Porous Titanium by Additive Manufacturing: A Focus on Surfaces for Bone Integration
Abstract
:1. Introduction
2. Additive Manufacturing of Titanium Alloys
2.1. AM Processes for Ti-Based Materials
2.2. Microstructures of AM Titanium-Based Components
2.3. Mechanical Properties of AM Ti-Based Components
2.3.1. Tensile/Compressive Properties
2.3.2. Fatigue Properties
2.3.3. Hardness and Wear Properties
2.4. Defects in AM Ti-Based Components
3. Surface Modifications of AM Ti-Based Materials
4. Conclusions and Future Perspectives
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Material and AM Strategy | Surface Treatment | Surface Features | Biologica Response | Ref. |
---|---|---|---|---|
Ti6Al4V-EBM and SLM | Variation of the building angle (0°, 15°, 30°, 45°) and evaluation of surface features. No post treatments. | Spherical unmelted particles on all the surfaces. More particles aggregates on EBM samples. Slight decrease in particles with increasing building angle. SLM samples slightly more hydrophibic (CA = 113–133°) than EBM (CA = 91–111°), no significant effect of building angle. SLM samples showed lower roughness and negligible effect of the building angle, while EBM presented higher roughness which decreases, increasing the building angle. | Both materials support osteoblasts adhesion proliferation and differentiation. Cell adhesion is quite high on SLM surfaces, however the hydrphobicity induce cell clustering on the samples center. SLM samples accelerate cellular mineralization, especially with low building angles. | [20] |
Ti6Al4V-SLM | Sandblasting (SiC) or Vibratory finishing (Al2O3) of the top and bottom surfaces. | Sandblasting completely removes the unmelted particles, slightly reduces roughness and wettability, but it contaminates the surface with SiC. Vibratory finishing does not completely remove the surface unmelted particles and slightly reduces wettability. | A certain reduction in bacterial (S. epidermidis and P. aeruginosa) adhesion can be observed on sandblasted and vibratory finished surfaces. | [21] |
Ti6Al4V-SLM | Chemical polishing (HF-HNO3 solution) | Removal of unmelted particles from the surface. Reduction in most of the surface defects. Process parameters should be optimized for specific lattice structures in order to maintain the main geometrical features. | - | [22] |
Pure Ti (grade 2)-SLM |
| The heat treatment at 1300 °C melts the particles on the surface and smoothens it. A submicrometric surface texture appears after the chemical and heat treatment and uniformly also covers the inner surface of the pores. Chemically treated samples are completely covered by apatite after 3 days in Simulated Body Fluid (SBF). | In vivo implantation in rabbits evidences the ability of the chemically treated implants to promote direct bonding of bone and new bone formation on all the surfaces (even into pores). | [23] |
Pure Ti-SLM | Chemical treatment in mixed solution of H2SO4 and HCl at 70 °C | High bone bonding ability during in vivo test (rat implantation) | [24] | |
Pure Ti mesh-SLM |
| Trated surfaces are able to promote hydroxyapatite precipitation after 24 h in SBF. The surface treated with mixed acids shows microscale apatite while nanoscale apatite was observed on the other surfaces. | After 2 weeks implantation in rats significantly higher bone formation was observed on the surfaces treated with mixed acids and thermal treatment. | [25] |
Ti6Al4V-SLM | Plasma Electrolytic Oxidation (PEO) in electrolyte containing calcium acetate, calcium glycerophosphate, strontium acetate, and silver nanoparticles. | After PEO treatment the surface presents a microporos surface layer constituted of titanium oxide, hydroxyapatite and Sr-substituted hydroxyapatite and silver nanoparticles. Release of silver and strontium ions up to 28 days. | Strong antibacterial activity against S. aureus MRSA. Biocompatibility and osteogenic activity for osteoblasts. | [26] |
Ti6Al4V-SLM | Chemical treatment (hydrogen peroxide and hydrochloric acid) | Surface nanotexture superimposed to the typical SLM microtopography (unmelted particles). Significant improvement of surface wettability. | Osteoblast increased mineralization in vitro and increased bone contact in vivo at short times (2 weeks). | [27] |
Ti6Al4V-EBM | Coating with polycaprolactone (PCL) or polycaprolactone/hydroxyapatite by dip coating | Uniform coating of the porous structure with reduction in the surface roughness. Top surface porous for solvent evaporation. Possibility to use recycled Ti6Al4V particles. | Increased adhesion and proliferation of mesenchymal stem cells on the coated scaffolds. Higher penetration of cells in the porous structure for the coated samples. | [28] |
Ti6Al4V-SLM | Variation of SLM parameters and hydrothermal treatment in NaOH. | Variation of SLM parameters to tailor surface microtexture (stripy, bulbous or combined textures). Hydrothermal treatment in NaOH produces surface nanotexturing superimposed on microtexture but induce also Al2O3 particles precipitation. Surface treatments increase protein absorption. | Increased cell adhesion was observed on bulbous and stripy-bulbous combined microtextures. Cell proliferation and differentiation were enhanced by bulbosus structures and nanotextures. | [29] |
Ti6Al4V-xCu-SLM | - | Cu presence induces antibacterial activity, however the proposed technology is not effective to obtain nanotextures | - | [30] |
Ti6Al4V-SLM | Acid etching (HCl-H2SO4), chemical oxidation (HCl-H2O2) and thermochemical treatment (400 °C). | The complete process produced micro and sub-micrometric surface texture and growth of a surface anatase layer. | - | [31] |
Ti-Ta porous coating on Ti6Al4V by DED | Anodic oxidation | DED allows the production of a porous coating of Ti-Ta alloy on Ti6Al4V substrate. The elastic modulus is reduced compared to Ti6Al4V. Anodic oxidation produces surface nanotubes containing both Ti and Ta oxides. The modified surface induces apatite deposition in vitro. | The modified surface promotes osteoblasts adhesion in vitro and bone formation in vivo. | [32] |
Ti6Al4V SLM | High temperature thermal treatment (1050 °C), HCl etching in inert atmosphere and NaOH treatment. | High temperature thermal treatment homogenizes the microstructure and removes unmelted particles from the surface. HCl etching and NaOH chemical treatment produce surface nanotexture and allows hydroxyapatite coating after 14 days immersion in simulated body fluid. | - | [33] |
Ti6Al4V, SLM | Laser polishing | Optimized laser polishing reduces surface roughness eliminating unmelted particles and surface defects. Tensile properties are not affected while fatigue life is improved. | Improved osteoblast adhesion and proliferation | [34] |
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Ferraris, S.; Spriano, S. Porous Titanium by Additive Manufacturing: A Focus on Surfaces for Bone Integration. Metals 2021, 11, 1343. https://doi.org/10.3390/met11091343
Ferraris S, Spriano S. Porous Titanium by Additive Manufacturing: A Focus on Surfaces for Bone Integration. Metals. 2021; 11(9):1343. https://doi.org/10.3390/met11091343
Chicago/Turabian StyleFerraris, Sara, and Silvia Spriano. 2021. "Porous Titanium by Additive Manufacturing: A Focus on Surfaces for Bone Integration" Metals 11, no. 9: 1343. https://doi.org/10.3390/met11091343