Synthesis of temperature and light sensitive mixed polymer brushes via combination of surface-initiated PET–ATRP and interface-mediated RAFT polymerization for cell sheet application

Abstract In this study, a series of temperature and light sensitive mixed polymer brushes consisting of poly(2-(2-methoxyethoxy) ethyl methacrylate) [poly(MEO2MA)] and poly(N-[4-[(4-nitrophenyl) azo] phenyl] acrylamide) [poly(NPAPAA)] units were grown on silicon wafer via the combination of surface-initiated photoinduced electron transfer-atom transfer radical polymerization (PET-ATRP) and interface-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. This process was realized in five consecutive steps: (i) coupling of previously synthesized (3-aminopropyl) triethoxysilane-2-bromoisobutyryl bromide (APTES-BIBB) and (3-aminopropyl) triethoxysilane-t-butoxycarbonyl (APTES-t-BOC) mixtures to the Si-OH surface under self-assembly monolayer conditions (ii) synthesis of poly(MEO2MA) units via surface-initiated PET-ATRP (iii) replacement of terminal-Br atoms at poly(MEO2MA) units with biocompatible maleimide molecules (iv) removal of the t-BOC group from APTES-t-BOC and bonding of the RAFT agent to the APTES, and (v) synthesis of poly(NPAPAA) units via the interface-mediated RAFT polymerization. The surface compositions of APTES-BIBB and APTES-t-BOC molecules were determined by the water contact angle data analyzed with the Israelachvili-Gee model and by the X-ray photoelectron spectroscopy measurements. The grafting density (σ, chains nm−2) and the average distance between grafting points (D, nm) of the mixed polymer brushes are about 0.56 chains nm−2 and 1.52 nm, respectively, indicating high grafting density. The lower critical solution temperatures (LCSTs), trans-cis and cis-trans transition times were in the range of 24.6–29.2 °C, 10–25 min and 8–20 min, respectively, depending on the surface composition of the polymer brushes. Cell culture studies revealed successful cell detachment either via the temperature reduction or UV irradiation methods. The cell recovery ratios were recorded as 99.05 ± 0.45% and 83.95% ± 0.58%, respectively. These experimental findings provided basic information at the molecular level in the preparation of temperature and light- sensitive bioactive surfaces for cell sheet preparation and detachment state.