Biodegradable controlled release tablets: II. Preparation and properties of poly(lactide-co-glycolide) powders

Abstract

A spray drying technique was adopted to prepare poly(lactide-co-glycolide) powders. Significant difficulties were encountered with the relatively high molecular weight polymers, the spray drying of which produced threads rather than particles, unless very dilute solutions were used (less than 2% w/v). The important factor for the successful ‘spray powdering’ of poly(lactide-co-glycolide) polymers appeared to be the molecular weight of the polymer and not the viscosity of the sprayed solution. The spray dried particles were porous, almost spherical agglomerates of tiny spheres. The agglomerated and rather loose texture of the particles probably enhanced the powder compressibility. Soft and ductile powders were obtained with yield pressure values ranging from 28 to 33 MPa. No correlation was found between polymer properties and yield pressure. The contact angle values between polymer compacts and water were in the range of 72–78°, indicating a moderate polymer hydrophobicity. The molecular weight of the polymers did not have any effect on the contact angle value, whereas an increase in glycolide content tended to lower the contact angle. Water uptake by poly(lactide-co-glycolide) matrices increased steadily as matrix hydrophobicity increased with time due to polymer degradation. The weight of the matrix increased with time but, when mass loss due to degradation outweighed the gain from water absorption, the weight of the matrix began to fall. An increase in glycolide content or a decrease in polymer molecular weight caused an increase in both the percent water uptake rate. The polymers swelled considerably, although they absorbed relatively small amounts of water and this may have significant implications for drug release from poly(lactide-co-glycolide) matrix tablets.