Biocompatibility of Orthopaedic Implants on Bone Forming Cells

Reindeer antler was studied for its possible use as a bone implant material. A molecular biological study showed that antler contains a growth factor promoting bone formation. Ectopic bone formation assay showed that antler is not an equally effective inducer as allogenic material. Ectopic bone formation assay was optimised for biocompatibility studies of orthopaedic NiTi implants. Ti-6Al-4V and stainless steel were used as reference materials. The assay showed differences in bone mineral densities, with superior qualities in NiTi. The rate of endochondral ossification varied between the implants, NiTi ossicles had larger cartilage and bone areas than ossicles of the two other materials. The cytocompatibility of NiTi was studied with three different methods. Cell viability, cell adhesion and TGF-β1 concentration were assessed in ROS-17/2.8 cell cultures. Cells grown on NiTi had better viability than cells grown on pure nickel or stainless steel. Cell attachment on the materials was studied with paxillin staining of focal contacts. The number of focal contacts was clearly higher in cells grown on NiTi than in cells grown on pure titanium, pure nickel or stainless steel. TGF-β1 concentration was measured with ELISA. The results showed that there was only some minor variation between NiTi, pure titanium and stainless steel. Nickel showed a lower TGF-β1 concentration. Taken together, these results suggest that NiTi is well tolerated by ROS-17/2.8 cells. The cytocompatibility of stainless steel is not so good as that of NiTi. The same tests were used to study the effects of the surface roughness of the implant on cytocompatibility. Three different surface roughness grades were compared in cell cultures on NiTi and titanium alloy discs. Titanium alloy was subjected to two different heat treatments, to compare the effects of the treatments on cytocompatibility. The studies showed that NiTi had a lesser impact on cell viability and attachment than titanium alloy. Further, rough NiTi was found to be a better tolerated surface than the others. In this study, heat treatment of titanium alloy at +850° C did not interfere with cell viability or attachment, as did the +1050° C treatment of the alloy. On the contrary, TGF-β1 concentrations decreased on the +850° C treated alloy and were approximately same on the +1050° C treated alloy and on NiTi.