pH-Sensitive Polyampholyte Microgels of Poly(Acrylic Acid--Vinylamine) as Injectable Hydrogel for Controlled Drug Release.

pH-sensitive polyampholyte microgels of poly(acrylic acid--vinylamine) (P(AA--VAm)) were developed as an injectable hydrogel for controlled drug release. The microgels of P(AA--VAm) were prepared via inverse suspension polymerization of acrylic acid and N-vinylformamide followed by hydrolysis of poly(-vinylformamide) (PNVF) chains of the resultant microgels under basic condition. The pH-sensitivity of the P(AA--VAm) microgels in zeta potential and swelling ratio were investigated using a zeta potential analyzer and optical microscope. The results showed that both the zeta potential and the swelling ratio of the microgels were highly affected by the solution pH. By changing the pH of P(AA--VAm) microgel dispersion, the interparticle interaction and the swelling ratio of the microgels could be well adjusted and a colloidal hydrogel could be fabricated at moderate pH, showing a pH-triggered reversible fluid-gel transition. Using the polyampholyte P(AA--VAm) microgels as an injectable hydrogel drug release system, a sustained drug release could be achieved, indicating the great potentials of the pH-sensitive P(AA--VAm) microgels for controlled drug delivery.