Objective selection of bone mimetic materials using impact microindentation

Background: Research and development for orthopedic medical devices, implants, surgical technique, and surgical education all require the appropriate selection of bone mimetic materials to align with the physiologic conditions. There is a critical need for an objective measure of material strength that can be collected, practically, on both bone mimetic materials and living human bone to improve mimetic material selection. Methods: This study stratifies commonly used synthetic materials in orthopedic research, as well as animal and human bone, using impact microindentation. The impact microindentation is performed with the OsteoProbe, an FDA-approved handheld medical device that can quantify material strength via the Bone Material Strength index in living human bone and mimetic materials non-destructively and in situ. Categories of Low, Mid, and High are created in reference to published living human tibia Bone Material Strength index ranges. All materials tested are classified into these categories for streamlined bone mimetic material selection. Results: Nine mimetic materials fell within the Low category. Two mimetic materials were classified as Mid and two as High. The male human cadaver cranium, radius, and femur fell within the High category; the male spine was classified in the Mid hardness category. In female cadaver tissue, the spine corresponded to the Low hardness category, the radius to Mid, and the femur to High. The ovine skull fell within the Mid category. Both the porcine thoracolumbar spine and bovine scapula fell within the High category. Conclusion: This unified scale of material strength allows for the comparison of human bones, animal bones and synthetic materials. By stratifying bone mimetics into three categories (Low, Mid, and High) of material strength based on healthy reference interval of living human Bone Material Strength index values, this study introduces a simplified framework to guide targeted material selection in orthopedic research and surgical training.