Fig. 5. Release of positively charged proteins can be tuned by changing the environmental pH.

(A) Release of SDF from composite XMC into media at pH 3, pH 5, or pH 7. Cumulative percentage release of SDF is significantly greater at pH 3 than at pH 5 (t < 10 days, P < 0.01) and pH 7 (t > 0 days, P < 0.0001), likely because PLGA carboxylate anions are protonated to carboxylic acids, thereby reducing electrostatic interactions with positively charged proteins. (B) Release of BDNF from HAMC with PLGA np with or without encapsulated magnesium carbonate (MgCO₃). Release is delayed with encapsulated MgCO₃ (a basic salt), which neutralizes acidic degradation products and thereby maintains a higher/neutral local pH (n = 3 for all releases, mean ± SD plotted).