Lattice structures used for medical implants offer advantages related to weight reduction, osseointegration, and minimization of stress shielding. This paper intends to study and to compare the mechanical behavior of three different lattice structures: tetrahedral vertex centroid (TVC), hexagonal prism vertex centroid (HPVC), and cubic diamond (CD), that are designed to be incorporated in a shoulder hemiprosthesis. The unit cell configurations were generated using nTopology Element Pro software with a uniform strut thickness of 0.5 mm. Fifteen cuboid samples of 25mm × 25mm × 15 mm, five for each unit cell configuration, were additively manufactured using Direct Light Printing (DLP) technology with a layer height of 50μm and a XY resolution of 73μm. The mechanical behavior of the 3D printed lattice structures was examined by performing mechanical compression testing. E-silicone (methacrylated silicone) was used for the fabrication of samples, and its mechanical properties were obtained from experimental tensile testing of dog-bone samples. A methodology for size optimization of lattice unit cells is provided, and the optimization is achieved using nTopology Element Pro software. The generated results are analyzed, and the HPVC configuration is selected to be incorporated in the further design of prosthesis for bone cancer patients.
Lattice structures offer great benefits when employed in medical implants for cell attachment and growth (osseointegration), minimization of stress shielding phenomena, and weight reduction. This study is focused on a proof of concept for developing a generic shoulder hemi-prosthesis, from a patient-specific case of a 46 years old male with a tumor on the upper part of his humerus. A personalized biomodel was designed and a lattice structure was integrated in its middle portion, to lighten weight without affecting humerus’ mechanical response. To select the most appropriate lattice structure, three different configurations were initially tested: Tetrahedral Vertex Centroid (TVC), Hexagonal Prism Vertex Centroid (HPVC), and Cubic Diamond (CD). They were fabricated in resin by digital light processing and its mechanical behavior was studied via compression testing and finite element modeling (FEM). The selected structure according to the results was the HPVC, which was integrated in a digital twin of the biomodel to validate its mechanical performance through FEM but substituting the bone material model with a biocompatible titanium alloy (Ti6Al4V) suitable for prostheses fabrication. Results of the simulation showed acceptable levels of Von Mises stresses (325 MPa max.), below the elastic limit of the titanium alloys, and a better response (52 MPa max.) in a model with equivalent elastic properties, with stress performance in the same order of magnitude than the showed in bone’s material model.
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