Visualization of an Endogenous Mitochondrial Azoreductase Activity under Normoxic Conditions Using a Naphthalimide Azo-Based Fluorogenic Probe.

In this paper, we demonstrate the existence of an endogenous mitochondrial azoreductase (AzoR) activity that can induce the cleavage of N═N double bonds of azobenzene compounds under normoxic conditions. To this end, 100% OFF-ON azo-based fluorogenic probes derived from 4-amino-1,8-naphthalimide fluorophores were synthesized and evaluated. The in vitro study conducted with other endogenous reducing agents of the cell, including reductases, demonstrated both the efficacy and the selectivity of the probe for AzoR. Confocal experiments with the probe revealed an AzoR activity in the mitochondria of living cells under normal oxygenation conditions, and we were able to demonstrate that this endogenous AzoR activity appears to be expressed at different levels across different cell lines. This discovery provides crucial information for our understanding of the biochemical processes occurring within the mitochondria. It thus contributes to a better understanding of its function, which is implicated in numerous pathologies.

A Naphthalimide Based "Turn-ON" Probe for Wash-Free Imaging of Lipid-Droplet in Living Cells With an Excellent Selectivity.

The impacts of dimethylation of 4-Amino-1,8-Naphthalimide (ANI) on its photophysical properties are reported. The resulting 4-DiMe-ANI displays completely different fluorescence properties, conferring it ability to selectively label lipid droplets in living cells. A comprehensive photophysical study revealed that this selectivity arises from an Internal Charge Transfer favored in lipophilic media to the detriment of a non-emissive TICT in more polar media. This results in a very high "LDs/Cytosol" signal ratio, enabling LDs to be imaged with an excellent signal-to-noise ratio, and positioning its performance above that of the BODIPY 493/503 commonly used to image LDs.

CinNapht AIE(E)gens for selective imaging of lipid droplets.

This article describes the synthesis and photophysical properties of Aggregation-Induced Emission (enhancement) luminogens derivated from CinNaphts dyes. These fluorophores can be obtained in good yields in a single SNAr step of a fluorinated CinNapht derivative by incorporating hindered aromatic amines. They exhibit AIE(E) behavior associated with solid-state fluorescence covering an emission range from 563 to 722 nm. One carbazole derivative demonstrates a remarkable efficiency in imaging lipid droplets in living cells through an original photophysical mechanism.

Evaluation of borinic acids as new, fast hydrogen peroxide-responsive triggers.

Hydrogen peroxide (H2O2) is responsible for numerous damages when overproduced, and its detection is crucial for a better understanding of H2O2-mediated signaling in physiological and pathological processes. For this purpose, various "off-on" small fluorescent probes relying on a boronate trigger have been prepared, and this design has also been involved in the development of H2O2-activated prodrugs or theranostic tools. However, this design suffers from slow kinetics, preventing activation by H2O2 with a short response time. Therefore, faster H2O2-reactive groups are awaited. To address this issue, we have successfully developed and characterized a prototypic borinic-based fluorescent probe containing a coumarin scaffold. We determined its in vitro kinetic constants toward H2O2-promoted oxidation. We measured 1.9 × 104 m-1⋅s-1 as a second-order rate constant, which is 10,000-fold faster than its well-established boronic counterpart (1.8 m-1⋅s-1). This improved reactivity was also effective in a cellular context, rendering borinic acids an advantageous trigger for H2O2-mediated release of effectors such as fluorescent moieties.

Lanthanide-Based Probes for Imaging Detection of Enzyme Activities by NIR Luminescence, T1- and ParaCEST MRI.

