Experimental model for observation of micromotion in cell culture.

It is known that the micromotion between implant and bone inhibits direct bone growth either on or into implant surfaces in vivo. Nevertheless, biocompatibility tests in vitro of biomaterials for bone/implant interfaces are mainly performed under static conditions. This work describes a dynamic, in vitro experimental simulation of the effect of mutual, small-scale implant surface-tissue displacement on adhered cells. Disks of simulated tissue (PVP hydrogel) were subjected to cyclic micromotion ranging from 0 at the center to 1000 microm at the periphery at approximately 13 Hz, relative to biomaterial surfaces or tissue culture polystyrene controls populated with human osteoblasts in standard tissue culture plate wells. The effect of the interfacial micromotion on the number of cells remaining attached was quantitated by XTT assay. The activity level of the remaining cells was determined by an alkaline phosphatase assay, and cell stress was evaluated by nitrogen assay. Significantly more cells (ANOVA) became detached from similarly prepared surfaces of titanium, hydroxyapatite, and alumina compared to the polystyrene control, and detachment from alumina was greater than for the other two materials. The activity of the remaining attached cells was lower as compared to the static (no micromotion) control but not significantly different among the biomaterials. All nitrogen assays were negative, suggesting minimal cell stress occurred. The method is proposed as a useful and discriminating in vitro tool for biocompatibility studies focused on cell adhesion to biomaterials under conditions related to those which exist at the implant/bone interface in vivo, and it allows subsequent studies of the still-viable cells by other methods.