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- ItemExperimental and numerical characterization of imperfect additively manufactured lattices based on triply periodic minimal surfaces(Amsterdam [u.a.] : Elsevier Science, 2023) Günther, Fabian; Pilz, Stefan; Hirsch, Franz; Wagner, Markus; Kästner, Markus; Gebert, Annett; Zimmermann, MartinaLattices based on triply periodic minimal surfaces (TPMS) are attracting increasing interest in seminal industries such as bone tissue engineering due to their excellent structure-property relationships. However, the potential can only be exploited if their structural integrity is ensured. This requires a fundamental understanding of the impact of imperfections that arise during additive manufacturing. Therefore, in the present study, the structure-property relationships of eight TPMS lattices, including their imperfections, are investigated experimentally and numerically. In particular, the focus is on biomimetic network TPMS lattices of the type Schoen I-WP and Gyroid, which are fabricated by laser powder bed fusion from the biocompatible alloy Ti-42Nb. The experimental studies include computed tomography measurements and compression tests. The results highlight the importance of process-related imperfections on the mechanical performance of TPMS lattices. In the numerical work, firstly the as-built morphology is artificially reconstructed before finite element analyses are performed. Here, the reconstruction procedure previously developed by the same authors is used and validated on a larger experimental matrix before more advanced calculations are conducted. Specifically, the reconstruction reduces the numerical overestimation of stiffness from up to 341% to a maximum of 26% and that of yield strength from 66% to 12%. Given a high simulation accuracy and flexibility, the presented procedure can become a key factor in the future design process of TPMS lattices.
- ItemSurface Modified β-Ti-18Mo-6Nb-5Ta (wt%) Alloy for Bone Implant Applications: Composite Characterization and Cytocompatibility Assessment(Basel : MDPI, 2023) Escobar, Michael; Careta, Oriol; Fernández Navas, Nora; Bartkowska, Aleksandra; Alberta, Ludovico Andrea; Fornell, Jordina; Solsona, Pau; Gemming, Thomas; Gebert, Annett; Ibáñez, Elena; Blanquer, Andreu; Nogués, Carme; Sort, Jordi; Pellicer, EvaCommercially available titanium alloys such as Ti-6Al-4V are established in clinical use as load-bearing bone implant materials. However, concerns about the toxic effects of vanadium and aluminum have prompted the development of Al- and V-free β-Ti alloys. Herein, a new alloy composed of non-toxic elements, namely Ti-18Mo-6Nb-5Ta (wt%), has been fabricated by arc melting. The resulting single β-phase alloy shows improved mechanical properties (Young’s modulus and hardness) and similar corrosion behavior in simulated body fluid when compared with commercial Ti-6Al-4V. To increase the cell proliferation capability of the new biomaterial, the surface of Ti-18Mo-6Nb-5Ta was modified by electrodepositing calcium phosphate (CaP) ceramic layers. Coatings with a Ca/P ratio of 1.47 were obtained at pulse current densities, −jc, of 1.8–8.2 mA/cm2, followed by 48 h of NaOH post-treatment. The thickness of the coatings has been measured by scanning electron microscopy from an ion beam cut, resulting in an average thickness of about 5 μm. Finally, cytocompatibility and cell adhesion have been evaluated using the osteosarcoma cell line Saos-2, demonstrating good biocompatibility and enhanced cell proliferation on the CaP-modified Ti-18Mo-6Nb-5Ta material compared with the bare alloy, even outperforming their CaP-modified Ti-6-Al-4V counterparts.
- ItemEffect of minor gallium addition on corrosion, passivity, and antibacterial behaviour of novel β-type Ti–Nb alloys(Sao Paulo : ABM, 2023) Akman, Adnan; Alberta, Ludovico Andrea; Giraldo-Osorno, Paula Milena; Turner, Adam Benedict; Hantusch, Martin; Palmquist, Anders; Trobos, Margarita; Calin, Mariana; Gebert, AnnettMetastable Ti–Nb alloys are promising bone-implant materials due to improved mechanical biofunctionality and biocompatibility. To overcome increasing bacterial infection risk, alloying with antibacterial elements is a promising strategy. This study investigates the effect of minor gallium (Ga) additions (4, 8 wt% Ga) to as-cast and solution-treated β-type Ti–45Nb-based alloy (96(Ti–45Nb)-4Ga, 92(Ti–45Nb)-8Ga (wt.%)) on corrosion and passive film properties, as well as cytocompatibility and antibacterial activity. The electrochemical properties were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses in phosphate-buffered saline (PBS). X-ray photoelectron spectroscopy (XPS) was performed to analyze the chemical composition of passive films. Early adhesion and viability of macrophages and Staphylococcus aureus were assessed by nucleocounting and colony-forming unit counting, respectively. The results showed that high corrosion resistance and passive film properties of Ti–45Nb are retained and even slightly improved with Ga. EIS results revealed that Ga addition improves the passive film resistance. XPS measurements of 92(Ti–45Nb)-8Ga show that the passive film contains Ti-, Nb- and Ga-based oxides, implying the formation of mixed (Ti–Nb-Ga) oxides. In addition, marginal Ga ion release rate was detected under free corrosion conditions. Therefore, it can be assumed that Ga species may contribute to passive film formation on Ga-containing alloys. The 92(Ti–45Nb)-8Ga elicited an antibacterial effect against S. aureus compared to cp-Ti at 4 h. Moreover, Ga-containing alloys showed good cytocompatibility with THP-1 macrophages at 24 h. In conclusion, it was demonstrated that Ga additions to Ti–45Nb are beneficial to corrosion resistance and showed promising initial host and bacterial interactions.
