Next-generation biomedical implants using additive manufacturing of complex, cellular and functional mesh arrays

TLDR

Complex functional biocompatible mesh arrays are of particular interest for biomedical implants. The study examines patient‑specific bone implants for knee, hip, and femoral applications fabricated by electron‑beam melting additive manufacturing. The authors use electron‑beam melting to fabricate Ti‑6Al‑4V implants with functionally graded mesh cells, tailoring densities through region‑specific cell designs, and evaluate the resulting microstructure and mechanical properties via resonant frequency, damping, microindentation, and CT‑guided CAD modeling. Optimized interface densities promote bone ingrowth, enabling cementless implant components.

Abstract

In this paper, we examine prospects for the manufacture of patient-specific biomedical implants replacing hard tissues (bone), particularly knee and hip stems and large bone (femoral) intramedullary rods, using additive manufacturing (AM) by electron beam melting (EBM). Of particular interest is the fabrication of complex functional (biocompatible) mesh arrays. Mesh elements or unit cells can be divided into different regions in order to use different cell designs in different areas of the component to produce various or continually varying (functionally graded) mesh densities. Numerous design elements have been used to fabricate prototypes by AM using EBM of Ti-6Al-4V powders, where the densities have been compared with the elastic (Young) moduli determined by resonant frequency and damping analysis. Density optimization at the bone–implant interface can allow for bone ingrowth and cementless implant components. Computerized tomography (CT) scans of metal (aluminium alloy) foam have also allowed for the building of Ti-6Al-4V foams by embedding the digital-layered scans in computer-aided design or software models for EBM. Variations in mesh complexity and especially strut (or truss) dimensions alter the cooling and solidification rate, which alters the α -phase (hexagonal close-packed) microstructure by creating mixtures of α / α ′ (martensite) observed by optical and electron metallography. Microindentation hardness measurements are characteristic of these microstructures and microstructure mixtures ( α / α ′) and sizes.