Thermoresponsive Polymer Brushes for Switchable Protein Adsorption via Dopamine-Assisted Grafting-To Strategy

Abstract

Surface modifications using responsive polymers give access to biomedical applications that rely on switchable properties, such as smart sensors and actuator systems. In this work, thermoresponsive polymer coatings are synthesized on silicon oxide surfaces using a facile and effective two-step grafting-to strategy. Briefly, the substrates are first functionalized with a poly(dopamine) (poly(DA)) primer layer. Subsequently, block copolymers of poly(glycidyl methacrylate) and poly(N-isopropylacrylamide) (poly(GMA)20-block-poly(NIPAM)n (n = 263, 528 and 705)) synthesized via reversible addition‑fragmentation chain‑transfer (RAFT) polymerization, are grafted to the poly(DA)-modified surfaces. Characterization using ellipsometry, X-ray photoelectron spectroscopy (XPS) and contact angle measurements confirmed polymer attachment with appreciable grafting densities. Quartz crystal microbalance with dissipation monitoring (QCM-D) is employed to investigate the thermoresponsive properties and degree of hydration of the polymers below and above their lower critical solution temperature (LCST). The longer the polymer chain, the more water is lost per repeating unit upon increasing the temperature above the LCST. The surfaces are exposed to diluted and undiluted human serum at 20 °C and 40 °C to demonstrate for all three polymer brushes switchable protein adsorption-repellence. In a broader perspective, this study presents a straightforward, robust and efficient procedure to modify virtually any surface type with a thermoresponsive coating.