Controlled uptake and release of lysozyme from glycerol diglycidyl ether cross-linked oxidized starch microgel

A biodegradable microgel system based on glycerol-1,3-diglycidyl ether (GDGE) cross-linked TEMPO-oxidized potato starch polymers was developed for controlled uptake and release of proteins. A series of microgels were prepared with a wide range of charge density and cross-link density. We found both swelling capacity (SW_w) and lysozyme uptake at saturation (Γ_sat) increased with increasing degree of oxidation (DO) and decreasing cross-link density. Microgel of DO100% with a low cross-link density (R_{GDGE/polymer (w/w)} of 0.025) was selected to be the optimum gel type for lysozyme absorption; Γ_sat increased with increasing pH and decreasing ionic strength. It suggests that the binding strength was the strongest at high pH and low ionic strength, which was recognized as the optimum absorption conditions. The lysozyme release was promoted at low pH and high ionic strength, which were considered to be the most suitable conditions for triggering protein release. These results may provide useful information for the controlled uptake and release of proteins by oxidized starch microgels.