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International audience; Poly(d,l-lactide-co-glycolide) (PLGA) copolyesters are commonly used in biomedical applications. Researches were carried out on nontoxic or low-toxic catalysts that are enough efficient to provide short polymerization times, adequate microstructure chains and similar properties than the commercial PLGA materials. In this study, PLGA were synthesized by ring-opening copolymerization (ROP) using three different catalysts. Stannous octoate is the first catalyst we used, as it is very efficient, even its toxicity is still on debate. Two others low-toxic catalysts [zinc lactate and bismuth subsalicylate (BiSS)] were also evaluated. The comparison of these ROP was realized in terms of kinetics and control of the polymerization. Then, the influence of the catalyst on the PLGA microstructure chains is reported. Finally, abiotic hydrolytic degradation rate is studied. Results described in this article show that BiSS is one very attractive catalyst to produce low toxic PLGA for biomedical applications.

The controlled synthesis of biodegradable copolymers of dextran grafted with aliphatic polyesters first requires the preparation of polysaccharide derivatives soluble in organic solvents. Silylation of dextran can thus lead to such organosoluble derivatives and allows the polymerization of cyclic esters initiated from the nonsilylated OH functions. Silylation of dextran was studied in DMSO by different reactants such as 1,1,1,3,3,3-hexamethyldisilazane (HMDS) in the presence of various catalysts and N,O-bis(trimethylsilyl)acetamide (BSA). According to the silylating agent and the used experimental conditions, it was possible to obtain highly or totally silylated dextrans. In parallel, an investigation of the chemical stability of the dextran chain during silylation was performed. Thus, it was found that, when used at 50 degrees C, HMDS with or without catalysts gives a relatively high silylation yield and does not alter the dextran chain length, whereas at 80 degrees C, dextran degradation was observed. BSA is a very good silylating agent, which allows reaching 100% silylation even at 50 degrees C but provokes the degradation of the polysaccharide chains. The work was completed by a study of the reactivity order of the glucosidic OH functions toward silylation reaction. This order was found to be (OH(2) > OH(4) > OH(3)) as already reported for other reactions. 2D-NMR of highly silylated dextrans demonstrated that they are constituted of both quantitatively silylated glucose units and two types of disilylated ones.

International audience; The strong associative behaviour between cholesterol-modified dextran (CMD) and short and long polyoxyethylene cholesteryl ether (ChEO10) micelles were investigated using rheology and small-angle neutron scattering (SANS). In solutions of short rod-like micelles (ChEO10 alone), the addition of 5.0 wt% CMD induced a remarkable transition from a Newtonian system to a highly solid-like viscoelastic network, with an increase in zero-shear viscosity of over 5 orders of magnitude. The frequency sweeps at ChEO10 concentrations above 2.5 wt% were fitted to a Maxwell model with 3 elements and, quite remarkably, fell onto a single master curve, while no network was formed at 2.5 wt% micelles. Viscoelastic solutions of wormlike micelles (WLMs) were obtained by adding the co-surfactant triethylene glycol monododecyl ether (C12EO3) to ChEO10 solutions at a constant ChEO10/C12EO3 ratio of 5/1. The introduction of CMD into the WLM solutions induced a transition to a more liquid-like behaviour (G″/G′ increased), however both moduli increased by one order of magnitude. At the lowest ChEO10 concentration (2.5%), the solid-like behaviour was lost. Overall, a comparable rheological response was obtained for the WLM and the short rods with CMD, however the WLM/CMD behaviour suggested a wider spectrum of relaxation processes, longer relaxation times and higher plateau moduli. SANS data from the polymer/micelles mixtures displayed a strong structural peak and were remarkably identical for both ChEO10/CMD and ChEO10/C12EO3/CMD systems, suggesting a very similar type of network structure, independently of the initial size of the micelles. Overall, all the results taken together show a very high affinity between the polymer and the micelles and suggest a breakup of the WLM induced by CMD. The resulting network is constituted by polymeric chains connected by micellar aggregates through hydrophobic interactions between the micellar cholesterol cores and the pendent cholesterol moieties of the polymer