Control of cell cultivation and cell sheet detachment on the surface of polymer/clay nanocomposite hydrogels

Cell cultivation on the surface of a novel poly(N-isopropylacrylamide) (PNIPA) hydrogel (N-NC gel), consisting of a specific type of organic (PNIPA)/inorganic (clay) network, was studied using three cell types; HepG2 human hepatoma cells, human dermal fibroblasts, and human umbilical vein endothelial cells. For the first time, it was found that cells could be cultured to be confluent on the surfaces of PNIPA hydrogels using N-NC gels, regardless of gel thickness. Cell adhesion and proliferation on N-NC gels exhibit strong dependencies on clay concentration (C-clay), and the numbers of cultured cells are maximum at about C-clay = 6 x 10(-2) mol (45.72 g)/1L of H2O. On the contrary, it was almost impossible to culture cells on conventional, chemically crosslinked PNIPA hydrogels, regardless of their cross-linker concentration. The reasons why cells cultured only on the surfaces of N-NC gels with their specific network structure and composition were discussed in terms of water content, protein adsorption, surface flatness, hydrophobicity of dehydrated PNIPA chains, and the anionic charge on exfoliated clay. Finally, it was found that cells cultured on the surfaces of N-NC gels could be detached in the forms of sheets of cells without trypsin treatment, but by just decreasing the temperature to 20 degrees C.