Céline Pochat-Bohatier

Structure formation of poly (ether-imide) films using non-solvent vapor induced phase separation: relationship between mass transfer and relative humidity

Structure formation of poly(ether-imide) films using vapor induced phase separation was studied in relation with the elaboration process. Dense and cellular structure can be obtained depending on the processing parameters. When the solvent evaporation took place under humidified air, kinetic data from gravimetric measurements showed that the overall mass of the film was first increasing before decreasing to a plateau. An analysis in terms of drying rate revealed that mass transfers were occurring as if there was a thin layer of volatile molecule at the top of the forming film. Solvent and non-solvent transfers were demonstrated to be closely dependent on the relative humidity.

Novel biocompatible electrospun gelatin fiber mats with antibiotic drug delivery properties

The aim of this study was to synthesize stable gelatin electrospun mats (ESMs) (cross-linked by glutaraldehyde (GTA) vapors) with tunable drug release properties using pH as a stimulus. Gelatin ESMs loaded with rhodamine as a model drug were first synthesized. The in vitro release of rhodamine was characterized to understand the mechanisms of drug release and the effects of both cross-linker concentration and pH on drug release. An optimal cross-linker concentration of 5% was evidenced to provide ESMs allowing both sustainable release of drugs at pH 7 and burst release at pH 2. The release profiles were then fitted with a power law model to describe the release kinetics. The chlorhexidine antibiotic drug was finally loaded into the optimal electrospun mat and its bactericidal activity was demonstrated against Gram-negative (E. coli) and Gram-positive (S. epidermidis) bacteria by agar diffusion tests. This biocompatible material was shown to efficiently destroy bacterial biofilms and prevent bacterial growth within a short time (3 h), while maintaining its antibacterial activity up to at least 72 h. This study provides a promising material, which could treat infected sites and prevent infections, with tunable drug releasing properties using pH as a stimulus.

Effect of chemical cross-linking on gelatin membrane solubility with a non-toxic and non-volatile agent: Terephthalaldehyde

In this paper, terephthalaldehyde (TPA) is proposed as non-toxic and non-volatile gelatin cross-linker. Optimal cross-linking parameters (TPA/gelatin ratio, temperature) were first determined from in situ rheological measurements on gelatin solutions and from chemical tests with 2,4,6-trinitrobenzenesulfonic acid (TNBS assays) on gelatin gel. The highest cross-linking ratio was achieved for a concentration of 0.005 g TPA/g gelatin at 60°C. The impact of TPA cross-linking on gelatin membrane functional properties (water swelling ratio, water vapor sorption and mechanical properties) was measured. TPA cross-linking increased 17 times the liquid water resistance duration of gelatin films, and delayed the entry of vapor water in the polymer matrix for 7 days, indicating that TPA increased the hydrophobic character of the gelatin matrix.

Effect of incorporation of boron nitride nanoparticles on the oxygen barrier and thermal properties of poly(3-hydroxybutyrate- co -hydroxyvalerate)

In this study poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and boron nitride (PHBV/BN) nanobiocomposites were prepared by incorporating various percentages of boron nitride using extrusion processing. The oxygen permeation properties of the PHBV nanocomposites were examined to compare their oxygen-barrier performance as affected by temperature and nanoparticle content. The resulting PHBV nanocomposites showed an increase in oxygen permeability as temperature increased, with an Arrhenius behavior, and an activation energy of 54.1 kJ mol−1 and 57.5 kJ mol−1 for neat PHBV and PHBV3BN composites, respectively. The barrier properties of the composites decreased with BN addition and reached 1.22 ± 0.06 (cm3 mm m−2 per day per atm) at 3 wt%. Thermal stabilities of the prepared nanobiocomposites were measured by thermogravimetric analysis (TGA) and it was found that the thermal stability of the composites was higher than that of neat PHBV. The differential scanning calorimetry results indicated that the addition of BN nanoparticles to the composites increased their crystallinity.

Design of Boron Nitride/Gelatin Electrospun Nanofibers for Bone Tissue Engineering

Gelatin is a biodegradable biopolymer obtained by collagen denaturation, which shows poor mechanical properties. Hence, improving its mechanical properties is very essential toward the fabrication of efficient nontoxic material for biomedical applications. For this aim, various methods are employed using external fillers such as ceramics or bioglass. In this report, we introduce boron nitride (BN)-reinforced gelatin as a new class of two-dimensional biocompatible nanomaterials. The effect of the nanofiller on the mechanical behavior is analyzed. BN is efficiently exfoliated using the biopolymer gelatin as shown through Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The exfoliated BN reinforces gelatin electrospun fibers, which results in an increase in the Youngs modulus. The Electrospun Mats (ESM) are stable after the glutaraldehyde cross-linking, and the fibrous morphology is preserved. The cross-linked gelatin/BN ESM is highly bioactive in forming bonelike hydroxyapatite as shown by scanning electron microscopy. Due to their enhanced mineralization ability, the cross-linked ESM have been tested on human bone cells (HOS osteosarcoma cell line). The cell attachment, proliferation, and biocompatibility results show that the ESM are nontoxic and biodegradable. The analysis of osteoblast gene expression and the measurement of alkaline phosphatase activity confirm that these materials are suitable for bone tissue engineering.