Applying a single molecular probe to monitor enzymatic activities in multiple, complementary imaging modalities is highly desirable to ascertain detection and to avoid the complexity associated with the use of agents of different chemical entities. We demonstrate here the versatility of lanthanide (Ln3+) complexes with respect to their optical and magnetic properties and their potential for enzymatic detection in NIR luminescence, CEST and T1 MR imaging, controlled by the nature of the Ln3+ ion, while using a unique chelator. Based on X-ray structural, photophysical, and solution NMR investigations of a family of Ln3+ DO3A-pyridine model complexes, we could rationalize the luminescence (Eu3+, Yb3+), CEST (Yb3+) and relaxation (Gd3+) properties and their variations between carbamate and amine derivatives. This allowed the design of L n L G a l 5 ${{{\bf L n L}}_{{\bf G a l}}^{5}}$ probes which undergo enzyme-mediated changes detectable in NIR luminescence, CEST and T1-weighted MRI, respectively governed by variations in their absorption energy, in their exchanging proton pool and in their size, thus relaxation efficacy. We demonstrate that these properties can be exploited for the visualization of ß-galactosidase activity in phantom samples by different imaging modalities: NIR optical imaging, CEST and T1-weighted MRI.

Characteristics of patients with atrial fibrillation treated with direct oral anticoagulants and new insights into inappropriate dosing: results from the French National Prospective Registry: PAFF.

AIMS: Since the introduction of direct oral anticoagulant (DOAC) for atrial fibrillation (AF) therapy, inappropriate and/or underdosing of these drugs has been a major clinical challenge. We evaluated the characteristics of patients with AF treated with inappropriate and low-dose DOACs. METHODS AND RESULTS: Patients with AF treated with inappropriate and low-dose DOACs from October 2021 to December 2021 were evaluated from the French National Prospective Registry (PAFF). We evaluated 1890 patients with AF receiving DOACs (apixaban 55%, dabigatran 7%, and rivaroxaban 38%). Inappropriate dosing was noted in 18% of the population. Patients with appropriate dosing had less comorbidities: younger age (75 ± 10 vs. 82 ± 8 years old, P < 0.0001), reduced chronic renal failure (26 vs. 61%, P < 0.0001), and lower CHA2DS2VASc and HASBLED scores (3 ± 2 vs. 4 ± 3, P < 0.0001; 2 ±1 vs. 2 ± 2, P < 0.0001), respectively. In multivariate analysis, older age (P < 0.0001) and a higher CHA2DS2VASc score (P = 0.0056) were independently associated with inappropriate DOAC dosing. Among 472 patients (27%) treated with low-dose rivaroxaban or apixaban, 46% were inappropriately underdosed. Patients inappropriately underdosed were younger (82.3 ± 8.4 vs. 85.9 ± 5.9 years, P < 0.0001) with less chronic renal disease (47 vs. 98%, P < 0.0001). However, these patients had higher rates of prior haemorrhagic events (18 vs. 10%, P = 0.01), clopidogrel use (11 vs. 3%, P = 0.0002), and apixaban prescription (74 vs. 50%, P < 0.0001). CONCLUSION: Within this large registry, DOACs were associated with inappropriate dosing in 18% of cases. Independent predictors of inappropriate dosing were high CHA2DS2VASc scores and older age. Moreover, 46% of patients treated with low-dose DOACs were inappropriately underdosed and more frequently in patients treated with apixaban.

Blood Purification with oXiris© in Critically Ill Children with Vasoplegic Shock.

