Integrating Protein Resistance and Bioconjugation in P(OEGMA-co-MAA) Brushes for Biosensing and Cell Culture: ToF-SIMS Profiling and Antibody Characterization.

To provide antifouling bioactive surfaces for biosensing and cell culture, we synthesized and characterized copolymer brush interfaces with minimized nonspecific adsorption combined with adjustable high-capacity bioconjugation of functional protein and examined the interfacial protein state that determines its biological activity. Brushes were fabricated using surface-initiated atom transfer radical polymerization with silicon-grafted chains copolymerized from 2-(2-methoxyethoxy)ethyl methacrylate (OEGMA) and methacrylic acid (MAA) taken in different proportions. For all P(OEGMA1-x-co-MAAx) coatings (0 ≤ x ≤ 1), X-ray photoelectron spectroscopy revealed the molar fraction x of MAA in the brush equal to that of the reaction mixture. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed a copolymer composition that is uniform with depth in the brush coatings, confirming a successful random copolymerization. Bioconjugation of immunoglobulin G antibody (IgG) within the brushes, enabled by the activation of MAA segments with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide (EDC/NHS), was examined together with nonspecific IgG adsorption to the nonactivated brushes using ToF-SIMS and fluorescence microscopy. Protein loading was controlled by copolymer composition and protein solution concentration. The optimal composition x = 0.25 was selected for the brushes with maximum bioconjugation (∼0.4 g/cm3) and low nonspecific adsorption. Protein loads per brush volume were estimated from ToF-SIMS depth profiles that evidenced IgG immobilization within the brush. For all P(OEGMA1-x-co-MAAx) brushes with conjugated IgG antibody, the coatings with x = 0.25 provided the highest amount of bound antigen with an antigen binding ratio higher than that of the PMAA coatings. This observation was related to the different interfacial antibody states in both coatings (determined by the residue involvement in the coupling with the MAA segments and the dominant antibody orientation), which were investigated with multivariate principal component analysis of ToF-SIMS data. Finally, human fibroblast cell culture showed the biocompatibility of the developed copolymer brush coatings, further promoted by brush conjugation with fibronectin.