Terminal-functionality effect of poly(N-isopropylacrylamide) brush surfaces on temperature-controlled cell adhesion/detachment.

Terminally functionalized poly(N-isopropylacrylamide) (PIPAAm) brush grafted glass surfaces were prepared by a surface-initiated reversible addition-fragmentation chain transfer radical (SI-RAFT) polymerization. SI-RAFT mediated PIPAAm chains possessed terminal dodecyl trithiocarbonate groups which can be substituted with various functional groups. In this study, dodecyl groups were substituted with hydrophilic maleimide groups for controlling the thermoresponsive character of PIPAAm brushes. PIPAAm brushes exhibited reversible temperature-dependent surface wettability changes around PIPAAm's lower critical solution temperature. Phase transition of dodecyl-terminated PIPAAm brushes clearly shifted to lower temperature than that of maleimide-terminated PIPAAm brushes, and this shift was attributed to promoted PIPAAm dehydration via terminal hydrophobes. By using this feature, the specific adhesion temperatures of bovine carotid artery endothelial cells (BAECs) on the PIPAAm brush surfaces were successfully controlled. BAECs were initiated to adhere on dodecyl-PIPAAm surfaces at 31 °C, while their adhesion was significantly suppressed on maleimide-PIPAAm surfaces under 33 °C. In contrast, terminal functionality scarcely affected the thermoresponsive behavior of PIPAAm brushes in the polymer rehydration process by reducing temperatures, and thus, the difference in spontaneous cell detachment from different PIPAAm-brush surface was negligible. Consequently, confluently cultured cells were able to be harvested as contiguous cell sheets from individual surfaces with comparable periods at 20 °C.