INTRODUCTION: Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. As such, circulating cytokines and danger- and pathogen-associated molecular patterns (such as endotoxins) are recognized as central in the pathogenesis of sepsis and organ dysfunction. Removing these compounds by extracorporeal blood filtration, commonly considered blood purification, may improve the septic patients' condition. This study aimed to assess the vaso-inotropic support evolution over time in pediatric patients with vasoplegic shock treated with oXiris©. METHODS: All patients aged below 18 years admitted at the Paris Saclay University Quaternary Pediatric Intensive Care Unit with vasoplegic shock and acute kidney injury and treated with oXiris© between October 2017 and January 2020 were included. The vaso-inotropic score and the 28-day mortality were assessed. Improvement under treatment was defined as a 50% decrease in the vaso-inotropic score following 24 h of oXiris© therapy. RESULTS: Eleven pediatric patients aged 2-15 years and weighing 11-60 kg were admitted with vasoplegic shock and acute kidney injury. They received thirteen sessions of oXiris© therapy for septic shock (N = 7) and liver failure (N = 6). Eight patients did not improve their condition during the session, and five ultimately died (37.5% survival). Five patients improved, decreasing their inotropic support by >50% in 24 h. Among them, four survived (80%). CONCLUSION: Hemofiltration and extracorporeal blood purification with oXiris© can be used in pediatric patients with vasoplegic shock with rapid improvement in hemodynamics in selected patients.

Pediatric hepatic hemangiomas: spectrum and prognostic significance of initial ultrasound findings.

BACKGROUND: Hepatic hemangiomas may be associated with serious complications; however, it is unknown whether ultrasound (US) features can predict complications. OBJECTIVE: To analyze initial US features of hepatic hemangiomas predictive of complications. MATERIALS AND METHODS: This is a single-center retrospective cohort study of clinical, biological, and imaging data of infants with hepatic hemangioma between 2000 and 2018. Patients were categorized as having or not having any complication(s). Associations between initial US features and complications were analyzed through logistic regression. Receiver operating characteristic (ROC) curve analyses were performed to determine optimal cutoff values for continuous variables. Stepwise forward logistic regression was used to construct risk prediction models with training and validation sets. Model calibration and discrimination were evaluated using Hosmer-Lemeshow tests, area under the ROC curve, and overall accuracy. RESULTS: Of 112 infants with hepatic hemangioma, 67 (60%) had focal, 32 (28%) had multifocal, and 13 (12%) had diffuse lesions, with complication rates of 51%, 34%, and 92%, respectively, mostly cardiac (54/57, 95%). The US characteristics of the hemangiomas were diverse. Risk factors for complications included diffuse subtype; large tumor volume (focal forms); elevated peak systolic hepatic arterial velocity (PSV); and hepatic vein dilation. For focal forms, initial tumor volume >40 ml and PSV >100 cm/s had >70% sensitivity and specificity, respectively, to predict complications; a model including these variables had 75% overall accuracy in the validation set. For multifocal/diffuse forms, a PSV >115 cm/s had sensitivity and specificity to predict complications of >70%; a model including this variable had 78% overall accuracy in the validation set. CONCLUSION: Diffuse subtype, large tumor volume, elevated hepatic arterial PSV, and hepatic vein dilation are risk factors for complications of hepatic hemangiomas.

High-Relaxivity Molecular MRI Contrast Agent to Target Gb3-Expressing Cancer Cells.

Targeted contrast agents (CAs) can improve magnetic resonance imaging (MRI) for accurate cancer diagnosis. In this work, we used the Shiga toxin B-subunit (STxB) as a targeting agent, which binds to Gb3, a glycosphingolipid highly overexpressed on the surface of tumor cells. We developed STxB-targeted MRI probes from cyclic peptide scaffolds functionalized with six to nine monoamide DO3A[Gd(III)] chelates. The influence of structural constraints on the longitudinal relaxivity (r1) of the CAs has been studied. The cyclic peptide carrying nine monoamide DO3A[Gd(III)] exhibited a r1 per compound of 32 and 93 mM-1s-1 at 9.4 and 1.5 T, respectively. Its conjugation to the pentameric STxB protein led to a 70 kDa compound with a higher r1 of 150 and 475 mM-1 s-1 at 9.4 and 1.5 T, respectively. Specific accumulation and cellular distribution of this conjugate in Gb3-expressing cancer cells were demonstrated using immunofluorescence microscopy and quantified by an inductively coupled plasma-mass spectrometry dosage of Gd(III). Such an agent should enable the in vivo detection by MRI of tumors expressing Gb3 receptors.

