Fig. 5.

Low pH in degrading PLGA microspheres decreases IPV stability over time. The pH surrounding PLGA microspheres decreases over the course of a release study, with the lowest pH measured just before IPV is released in measurable amounts (A). The difference in release kinetics between cargo of varying molecular weight from approximately 1 to 8500 kDa suggests that IPV would be trapped inside the degrading particles before acidic protons are released and would therefore experience a low-pH environment (B). Stability studies show that IPV, particularly type 1, is very unstable in even slightly basic or acidic pH after 2 days (C) or 7 days (D) of incubation at 37 °C, further emphasizing the need to relieve the acidity within particles.