Title

Additively Manufactured Ti-6Al-4V Biomimetic Lattice Structures for Patient-Specific Orthopedic Implants

Date of Award

2023

Degree Name

Ph.D. in Electrical and Computer Engineering

Department

Department of Electrical and Computer Engineering

Advisor/Chair

Amy Neidhard-Doll

Abstract

The development of patient-specific implants for reconstructive applications involving unique deformities or injuries has demonstrated the promise of additive manufacturing (AM) in the medical setting. Biomimetic lattice structures can facilitate internal bone growth due to their porous nature, which can reduce stress shielding and improve the lifespan of an implant. In addition, pulsed electromagnetic field therapy can be implemented to accelerate the osseointegration process internally in the lattice structures by improving cellular proliferation and attachment. In this research, cubic and body-centered cubic (BCC) unit cell geometries were 3D printed using selective laser melting and biocompatible Ti-6Al-4V feedstock powder. The lattices were designed with four different pore sizes (400, 500, 600, and 900 µm, representing 40-90% porosity in a 10 mm cube). Compression and tensile testing were performed to evaluate the mechanical properties of the lattice structures, with results compared to human cancellous bone. SEM microstructural characterization of the manufactured lattices exhibited deviations in AM pore sizes and strut diameters when compared to original CAD designs in nTopology. It was found that the elastic modulus of human cancellous bone (10 - 900 MPa) could be matched for both tensile (92.7 - 129.6 MPa) and compressive (185.2 - 996.1 MPa) elastic modulus of cubic and BCC lattices. BCC lattices exhibited higher compressive properties over cubic, whereas cubic lattices exhibited superior tensile properties over BCC. To determine the effects of porosity and unit cell geometry on the osteogenesis of human MG-63 osteoblastic cell lines in vitro, glucose consumption, alkaline phosphate (ALP), and end-of-culture cell count activity was analyzed as markers for osteogenic growth. The results indicated that lattices with a 900 µm pore size exhibited the highest glucose consumption and the greatest change in alkaline phosphate activity when compared to other pore sizes, for both strut geometries. On average, the cubic unit cell geometry exhibited higher glucose consumption, and a larger cell count when compared to their counterparts with body-centered cubic strut geometries. Irrespective of a particular pore size or unit cell geometry, it was found that all lattices can promote osteogenic growth. A pulsed electromagnetic field (PEMF) was then applied (15 Hz, 300 µs pulse width, 20 VPP, 0.5 mT field intensity) to cell cultures in vitro (2 hours/day for 14 days) and compared to non-PEMF stimulated controls. The results indicated that PEMF had a greater impact on glucose concentration than ALP activity for all lattices. This may indicate that at lower field intensities, PEMF had an increased effect on the early formation (surface attachment) stage of bone cell differentiation.

Keywords

Biomedical Engineering, Biomedical Research, Electromagnetics, Electrical Engineering, Mechanical Engineering, Biology, Biomimetic, Lattice Structures, Orthopedic, Additive Manufacturing, Selective Laser Melting, Pulsed Electromagnetic Field, MG-63, Osseointegration

Rights Statement

Copyright © 2023, author

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