"Fuzzy hair" promotes cell sheet detachment from thermoresponsive brushes already above their volume phase transition temperature.

Abstract

Thermoresponsive poly(glycidyl ether) (PGE) brushes have shown to be viable substrates for the culture and temperature-triggered detachment of confluent cell sheets. Surface-tethered PGEs with a cloud point temperature (TCP) around ~30°C exhibit phase transitions well-centered within the physiological range (20-37°C), which makes them ideal candidates for cell sheet fabrication. However, PGEs with TCPs at ~20°C also afford the detachment of various types of cell sheets, even at room temperature (20-23°C), i.e., above the polymers' TCPs. In this study, we investigate the phase transition of PGE brushes tethered to polystyrene (PS) culture substrates with varying grafting density and TCP to arrive at a mechanistic understanding of their functionality in cell sheet fabrication. Using quartz crystal microbalance with dissipation (QCM-D) monitoring, we demonstrate that brushes fabricated from PGEs with TCPs at ~20°C display volume phase transition temperatures (VPTTs) well below room temperature. Although the investigated coatings obviously do not exhibit marked thermal switching in terms of brush hydration and layer thickness, their physical properties at the brush-water interface, as ascertained by QCM-D and AFM measurements, undergo subtle changes upon cooling from 37°C to room temperature which is sufficient to promote cell sheet detachment. Thus, it appears that discreet rehydration of the outmost brush layer, resembling "fuzzy hair" at the brush-water interface, renders the surfaces less protein- and cell-adhesive at room temperature. This minor structural change of the interface allows for the reliable detachment of human dermal fibroblast sheets already at 20°C well above the VPTT of the brushes.