PLLA/nHA Composite Films and Scaffolds for Medical Implants: In Vitro Degradation, Thermal and Mechanical Properties

Two poly(l-lactide) (PLLA) materials and changes in their mechanical, thermal, physical, and chemical properties while undergoing in vitro degradation are studied. The potential applications of PLLA implants extend to films for controlled drug release systems and biodegradable scaffolds for bone implants (fabricated with thermal induced phase separation) (TIPS) using bioactive nanohydroxyapatite particles. The study was conducted in a phosphate buffer saline (PBS) solution at 37 degrees C over 8 weeks. Reinforcement with nHA particles increased the elastic modulus and the yield stress, due perhaps to restricted C-C bond rotations and polymer sliding, although that increase was not proportional with the added percentages of nanoparticles. The elastic modulus and the yield stress of the films decreased faster than those of the scaffolds. As from the seventh week some samples could not be tested due to the fragility of the specimens. The scaffolds had a higher enthalpy of fusion than the films, suggesting that crystalline domains formed more easily in the scaffolds than in the films. The films degraded more quickly than the scaffolds, because the acid products resulting from the degradation process were evacuated from the films with greater difficulty than from the scaffolds in which the autocatalytic effect was of greater importance. Porosity was decisive in the rate of degradation.