Controlling biological interactions with poly(lactic acid) by surface entrapment modification

Poly(ethylene glycol) (PEG)-modified poly(lactic acid) (PLA) systems were c reated by physically entrapping the modifying species at the PLA surface. T he surface characterization and biological performance of these materials a re described. This modification strategy is performed by reversible gelatio n of the PLA surface following exposure to a solvent/nonsolvent mixture. PE G is then able to diffuse into the swollen surface region, before it is col lapsed by the addition of more nonsolvent. This results in the localized ph ysical entrapment of the diffused material. We have demonstrated by high-re solution X-ray photoelectron spectroscopy that control over the PEG surface density may be achieved by using predetermined process conditions, such as a particular solvent/nonsolvent ratio or a set polymer treatment time, and that surface coverage of around 75% is possible. Cell adhesion studies hav e shown that even in serum-containing media PEG entrapment will prevent att achment, with a 95% reduction in cell number compared to unmodified PLA. Th is modification strategy was also used to coentrap both PEG and poly(L-lysi ne)-RGD within the PLA surface region. The attachment of cells to this mate rial shows that the entrapment approach may be used to create highly select ive biomaterial surfaces that are able to prevent unwanted cell or protein adhesion yet actively promote specific cellular interaction.