Thermoresponsive terpolymeric films applicable for osteoblastic cell growth and noninvasive cell sheet harvesting

A novel multifunctional linear block copolymer, poly(N-isopropylacrylamide- co-acrylic acid)-b-poly(L-lactic acid) (NAL), was synthesized to expand the concept of cell sheet engineering by using its thermoresponsive property and processibility. The chemical structure of synthesized NAL was confirmed by Fourier transform infrared spectroscopy, and its molar mass (103,500 g · mol^-1) and molar mass distribution were determined by matrix-assisted laser desorption/ionization-time of flight mass spectroscopy. NAL copolymer was fabricated into thin films by spin-casting. Spin-cast NAL films displayed thermoresponsive properties as demonstrated by surface wettability and topology changes from relatively more hydrophobic (contact angle of 56°) and rougher at 37°C to relatively more hydrophilic (contact angle of 40°) and smoother at 22°C, as assessed by contact angle measurement and atomic force microscopy, respectively. Murine osteoblastic MC3T3-E1 cells displayed comparable adhesion but slower proliferation on NAL films than on poly(L-lactic acid) (PLLA) films and tissue culture polystyrene (TCPS). Within 9 days of cell culture, the highest alkaline phosphatase activity of MC3T3-E1 cells occurred later (on day 9) on NAL films than on PLLA films and TCPS (on day 6). A well-established MC3T3-E1 cell sheet was successfully detached from NAL films, in the absence of enzymes, within about 5 min by simply lowering the temperature from 37°C to room temperature. NAL copolymer has potential for use in the controlled release of therapeutic agents while simultaneously supporting cell growth. In addition, it may be applicable for noninvasive two- or three-dimensional cell sheet harvesting.