The Optimization of a Porous Ti6Al4V Bone Construct Using Additive Manufacturing

Abstract

Patient specific implants are becoming viable treatment options in some orthopaedic applications through advances in additive manufacturing and 3D printing techniques. One potential application is for treatment of segmental bone defects, particularly in patients suffering from bone cancer. Current treatment options are: Amputation, megaprosthesis, or allografts. These treatments are often highly invasive, may require a partial/full joint replacement and are limited by mechanical properties, which affect the life of the implant. The Ti6Al4V implant proposed in this research was designed to fit a mid-diaphyseal segmental bone defect, mimic the mechanical properties of bone, facilitate osseointegration and reduce wear at the bone-implant surface. Computer-Aided Designs (CAD) were constructed of patient-specific Ti6Al4V implants based off the geometry of (1) a patient suffering from a lesion on the mid-diaphysis of the femur and, (2) a 4th Generation right Sawbones® femur. Pore size and shape were assessed using Finite Element Analyses (FEA) software. The overall porosity was maximized to develop an implant with an effective elastic modulus equivalent to bone. The two implants were then fabricated using Direct Metal Laser Sintering (DMLS). The geometry of the physical implant was measured and mechanically loaded under compression to validate the computational model. FEA was an effective tool for optimizing the pore size, shape and overall porosity of the implant, which indicated that 1mm circular pores in three orthogonal planes at an overall porosity of 54-76% would produce an implant with an effective elastic modulus equivalent to cortical bone. Geometric analysis of the 3D printed implant indicated the pore sizes were reduced by an average of 16% as compared to the computational model and that there was a correlation between the size and precision of the pore and the orientation of the implant during the additive build. Compression testing of the implants indicated that they had an effective elastic modulus of 20.8 and 10.5 GPa, which is within the accepted values for cortical bone.