(193b) The Effect of Crystallization and Glass Transition Temperature in Thin Poly(D,L-lactic acid) Copolymers for Controlling Osteoblast Recruitment and Adhesion

Polylactic acid coatings have significant potential as bioresorbable thin films. The film thickness is also known to affect the transition temperature and crystalline morphology, which is expected to impact cellular adhesion to the coating. Herein, poly(D,L-lactic-co-glycolic acid), PLDG, coatings of various thickness were prepared by spin-coating yielding amorphous films. The amorphous PLDG thin films were annealed at 100ËšC for 24 hours, 48 hours, and five days and were compared to non-annealed thin film samples. Atomic force microscopy, AFM, was used to analyze the morphology of the thin films for indications of crystallization. AFM confirmed that no crystallization was apparent on the surface of the non-annealed thin films. However, crystalline morphology was evident on the surface of the annealed thin films. The crystalline content increased as the annealing time increased from 24 hours to five days. The thickness of the thin films was characterized using ellipsometry. Heat scans from 30ËšC to 150ËšC were performed using ellipsometry to determine the linear expansion coefficient as a function of temperature. The linear expansion coefficient is lower below the glass transition temperature and significantly higher above the glass transition temperature. For example, for a 212 nm film, the linear expansion coefficient below the glass transition is 4.23x10^-4 ËšC^-1 and above the glass transition the linear expansion coefficient is 2.03x10^-3 ËšC^-1. In these scans, both the glass transition and melt temperatures could be clearly identified. Preliminary results reveal that the glass transition temperature in thin PLDG films were lower than the bulk PLDG glass transition temperature. Control of the crystallization may help promote better adhesion of osteoblast cells to thin films. Future work will investigate the effect of crystallization on the degradation of thin films and the role of crystallization on the osseointegration of osteoblast cells to thin films.