Characterization and modeling of additively manufactured Ti-6Al-4V alloy with modified surfaces for medical applications

Abstract

In the field of biomedical implants, additively manufactured titanium alloys, particularly Ti-6Al-4V, hold significant potential due to their biocompatibility and mechanical properties. This study focuses on the characterization and modeling of additively manufactured Ti-6Al-4V alloy for dental and maxillofacial implants, emphasizing fatigue behavior, surface modification, and their combined effects on cyto- and osseocompatibility. Experimental methods, including tensile, compression, and fatigue testing, were applied alongside in silico simulations to assess the long-term mechanical performance of the material. Surface properties were further modified through sandblasting and coating techniques to enhance cell adhesion and proliferation. By using in-vitro methods, the cytocompatibility of the coatings and materials was examined followed by in-vivo tests to determine osseocompatibility. Results demonstrated that appropriate surface roughness and modifications are essential in optimizing osseointegration, while the layer-by-layer additive manufacturing process influenced the fatigue life and stability. These findings contribute to the development of patient-specific implants, optimizing both mechanical integrity and biological integration for enhanced clinical outcomes. This work summarizes the investigations on additively manufactured Ti-6Al-4V alloy of the research unit 5250 "Mechanism-based characterization and modeling of permanent and bioresorbable implants with tailored functionality based on innovative in vivo, in vitro and in silico methods" funded by the Germany Research Foundation (DFG).

Keywords: Ti-6Al-4V alloy; additive manufacturing; dental implants; fatigue behavior; finite element method; osseointegration; surface modification.

FIGURE 1

Additive manufacturing build job design of Ti-6Al-4V alloy: (a) Specimens for tensile and compression testing; (b) Discs for cell testing; dimensions of Ti-6Al-4V specimens for (c) tensile, compression and fatigue testing; (d) machined discs; (e) testing setup for investigations of Ti-6Al-4V.

FIGURE 2

Boundary conditions for the hourglass specimen: fixed boundary conditions at the bottom (blue) and displacement boundary condition at the top (yellow).

FIGURE 3

(a) Quasi-static tensile and (b) compression tests of Ti-6Al-4V alloy.

FIGURE 4

(a) Microstructure after heat treatment and (b) experimental S-N (Woehler) curve of Ti-6Al-4V alloy.

FIGURE 5

SEM images of (a, d) MTi surface (b, e) SBTi surface (c, f) AMTi15 surface; uncoated (upper row) and PEM coated (lower row).

FIGURE 6

Cell viability of (a, d) L929 murine fibroblast (b, e) MC3T3 preosteoblasts; and (c, f) human dental pulp stem cells (hDPSCs) on toxic positive control (white columns), non-toxic negative control (dark grey columns), non-coated AMTi discs with roughness 12 μm, 15 μm and 17 µm (light gray columns), and PAA/PAH-coated AMTi discs with roughness 12 μm, 15 μm and 17 µm (light gray hatched columns), estimated by LDH assay (a-c) and XTT assay (d-f), (* designates values that are significantly different, p < 0.05).

FIGURE 7

(a) NHOst viability (relative to the positive control) after 24 h of cultivation (white columns), showing the extent of cell adhesion and after 72 h of cultivation (gray columns), showing the extent of cell proliferation, examined on MTi, SBTi and AMTi discs, non-coated (normal bars) and coated with PEM coating (hatched bars) (* designates values that are significantly different, p < 0.05). SEM images of NHOst cultured for 24 h (upper row) and 72 h (bottom row) on Ti-6Al-4V discs with increasing roughness: (b, e) MTi, (c, f) SBTi, and (d, g) AMTi. Magnification 1,200×.

FIGURE 8

Representative histological microphotographs of the tissue reactions to the additive manufactured Ti-6Al-4V discs (uncoated- AMTi) at day 10 (left column) (a,c,e) and day 30 (b,d,f) post-implantation (right column) within the subcutaneous connective tissue (CT). Black arrows = macrophages, red arrows = blood vessels, green arrows = granulocytes, yellow arrows = lymphocytes (HE-stainings, magnification x400, scalebars = 20 µm).