In this work, we developed a synthetic strategy to synthesize dual-temperature-responsive low surface fouling zwitterionic microgels. Statistical poly(N-vinylcaprolactam-co-glycidyl methacrylate) copolymers were synthesized by RAFT polymerization and post-modified by thiol-epoxy click reaction with thiol end-group-modified poly(sulfobetaine) macro-RAFT (PSB-SH) to obtain poly(N-vinylcaprolactam-co-glycidyl methacrylate)-graft-poly(sulfobetaine) (PVCL-co-PGMA-g-PSB) graft copolymers. Synthesized graft copolymers were cross-linked by diamine cross-linker in water-in-oil (w/o) inverse mini-emulsion to obtain zwitterionic microgels. Using this approach, we synthesized microgels with unique microstructure, high loading and uniform distribution of poly(sulfobetaine) chains, which exhibits tunable dual-volume phase transition temperatures. The microgels also showed excellent antifouling property reflected in strongly reduced protein absorption on a microgel-coated surface observed in real time by a Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring experiment with continuous flow of protein solution. Therefore, this kind of zwitterionic microgel can be potentially used for temperature-triggered drug delivery and anti-bioadhesion coating material as well.
Adsorption of proteins on biological surfaces is a detrimental phenomenon that reduces the work‐life of the implants in various biomedical applications. Here, we synthesized a new class of thermoresponsive zwitterionic poly(phosphobetaine) (PMPC) microgel with excellent surface antifouling property by macro‐RAFT mediated thiol‐epoxy click reaction. End‐group modified zwitterionic PMPC homopolymers with well‐defined molecular weight and narrow dispersity were grafted onto poly(N‐vinylcaprolactam‐co‐glycidyl methacrylate) (PVG) copolymer backbone followed by addition of a cross‐linker, leading to microgel formation. While no upper critical solution temperature (UCST) was found in poly(N‐vinylcaprolactam‐co‐glycidyl methacrylate‐g‐2‐methacryloyloxyethyl phosphorylcholine) (PVGP) graft copolymers, the corresponding microgels exhibited both UCST and lower critical solution temperature (LCST) transitions, related to the swelling and collapse of PMPC and poly (N‐vinylcaprolactam) (PVCL) components respectively. An increase in the molecular chain length of the PMPC increased the shifting of UCST and LCST of the microgels to higher temperatures, due to the ability of zwitterionic groups to coordinate a large number of water molecules. The effect of the variation in the molecular weights of amphiphilic poly(ethylene glycol) diamine (PEG‐NH2) cross‐linker was also reflected in both temperature and salt responsiveness of the microgels. The efficacy of the microgels as potential antifouling materials was further studied by fluorescence microscopy and XPS analysis on microgel coatings treated with FITC‐BSA solution and pure BSA solution respectively. Lower protein adsorption was observed for microgels grafted with higher molecular chain length of PMPC, whereas, the microgels synthesized using higher molecular weight PEG‐NH2 diamine cross‐linker displayed greater protein adsorption on their surfaces.
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