Feasibility evaluation of a new lattice for porous surface design in additive manufacturing medical implants under interfacial tensile bonded testing

Porous titanium implant surfaces fabricated with suitable porosity and size using additive manufacturing (AM) can enhance bone–implant stability. There is a critical need to understand the biomechanical performance of porous (lattice) type implants to improve bone ingrowth efficiency and interfacial bonded strength. This study proposes a new lattice type implant with appropriate/favorable physiological environment within the lattice for bone ingrowth and increasing bone-implant bonded strength. A unit (1mm³ cube) YM lattice with 65 % porosity and average pore size of 750 µm was designed as a 3D spherical structure to increase bone cell growth capacity with multiple-corners for accepting cell clustering and the transport of fluids, nutrients and the expelling of impurities between these interconnected through-holes. The finite element (FE) sub-modeling technique was used to investigate the implant-bone interface micro mechanical behavior, to include lattice pillars, bone within/around lattices for four different lattice types with YMU, YMR (YM lattice without deformation and with 30 % deformation), DU and DR (Diamond lattice without deformation and with 30 % deformation). The DU and YMR lattice implants (6 × 6 × 3 mm³ block) were selected and fabricated using a Ti6Al4V AM (each n = 5) and implanted into the distal right femurs of 10 rabbits for 8 weeks for observation. The interface tensile bonded strength test was performed after the rabbits were sacrificed. No lattice implant slipped in any of the rabbits after surgery. This confirms postoperative radiographs. The test results showed that both the bonded force and strength of the YMR lattice were found significantly higher than those of DU. The corresponding values were 113.14 ± 21.96 N and 5.39 ± 1.04 MPa for the YMR lattice and 41.41 ± 15.32 N and 1.97 ± 0.73 MPa for the DU lattice. This study proposed a YMR lattice that presented a suitable bone ingrowth environment and interfacial bond strength test for surface porous design for the AM medical implant.