Jean-François Tranchant

Carbon Nanotubes as Structural Nanofibers for Hyaluronic Acid Hydrogel Scaffolds

We have successfully dispersed functionalized single-walled carbon nanotubes (SWNTs) within hyaluronic acid-water solutions. Hybrid hyaluronic acid (HA) hydrogels with SWNTs were then formed by cross-linking with divinyl sulfone. We have found a considerable change in the morphology of the lyophilized hybrid hydrogels compared to HA hydrogels. The high water uptake capacity, an important property of HA hydrogels, remained almost unchanged after 2 wt % SWNT (vs HA) incorporation, despite a dramatic enhancement in the dynamic mechanical properties of the hybrid hydrogels compared to native ones. We have found a 300% enhancement in the storage modulus of hybrid hydrogel with only 2 wt % of SWNTs vs HA (0.06 wt % vs total weight including water content). This apparent contradiction can be explained by a networking effect between SWNTs, mediated by HA chains. As in biological tissue, HA plays a dual role of matrix and linker for the rigid reinforcing nanofibers.

Internally structured pickering emulsions stabilized by clay mineral particles

The present study aims to describe emulsion particles containing a dispersed phase composed of nanostructured lipid mesophases and stabilized by montmorillonite and/or Laponite clay platelets. The size distributions of these emulsion particles were found independent of the clay mineral content and of the initial internal composition that determines the internal structure. The stabilization of the droplets by a shell of smectite layers was found possible even by montmorillonite which has a length of the same order or more than the droplets to stabilize. The clay platelets give a local flatness to the droplets that may influence the internal structure. In this paper, we describe the conditions to obtain such soft particles of about 220 nm, and we show by direct visualization the internal mesophase complexity and the shape of the particles. In particular, TEM analysis showed elongated particles with bent-back channels at their center but a different morphology at the periphery due to flat border conditions imposed by the presence of the clay minerals.

Percutaneous absorption of sunscreens from liquid crystalline phases.

The purpose of the present study was to investigate the effects of two nonionic surfactants with liquid crystalline structures on the cutaneous availability of two sunscreens. Three liquid crystalline structures were investigated: lamellar, hexagonal and cubic. The diffusion of sunscreens within the liquid crystals was determined by measuring transport kinetics into an unloaded surfactant medium from a similar system loaded with the sunscreens. The diffusion coefficients were the greatest in the cubic systems for benzophenone-4 (a hydrosoluble sunscreen) and in lamellar systems for octyl methoxycinnamate (a liposoluble sunscreen). So the diffusion in this surfactant systems was strongly dependent on the structure of the liquid crystal and on the physicochemical properties of the solute. The transcutaneous fluxes were determined using a Franz-type diffusion cell. The liquid crystalline vehicles modified the transcutaneous fluxes of benzophenone-4 but did not change those of octyl methoxycinnamate. The solute diffusion within the vehicle was not the rate-determining step for transcutaneous permeation for either sunscreen. The diffusion of benzopenone-4 within the stratum corneum and that of octyl methoxycinnamate within the dermis could be the rate-determining steps for their transcutaneous permeation. These two steps could be affected differently by nonionic surfactant vehicles.

Dual stimuli-responsive oligo(ethylene glycol)-based microgels: insight into the role of internal structure in volume phase transitions and loading of magnetic nanoparticles to design stable thermoresponsive hybrid microgels

Multi-responsive biocompatible microgels with long term stability were synthesized by precipitation copolymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA), di(ethylene glycol) methyl ether methacrylate (MEO2MA), methacrylic acid (MAA) and crosslinkers in aqueous dispersed media. Different crosslinkers, i.e. ethylene glycol dimethacrylate (EGDMA), oligo(ethylene glycol) diacrylate (OEGDA) or N,N-methylenebisacrylamide (MBA) were used for the synthesis of the microgels. The present work investigates for the first time how the inner structure of the biocompatible P(MEO2MA-co-OEGMA-co-MAA) microgels impacts their swelling-to-collapse transition in response to both temperature and pH. The EGDMA-crosslinked microgels obviously differ from the OEGDA- and MBA-crosslinked microgels. The OEGDA-crosslinked P(MEO2MA-co-OEGMA-co-MAA) microgels are ideal candidates to prepare robust thermoresponsive hybrid magnetic microgels by a straightforward method involving simple loading of pre-formed magnetic nanoparticles (NP) in the absence of NP release. The crosslinker distribution is at the origin of differences in the distribution of iron oxide nanoparticles. The homogeneous distribution of both MAA units and the OEGDA crosslinker in the P(MEO2MA-co-OEGMA-co-MAA) microgels ensured a sharp VPTT of microgels over a wide range of pH values (from pH 4 to 9) and the retention of the thermoresponsiveness of the corresponding hybrid microgels for the different contents of magnetic nanoparticles (from 7 to 33 wt% of γ-Fe2O3versus polymer). Turbidimetry measurements highlighted the unique stability of the hybrid microgels over several hours even for the highest content of iron oxide nanoparticles.