Optimization of the composition of zwitterionic copolymers for the easy-construction of bio-inactive surfaces

Random copolymers (S-PCMBx) of the zwitterionic monomer carboxymethylbetaine (CMB) and a small percentage of 3-methacryloyloxypropyl trimethoxysilane with various composition ratios were synthesized in ethanol using 2,2′-azobisisobutyronitrile as the initiator. An S-PCMBx layer formed on the glass substrate after soaking in the copolymer solution and had a thickness of 2–3 nm. The S-PCMBx-modified surface was highly hydrophilic and suppressed both the non-specific adsorption of protein (bovine serum albumin) and NIH3T3-fibroblast adhesion. The degree of adsorption suppression increased with increasing copolymer CMB content with a maximum at 90 mol % CMB. In contrast, the modification of the glass substrate with a PCMB homopolymer terminally modified with a trimethoxysilyl group did not effectively suppress protein adsorption and cell adhesion due to the low graft density. The importance of balancing the number of fixation points and the length of the zwitterionic polymer loops to produce bio-inactive metal oxide surfaces is suggested.