Hydrolytic degradation of PLLA/PCL microporous membranes prepared by freeze extraction

Poly(l-lactic acid) - Poly(ε-caprolactone) blends (PLLA/PCL) porous membranes were prepared by freeze extraction (a modification of freeze drying) with ratios 100/0, 80/20, 60/40, 40/60, 20/80, 0/100 in weight. Degradation of the membranes in phosphate buffer solution (PBS) up to 65 weeks was studied using weight loss measurements, high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), mechanical indentation, gel permeation chromatography (GPC), and scanning electron microscopy (SEM). Degradation rate as observed by weight loss and reduction of molecular weight and mechanical properties depended on the composition of the blends. In most blends the degradation was more prominent in the PLLA phase and was accompanied by consequent recrystallization that formed a crystalline phase with increased resistance to hydrolysis. Occurrence of such crystalline phases and degradation of intercrystalline domain led to formation of nearly monodisperse molecular weight populations.Membranes with only 20% PCL presented favorable behavior compared to pure PLLA membranes as reflected in a lower degradation rate and a limited loss of the mechanical properties. At the same time, degradation rate of 80/20 membranes was enhanced with respect to pure PCL, and membranes were stiffer than PCL membranes at all degradation times. This composition could thus be useful for use in tissue engineering for bone or cartilage applications.