Stimuli-Responsive Liquid Cell Scaffold: Reversible Viscoelasticity Switching of a Polymer in an Ionic Liquid by Visible-Light

Abstract

Cell culture at liquid | liquid interfaces has gained attention from the perspective of the mechanobiology. We recently reported cell culture at water-immiscible ionic liquids (ILs) interface, which have an advantage of polymer compatibility over the conventional non-polar liquid scaffold capable of interfacial cell culturing. Herein, we report a light-responsive polymer solution in a noncytotoxic IL (NCIL) that reversibly changes its viscosity. Methoxyazobenzene (mAzoA) was selected as the chromophore for reversible photoisomerization under non-phototoxic visible light. For a main polymer, poly(methyl methacrylate) (PMMA) was chosen because of exhibiting upper critical solution temperature (UCST) type phase transition in an NCIL ([P8,8,8,8][TFSI]) near cell culturing temperature. We successfully demonstrated that the loss modulus of the polymer solution was switched reversibly triggered by visible light photochromism of mAzoA. We also revealed that the polymer solution showed no cytotoxicity, confirming that they can be applied to liquid cell scaffold materials. Furthermore, the thermal isomerization of cis-mAzoA to trans-mAzoA was extremely retarded in [P8,8,8,8][TFSI] (τ1/2 = 2911 h at 37 °C), suggesting the avoidance of undesired aging degradation during cell culturing operation. The system ability to switch between higher and lower viscoelasticity offers a powerful tool for real-time control of the cellular environment.