Further biocompatibility testing of silica-chitosan complex membrane in the production of tissue plasminogen activator by epithelial and fibroblast cells

The effects of the physicochemical characteristics of a silica-chitosan com plex membrane (SiCM) on the expression of tissue plasminogen activator (tPA ) by contacting cells were investigated with the aim of improving the bioco mpatibility of the novel implant biomaterial. Expression of fPA is consider ed to be effective in wound healing by preventing thrombus formation, which causes inflammatory responses and rejection of implant materials. Inducing the epithelial cells surrounding implant materials to secrete tPA, which s erves as an early signaling system to proliferate cells underlying connecti ve tissues, would be further effective in accelerating mound healing. An ep ithelial 293 cell line derived From human embryonic kidney and a fibroblast IMR-90 cell line from human lung possessing the ability to secrete tPA wer e cultured on SiCMs, whose composition was stepwise controlled by adjusting the mixing ratio between silica and chitosan to give silica contents of 20 , 33, 43, and 50wt%. Both strains showed strong adhesion on chitosan (0%-Si CM) and 50%-SiCM, The cell proliferation rates were also accelerated in a m anner that was dependent on the increase in the adhesion strength of the ce lls cultured on the SiCMs. Furthermore, the tPA activity in the culture med ium increased in accordance with the cell density, while the cellular speci fic activity of IMR-90 cells to secrete tPA was synergistically enhanced by strong adhesion and a high cell density on the surface of chitosan and 50% -SiCM. Analysis of the physicochemical effects of the SiCMs revealed that t he cells were dominantly affected by the surface hydrophobicity rather than by the zeta potential, as well as by the mixing ratio between chitosan and silica. The met contact angles of 50%-SiCM and chitosan, which were 68 deg rees and 65 degrees, respectively, were found to be suitable for adhesion a nd growth of Both the epithelial 293 cells and fibroblast IMR-90 cells. A h ydrophobic surface at 65 degrees-68 degrees was also effective for the prod uction of tPA by IMR-90 cells, whereas the tPA activity of 293 cells reache d its highest level on the SiCM with a wet contact angle of 63 degrees. The se results suggest that a suitable adhesion strength is a significant facto r in the expression of tPA by cells contacting an implant biomaterial.