There is an increasing interest in biodegradable metal implants made from magnesium (Mg), iron (Fe), zinc (Zn) and their alloys because they are well tolerated in vivo and have mechanical properties that approach those of non-degradable metals. In particular, Zn and its alloys show the potential to be the next generation of biodegradable materials for medical implants. However, Zn has not been as well-studied as Mg, especially for stent applications. Manufacturing stents by laser cutting has become an industry standard. Nevertheless, the use of this approach with Zn faces some challenges, such as generating thermal stress, dross sticking on the device, surface oxidation, and the need for expensive thin-walled Zn tubing and post-treatment. All of these challenges motivated us to employ photo-chemical etching for fabricating different designs of Zn (99.95% pure) stents. The stents were constructed with different strut patterns, made by photo-chemical etching, and mechanically tested to evaluate radial forces. Stents with rhombus design patterns showed a promising 0.167N/mm radial force, which was comparable to Mg-based stents. In vitro studies were conducted with uncoated Zn stents as control and Parylene C-coated Zn stents to determine corrosion rates. The Parylene C coating reduced the corrosion rate by 50% compared to uncoated stents. In vivo studies were carried out by implanting photo-chemically etched, uncoated Zn stent segments subcutaneously in a C57BL/6 mice model. Histological analyses provided favorable data about the surrounding tissue status, as well as nerve and blood vessel responses near the implant, providing insights into the in vivo degradation of the metal struts. All of these experiments confirmed that Zn has the potential for use in biodegradable stent applications.

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The new nanocrystalline composition was synthesized using NiSO 4 and MoO 3 and PPDA (p-phenylenediamine) via the hydrothermal method. The structure, morphology and photoluminescence property of nanocrystal were studied using X-ray diffraction (XRD), Fourier transform infra red (FT-IR) spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) spectra, thermogravimetric analysis (TGA-DTA) and energy-dispersive X-ray spectroscopy (EDX). The effect of factors such as type and concentration of initial materials, pH values, temperature and reaction duration on the structure and morphology of nanocrystals was investigated in the preparation of composition. The results show that the pH of the initial solution affects the size of the prepared nanocrystals; the size of the crystals is increased and the morphology of the nanostructures is changed with the increment in pH value. According to the obtained results, neutral or low alkaline conditions of pH are more favorable for the formation of the nanocrystals. The obtained nanocrystal shows an intense PL emission at room temperature with a maximum peak at 461 nm and excitation at the wavelength of 300 nm. TGA and DTA analysis display a total weight loss of 13.42%.

During the last decade, magnesium and its alloys have been extensively studied to develop a new generation of biodegradable medical implants. The fast degradation rate of pure magnesium and related alloys in the physiological environment poses significant challenges to devices made of these materials for biomedical applications. In this study, we have designed and fabricated biodegradable helical stents made of AZ31 magnesium alloy, and have explored theirs in vitro corrosion behavior in Dulbecco's Modified Eagle's Medium (DMEM). The corrosion rate was significantly reduced by surface modifications of the helical stent, achieved through applying a biocompatible Parylene C polymer coating, or via chemical etching of the devices in inorganic solutions. The corrosion rates of the coated AZ31 Mg helical stents were compared, with uncoated samples used as a control. The results achieved indicated that all tested surface modifications successfully inhibited metal corrosion rates in vitro. Materials coated with Parylene C coating revealed a maximum corrosion rate reduction of 70% to 85% in DMEM solution.

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