REGULATION OF PROTEIN ADSORPTION ON pH-RESPONSIVE SURFACES

Poly(methacrylic acid) (PMAA) modified silicon surface (Si-PMAA) was prepared via surface-initiated atom transfer radical polymerization (ATRP) of tert-butyl methacrylate (tBMA) on initiator-immobilized silicon followed by the hydrolysis of PtBMA to PMAA,The successful graft process was confirmed by X-ray photoelectron spectroscopy (XPS), ellipsometry and water contact angle characterization, The PMAA modified surface exhibited pH responsibility of both surface wettability and protein adsorption, At lower pH (pH = 4), the Si-PMAA surface was relative hydrophobic (with a water contact angle (WCA) value ca. 48.9 degrees),With an increasing pH, the surface turned more hydrophilic and at pH = 9 the WCA value was ca. 12.1 degrees, This pH-responsive surface wettability can be explained by the conformational transition of polymer chains,The addition of base will deprotonate the pendant carboxylic acidic groups, resulting in swollen polymer chains with many ionized COO(-), which are favorable for the entrance of water molecules and make the surface more hydrophilic, This pH-sensitive wettability of the Si-PMAA surface was reversible for repeated cycles of alternating treatment by solution with different pH, Fibrinogen adsorption on the Si-PMAA and unmodified silicon surface was evaluated by radio-labeling method, The results indicated that fibrinogen adsorption on unmodified silicon surface at pH 9 was slightly lower than that at pH 4, while after modification with PMAA, the effect of pH was greater, The adsorption at pH 4 was ca. 39 times higher than that at pH 9,suggesting that control over the adsorption of proteins through adjusting the pH value could be achieved on the PMAA modified surface.