Browsing by Author "Vrana, N. E."

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Open Access
An in-silico corrosion model for biomedical applications for coupling with in-vitro biocompatibility tests for estimation of long-term effects
(Frontiers Media, 2021-09-07) Šušteršič, T.; Şimsek, Görkem Muttalip; Yapıcı, Güney Güven; Nikolić, M.; Vulović, R.; Filipovic, N.; Vrana, N. E.; Mechanical Engineering; YAPICI, Güney Güven; Şimsek, Görkem Muttalip
The release of metal particles and ions due to wear and corrosion is one of the main underlying reasons for the long-term complications of implantable metallic implants. The rather short-term focus of the established in-vitro biocompatibility tests cannot take into account such effects. Corrosion behavior of metallic implants mostly investigated in in-vitro body-like environments for long time periods and their coupling with long-term in-vitro experiments are not practical. Mathematical modeling and modeling the corrosion mechanisms of metals and alloys is receiving a considerable attention to make predictions in particular for long term applications by decreasing the required experimental duration. By using such in-silico approaches, the corrosion conditions for later stages can be mimicked immediately in in-vitro experiments. For this end, we have developed a mathematical model for multi-pit corrosion based on Cellular Automata (CA). The model consists of two sub-models, corrosion initialization and corrosion progression, each driven by a set of rules. The model takes into account several environmental factors (pH, temperature, potential difference, etc.), as well as stochastic component, present in phenomena such as corrosion. The selection of NiTi was based on the risk of Ni release from the implant surface as it leads to immune reactions. We have also performed experiments with Nickel Titanium (NiTi) shape memory alloys. The images both from simulation and experiments can be analyzed using a set of statistical methods, also investigated in this paper (mean corrosion, standard deviation, entropy etc.). For more widespread implementation, both simulation model, as well as analysis of output images are implemented as a web tool. Described methodology could be applied to any metal provided that the parameters for the model are available. Such tool can help biomedical researchers to test their new metallic implant systems at different time points with respect to ion release and corrosion and couple the obtained information directly with in-vitro tests.
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PVA/gelatin-based hydrogel coating of nickel-titanium alloy for improved tissue-implant interface
(Springer, 2021-05) Şimşek, Görkem Muttalip; Barthes, J.; Muller, C.; McGuinness, G. B.; Vrana, N. E.; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Şimşek, Görkem Muttalip
Nickel-titanium shape memory alloys have attracted notable interest for biomedical applications due to their unique properties. However, there are still some concerns on the potential release of nickel ions causing adverse reactions in-vivo at high concentrations. In this work, samples were coated with a polyvinyl alcohol/gelatin hydrogel. Coating stability, corrosion resistance and biocompatibility were investigated. Coated samples exhibited similar shape memory response to that of the uncoated substrates in wire form. Additionally, the hydrogel coating led to a decrease in the surface temperature and significantly improved the corrosion resistance of the shape memory substrate. The presence of the hydrogel layer does not affect the biocompatibility of the alloy while providing a semi-degradable, hydrophilic surface that forms a cushion at the tissue-implant interfaces.