Photo- and thermo-responsive extracellular matrix mimicking nano-coatings prepared from poly(N-isopropylacrylamide)-spiropyran copolymer for effective cell sheet harvesting

Abstract

Poly(N-isopropylacrylamide)-spiropyran (PNIPAAm-SP) copolymers were tethered onto the glass substrate using surface-initiated atom transfer radical polymerization (SI-ATRP). The substrate was previously activated by ultra-violet ozone (UVO) irradiation and the pre-synthesized initiator was immobilized on it. A block of PNIPAAm was grafted onto the glass substrates, followed by a second block of mixed NIPAAm and spiropyran acrylate (SPA). The effects of UVO irradiation time and polymerization time of spiropyran containing block on cell sheet formation and detachment characteristics were evaluated. The photo-responsiveness of SPA was evaluated by ultra-violet visible spectroscopy (UV–vis). The presence and thickness of the grafted polymer layers were evidenced by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). The results of water contact angle (WCA) analysis showed that the modified surfaces became hydrophilic with decreasing temperature from 37 to 20 °C as well as with light irradiation. L929 mouse fibroblast cell culture results indicated a complete cell sheet formation. By applying temperature or light stimuli, the cell sheets were detached in a trypsin-free procedure.