Precipitation polymerization of N-isopropylacrylamide (NIPAM) with methylenebisacrylamide (MBAAm) in water at 70°C gave thermosensitive hydrogel microspheres. The adsorbability of proteins on the poly-NIPAM microspheres was found to depend on temperature. Below the lower critical solution temperature (LCST) of poly-NIPAM in an aqueous medium, that is, around 32°C, the microspheres hold a large amount of water inside and their surface is hydrophilic enough to suppress the adsorption of proteins. On the contrary, above 32°C, the micropheres deswell and their surface becomes hydrophobic and, consequently, susceptible to adsorption of a large amount of proteins. Proteins once adsorbed on the microspheres at a high temperature could be desorbed more or less by lowering the temperature to below 32°C. The extent of desorption at low temperatures was found to depend on the incubation time for adsorption at high temperatures.
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