Investigation of the Fuzzy Complex between RSV Nucleoprotein and Phosphoprotein to Optimize an Inhibition Assay by Fluorescence Polarization.

The interaction between Respiratory Syncytial Virus phosphoprotein P and nucleoprotein N is essential for the formation of the holo RSV polymerase that carries out replication. In vitro screening of antivirals targeting the N-P protein interaction requires a molecular interaction model, ideally consisting of a complex between N protein and a short peptide corresponding to the C-terminal tail of the P protein. However, the flexibility of C-terminal P peptides as well as their phosphorylation status play a role in binding and may bias the outcome of an inhibition assay. We therefore investigated binding affinities and dynamics of this interaction by testing two N protein constructs and P peptides of different lengths and composition, using nuclear magnetic resonance and fluorescence polarization (FP). We show that, although the last C-terminal Phe241 residue is the main determinant for anchoring P to N, only longer peptides afford sub-micromolar affinity, despite increasing mobility towards the N-terminus. We investigated competitive binding by peptides and small compounds, including molecules used as fluorescent labels in FP. Based on these results, we draw optimized parameters for a robust RSV N-P inhibition assay and validated this assay with the M76 molecule, which displays antiviral properties, for further screening of chemical libraries.

Cytotoxic and Antioxidant Activities of Imine Analogs of Trans-Resveratrol towards Murine Neuronal N2a Cells.

Trans-resveratrol is a natural polyphenol showing numerous biological properties, especially anti-tumoral and antioxidant activity. Among numerous resveratrol derivatives, aza-stilbenes, which bear an imine bound, show interesting biological activities. In the present study, we synthesized a series of imine analogs of trans-resveratrol (seven aza-stilbenes) following an easy and low-cost procedure of green chemistry. The toxicity of synthesized aza-stilbenes, which is currently unknown, was evaluated on murine neuronal N2a cells, comparatively to trans-resveratrol, by considering: cell density evaluated by staining with sulforhodamine 101; esterase activity, which is a criteria of cell viability, by staining with fluorescein diacetate; and transmembrane mitochondrial potential, which is known to decrease during cell death, by staining with DiOC6(3) using flow cytometry. In addition, the antioxidant activity was quantified with the KRL (Kit Radicaux Libres) assay, the DPPH (2,2'-diphenyl-1-picrylhydrazyl radical) assay and the FRAP (ferric reducing antioxidant power) assay. The PAOT (Pouvoir Antioxidant Total) score was also used. The aza-stilbenes provide different cytotoxic and antioxidant activities, which are either higher or lower than those of trans-resveratrol. Based on their cytotoxic and antioxidant characteristics, all synthesized aza-stilbenes are distinguished from trans-resveratrol.

A randomised trial of high-flow nasal cannula in infants with moderate bronchiolitis.

BACKGROUND: The objective was to determine whether high-flow nasal cannula (HFNC), a promising respiratory support in infant bronchiolitis, could reduce the proportion of treatment failure requiring escalation of care. METHODS: In this randomised controlled trial, we assigned infants aged <6 months who had moderate bronchiolitis to receive either HFNC at 3 L·kg-1·min-1 or standard oxygen therapy. Crossover was not allowed. The primary outcome was the proportion of patients in treatment failure requiring escalation of care (mostly noninvasive ventilation) within 7 days following randomisation. Secondary outcomes included rates of transfer to the paediatric intensive care unit (PICU), oxygen, number of artificial nutritional support-free days and adverse events. RESULTS: The analyses included 268 patients among the 2621 infants assessed for inclusion during two consecutive seasons in 17 French paediatric emergency departments. The percentage of infants in treatment failure was 14% (19 out of 133) in the study group, compared to 20% (27 out of 135) in the control group (OR 0.66, 95% CI 0.35-1.26; p=0.21). HFNC did not reduce the risk of admission to PICU (21 (15%) out of 133 in the study group versus 26 (19%) out of 135 in the control group) (OR 0.78, 95% CI 0.41-1.41; p=0.45). The main reason for treatment failure was the worsening of modified Wood clinical asthma score (m-WCAS). Short-term assessment of respiratory status showed a significant difference for m-WCAS and respiratory rate in favour of HFNC. Three pneumothoraces were reported in the study group. CONCLUSIONS: In patients with moderate bronchiolitis, there was no evidence of lower rate of escalating respiratory support among those receiving HFNC therapy.

