Triply-responsive OEG-based microgels and hydrogels: regulation of swelling ratio, volume phase transition temperatures and mechanical properties

Abstract

Thermally- and pH-responsive microgels (MGs) and hydrogels are fascinating network systems that have been applied in biomedical engineering and sensing. The volume-swelling ratio (Q) and the volume-phase transition temperatures (VPTTs) are important parameters that govern the gels applications. Poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) MGs are attractive thermal-responsive MGs due to their biocompatibility and controllable VPTTs. Herein, we investigate a series of pH- and thermal-responsive poly (2-(2-methoxyethoxy) ethyl methacrylate-co-methacrylic acid-co-ethyleneglycol dimethacrylate) P(MEO₂MA-MAA-EGD) MGs via precipitation polymersation. The MGs are vinyl-functionalised using glycidyl methacrylate (GMA). These vinyl functional MGs were covalently interlinked to construct the multi-responsive doubly crosslinked MG hydrogels (DX MGs). The MGs and DX MGs swell at high pH and low temperature. They also collapse at low pH and high temperature. The Q and VPTT values of MGs can be regulated precisely by the MAA content and pH. The MGs and DX MGs also exhibit responses to ionic species (cations). We compare the swelling tendencies of the DX MGs and parent MGs. The mechanical properties and swelling of the DX MGs can be changed using added Na⁺, Mg²⁺ and Al³⁺ or Fe³⁺ ions. The latter provides ionic crosslinking via the RCOO⁻ groups. We believe this work provides improved insight for designing and controlling the properties of multi-responsive MGs and DX MGs.