The renaturation of lysozyme assisted by a novel type of hairy particles was investigated. The particles used consisted of polystyrene (PS) cores onto which long chains of thermosensitive poly(N-isopropylacrylamide) (PNIPAM) were grafted as shell. Here, two kinds of particles were synthesized as sub-micron PS cores and 89 nm brush thickness (Particle A) and 122 nm brush thickness (Particle B), respectively. Thermosensitive characteristics of the above prepared hairy uniform PS particles with PNIPAM brushes were studied and the results indicated that the lower critical solution temperature (LCST) of PNIPAM brushes grafted on the surface of uniform PS cores was between 33 and 34 degrees C. It was proved that the particles were quite efficient in assisting lysozyme renaturation at high initial protein concentration. When the protein concentration was increased to 500 mu g/mL, the refolding yield of the recovery of lysozyme activity could achieve 58.0% (Particle A) and 71.5% (Particle B), compared with only 34.8% by simple dilution refolding. Furthermore, the kinetics of lysozyme refolding in the absence and the presence of the colloidal particles were studied accordingly. The results indicated that the time required for the refolding with colloidal particles was a little bit delayed than that by the simple dilution method owing to the hydrophobic interactions between lysozyme and the PNIPAM brushes. The mechanism of the enhancement for the hairy uniform PS particles with PNIPAM brushes assisted refolding was further discussed. All results above demonstrated that the spherical PNIPAM brushes presented an alternative way to assist protein renaturation in vitro. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114:1270-1277, 2009