Biodegradable and biocompatible polyampholyte microgels derived from chitosan, carboxymethyl cellulose and modified methyl cellulose.

Two biocompatible and biodegradable polyampholyte microgels, namely chitosan-carboxymethyl cellulose (CS-CMC) and chitosan-modified methyl cellulose (CS-ModMC) were synthesized by an inverse microemulsion technique. The CS-CMC microgel system was pH-responsive while the CS-ModMC system possessed both pH and thermo-responsive properties. For CS-CMC system, the number of -OCH2COOH and -NH2 groups was determined to be 1.5 and 1.1meq/g of microgel, respectively. In the pH range of 4-9, the zeta potential values varied from +10 to -40mV, while the hydrodynamic radius varied from 160nm in the swollen state (acidic and basic pH) to 110nm in the "collapse" state (neutral pH). Furthermore, TEM micrographs confirmed the swelling/deswelling behaviour of CS-CMC microgel particles at acidic, neutral and basic conditions. For CS-ModMC system, the number of -OCH2COOH and -NH2 groups was determined to be 0.8 and 0.6meq/g microgel, respectively. In the pH range of 4-9, the surface charge on the microgels varied from +25 to -60mV and the hydrodynamic radii were 190nm at low pH, 80nm at neutral pH, to 120nm at a high pH. In vitro drug release studies confirmed that CS-CMC microgels could encapsulate and release a model drug, thus they could potentially be used as biocompatible and biodegradable drug carriers.