Evaluation of Bone Fixation Implants

This research investigates the effects of the human body on the mechanical, chemical, and morphological properties of the surface of internal fixation devices. Stainless steel and titanium devices that had failed were provided from the Shandong Provincial Hospital in China, along with controls: implants that had never been used. Comparative study was conducted by evaluating properties of these implants before and after implanting.

The first part of the research was simulation, and a model of the human femur was analyzed in Solidworks. The stress analysis software simulated the stress distribution, the strain distribution, and the deformation pattern. Two cases were simulated: walking and car accident. The simulations showed the points of highest stress and led to the analysis of the implants that were used in those regions.

The next part of the research was to experimentally examine the properties and behavior of materials. Test samples fell into one of three categories: stainless steel femur implant, stainless steel tibia implant, and titanium femur implant. Material properties were characterized and effects of the human body on each of these groups were studied. Hardness was measured using Vickers hardness indentation. Surface roughness was analyzed using light interferometric technique. Potentiodynamic polarization analysis was performed to evaluate corrosive behavior before and after implanting. Scratch tests were conducted to evaluate wear resistance and the microstructure was analyzed to further understand the morphological changes that occurred of implanted samples.

Results showed that the human body generally degraded the material properties of the stainless steel femur implant. There were no measurable effects of the same on stainless steel tibia and on titanium alloy.