Browsing by Author "Voss, Andrea"
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- 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.
- ItemEffect of Selective Laser Melting on Microstructure, Mechanical, and Corrosion Properties of Biodegradable FeMnCS for Implant Applications(Weinheim : Wiley-VCH Verl., 2020) Hufenbach, Julia; Sander, Jan; Kochta, Fabian; Pilz, Stefan; Voss, Andrea; Kühn, Uta; Gebert, AnnettSelective laser melting (SLM) of biodegradable metallic materials offers a great potential for manufacturing customized implants. Herein, SLM processing of a novel Fe–30Mn–1C–0.02S twinning-induced plasticity (TWIP) alloy and the resulting structural, mechanical, and corrosion properties are presented. The occurring rapid solidification results in a fine-grained austenitic microstructure with mainly homogeneous element distribution, which is investigated by scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD) as well as X-ray diffraction (XRD). By processing the alloy via SLM, significantly higher strengths under tensile and compressive load in comparison with those for the as-cast counterpart and a 316L reference steel are achieved. Electrochemical corrosion tests in a simulated body fluid (SBF) indicate a moderate corrosion activity, and a beneficial uniform degradation is shown in immersion tests in SBF. Regarding the envisaged application for vascular implants, SLM-processed stent prototypes out of the novel alloy are presented and a first functionality test is shown. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemElectrodeposition of Sr-substituted hydroxyapatite on low modulus beta-type Ti-45Nb and effect on in vitro Sr release and cell response(Amsterdam : Elsevier, 2019) Schmidt, Romy; Gebert, Annett; Schumacher, Matthias; Hoffmann, Volker; Voss, Andrea; Pilz, Stefan; Uhlemann, Margitta; Lode, Anja; Gelinsky, MichaelBeta-type Ti-based alloys are promising new materials for bone implants owing to their excellent mechanical biofunctionality and biocompatibility. For treatment of fractures in case of systemic diseases like osteoporosis the generation of implant surfaces which actively support the problematic bone healing is a most important aspect. This work aimed at developing suitable approaches for electrodeposition of Sr-substituted hydroxyapatite (Srx-HAp) coatings onto Ti-45Nb. Potentiodynamic polarization measurements in electrolytes with 1.67 mmol/L Ca(NO3)2, which was substituted by 0, 10, 50 and 100% Sr(NO3)2, and 1 mmol/L NH4H2PO4 at 333 K revealed the basic reaction steps for OH– and PO4 3− formation needed for the chemical precipitation of Srx-HAp. Studies under potentiostatic control confirmed that partial or complete substitution of Ca2+- by Sr2+-ions in solution has a significant effect on the complex reaction process. High Sr2+-ion contents yield intermediate phases and a subsequent growth of more refined Srx-HAp coatings. Upon galvanostatic pulse-deposition higher reaction rates are controlled and in all electrolytes very fine needle-like crystalline coatings are obtained. With XRD the incorporation of Sr-species in the hexagonal HAp lattice is evidenced. Coatings formed in electrolytes with 10 and 50% Sr-nitrate were chemically analyzed with EDX mapping and GD-OES depth profiling. Only a fraction of the Sr-ions in solution is incorporated into the Srx-HAp coatings. Therein, the Sr-distribution is laterally homogeneous but non-homogeneous along the cross-section. Increasing Sr-content retards the coating thickness growth. Most promising coatings formed in the electrolyte with 10% Sr-nitrate were employed for Ca, P and Sr release analysis in Tris-Buffered Saline (150 mM NaCl, pH 7.6) at 310 K. At a sample surface: solution volume ratio of 1:200, after 24 h the amount of released Sr-ions was about 30–35% of that determined in the deposited Srx-HAp coating. In vitro studies with human bone marrow stromal cells (hBMSC) revealed that the released Sr-ions led to a significantly enhanced cell proliferation and osteogenic differentiation and that the Sr-HAp surface supported cell adhesion indicating its excellent cytocompatibility. © 2019 The Authors