Nonfouling polyampholyte polymer brushes with protein conjugation capacity

The elimination of nonspecific protein adsorption is an important challenge in many biomaterial applications. To address this issue, numerous nonfouling chemistries have been investigated. This work reports on the dual functional properties of a polyampholyte copolymer composed of positively charged [2-(acryloyloxy) ethyl] trimethyl ammonium chloride (TMA) and negatively charged 2-carboxy ethyl acrylate (CAA) monomers. TMA:CAA copolymers have previously been shown to have nonfouling properties, but the optimal conditions for nonfouling have not been determined. To accomplish this, the thickness of the polymer brush coating was varied by manipulating the surface-initiated atom transfer radical polymerization conditions. The nonspecific adsorption of fibrinogen and lysozyme was measured as a function of the copolymer brush thickness using a surface plasmon resonance biosensor. At the optimal thickness for nonfouling, nonspecific adsorption from 10% and 100% fetal bovine serum (FBS) was determined. The results indicate that at the optimal copolymer brush thickness, TMA:CAA polyampholyte materials have ultralow fouling characteristics even upon exposure to 100% FBS. The dual functional properties of TMA:CAA copolymers were demonstrated by conjugating fibrinogen to the copolymer brush over a range of brush thicknesses. The conjugation experiments clearly demonstrate that TMA:CAA copolymers have the capacity for protein conjugation at the optimal thickness for nonfouling. However, the conformational state of the copolymer brush chains impacts the overall conjugation capacity of the system. The results of this investigation indicate that TMA:CAA polyampholyte surfaces show promise for biosensor and biomaterial applications where their dual functional properties would be beneficial.