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The effect of alkaline hydrolysis on several surface properties of poly(hydroxybutyrate-hydroxyvalerate) (92/8) (PHB/HV) and poly(epsilon-caprolactone) (PCL) films and of poly(ethylene terephtalate) (PET) track-etched membranes have been characterized, as well as the adsorption of three proteins normally encountered by mammalian cells in vivo, namely albumin, collagen, and fibronectin. The water contact angle decreases and the number of -COOH functions accessible to a chemical reaction at the surface of PCL increases with alkaline hydrolysis. Analysis by atomic force microscopy pictures reveals a change in surface morphology. The modifications of surface properties are correlated with a two times increase of the adsorption of three radiolabelled proteins. The hydrolysis results in a slight increase in the water contact angle of one face of the PHB/HV film and a sharp increase in the number of -COOH functions. Important morphology changes are also induced. The adsorption of the radiolabelled proteins is almost 100 times higher on the hydrolyzed polymer than on the native surface. The increase in hydrophilicity of different PET batches correlates to an increase in the number of -COOH functions. Nevertheless, the surface chemical composition and rugosity are constant and no significant difference in the amount of radiolabelled fibronectin adsorbed on the different surfaces is detectable. In conclusion, the effect of hydrolysis on the surface properties of each of the polyesters studied as well as the proteins adsorption on the different surfaces are different. The results strongly support the hypothesis that, in the system studied, parameters other than hydrophilicity influence protein adsorption: the main parameters that might play a role are the total surface area accessible to the proteins, as well as the surface chemical composition.

Purpose. To develop self-assembling systems increasing the solubility of poorly water-soluble drugs. Methods. Low molecular weight liquid biodegradable copolymers were synthesized by ring-opening polymerization using caprolactone (CAP) and trimethylenecarbonate (TMC) as monomers. Various initiators were evaluated. The emulsifying and self-assembling properties were investigated by a water titration method. The selfassembling systems were characterized for size, shape, isotropic behavior, cloud point, surface charge, and critical micellar concentration in order to optimize the polymer synthesis. Finally, the improvement of solubility of model drugs was assessed. Results. Only diblock monomethyl ether PEG-CAP/TMC copolymers synthesized with monomethyl ether polyethyleneglycol 550 to 2000 as initiator have shown self-assembling properties: upon dilution, these copolymers formed an isotropically clear solution with droplet sizes in the range of 20 to 100 nm. The hypothesis that these diblock polymers form micelles was confirmed by their low critical micellar concentration (10 −5 g/ml). The copolymers initated with mmePEG750 had a higher cloud point and better colloidal stability than those initiated with mmePEG 550. The solubility of the poorly water-soluble drugs was increased by 1 to 2 orders of magnitude. Good reproducibility was observed from batch to batch. Conclusions. The polyester diblock copolymer mmePEG750-CAP/ TMC forms spontaneously stable micelles in aqueous medium and increases the solubility of lipophilic drugs. They are very promising vehicles for the oral delivery of poorly water-soluble drugs.

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