinicians alike.

Discussion

Based on the clinical literature on ASD (see intro) and the set of studies using humanmachine interaction that we performed with children with ASD, it appears that the way children with autism behave during motor tasks expresses a specific behavioral signature. This signature is evidenced from the robot-learning-centered perspective we used in our developmental robotics studies [START_REF] Boucenna | Learning of social signatures through imitation game between a robot and a human partner[END_REF][START_REF] Boucenna | Cognitive developmental robotics: How robots learn to recognize individuals from imitating children with autism and other agents[END_REF][START_REF] Guedjou | The influence of individual social traits on robot learning in a human-robot interaction[END_REF]. The signature is also captured during the ecological dynamic task with the TW avatar [START_REF] Xavier | Interpersonal synchronization, motor coordination and control are impaired during a dynamic imitation task in children with autism spectrum disorder[END_REF]. However, to be specific, this motor signature needs to ascertain three conditions. First, it should be specific in terms of clinical label within the neurodevelopmental disorder group. The fact that children with ASD significantly differ from children with DCD in our tightrope walker ecological paradigm is encouraging.

Second, we need to ascertain whether the so-called behavioral signature found during motor interaction between children with ASD and machine is motor in essence [START_REF] Burdet | Quantization of human motions and learning of accurate movements[END_REF]. Indeed, motor activity is a behavioral output that is a cascade of different skills. Development of motor control requires forming an internal model of action relying on the coupling between action (motor commands) and perception (sensory feedback). Critical to the development of social, communicative, and motor coordination behaviors, internal model of action accurately predicts the sensory consequences of motor commands [START_REF] Krakauer | Towards a computational neuropsychology of action[END_REF]. To disentangle the contribution of motor dysfunction per se in these motor activities, research should focus on specific metrics that may capture both sub-movements and their possible effect on movement smoothness (see below). The jerk and the jerk ratio may be a first approximation [START_REF] Salmond | Proximal-distal differences in movement smoothness reflect differences in biomechanics[END_REF]. Jerk is the 3 rd derivative of shifting. Jerk ratio is the integrated squared jerk of a movement. Comparison between tasks usually requires normalization [START_REF] Salmond | Proximal-distal differences in movement smoothness reflect differences in biomechanics[END_REF]. Another method may be to define speed profile during the task meaning calculating the duration and number of pics of speed.

A common expected result is a positive correlation between the number of pics of speed and duration. Finally, the study of movement phases through spectral analysis. This task is delicate as it may be necessary to distinguish postural oscillation [START_REF] Loram | Human balancing of an inverted pendulum: Is sway size controlled by ankle impedance?[END_REF].

Third, we also need to ascertain whether this motor signature is found in all or a limited set of motor tasks (e.g. pointing; writing; motor imitating). Back to the studies that have specifically investigated motor characteristics in ASD, we found several studies describing disruption in movement kinematics in ASD during goal directed actions [START_REF] Schmitz | Motor control and children with autism: deficit of anticipatory function?[END_REF][START_REF] Cook | Atypical basic movement kinematics in autism spectrum conditions[END_REF][START_REF] Rinehart | An examination of movement kinematics in young people with high-functioning autism and Asperger's disorder: Further evidence for a motor planning deficit[END_REF][START_REF] Sacrey | Reaching and grasping in autism spectrum disorder: a review of recent literature[END_REF][START_REF] Stoit | Grasping motor impairments in autism: not action planning but movement execution is deficient[END_REF][START_REF] Dowd | Do planning and visual integration difficulties underpin motor dysfunction in autism? A kinematic study of young children with autism[END_REF][START_REF] Kushki | Handwriting difficulties in children with autism spectrum disorders: a scoping review[END_REF]. Since motor action needs some kind of continuous control during the execution of a given movement [START_REF] Burdet | Quantization of human motions and learning of accurate movements[END_REF][START_REF] Navas | Sampling or intermittency in hand control systems dynamics[END_REF][START_REF] Miall | Is the cerebellum a Smith Predictor?[END_REF][START_REF] Miall | Forward models for physiological motor control[END_REF][START_REF] Morasso | A neural mechanism of synergy formation for whole body reaching[END_REF][START_REF] Gawthrop | Intermittent control: a computational theory of human control[END_REF][START_REF] Woodworth | The accuracy of voluntary movement[END_REF], voluntary movements have discontinuities whose frequency (around 10Hz) is a fundamental characteristic of motor control. These intermittencies, called sub-movements, are corrections made to counter the effect of initial inaccuracy of movements [START_REF] Milner | The effect of accuracy constraints on three-dimensional movement kinematics[END_REF]. During child development, the gradual progression of motor control with higher levels of spatial/temporal movement accuracy results in an increase of its smoothness [START_REF] Berthier | Development of reaching in infancy[END_REF] and a decrease of its jerkiness. This phenomenon includes a reduction in the number of the sub-movements [START_REF] Van Der Meer | Prospective control in catching by infants[END_REF][START_REF] Caljouw | Savelsbergh GJP Catching optical information for the regulation of timing[END_REF][START_REF] Hofsten | Action in development[END_REF] which appear higher in peak speed, longer in duration, and more overlapped [START_REF] Rohrer | Avoiding spurious submovement decompositions: a globally optimal algorithm[END_REF].

