DOI: 10.14457/tu.the.2015.16
title: TIME STUDY OF PHOTOGRAFTING POLY (N-ISOPROPYLACRYLAMIDE-CO-ACRYLAMIDE) ONTO POLYSTYRENE SURFACE FOR TISSUE CULTURE ENGINEERING

description: Poly (N-isopropyl acrylamide-co-acrylamide) (PNIAM-co-AM) is a temperature-responsive polymer that has been widely utilized for modification of tissue culture surfaces in cell sheet engineering. Its phase transition from hydrophobic to hydrophilic characteristics occurs at the lower critical solution temperature (LCST) of 32oC which can support cell adhesion and detachment under human physiological conditions. This study investigates the ultraviolet (UV) irradiation method to graft PNIAM-co-AM onto tissue culture polystyrene surface (TCPS) and the effect of UV polymerization time on the grafted amount of PNIAM-co-AM onto TCPS surfaces. The purpose is to determine the effective UV exposure time which provides the optimum grafting density of 1.4–2 µg/cm2 that is suitable for proper cell adhesion and detachment. This quantitative analysis on the amount of grafted copolymer with different UV exposure times was characterized by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR). The relationship between the peak area ratio (A1654/A1600) and grafting density (µg/cm2) was determined. From the results of ATR-FTIR measurement, the grafted PNIAM-co-AM amount increases with increasing UV polymerization time from 30 minutes to 2.50 hours. From 1 to 2 hours of UV exposure time, the amount of grafted copolymer was obtained between 1.68 and 2.03 µg/cm2. From the estimation of PNIAM content in the copolymer grafted layer by FTIR and NMR analysis, the grafted amount of PNIAM in 1–2-hour UV exposure surfaces was obtained between 1.3 and 1.7 µg/cm2 which is close to the optimum range of grafting density. The hydrophobic-hydrophilic transition behaviour of the grafted PNIAM-co-AM surfaces was also examined by contact angle measurement. The grafted surface with the UV exposure time of between 1 and 2 hours showed an obvious transition in contact angles when the temperature was lowered from 40 to 10°C. The results of cell study analysis show that a successful detachment of a Human Dermal Fibroblast (HDFa) monolayer cell sheet is observed in PNIAM-co-AM grafted surfaces with 1- and 2-hour UV exposure time.Along with this research, synthesis of PNIAM-co-AM was also carried out in order to reach the quantitative analysis of ATR-FTIR. The synthesized PNIAM-co-AM was first confirmed as a linear copolymer by using KBr technique of Fourier Transform Infrared Spectroscopy (FTIR). The estimated composition of PNIAM in the synthesized copolymer was obtained as 76.3% and 80.6% from FTIR and NMR analysis. The resulting linear copolymer was applied in the preparation of the known grafted amount of PNIAM-co-AM grafted surfaces. It was very useful in constructing the calibration curve of the peak area ratio (A1654/A1600) and grafting density (µg/cm2). As a related study, the natures of synthesized PNIAM-co-AM in aqueous solution at 10, 20 and 37oC were also studied by intrinsic viscosity determination. From the results, the drop in viscosity from 10oC to 37oC refers to the change in conformation of PNIAM from extended chain at below LCST to coiled-globule at above LCST. A significant drop of intrinsic viscosity is observed at 20oC which can be affected by the temperature-dependent factors such as the interaction between water and PNIAM, molecular weight, and radial of gyration of the synthesized copolymer.