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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[...]

Environmental degradation of Ti alloys in artificial saliva and a role of fluorides


  Titanium and its alloys possess specific properties, among them high corrosion resistance and biocompatibility. Bioinertness of Ti assed in short time tests seems almost perfect: the corrosion rate in simulated body fluids varied between 0.01 and 0.1 μg/cm2d, and after 48 weeks from an implantation of the Ti6Al4V alloy into animal body, only traces of metallic elements were found in tissues [1]. The corrosion resistance significantly depends on acidity of solution: in lactic and formic acids the general corrosion of the Ti6Al4V alloy was observed after 4 weeks [2]. Even if titanium is bioinert in neutral solutions, corrosion may appear in physiological saliva [3]. The saliva can be assumed as relatively aggressive environment [4]. The weight corrosion rate in artificial saliva was assessed as 0.28 g/cm2. At pH = 3 or lower, the passive current density for commercially pure Ti increased markedly with decreasing pH. The corrosion was observed [5] in saliva as dependent on a surface state, with a few times higher corrosion after sandblasting than after polishing. Fluoride ions are aggressive ions for the oxide layers of Ti and its alloys. Their presence may initiate localized degradation by pitting and crevice corrosion. Such conditions may happen as the toothpastes and prophylactic gels contain fluoride ions. So far results are confusing. As shown in [6], the effect of fluoride ions was weak at pH from 6.15 to 3.0 but below the last value Ti and its alloys suffered from localized corrosion. On the other side, even if titanium revealed ion releases 0.01÷0.1 μg/cm2.d, similar as gold alloys, the ion release increased to 500 μg/cm2.d in presence of fluoride [7]. Low pH values accelerate this effect even more. Therefore it is recommended to avoid the presence of fluoride or to reduce contact time. In another paper [8] the strong effect of presence of fluorides on corrosion density was observed for pure Ti and Ti6Al4V[...]

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[...]

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