Photothermal dual-responsive polymers for trypsin-free cell sheet harvesting

Abstract

Cell sheet engineering has emerged to tackle cell therapy's bottlenecks and increase the likelihood of life-saving potentials of tissue engineering. In this study, Poly(N-isopropylacrylamide-co-spiropyran) (P(NIPAAm-co-Sp)) copolymer and Poly(N-isopropylacrylamide-co-styrene-co-spiropyran) (P(NIPAAm-co-St-co-Sp)) terpolymer were synthesized by free radical polymerization (FRP). Fourier transform infrared (FTIR) was utilized to characterize the chemical structure of the resultant polymers. The molecular weight and molecular weight distribution were measured by gel permeation chromatography (GPC). The reversible photosensitivity of the synthesized polymers was proved by ultraviolet–visible (UV–Vis) spectroscopy. Thin layers of polymers were spin-coated onto ultraviolet/ozone (UV-O3) and silane-modified glass slides. To confirm the coating process, the attenuated total reflection FTIR spectroscopy (ATR-FTIR) was used. The cross-sectional images of the spin-coated glass slides, obtained using field emission scanning electron microscopy (FESEM), showed thin layers about 300 to 400 nm thick. The roughness of the coated layers was examined by atomic force microscopy which were below 1 nm. The water contact angle (WCA) measurements showed that changes in the surface wettability of thin layers occurred in response to temperature alteration and light illumination. The spin-coated glass slides were used to culture the mouse fibroblast cell line L929. The cell culture results showed that the thickness of the thin layers was adequate for forming a confluent and integrated sheet of L929 cells. By reducing the temperature from 37 °C to 20 °C and illuminating the glass slide, fragments of the cell sheet were harvested. The use of light besides temperature reduction decreased the time needed for cell sheet detachment from 2 h to 1 h.