Electrophoretic study of the degradation properties of poly(L-lactide) microcapsules

The degree of degradation of poly(L-lactide) microcapsules was measured as a function of the time elapsed in solutions of different pH values. To determine how the distribution of poly(L-lactide) molecules in the microcapsule membrane changes during degradation, poly(L-lactide) microcapsules, at various stages of the degradation process in various solutions, were sampled and redispersed in pH 7.6 buffer solutions of different ionic strengths and their zeta potentials determined. In the early stages of the process, the zeta potential became more negative as time elapsed. Analysis of the ionic strength dependence of the surface potential on the basis of a simple model shows that hydrolytic scission of ester bonds in the polymer chains takes place preferentially at the microcapsule membrane surface creating negative charges localized at the membrane/solution interface. In the later stages of the degradation process, the zeta potential again became less negative. This suggests that liberation of degraded segments takes place in the later stages.