BACKGROUND: Non-specific protein adsorption resistance is the most important factor for biocompatibility; pre-adsorption of hydrophilic polymer on artificial material surface is one of the effective methods to inhibit protein adsorption. OBJECTIVE: To study pre-adsorption and protein adsorption resistance of poly (isopropylacrylamide) (PNIPAM)-based amphiphilic comb-block copolymers on polystyrene (PS) surface, and to understand the effect of the copolymer structure, i.e. the chain length and the number of hydrophilic polyvinylpyrrolidone (PVP) or polyethylene oxide (PEO) comb-branches, on protein adsorption resistance. DESIGN, TIME AND SETTING: An observational study was performed at College of Materials Science and Engineering, Beijing University of Chemical Technology from November 2007 to November 2008. MATERIALS: Monodisperse PS microsphere was employed to simulate surface of hydrophobic materials, and lysozyme was used as protein model. METHODS:① Qualitative analysis: Aqueous suspension of PS microspheres (0.1 g/L) was treated with PNIPAM-based copolymer (0.1 g/L) at room temperature for 24 hours to allow pre-adsorption of the copolymer on PS surface to build up a hydrophilic layer. Lysozyme (0.1 g/L) was mixed with the PS suspension at 37 ℃ and the mixture was kept for 24 hours. Apparent particle size and turbidity of the suspension were measured at 37C to observe coagulation or flocculation of PS microspheres, which related to the extent of protein adsorption on PS surface. ②Quantitative analysis of protein adsorption: The PS suspension containing lysozyme was subjected to ultracentrifuge (15 000 r/min) to collect clear aqueous solution. The lysozyme concentration in the clear solution was measured by spectrophotometry at 280 nm. The amount of protein adsorbed on PS surface was calculated based on the decrease in the protein concentration in the supernatant solution. MAIN OUTCOME MEASURES: Apparent particle diameter, turbidity, mass concentration of aqueous phase residual protein. RESULTS: ① Suspension of bare PS microspheres flocculated in the presence of lysozyme at 37℃ due to protein adsorption,which caused significant decrease in the turbidity of the suspension. Bare PS surface could adsorb 25.5 mg lysozyme per square meter.② PS microsphere surface pre-adsorbed by PNIPAM-based amphiphilic comb-block copolymer adsorbed much less protein. No flocculation and only limit coagulation was observed when the suspension of the surface modified PS microspheres was mixed with lysozyme, due to less protein adsorption on the PS surface. CONCLUSIONS: ① Pre-adsorption of water-soluble PNIPAM-based comb-block copolymer on PS microsphere surface can inhibit protein adhesion on the surface. ② The structure of the copolymer strongly affects the performance of protein resistance. A proper amount of hydrophilic branch unit, VP or EO, is required to exhibit good protein resistance of the copolymer. However, excess hydrophilic branches in the copolymer results in worse protein resistance probably due to less stability of the pre-adlayer of the copolymer on PS surface.