Design of graphene oxide/gelatin electrospun nanocomposite fibers for tissue engineering applications

Gelatin is a biodegradable, nontoxic and biocompatible biopolymer. The biomedical application of un-crosslinked gelatin is limited, due to poor mechanical strength and high solubility. Hence, 2D graphene oxide (GO) nanosheets are used as reinforcing agents to enhance the mechanical properties. The GO exfoliation in gelatin is confirmed using X-ray diffraction (XRD) analysis. The GO reinforcement enhances Young modulus (E) by 70% and tensile stress is also significantly improved. Moreover, the fibrous cross-linked electrospun mats are stable in phosphate buffered saline solution. The cell attachment and proliferation of the ESM are evaluated with human osteosarcoma cells (HOS) and the ESM is found to be biocompatible. However, the expression of osteoblast genes decreases with increasing GO incorporation. This report demonstrates that GO with high degree of oxidation, effectively reinforces and enhances the mechanical properties of the gelatin fibers. Also, increasing the concentration of GO does not show any significant influence on cell viability and cell attachment even though the expression of osteoblast gene is affected.

Inverse Pickering Emulsion Stabilized by Exfoliated Hexagonal-Boron Nitride (h-BN)

The formation of inverse Pickering emulsions using exfoliated hexagonal boron nitride (h-BN) as an effective particulate stabilizer without using any surfactants is reported for the first time. The stability and the type of h-BN Pickering emulsions formulated with different BN concentrations and by varying oil/water (o/w) ratios are studied and discussed. First the emulsion structure is analyzed microscopically through optical and epifluorescence microscopy and macroscopically by the study of the rheological behavior. The average droplet size decreases with h-BN concentration whereas the emulsions achieve good stability at 2 wt % BN concentrations and for a 1:1 o/w ratio. In all formulations, the emulsions are of water-in-oil (w/o) type due mainly to the hydrophobicity of h-BN.

Experimental and Numerical Study on the Drying Process of Natural Rubber Latex Films

The formation of dry films from natural rubber latex was studied through the drying kinetics and compared with film preparations from two synthetic lattices. The experimental results clearly showed that all films displayed very similar behavior, although their chemical composition and particle size distribution were completely different. During the whole process, the evaporation flux was shown to be directly related to the remaining water volume fraction within the film and the reduction in the film transfer area. A numerical model was developed to describe the film formation process and the simulated results were in good agreement with the experimental results.

Preparation and characterization of chitin hydrogels by water vapor induced gelation route

A novel method of chitin hydrogel preparation, called vapor induced gelation, using exposure of chitin/N-methyl-pyrrolidone/LiCl solution to water vapors is presented. Compared to gelation induced by direct immersion in water, hydrogels are characterized by smaller deformation during gelation (area shrinkage is 20% instead of 65%), larger water volume fraction (75 instead of 62%, v/v) and 10 times higher apparent compression moduli. Their nanostructure consists of thicker and larger crystalline platelets network (thickness=37 Å, apparent coherent crystalline size L₀₂₀=145 Å) comparatively to direct immersion gels (25 Å and L₀₂₀=95 Å). Drug delivery potential of chitin hydrogels was determined for non-interactive low molecular molecules.

Preparation of Composite Hydrogels for Medical Applications: Experimental Study and Modeling of Mass Transfers

The aim of this work is to prepare wound dressing hydrogels permitting (i) to cure chronicle pathologies; (ii) to remove unsuitable odors coming from healing. Thus, chitosan, a natural polymer with biological properties, and activated carbon (AC), a well-known adsorbent, are mixed within a composite hydrogel. To get a suitable porous structure for healing, the vapor induced phase separation process (VIPS) is used. It permits to slow down mass transfers kinetics compared to other elaboration processes such as the wet process. Hence, a better control of the final porous matrix is reached throughout the elaboration process.In this work, the mass transfers occurring through the elaboration of the composites were studied thanks to gravimetric measurements carried out during the VIPS process. Results showed there were two main steps in the gelation process. A weight intake, due to an ammonia flux allowing the gelation to happen, was followed by a weight loss, mainly controlled by a water outtake. This second part could be compared to a slow drying in smooth conditions. Gelation with a color indicator was also performed, which provided complementary experimental information on mass transfers barrier.A modeling of mass transfers mechanisms occurring during the gel elaboration is presented to get an overview of limiting phenomena leading to the final composite structures. It involves a coupling between chemical reactions, external mass transfers and internal diffusion within the polymeric matrix. Results show that internal diffusion is the main barrier to gelation.To qualify the gel structure, drying kinetics were compared on the elaborated gels. Whatever the gel, the drying kinetics were globally the same and could be divided into three steps. Considering the process used and this result, it was believed that the matrixes prepared were homogeneous and rather symmetric. They could constitute the first layer of wound dressings.