Fluoride Treatment and In Vitro Corrosion Behavior of Mg-Nd-Y-Zn-Zr Alloys Type

Fluoride conversion coatings on Mg present many advantages, among which one can find the reduction of the corrosion rate under “in vivo” or “in vitro” conditions and the promotion of the calcium phosphate deposition. Moreover, the fluoride ions released from MgF2 do not present cytotoxic effects and inhibit the biofilm formation, and thus these treated alloys are very suitable for cardiovascular stents and biodegradable orthopedic implants. In this paper, the biodegradation behavior of four new magnesium biodegradable alloys that have been developed in the laboratory conditions, before and after surface modifications by fluoride conversion (and sandblasting) coatings, are analyzed. We performed structural and surface analysis (XRD, SEM, contact angle) before and after applying different surface treatments. Furthermore, we studied the electrochemical behavior and biodegradation of all experimental samples after immersion test performed in NaCl solution. For a better evaluation, we also used LM and SEM for evaluation of the corroded samples after immersion test. The results showed an improved corrosion resistance for HF treated alloy in the NaCl solution. The chemical composition, uniformity, thickness and stability of the layers generated on the surface of the alloys significantly influence their corrosion behavior. Our study reveals that HF treatment is a beneficial way to improve the biofunctional properties required for the studied magnesium alloys to be used as biomaterials for manufacturing the orthopedic implants.

Recent Advances in Polyurethane/POSS Hybrids for Biomedical Applications

Advanced organic-inorganic materials-composites, nanocomposites, and hybrids with various compositions offer unique properties required for biomedical applications. One of the most promising inorganic (nano)additives are polyhedral oligomeric silsesquioxanes (POSS); their biocompatibility, non-toxicity, and phase separation ability that modifies the material porosity are fundamental properties required in modern biomedical applications. When incorporated, chemically or physically, into polyurethane matrices, they substantially change polymer properties, including mechanical properties, surface characteristics, and bioactivity. Hence, this review is dedicated to POSS-PU composites that have recently been developed for applications in the biomedical field. First, different modes of POSS incorporation into PU structure have been presented, then recent developments of PU/POSS hybrids as bio-active composites for scaffolds, cardiovascular stents, valves, and membranes, as well as in bio-imaging and cancer treatment, have been described. Finally, characterization and methods of modification routes of polyurethane-based materials with silsesquioxanes were presented.

Method to determine particle release during long-term loading for assessment of coating durability of cardiovascular stents

Many catheters and vascular implants are coated to increase biocompatibility or to reduce friction during catheter based implantation. Several regulations require assessment of coating durability over the implant’s life time. An in vitro method for stent testing is presented to measure released particulate matter at defined inspection intervals. The method was validated using polystyrene microspheres with a size of 10, 25 and 50 μm to check for particle recovery (n=6). Two cleaning steps followed. Particle counting was performed by light obscuration method. The recovery rate was 103±5% (10μm), 94±4% (25 μm) and 78±12% (50 μm), respectively, meeting the requirements of FDA guidance documents (i.e. FDA 1545). Less than 3% of the particles were found in the cleaning solutions. The method using a fixed volume during stent loading can be adapted to all durability testers where tubes are used to fix the stents (radial pulsatile, bending, axial compression, torsion).

Surface Machining of Stainless Steel Cardiovascular Stents by Fluid Abrasive Machining and Electropolishing

The typical manufacturing process of tubular metallic cardiovascular stents includes laser cutting, sand blasting, acid pickling, electropolishing, surface passivation, and cleaning. The most commonly used material for cardiovascular stents is stainless steel, such as SUS 304 and SUS 316. After the laser cutting process, substantial improvement of the stent surface morphology is required to obtain acceptable surface roughness, edge roundness, and reduction of surface defects. This study focuses on a novel post-treatment method of fluid abrasive machining to replace the conventional sand blasting and acid pickling processes, resulting in the surface smoothness and edge roundness that are suitable for cardiovascular stent fabrication. The dross deposition and striations retained after laser cutting can be significantly removed with fluid abrasive machining. Both DC current and pulse current electropolishing techniques were performed to attain the final surface and structural quality after the fluid abrasive machining process. The experimental results show that an extremely fine surface roughness and a satisfactory edge roundness can be achieved for stents through both DC current and pulse current electropolishing. The pulse electropolishing process is more effective than the DC current electropolishing process to achieve edge roundness with less weight removal.