Bacterial infections in children after liver transplantation: A single-center surveillance study of 345 consecutive transplantations.

BACKGROUND: Infectious complications after pediatric liver transplantation frequently occur and are potentially serious. Data concerning strictly defined bacterial infections and their associated risk factors are lacking. METHODS: For the pediatric liver transplant postoperative period, we analyzed data from the nosocomial infection surveillance (2006-2015). RESULTS: A total of 235 bacterial infections in 162 transplantations (47%) occurred, including 32 bacterial pneumonia cases, 104 surgical site infections, 27 urinary tract infections, and 40 bloodstream infections. Sepsis was diagnosed in 127 cases (54%), severe sepsis in 22 (9%) cases, and septic shock in 41 (17%) cases. Thirty patients (9%) died, and septic shock was the leading cause of death. The carrier status of multi-drug resistant bacteria and a tacrolimus level >20 ng/mL were independent risk factors for surgical site infections and the occurrence of severe sepsis or septic shock. The length of mechanical ventilation was an independent risk factor for pneumonia and surgical site infection. CONCLUSION: Bacterial infections in the early postoperative period after pediatric liver transplantation are associated with high morbidity and mortality. Physicians involved in the medical care of these patients should be aware of the specific risk factors, and further development of prevention programs is highly recommended.

International evidence-based guidelines on Point of Care Ultrasound (POCUS) for critically ill neonates and children issued by the POCUS Working Group of the European Society of Paediatric and Neonatal Intensive Care (ESPNIC).

BACKGROUND: Point-of-care ultrasound (POCUS) is nowadays an essential tool in critical care. Its role seems more important in neonates and children where other monitoring techniques may be unavailable. POCUS Working Group of the European Society of Paediatric and Neonatal Intensive Care (ESPNIC) aimed to provide evidence-based clinical guidelines for the use of POCUS in critically ill neonates and children. METHODS: Creation of an international Euro-American panel of paediatric and neonatal intensivists expert in POCUS and systematic review of relevant literature. A literature search was performed, and the level of evidence was assessed according to a GRADE method. Recommendations were developed through discussions managed following a Quaker-based consensus technique and evaluating appropriateness using a modified blind RAND/UCLA voting method. AGREE statement was followed to prepare this document. RESULTS: Panellists agreed on 39 out of 41 recommendations for the use of cardiac, lung, vascular, cerebral and abdominal POCUS in critically ill neonates and children. Recommendations were mostly (28 out of 39) based on moderate quality of evidence (B and C). CONCLUSIONS: Evidence-based guidelines for the use of POCUS in critically ill neonates and children are now available. They will be useful to optimise the use of POCUS, training programs and further research, which are urgently needed given the weak quality of evidence available.

Long-term outcome of vein of Galen malformation.

