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 1.1 meq/g of microgel, respectively. In the pH range of 4–9, the zeta potential values varied from +10 to −40 mV, while the hydrodynamic radius varied from 160 nm in the swollen state (acidic and basic pH) to 110 nm 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 0.6 meq/g microgel, respectively. In the pH range of 4–9, the surface charge on the microgels varied from +25 to −60 mV and the hydrodynamic radii were 190 nm at low pH, 80 nm at neutral pH, to 120 nm 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.