Effect of Process Parameters and Geometry on the Quasi-Static and Dynamic Behavior of Additively Manufactured Lower-Extremity Metallic Lattice Bone Implants: A Design-of-Experiment Study

Additively manufactured metallic lattice biomaterials have revolutionized the mechanical properties of lower-extremity bone and joint implants. Most designers have followed a quasi-static approach, where material properties are solely represented by their elastic modulus. In reality, however, the human body experiences repeated dynamic and impact loads in vivo , and bone acts as a passive shock absorber and wave modulator. Most importantly, bone cells sense no load under quasi-static loading and must rather be subjected to impact loads at frequencies near their natural frequencies and high enough accelerations to conduct optimum mechanotransduction. This indicates the necessity of developing a dynamic design strategy that further considers damping and natural frequency. This research is an attempt to study the dynamic performance of selective laser melted lattice implants with the help of design of experiments and finite-element method (FEM). In many cases, lattice implants exhibit up to 80% similar values of elastic modulus and natural frequency to the bone. Regarding the damping, however, the similarity rarely reaches 10%. For the most part, the dynamic material properties of the implants are more significantly affected by their geometry and printability rather than process parameters. Damping decreases with power and increases with porosity and scanning speed. Natural frequency increases with power and remains almost constant with scanning speed. Generally, any change to the process parameters and geometry that improves the elastic modulus affects the natural frequency and damping directly and inversely, respectively. Capturing the main trends of dynamic behavior successfully, FEM accuracy is controlled by the geometry and hence can be distorted by manufacturing defects. All in all, there is a balance between the elastic modulus and damping. Dynamic performance improves with porosity, albeit up to an optimum point.