BIODEGRADABLE CONTROLLED-RELEASE TABLETS .2. PREPARATION AND PROPERTIES OF POLY(LACTIDE-CO-GLYCOLIDE) POWDERS

A spray drying technique was adopted to prepare poly(lactide-co-glycol ide) powders. Significant difficulties were encountered with the relat ively high molecular weight polymers, the spray drying of which produc ed threads rather than particles, unless very dilute solutions were us ed (less than 2% w/v). The important factor for the successful 'spray powdering' of poly(lactide-co-glycolide) polymers appeared to be the m olecular weight of the polymer and not the viscosity of the sprayed so lution. The spray dried particles were porous, almost spherical agglom erates of tiny spheres. The agglomerated and rather loose texture of t he particles probably enhanced the powder compressibility. Soft and du ctile powders were obtained with yield pressure values ranging from 28 to 33 MPa. No correlation was found between polymer properties and yi eld pressure. The contact angle values between polymer compacts and wa ter were in the range of 72-78-degrees, 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 co ntent tended to lower the contact angle, Water uptake by poly(lactide- co-glycolide) matrices increased steadily as matrix hydrophobicity inc reased 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 and water u ptake rate. The polymers swelled considerably, although they absorbed relatively small amounts of water and this may have significant implic ations for drug release from poly(lactide-co-glycolide) matrix tablets .