Phase Transition Control of pNIPAAm-<i>b</i>-pMMA Thin Films via UV/Ozone Irradiation and Direct Immersion Annealing for Biomedical Applications

Poly(<i>N</i>-isopropylacrylamide) (pNIPAAm) and its copolymers with poly(methyl methacrylate) (pMMA), due to their lower critical solution temperature (LCST) within the physiological temperature range, have attracted attention in many studies as responsive surfaces for cell sheet growth. The behavior of pNIPAAm and its block copolymer with pMMA (pNIPAAm-<i>b</i>-pMMA) films is not fully understood. In this study, the effects of ultraviolet/ozone (UV/O₃), interdiffusion, and direct immersion annealing (DIA) treatments on the responsiveness and adhesion of spin-coated thin films of pNIPAAm and pNIPAAm-<i>b</i>-pMMA were investigated. The water contact angle (WCA) measurements were used to record changes in hydrophilicity and relaxation time for the films immersed in deionized water, as well as hydrophilicity changes during cyclic measurements. Atomic force microscopy was utilized to track phase transitions in the films over three complete and continuous thermal cycles. The phase transition behavior of the films across the LCST range remains insufficiently understood, particularly in relation to the influence of different treatment types and the underlying chemophysical mechanisms that regulate the orientation of functional groups along the polymer chains. In this study, we address these gaps by examining how these factors, along with the globule-to-coil transition of pNIPAAm chains, impact the films' thermoresponsiveness and the time required for complete cell sheet detachment. This study evaluated the potential of utilizing straightforward and environmentally sustainable methods for producing cell culture dishes as alternatives to conventional, costly, and environmentally detrimental techniques. The findings confirmed the significant promise of these methods for the intended applications.