Few studies using different motor tasks (pointing, reaching to grasp, reaching and dropping) found atypical sub-movement patterns in children with ASD [START_REF] Torres | Autism: the micro-movement perspective[END_REF][START_REF] Forti | Motor planning and control in autism. A kinematic analysis of preschool children[END_REF][START_REF] Mari | The reach-to-grasp movement in children with autism spectrum disorder[END_REF]. Interpretations are not consensual and authors have proposed several underlying mechanisms: desynchronization of submovements within a single action; impairments of motor control; difference in nature regarding submovements (called micro-movements); disrupted patterns of proprioceptive sensory feedback [START_REF] Torres | Autism: the micro-movement perspective[END_REF][START_REF] Torres | Motor noise is rich signal in autism research and pharmacological treatments[END_REF]. However, postural control is integral to the execution of action, serving as a reference frame for the production of accurate, smoothly continuous and sustained movements [START_REF] Thelen | Postural control during reaching in young infants: a dynamic systems approach[END_REF][START_REF] Frank | Coordination of posture and movement[END_REF][START_REF] Mouel | Mobility as the Purpose of Postural Control[END_REF]. From the current literature, it remains also difficult to ascertain that the behavioral signature present during movement kinematics is different in nature to the posture variability found in ASD.

As we said previously, besides motor signature per se, it remains difficult to ascertain to what extent some of these motor problems are specific to autism [START_REF] Bucci | Motor impairment in children with autistic spectrum disorder and in children with attention deficit hyperactivity disorder[END_REF], i.e. could constitute a motor signature, notably in comparison to other neurodevelopmental disorders such as developmental coordination disorder (DCD) that also display poor motor coordination and skills [START_REF]Developmental Coordination Disorder[END_REF][START_REF] Macnab | The search for subtypes of DCD: Is cluster analysis the answer?[END_REF]. Direct comparisons between the two conditions has been limited in the literature. More work should be implemented comparing the two conditions and including motor capture kinematics allowing analysis at a temporal level that addresses movement variation at high frequency range with sufficient measurement quality.

(figure 1 )

 1 , Nao was used as a tool for clinical evaluation of interaction abilities of children, allowing the extraction of social movement signatures. The robot learning was evaluated with 3 different groups of participants: adults, TD children, and children with ASD. A "social signature" was generated for each participant based on the number of neurons required by the robot to learn by imitation. The architecture used in these experiments is summarized in figure 2A. The neural networks architecture that allows learning by imitation is composed of a Visual Feature NN (VF-NN), a Robot Internal State NN (RIS-NN), an Internal State Prediction NN (ISP-NN) that coupled what the robot sees with what it does, a Short Term Memory NN (STM-NN). To assess posture recognition (PR-NN),

Figure 1 .

 1 Figure 1. The robot and the human participant producing the five postures during the imitation task.

Figure 2 .

 2 Figure 2. Summary of the experiments using imtation learnin with Nao robot. (1A) Neural net architecture; (2B) Number of neurons needed to learn in VF during learning by imitation as a function of time; (3C) Posture recognition score (%) as a function of time (3D) Number of neurons needed to learn in IR during learning by imitation (down) and Identity recognition score (%)(down) as a function of novelty detector threshold. Red=Adults; Green=Typical developing children; Red=Children with ASD. RIS= Robot Internal State; VF=Visual Feature; ISP=Internal State Prediction; STM=Short Term Memory; PR=Posture recognition; IR=Identity recognition.

Figure 3 .

 3 Figure 3. Principles and set-up of the experiment: (3A) Schematic illustration of the experimental room; (3B) tightrope walker's bar inclination measurement; (3C) The roll angle of the head and of the bar in the frontal plane were recorded (left) projection on the wall of a tightrope walker avatar; (3D) Registration of participant's and TW avatar's heads and of participant's and TW avatar's bars.

Acknowledgments

These works were partially supported by the Labex SMART (ANR-11-LABX-65) under French state funds managed by the ANR within the Investissements d'Avenir programme (ANR-11-IDEX-0004-02); by the Groupement de Recherche en Psychiatrie (GDR-3557); and by the IHU-A-ICM (Institut des Neurosciences Translationnelles de Paris). Sponsor had no involvement in the study design, data analysis, or interpretation of the results. The authors thank Alain Berthoz, Mohamed Zaoui and Soizic Gauthier for collaborating with the tightrope walker experiment, and Andrew Meltzoff for collaborating with the human-robot imitation experiment.

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.