A novel biocompatible and biodegradable microgel system has been developed for controlled uptake and release of especially proteins. It contains TEMPO-oxidized potato starch polymers, which are chemically cross-linked by sodium trimetaphosphate (STMP). Physical chemical properties have been determined for microgels of different weight ratios of cross-linker to polymer (0.10, 0.15, 0.20, 0.30, and 0.40) and degrees of oxidation (30, 50, 70, and 100%). The charge density of the microgels as determined by proton titration is found to be in good agreement with the expected degree of oxidation (DO). The electrophoretic mobility of the microgel particles is used as a qualitative indicator of the pore size and scales with microgel swelling capacity as expected. The swelling capacity increases with increasing pH and decreasing salt concentration. Preliminary data for the uptake of the globular protein lysozyme by the microgels show it increases with increasing DO and decreasing cross-linker to polymer ratio. Highly charged microgels with intermediate cross-linker to polymer ratios (0.15 and 0.2) are found to be optimal for encapsulating lysozyme. © 2009 American Chemical Society. Chemicals / CAS: lysozyme, 9001-63-2; oxidoreductase, 9035-73-8, 9035-82-9, 9037-80-3, 9055-15-6; proton, 12408-02-5, 12586-59-3; sodium chloride, 7647-14-5; trimetaphosphoric acid, 13566-25-1, 7785-84-4