Electron beam induced grafting of N-isopropylacrylamide to a poly(ethylene-terephthalate) membrane for rapid cell sheet detachment

Intact sheets of human prostate epithelium cells were successfully detached from a poly(N-isopropylacrylamide) (pNIPAM) membrane radiolytically grafted to poly(ethlylene-terephthalate (PET) culture dishes. The detachment process took less than 20 min without damaging the sheet structure. The grafting was performed using a high-energy electron beam to covalently bond NIPAM to the surface of PET culture dishes. This work demonstrates that the optimal conditions for uniform grafting can be achieved by adding argon-saturated solutions of NIPAM monomer onto pre-irradiated, surface-activated PET membranes. The solutions and the membranes were then irradiated under anaerobic conditions to a total absorbed dose of 25 kGy. This grafting method involves producing carbon-centered free radicals NIPAM and PET from both NIPAM and PET, respectively. An investigation of the kinetics of the early stages of polymerization of NIPAM was performed through electron beam pulse radiolysis with optical detection. The pulse radiolysis experiments of anaerobic NIPAM methanol solutions show that the esol− reacts very rapidly with NIPAM producing NIPAM− anions with a reaction rate constant of 1.4×109±10% L mol−1 s−1. The NIPAM− anions then undergo a protonation reaction producing the initiation free radical (NIPAM) with a reaction rate constant of 9×102 L mol−1 s−1. Along with pulse radiolysis, electron paramagnetic resonance (EPR) measurements show that the radiolytically produced carbon-centered free radicals of the PET, PET, decay following an overall observed pseudo-first-order reaction with rate constants of k=2.0×10−4 and 7.0×10−4 s−1 produced in argon and in air, respectively. The overall observed decay reaction involve PET+PET cross-linking, PET+O2, PET+HO2, and PET+H-atoms, since these EPR measurements were conducted under aerobic conditions.