AIM: To describe the long-term outcomes of children by the time they reached school age with vein of Galen aneurysmal malformation (VGAM). METHOD: This was a retrospective observational study on a consecutive cohort of patients with VGAM. We included patients with at least one Francophone parent, aged between 6 and 11 years at the time of long-term evaluation. The neurological outcome was assessed with the King's Outcome Scale for Childhood Injury score and eight neurological and behavioural items from the Rivermead Postconcussion Symptoms questionnaire. RESULTS: All 52 patients (17 females, 32 males [data missing for n=3]) with at least one Francophone parent (5 fetuses and 47 children) were included. At the long-term evaluation time-point, 33 patients were alive and 19 patients had died. Risk of postnatal death was associated with severe neonatal cardiac failure (p=0.007) or isosystemic or suprasystemic pulmonary hypertension (p=0.014). Among survivors, 19 had a good outcome with normal schooling and 14 had a poor outcome. Moreover, among the good outcome patients, a large proportion had neurodevelopmental alterations. INTERPRETATION: Long-term outcome of patients with VGAM appears to be less favourable than outcome described at the short- and medium-term, even in the absence of encephalomalacia at birth. Even patients with good outcome often have neuropsychological disorders that may have repercussions on learning and requiring appropriate rehabilitation or medical management. WHAT THIS PAPER ADDS: Long-term outcome appears to be less favourable than described at short- and medium-term follow-up. Even patients with good outcome at these time-points often have minor neuropsychological disorders.

Pseudofeeders on fetal magnetic resonance imaging predict outcome in vein of Galen malformations.

OBJECTIVE: Although vein of Galen aneurysmal malformations (VGAM) can be diagnosed in the fetus, the challenge is predicting the occurrence of its 2 major complications: cardiopulmonary failure and encephalomalacia. This study attempts to determine which fetal brain magnetic resonance imaging (MRI) features might be used to predict the development of these complications at birth. METHODS: The cohort was extracted from a prospectively assembled database of VGAM cases managed at a single referral center from 2000 to 2014. Of 251 patients with VGAM, 83 cases were diagnosed prenatally. A total of 58 patient charts having at least 1 fetal MRI were reviewed. Patterns of brain parenchyma, hydrocephalus, and so-called middle cerebral artery (MCA) "pseudofeeders" were correlated with cardiac failure, pulmonary hypertension, and encephalomalacia at birth. RESULTS: The median gestational age at fetal MRI was 32.3 weeks of pregnancy (±2.3). Nine fetuses (16%) had encephalomalacia. Thirty-one fetuses (53%) had MCA pseudofeeders. Twenty-six fetuses (45%) had prenatal hydrocephalus. Prenatal MCA pseudofeeders were a risk factor for encephalomalacia at birth (p = 0.001). MCA pseudofeeders and hydrocephalus were risk factors for both severe cardiac failure (p = 0.01 and p = 0.04, respectively) and severe pulmonary hypertension (p = 0.014 and p = 0.05, respectively) at birth. INTERPRETATION: MCA pseudofeeders are the result of impaired cerebral blood flow, and are thus a risk factor for further brain melting at birth. Their presence can be used for informing parents and as an aid in management decisions. Ann Neurol 2017;81:278-286.

Differences of Medical Care for Acute Severe Viral Bronchiolitis in Two Urban Areas in Europe.

BACKGROUND: Acute viral bronchiolitis is a frequent disease in infancy. There is little knowledge on medical care of severely affected infants in different European countries. PATIENTS: Infants (n=146) with bronchiolitis requiring respiratory support in winter season 2015/2016 treated in either one of two regions in Central Europe: South of greater Paris region in France (group 1) and Ruhr area in Germany (group 2). METHODS: Retrospective chart review. Primary outcome parameter was duration of respiratory support. RESULTS: Infants in group 1 (n=96) were younger, suffered less frequently from neurologic disorders and had lower respiratory rates than in group 2 (n=50). CO2 levels and dyspnea score were similar. Ninety percent of infants in group 1 were treated by nasal Continuous Airway Pressure CPAP, while 80% of infants in group 2 were treated by High Flow Nasal Cannula HFNC. Duration of respiratory support was significantly shorter in group 1. Infants in group 2 received more frequently infusion therapy, more antibiotics and more inhalation therapy. DISCUSSION: Our results show better outcome for infants with viral bronchiolitis treated in France. Striking differences were the practice of respiratory support (nasal CPAP vs. HFNC) and the prescription of supportive treatments. CONCLUSION: Treatment approaches in severe acute viral bronchiolitis differ widely between a French and a German urban region.

