Micro- and macrothermal analysis of a bioactive surface-engineered polymer formed by physical entrapment of poly(ethylene glycol) into poly(lactic acid)

Poly(DL-lactic acid) (PLA) materials have been surface engineered via an entrapment method to present high densities of poly(ethylene glycol) (PEG) to control protein adsorption. The resultant change in physical properties was characterized on the surface and bulk of the entrapped PEG/PLA system through microthermal analysis by scanning thermal microscopy (SThM). It was found that the inclusion of the PEG significantly reduced the glass transition temperature (T-g) of the modified PLA and that the magnitude of this T-g reduction remained unchanged throughout the PEG-modified PLA regions. This suggests that the entrapped PEG was in a miscible state with, and homogeneously distributed into, the PLA. This finding was confirmed using macrothermal analysis by differential scanning calorimetry. The amount of the PEG entrapped in the modified region was calculated to be 18 wt %. In addition, a sharp contrast was observed in the SThM thermal conductivity data on cross-sectioned samples designed to reveal the boundary between the modified and unmodified regions of the PLA. This unambiguously demonstrates that the physical properties of the PLA surface and near surface have been modified by the entrapment of PEG. We propose that the observed thermal contrast results from the temperature dependency of thermal conductivity (lambda) of the parent PLA being altered by the inclusion of miscible PEG.