Photoelastic Analysis of Relationship between Internal Stress and Cell Attachment

Objectives: Since biomaterial applications are introduced to oral rehabilitation, researchers have increasing interest as to how to have cells integrate onto implants efficiently. In 1965, Carter first discovered the correlation between cell attachment and chemotaxis, factors affecting the attachment and migration of cells such as phototaxis, galvanotaxis, geotaxis, mechanical stress, pore size, and roughness etc. have continuously been discussed over years. However, the effects of internal stress distribution within the substrate itself (ex. implant) on cell attachment have not yet been systematic investigated. Thus, the objective of this research is to analyze the relationship between the distribution of internal stress within the substrate and cell attachment. Methods: There are a variety of biomaterials introduced into medical field, such as metallic materials (ex. titanium), polymeric materials (ex. poly(L-lactide)), etc.. This study uses poly(L-lactide)(PLLA) as substrate. PLLA is clinically accepted, able to be used in implant surgery, and possesses good biocompatibility. To alternate the internal stress of PLLA discs, discs were set at various temperature and time of polymerization. The distributions of internal stress were examined by photoelastic method. NIH/3T3 fibroblast cells were cultured on PLLA discs, and cell distributions at high-stress region and low-stress region were compared after 36 hours. Results: Our results demonstrated that the cell number at low-stress region is 256.67% larger than high-stress region (p<0.01). Furthermore, there is no significant difference (p>0.05) in cell number between the two regions with equal stress. Conclusions: The results of this study indicate that the distributions of internal stress of the substrate (i.e. the implant itself) do affect the behavior of early cell attachment. These results give more insight into the interaction behavior between cell and substrate. It will serve as an important reference for future clinical study.