Lung Ultrasound Findings in Congenital Pulmonary Airway Malformation.

BACKGROUND AND OBJECTIVE: Congenital pulmonary airway malformation (CPAM) is a group of rare congenital malformations of the lung and airways. Lung ultrasound (LU) is increasingly used to diagnose neonatal respiratory diseases since it is quick, easy to learn, and radiation-free, but no formal data exist for congenital lung malformations. We aimed to describe LU findings in CPAM neonates needing neonatal intensive care unit (NICU) admission and to compare them with a control population. METHODS: A retrospective review of CPAM cases from three tertiary academic NICUs over 3 years (2014-2016) identified five patients with CPAM who had undergone LU examination. LU was compared with chest radiograms and computed tomography (CT) scans that were used as references. RESULTS: CPAM lesions were easily identified and corresponded well with CT scans; they varied from a single large cystic lesion, multiple hypoechoic lesions, and/or consolidation. The first two LU findings have not been described in other respiratory conditions and were not found in controls. CONCLUSION: We provide the first description of LU findings in neonates with CPAM. LU may be used to confirm antenatally diagnosed CPAM and to suspect CPAM in infants with respiratory distress if cystic lung lesions are revealed. Further studies are necessary to define the place of LU in the management of CPAM.

The RNA-binding protein Mex3b regulates the spatial organization of the Rap1 pathway.

The four related mammalian MEX-3 RNA-binding proteins are evolutionarily conserved molecules for which the in vivo functions have not yet been fully characterized. Here, we report that male mice deficient for the gene encoding Mex3b are subfertile. Seminiferous tubules of Mex3b-deficient mice are obstructed as a consequence of the disrupted phagocytic capacity of somatic Sertoli cells. In addition, both the formation and the integrity of the blood-testis barrier are compromised owing to mislocalization of N-cadherin and connexin 43 at the surface of Sertoli cells. We further establish that Mex3b acts to regulate the cortical level of activated Rap1, a small G protein controlling phagocytosis and cell-cell interaction, through the activation and transport of Rap1GAP. The active form of Rap1 (Rap1-GTP) is abnormally increased at the membrane cortex and chemically restoring Rap1-GTP to physiological levels rescues the phagocytic and adhesion abilities of Sertoli cells. Overall, these findings implicate Mex3b in the spatial organization of the Rap1 pathway that orchestrates Sertoli cell functions.

Dynamic Structuration of Physical Chitosan Hydrogels.

We studied the microstructure of physical chitosan hydrogels formed by the neutralization of chitosan aqueous solutions highlighting the structural gradients within thick gels (up to a thickness of 16 mm). We explored a high polymer concentrations range (Cp ≥ 1.0% w/w) with different molar masses of chitosan and different concentrations of the coagulation agent. The effect of these processing parameters on the morphology was evaluated mainly through small-angle light scattering (SALS) measurements and confocal laser scanning microscopy (CLSM) observations. As a result, we reported that the microstructure is continuously evolving from the surface to the bulk, with mainly two structural transitions zones separating three types of hydrogels. The first zone (zone I) is located close to the surface of the hydrogel and constitutes a hard (entangled) layer formed under fast neutralization conditions. It is followed by a second zone (zone II) with a larger thickness (∼3-4 mm), where in some cases large pores or capillaries (diameter ∼10 µm) oriented parallel to the direction of the gel front are present. Deeper in the hydrogel (zone III), a finer oriented microstructure, with characteristic sizes lower than 2-3 µm, gradually replace the capillary morphology. However, this last bulk morphology cannot be regarded as structurally uniform because the size of small micrometer-range-oriented pores continuously increases as the distance to the surface of the hydrogel increases. These results could be rationalized through the effect of coagulation kinetics impacting the morphology obtained during neutralization.