- ItemAcid Treatments of Ti-Based Metallic Glasses for Improving Corrosion Resistance in Implant Applications(Basel : MDPI, 2024) Fernández-Navas, Nora; Shtefan, Viktoriia; Hantusch, Martin; Gebert, AnnettTi-based bulk metallic glasses are promising materials for metallic bone implants, mainly due to their mechanical biofunctionality. A major drawback is their limited corrosion resistance, with high sensitivity to pitting. Thus, effective surface treatments for these alloys must be developed. This work investigates the electrochemical treatment feasibility of nitric acid (HNO3) solution for two bulk glass-forming alloys. The surface states obtained at different anodic potentials are characterized with electron microscopy and Auger electron spectroscopy. The corrosion behavior of the treated glassy alloys is analyzed via comparison to non-treated states in phosphate-buffered saline solution (PBS) at 37 °C. For the glassy Ti47Zr7.5Cu38Fe2.5Sn2Si1Ag2 alloy, the pre-treatment causes pseudo-dealloying, with a transformation from naturally passivated surfaces to Ti- and Zr-oxide nanoporous layers and Cu-species removal from the near-surface regions. This results in effective suppression of chloride-induced pitting in PBS. The glassy Ti40Zr10Cu34Pd14Sn2 alloy shows lower free corrosion activity in HNO3 and PBS due to Pd stabilizing its strong passivity. However, this alloy undergoes pitting under anodic conditions. Surface pre-treatment results in Cu depletion but causes enrichment of Pd species and non-homogeneous surface oxidation. Therefore, for this glassy alloy, pitting cannot be completely inhibited in PBS. Concluding, anodic treatments in HNO3 are more suitable for Pd-free glassy Ti-based alloys.
- ItemDesigning Gallium-Containing Hydroxyapatite Coatings on Low Modulus Beta Ti-45Nb Alloy(Basel : MDPI, 2023) Vishnu, Jithin; Voss, Andrea; Hoffmann, Volker; Alberta, Ludovico Andrea; Akman, Adnan; Shankar, Balakrishnan; Gebert, Annett; Calin, MarianaLow-modulus β-type Ti-45Nb alloy is a promising implant material due to its good mechanical biocompatibility, non-toxicity, and outstanding corrosion resistance. Its excellent chemical stability brings new challenges to chemical surface modification treatments, which are indispensable for both osteogenesis and antibacterial performance. Coatings containing metal ions as anti-microbial agents can be an effective way to reduce implant-associated infections caused by bacterial biofilm. Gallium ion (Ga3+) has the potential to reduce bacterial viability and biofilm formation on implant surfaces. In this study, a novel two-step process has been proposed for Ga3+ incorporation in hydroxyapatite (HAP) to develop bioactive and antibacterial surfaces on Ti-45Nb alloy. For the generation of bioactive surface states, HAP electrodeposition was conducted, followed by wet chemical immersion treatments in gallium nitrate (1 mM). Different buffers such as phosphate, sodium bicarbonate, ammonium acetate, and citrate were added to the solution to maintain a pH value in the range of 6.5–6.9. Coating morphology and HAP phases were retained after treatment with gallium nitrate, and Ga3+ ion presence on the surface up to 1 wt.% was confirmed. Combining Ga and HAP shows great promise to enable the local delivery of Ga3+ ions and consequent antibacterial protection during bone regeneration, without using growth factors or antibiotics.
- ItemTribocorrosion behavior of β-type Ti-Nb-Ga alloys in a physiological solution(Amsterdam [u.a.] : Elsevier Science, 2023) Alberta, Ludovico Andrea; Vishnu, Jithin; Douest, Yohan; Perrin, Kevin; Trunfio-Sfarghiu, Ana-Maria; Courtois, Nicolas; Gebert, Annett; Ter-Ovanessian, Benoit; Calin, MarianaTribo-electrochemical behavior in physiological solution of two β-type (100-x)(Ti-45Nb)-xGa (x = 4, 8 wt%) alloys, alongside β-Ti-45Nb and medical grade Ti-6Al-4V ELI, was investigated. Microstructure and mechanical behavior were evaluated by X-ray diffraction, microhardness and ultrasonic method. Tribocorrosion tests (open circuit potential, anodic potentiostatic tests) were performed using a reciprocating pin-on-disk tribometer under constant load. Degradation mechanisms are similar for the alloys: plastic deformation, delamination, abrasive and adhesive wear. Among the β-Ti-Nb alloys, an improved wear resistance with lower damage was remarked for β-92(Ti-45Nb)-8Ga alloy, attributed to increased microhardness. Content of Ga3+ ions released in the test solutions were found to be in very low amounts (few ppb). Addition of Ga to Ti-45Nb resulted in improved corrosion resistance under mechanical loading.