Optimum Design of Printable Tunable Stiffness Metamaterial for Bone Healing

A tunable stiffness bone rod was designed, optimized, and 3D printed to address the common shortcomings of existing bone rods in the healing of long fractured bones. The common deficiencies of existing bone fixations are high stiffness, thereby negligible flexibility in deformation for best bone growth results, and stress-shielding effect. Our novel design framework provides the surgeons with ready-for-3D-printing patient-specific designs, optimized to have desired force-displacement response with a stopping mechanism for preventing further deformation under higher than usual loads such as falling. The framework is a design optimization based on the multi-objective genetic algorithm (GA) optimization to quantify the objectives, tunning the varied stiffness while minimizing the maximum Mises stress of the model to avoid plastic and permanent deformation of the bone rod. The optimum design computational framework of tunable stiffness material presented in this paper is not specific for a tibia bone rod. It can be used for any application where bilinear stiffness is desirable.