Relevance of lactic acid generation to mass loss profile for polylactides

The bulk degradation of synthetic absorbable polyesters is thought to occur from the center of the material outward, and the degradation pattern is therefore attributed largely to the chemical composition of the material. It is hypothesized that this pattern may be altered by changing the morphological mapping of the material, i.e., by introducing molecular orientation into the system. A new solid state uniaxial orientation (SS-UO) process was used to orient two types of polylactide films. The films were exposed to a phosphate buffered solution, and the percent mass loss, dimensional change, and lactic acid release was monitored at predetermined times. The results, obtained using an analysis of variance and a Linear correlation analysis, show that the release of lactic acid commences in the first month, but it is not until after 6 months that the oriented and nonoriented release rates differ. The mass loss is dependent on the polylactide type, as are the dimensional changes, while the lactic acid release is not material dependent. The mass loss may, in specific cases, be correlated to the lactic acid release.