Characterization of the spatial distributions of entrapped polymers following the surface engineering of poly(lactic acid)

In earlier studies we have demonstrated physical entrapment as a method of surface-modifying poly(lactic acid) (PLA) by immobilizing poly(L-lysine) (P LL) and poly(ethylene glycol) (PEG) at the PLA surface. In this study, we h ave used a combination of time-of-flight (ToF) SIMS and XPS image analysis to determine the surface homogeneity of these systems. The ToF-SIMS imaging was used to investigate the effect of various surface-engineering conditio ns on the lateral distribution of PLL-modified PLA. The PLA surface modific ation was revealed to pro duce micron-scale PLL-rich domains following prol onged exposure to the partial solvent system that is used during the entrap ment process. As the static SIMS analysis of PEG/PLA surfaces did not produ ce distinguishing ions of a sufficient intensity between the two polymers, this technique could not generate lateral contrast, and imaging XPS was the refore employed to determine the surface distributions of these two species . Phase separation was again detected under extended surface engineering co nditions. With both systems, optimization of the process conditions was sho wn to inhibit the creation of a heterogeneous surface. Surface segregation may result in suboptimal performance of the biomaterial and this study ther efore highlights the importance of determining spatial organizations when m odifying polymer interfaces. Copyright (C) 2001 John WiIey & Sons, Ltd.