A Surface Grafting Strategy for Antifouling/bioadhesive Properties on a Janus-type Polymeric Thin Film

There have been great technical challenges in preparation of a transparent polymeric thin film with Janus-type antifouling and bioadhesive properties on both surfaces, while maintaining the optical and mechanical characteristics of the bulk material. Herein, poly(2-hydroxyethyl methacrylate) (PHEMA), which is commonly used as an ophthalmic hydrogel, was employed as the bulk material for allowing consecutive surface grafting of functional polymer brushes, which eventually resulted in a Janus-type transparent thin film for potential biomedical implantation. First, a bromine-containing reagent served as the reactive initiator was silanized onto both surfaces of the PHEMA hydrogel thin film under a mild condition. Then, with the presence of selected physical shielding on one side using a scotch tape, polymer brushes with cell-adhesive Arg-Gly-Asp (RGD) peptide pendent groups were grafted from the other side of the PHEMA thin film, resulted in a highly improved cell attachment capability. Once the tape was removed and the RGD-modified surface was shielded, the zwitterionic polymer brushes comprising poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) segments were grafted on the surface, again through surface-initiated activators regenerated by electron transfer atom-transfer radical polymerization (SI-ARGET-ATRP). Hence, this side of the PHEMA film became super hydrophilic and exhibited antifouling properties on the surface. After the surface grafting modification, the whole PHEMA hydrogel maintained highly transparent and biocompatible for potential ophthalmic applications. This study provides a simple and rather universal strategy for fabricating Janus-type polymeric thin films with distinct biophysical/biochemical properties on both sides, which potentially applicable for the multifunctional requirements in biomedical applications.