Thermoresponsive Brush Coatings for Cell Sheet Engineering with Low Protein Adsorption above the Polymers’ Phase Transition Temperature

Abstract

Thermoresponsive polymer coatings on cell culture substrates enable noninvasive cell detachment and cell sheet fabrication for biomedical applications. Optimized coatings should support controlled culture and detachment of various cell types and allow chemical modifications, e.g., to introduce specific growth factors for enhanced gene expression. Furthermore, the sterilization and storage stability of the coatings must be assessed for translational attempts. Poly(glycidyl ether) (PGE) brush coatings with short alkoxy side chains provide a versatile platform for cell culture and detachment, but their polyether backbones are susceptible to oxidation and degradation. Thus, we rationally designed potential alternatives with thermoresponsive glycerol-based block copolymers comprising a stable polyacrylate or polymethacrylate backbone and an oligomeric benzophenone (BP)-based anchor. The resulting poly(ethoxy hydroxypropyl acrylate-b-benzophenone acrylate) (pEHPA-b-BP) and poly(ethoxy hydroxypropyl methacrylate-b-benzophenone methacrylate) (pEHPMA-b-BP) block copolymers preserve the short alkoxy-terminated side chains of the PGE derived structure on a stable, but hydrophobic, aliphatic backbone. The amphiphilicity balance is maintained through incorporated hydroxyl groups, which simultaneously can be used for chemical modification. The polymers were tailored into brush coatings on polystyrene surfaces via directed adsorption using the BP oligomer anchor. The resulting coatings with thickness values up to ∼3 nm supported efficient adhesion and proliferation of human fibroblasts despite minimal protein adsorption. The conditions for cell sheet fabrication on pEHPA-b-BP were gentler and more reliable than on pEHPMA-b-BP, which required additional cooling. Hence, the stability of pEHPA-b-BP and PGE coatings was evaluated post gamma and formaldehyde (FO) gas sterilization. Gamma sterilization partially degraded PGE coatings and hindered cell detachment on pEHPA-b-BP. In contrast, FO sterilization only slowed detachment on PGE coatings and had no adverse effects on pEHPA-b-BP, maintaining their efficient performance in cell sheet fabrication.