Thierry Hamaide

Association states of multisensitive smart polysaccharide–block-polyetheramine copolymers

The water soluble properties of different copolymers based on pullulan-block-polyetheramine have been deeply studied. The polyetheramine group (PEA) corresponding to a propylene oxyde/ethylene oxyde ratio (PO/EO) of 29/6, is condensed, via amine link, to pullulans with various chain lengths. Different polysaccharide/PEA (PS/PEA) ratio copolymers have been investigated through macroscopic (cloud point, enthalpy) and mesoscopic scale approaches (critical aggregation concentration (CAC), mean number average hydrodynamic diameter (Dh) or aggregation number (Nag)). These systems are both pH and/or thermo-sensitive. Finally, it seems that three states can describe such systems (i) isolated copolymers (unimers) below the CAC, (ii) water soluble aggregates above the CAC and whatever the PS/PEA ratio is due to hydrophobic interactions and (iii) non-soluble aggregates (above the critical temperature) due to dehydration of polyetheramine groups but only if PS/PEA ratio is low enough.

Toward tunable amphiphilic copolymers via CuAAC click chemistry of oligocaprolactones onto starch backbone

Starch-based tunable amphiphilic copolymers are easily obtained by grafting polycaprolactone chains via 1,3 dipolar Copper-Catalyzed Azide-Alkyne Cycloaddition (click chemistry CuAAC), starting from propargylated starch and azido oligocaprolactones with different chain lengths as the precursors. The copolymers are characterized by (1)H and (13)C NMR, from which a degree of substitution of starch can tentatively be deduced. Besides these bulk characterizations, the surface of the functionalized starch is also characterized by XPS which confirms the triazole formation, particularly through the deconvolution of the N 1s peak, and by ToF-SIMS which, not only confirms the surface modification, but also highlights the disappearance of the Cu(+) cations. The solubility and swelling behaviours of these copolymers have been investigated, which clearly show the dependence both on the solvent and the PCL chain length. These investigations highlight the swelling dependence on the δd component of the Hansen solubility parameter of solvents. Finally, at low concentration, they present the capacity to organize themselves in aggregates in aqueous solutions, as seen from TEM and DLS investigations.

Internally gelled W/O and W/O/W double emulsions

Abstract Water-in-oil emulsions having their aqueous internal phase gelled with starch were prepared and investigated. They were the primary emulsions required for the preparation of double w/o/w emulsions that could encapsulate hydrophilic materials inside the internal aqueous gel. The emulsification could be achieved at high temperature in spite of the high viscosity of the aqueous phase; the internal phase gelled upon cooling to room temperature. The high viscosity of the aqueous phase limited the possible concentration range of starch in the aqueous phase. The presence of starch made the surfactant demand larger for both the emulsification and the stabilization of the w/o emulsions. The larger the starch content, the larger the amount of required surfactant. One reason for the high surfactant demand was the high viscosity of the aqueous phase containing starch. Another cause of high surfactant demand was disclosed and it appeared that predominantly the interactions of the nonionic surfactants with starch retained the former inside the aqueous phase. The immobilized amount of surfactant had to be compensated by a supplementary concentration. Experimental evidence of the interactions between starch and the nonionic surfactants was given by interfacial tension measurements. Lastly, w/o/w double emulsions were prepared using the gelled w/o emulsions and a model hydrophilic molecule (caffeine) was encapsulated inside the internal gelled aqueous phase. The release rate of caffeine from the internally gelled double emulsions was slower than for the non-gelled emulsions, demonstrating the efficiency of the encapsulation and the possible control of the delivery.

Modified Starch-Based Hydrogels Cross-Linked with Citric Acid and their use as Drug Delivery Systems for Levofloxacin

New amphiphilic starch-polyester graft copolymer and chemically modified starch with fatty acid chains were synthesized and then cross-linked with a nontoxic agent, citric acid, in order to obtain hydrogels with a controlled hydrophilicity. They present well-defined pores, a controlled water retention degree and different time ranges for releasing the drug, depending on the synthesis parameters. The new hydrogels may be used in the biomaterials field as matrices for delivering biologically active agents, for coating a surface or a synthetic implant.

Novel polymeric surfactants and their applications in miniemulsions

Abstract N-Vinyl-2-pyrrolidone (NVP) and maleic anhydride (MA) copolymers were synthesized via radical polymerization. The synthesized copolymers were grafted with methoxypolyethylene glycol (MPEG) chains of different average molecular weights (350, 550, 750 Da). The grafted copolymers were used as surfactants in the synthesis of poly(ε-caprolactone) (PCL) nanoparticles in water by solvent evaporation technique. In order to further test the synthesized surfactants, the miniemulsion polymerization of vinyl acetate was performed. Two methods of obtaining miniemulsion were employed: a sonicator and a static mixer. The synthesized surfactants performed well in both type of experiments while in the case of static mixer nanoparticles with a lower polydispersity were obtained. Droplets with a mean diameter of 250 nm were obtained when using the sonicator while the static mixer led to formation of droplets with a mean diameter of 600 nm.

Improvement of the Mechanical Properties of Calcium Phosphate Bone Substitutes by Polycaprolactone Infiltration

In this study we show that mechanical properties of bioceramic scaffolds can be significantly improved by repeated infiltration with a low-viscosity polycaprolactone solution. Biphasic calcium phosphate (BCP: 70% hydroxyapatite, 30% β-tricalcium phosphate) scaffolds characterized by a bimodal pore size distribution and a global porosity of 70% have been chosen as starting materials. Polymer content in the ceramic scaffold was varied so that an inorganic/organic ratio close to that of bone may be achieved. Work of fracture at maximum stress was 36 J/m2 for the ceramic scaffold alone and reached 127 J/m2 for the 8-times infiltrated samples. These results are superior to the ones previously obtained with polycaprolactone infiltrated alumina due to higher micropore content. We show that during bending tests, polycaprolactone phase formed fibrils while the crack propagated. Crack bridging by polycaprolactone ensured the integrity of the composite once the ceramic scaffold was broken and directly involved in the composite toughening. Because of its composition, microstructure and mechanical behavior of this kind composite can be an interesting candidate for bone substitution.