Interactions between thermosensitive hydrogel microspheres and proteins

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel microspheres show volume transition based on the LCST around 32°C. It is thought that the surface of the microspheres becomes hydrophobic due to association of segments induced by the hydrophobic interaction above the LCST. Protein adsorption and desorption are dependent both on surface properties of microspheres and on characteristics of protein molecules. In this study, we reported adsorption and desorption of proteins with similar molecular size and shape on poly(styrene) (PSt) and PNIPAM microspheres. Proteins used for this study were myoglobin (MG), α-lactalbumin (LA), lysozyme (LZ), and ribonuclease A (RNase). In addition, peroxidase was used to evaluate the extent of the denaturation induced by adsorption and desorption, and its residual enzyme activity was measured. PNIPAM showed the temperature dependence of protein adsorption, especially in the adsorption of flexible proteins such as LA and MG. It seemed probable that structure rearrangement resulted in the entropy gain. The desorption behavior was also related to the protein's flexibility. It was confirmed from the residual activity that peroxidase desorbed from PNIPAM microspheres remained more stable than peroxidase desorbed from PSt. These hydrogel microspheres were found to be the potent thermosensitive carrier or adsorbent for proteins.