The Impact of As-Built Surface Characteristics of Selective-Laser-Melted Ti-6Al-4V on Early Osteoblastic Response for Potential Dental Applications

Abstract

This study investigates the potential of Selective Laser Melting (SLM) to tailor the surface characteristics of Ti6Al4V directly during fabrication, eliminating the need for post-processing treatments potentially for dental implants. By adjusting the Volumetric Energy Density (VED) through controlled variations in the laser scanning speed, we achieved customized surface textures at both the micro- and nanoscale levels. SLM samples fabricated at moderate VED levels (50-100 W·mm³/s) exhibited optimized dual-scale surface roughness-a macro-roughness of up to 25.5-27.6 µm and micro-roughness of as low as 58.8-64.2 nm-resulting in significantly enhanced hydrophilicity, with water contact angles (WCAs) decreasing to ~62°, compared to ~80° on a standard grade 5 machined Ti6Al4V plate. The XPS analysis revealed that the surface oxygen content remains relatively stable at low VED values, with no significant increase. The surface topography plays a significant role in influencing the WCA, particularly when the VED values are low (below 200 W·mm³/s) during SLM, indicating the dominant effect of surface morphology over chemistry in these conditions. Biological assays using osteoblast-like MG-63 cells demonstrated that these as-built SLM surfaces supported a 1.5-fold-higher proliferation and improved cytoskeletal organization relative to the control, confirming the enhanced early cellular responses. These results highlight the capability of SLM to engineer bioactive implant surfaces through process-controlled morphology and chemistry, presenting a promising strategy for the next generation of dental implants suitable for immediate placement and osseointegration.

Keywords: Selective Laser Melting (SLM); TiAl6V4; dental implant; osteoblast; surface topography.

Figure 1

(a) Arrangement of SLM samples on a custom-designed holder. (b) Volumetric Energy Densities (VEDs) for different SLM samples.

Figure 2

Optical images of SLM samples (SLM-Ti1, SLM-Ti2, SLM-Ti3, and SLM-Ti4) (a–d); their corresponding low magnification SEM images (e–h); and corresponding high magnification SEM images (i–l). Arrows indicates insufficient melting, lack of fusion, defects, and porosity. Visual comparisons reveal clear differences in surface morphology as a function of VEDs. SLM-Ti1 and SLM-Ti2, produced at higher energy inputs, exhibit more uniform surfaces with smoother melt tracks and fewer defects. In contrast, SLM-Ti3 and SLM-Ti4 show signs of insufficient melting and increased surface irregularities, including lack of fusion, porosity, and partially bonded particles. Opposite to the trend observed at the macro-scale, SLM-Ti4 exhibits smoother fine-scale features at the micro-scale compared to the other groups. This behavior reflects a surface-smoothing effect induced by lower VED at micro-scale during the SLM process.

Figure 3

(a) Surface macro-roughness (Ra) values of Ti6Al4V samples fabricated by SLM at varying VEDs, compared to the polished control substrate. Results show a clear increase in surface roughness with higher VED, highlighting the influence of processing parameters on as-built surface morphology. (b) Percentage difference in macro-roughness measured along scanning directions parallel and perpendicular to the laser path for each SLM condition. The results emphasize the anisotropic nature of surface texture formation in SLM due to laser scanning strategy.

Figure 4

(a) Surface micro-roughness (Ra) values of Ti6Al4V samples fabricated via SLM at varying VEDs, compared to the control substrate. Unlike macro-roughness, micro-roughness decreases with increasing VED, indicating smoother fine-scale texture at higher energy inputs. (b) Percentage difference in micro-roughness measured along scanning directions parallel and perpendicular to the laser path for each SLM condition. Results demonstrate a reversed trend compared to macro-roughness, suggesting that fine-scale surface features are less anisotropic and more homogenized at higher energy levels.

Figure 5

Water contact angle (WCA) measurements of Ti6Al4V samples produced via SLM at different VEDs, compared to the control substrate. The results demonstrate that as-built SLM surfaces (except SLM-Ti1) exhibit significantly reduced WCAs relative to the control, indicating enhanced hydrophilicity.

Figure 6

XPS-based surface elemental composition of Ti6Al4V samples fabricated via Selective Laser Melting (SLM) under varying process conditions: (a) titanium (Ti), (b) oxygen (O), and (c) aluminum (Al) content for samples SLM-Ti1 through SLM-Ti4. A gradual increase in surface Ti content is observed with increasing energy input. In contrast, oxygen concentration rises from SLM-Ti1 to SLM-Ti3 and plateaus at SLM-Ti4, likely due to enhanced surface oxidation during laser exposure. Aluminum levels remain relatively stable with slight variation, indicating minimal surface segregation.

Figure 7

(a) Cell viability assessed by MTT assay for osteoblast-like MG-63 cells cultured on Ti6Al4V SLM samples and the control substrate after 24 h. Results show that all SLM-treated surfaces support high cell viability (SLM-Ti3 showed the highest viability), with no indication of cytotoxicity. (b) Cell proliferation assessed by BrdU assay for MG-63 cells cultured on the same samples for 24 h. Increased BrdU incorporation on select SLM-Ti3 and SLM-Ti4 surfaces indicates enhanced early-stage proliferation, highlighting the influence of as-built surface characteristics on osteoblastic response.

Figure 8

Fluorescence microscopy images of osteoblast-like MG-63 cells cultured for 24 h on Ti6Al4V samples: (a) machined TiAl6V4 control substrate, (b) SLM-Ti1, (c) SLM-Ti2, (d) SLM-Ti3, and (e) SLM-Ti4. Cells were stained with phalloidin to visualize F-actin, highlighting cytoskeletal organization and cell spreading. Compared to the control and lower-energy SLM surfaces, SLM-Ti3 and SLM-Ti4 exhibited the highest cell spreading and density, indicating that their dual-scale surface topography significantly enhances early cellular attachment and morphological development.