Thermodynamic confinement and alpha-helix persistence length in poly(gamma-benzyl-L-glutamate)-b-poly(dimethyl siloxane)-b-poly(gamma-benzyl-L-glutamate) triblock copolymers.

The structure and the associated dynamics of a series of poly(gamma-benzyl-L-glutamate)-b-poly(dimethyl siloxane)-b-poly(gamma-benzyl-L-glutamate) (PBLG-b-PDMS-b-PBLG) triblock copolymers were investigated using small- and wide-angle X-ray scattering, NMR, transmission electron microscopy, and dielectric spectroscopy, respectively. The structural analysis revealed phase separation in the case of the longer blocks with defected alpha-helical segments embedded within the block copolymer nanodomains. The alpha-helical persistence length was found to depend on the degree of segregation; thermodynamic confinement and chain stretching results in the partial annihilation of helical defects.

Modulated release of triterpenic compounds from a O/W/O multiple emulsion formulated with dimethicones: infrared spectrophotometric and differential calorimetric approaches.

From the use of silicones within O/W/O multiple emulsions, we can expect, two principal advantages: (1) the silicones with the lowest molecular weight decrease the oily touch; (2) due to the large range of viscosity, this excipient should influence the skin distribution of actives after topical application. The purpose of our work is to highlight these advantages. Multiple emulsions were formulated with several dimethicones and with drug model. Firstly, the effects of different dimethicones incorporated within multiple emulsions were studied, through in vitro penetration results. Secondly, we investigated the residual film on the skin by Differential Scanning Calorimetry (DSC) and by Fourier Transform Infrared (FTIR) to determine its structure. Correlations were established between the silicone structure and the distribution of drugs in different skin levels or between the silicone structure and the percutaneous penetration. The incorporation of silicones within O/W/O multiple emulsions seems to be an efficient means of modulating the penetration and the distribution of drugs in the skin.

Gas permeability of the film of block and graft copolymers of polydimethylsiloxane and poly(gamma-benzyl L-glutamate).

A-B-A type block copolymers of poly(gamma-benzyl L-glutamate) (PBLG, A segment) and polydimethylsiloxane (PDMS, B segment) and PDMS (trunk)-PBLG (branch) graft copolymers were synthesized, and the permeation of oxygen in water and the permeation of oxygen and carbon dioxide in the dry state were investigated. The gas permeation coefficient (P) increased with increasing content of PDMS. However, PCO2/PO2 values of copolymer films were in the range 6-9, i.e. larger than 5.4 for PDMS film. The oxygen permeation in water suffered from the interfacial resistance, which was reduced by the hydrolysis of film surface. The Arrhenius plot of the gas permeation coefficient in the dry state of the block copolymer B showed a turning point at about 40 degrees C. This temperature is close to beta-peak temperature (39 degrees C) and may be ascribed to the molecular motion of the PBLG segment. Transmission electron microscopy showed that one of the block copolymer films (PDMS 46 mol%) appears to have PDMS segments dispersed in the PBLG matrix (island-in-sea structure) and one of the graft copolymer films (PDMS 58 mol%) appears to take a lamellar structure. The gas permeation across the graft copolymer film appears to occur through the continuous PDMS phase, leading to a near-negligible activation energy in this process.