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Development of Ti-based materials for alloplastic implants

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The Ti-based biomaterials, light materials of highest corrosion resistance and biocompatibility [1], have also some disadvantages. They may slowly dissolve and result in serious illnesses if the Ti-Al-V alloy is applied [2]. The Ti alloys have Young modulus too high as compared to that of a bone [3], fatigue limit too low [4], and the bone-implant interface strength too weak [5]. The new no Al and no V alloys are developed [6]. This paper is aimed at demonstrating the previous results and current research work in this area made by Advanced Biomaterials Research Group at the Faculty of Mechanical Engineering, GUT. EARLY AND LATE REACTIONS TO METALLIC IMPLANTS The research is made on possible allergies of patients to titanium and Ti alloys. The cases of such allergies were discovered in hospital examinations, mainly for stainless steels but also a case for Ti alloy was found. The biodegradation can result from different origin: presence of bacteria [1÷3], wear of surgical tools, improper material [3, 4]. Even for Ti alloy severe degradation can occur (Fig. 1). The modelisation of change in biological environment of an implant following inflammation process and assessment of metallic ions` release by special tests and sensitive chemical techniques are performed. EFFECTS OF BACTERIA ON CORROSION One of possible determinants of early allergies and inflammation processes can be presence of bacteria [1, 4, 5]. The exposure tests in biological environments have shown that different bacteria may have different and substantial effect on corrosion resistance of titanium alloy. Especially, in presence of Staphylococcus aureus no important corrosion occurs and Enterobacter cloacae presence results in fast corrosion - Figure 2. The results are explained by a model under elaboration in which biofilm of different thickness, permeability and distance from a metal surface affects composition and pH of solution adjacent to a metal, creating c[...]

Nowe metody badań korozji i pękania wodorowego materiałów eksploatowanych w umiarkowanych warunkach

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Przedstawiono założenia testu niskocyklowego zmęczenia nawodorowanego materiału oraz oceny odporności korozyjnej biomateriału bazującej na oznaczaniu ilości metalu w roztworze. Słowa kluczowe: biomateriały, degradacja wodorowa, korozja New research methods of corrosion and hydrogen degradation of materials used in moderate conditions The outlines of low cycle fatigues test of moderately hydrogen charged and of an assessment of corrosion resistance of biomaterial based on an assessment of quantity of dissolved metal are proposed. Keywords: biomaterials, corrosion, hydrogen degradation.Obecne metody badań niszczenia korozyjnego i mechano-korozyjnego są najczęściej testami przyspieszonymi, stosunkowo mało wiarygodnymi w przypadku oceny materiałów pracujących w łagodnych warunkach i dość odpornych na degradacje. Przykłady to korozja naprężeniowa w elektrowniach jądrowych [1], pękanie stali stopowych w olejach [2], czy korozja implantów tytanowych wcześniejsza od przewidywanej [3, 4]. Zachodzi więc potrzeba opracowania nowych testów opartych na analizie przewidywanych warunków eksploatacji, znajomości mechanizmów korozji i wiarygodności testów oraz utrzymania w miarę szybkiego czasu oceny, czemu poświęcony jest ten artykuł. 2. Metodyka badań podatności tworzyw metalowych na degradację wodorową Obecne procedury badawcze przewidują stosowanie metody rozciągania ze stałą małą prędkością (Slow Strain Rate Test SSRT) jako metody referencyjnej, a następnie metody rozciągania przy stałym obciążeniu (Constant Load CL) lub odkształceniu (Constant Elongation CE) jako zbliżonych do warunków rzeczywistych i pozwalających na określenie, czy materiał ulegnie w praktyce degradacji wodorowej. Warunki narzucane przez me[...]

Surface treatment of porous Ti13Nb13Zr alloy for biomedical applications

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The Ti and its alloys are considered as the best biomaterials for load-bearing applications. As the most popular Ti6Al4V alloy may be potentially harmful [1, 2], the number of another alloys have been proposed or implemented, e.g. Ti6Al7Nb, Ti29Nb13Ta4.6Zr, Ti13Nb13Zr, Ti15Mo5Zr3Al, Ti15Zr4Nb4Ta [3]. They are widely used, especially for load-carrying implants. However, in order to achieve the bioactivity, long term stability and bioactivity, new solutions are looking for. They may include: an use of scaffold/ porous structures, anticorrosion and nanooxidation, deposition of hydroxyapatite coatings with immersion techniques. The scaffold metallic materials possessing open porous structure are recently used to enhance bioactivity, i.e. the tissue in-growth rate and long term stability are considered. The pore size of 30÷400 μm seems the most plausible [4]. The greater pore size enhances the faster tissue growth, the smaller - better adhesion strength. Porous structures in a bulk or within the surface layer can be obtained by various methods: powder metallurgy (P/M) with or without space holders, rapid prototyping with an use of selective laser melting (SLM) or electron beam melting (EBM), plasma spraying etc. [5]. Corrosion rate of Ti measured may be substantial [6]; in electrochemical and gravimetric tests changes in simulated body fluids (SBF) between 0.01 and 0.1 μg/cm2·day, and after 48 weeks of an exposure of the Ti6Al4V alloy implant only traces of Ti, Al i V can be found in body tissues [7]. At low pH corrosion increases: in lactic and formic acids general corrosion occurs already after 3 weeks [8]. Ti alloys degrade in presence of chlorides saline and artificial saliva [9] and in phosphate buffered saline (PBS) [10]. Increase in roughness [11], increase in temperature, low pH and wear conditions increase corrosion rate of Ti alloys [6]. Improvement of corrosion resistance and bioactivity of titanium and it[...]

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