Mechanical Properties and Corrosion Rate of ZnAg3 as a Novel Bioabsorbable Material for Osteosynthesis.

Osteosynthesis in fracture treatment typically uses hardware that remains in the patient's body, which brings a permanent risk of negative side effects such as foreign body reactions or chronic inflammation. Bioabsorbable materials, however, can degrade and slowly be replaced by autologous bone tissue. A suitable material is requested to offer great biocompatibility alongside excellent mechanical properties and a reasonable corrosion rate. Zinc-silver alloys provide these characteristics, which makes them a promising candidate for research. This study investigated the aptitude as a bioabsorbable implant of a novel zinc-silver alloy containing 3.3 wt% silver (ZnAg3). Here, the tensile strength as well as the corrosion rate in PBS solution (phosphate buffered solution) of ZnAg3 were assessed. Furthermore, shear tests, including fatigue and quasi-static testing, were conducted with ZnAg3 and magnesium pins (MAGNEZIX®, Syntellix AG, Hannover, Germany), which are already in clinical use. The detected corrosion rate of 0.10 mm/year for ZnAg3 was within the proposed range for bioabsorbable implants. With a tensile strength of 237.5 ± 2.12 MPa and a shear strength of 144.8 ± 13.2 N, ZnAg3 satisfied the mechanical requirements for bioabsorbable implants. The fatigue testing did not show any significant difference between ZnAg3 and magnesium pins, whereas both materials withstood the cyclic loading. Thus, the results support the assumption that ZnAg3 is qualified for further investigation.

Biocompatibility Assessment of Zinc Alloys as a New Potential Material for Bioabsorbable Implants for Osteosynthesis.

In the last several years, zinc and its alloys have come into focus as bioabsorbable materials by qualifying themselves with an excellent corrosion rate, mechanical properties, anti-bacterial effects. and considerable biocompatibility. In this study, the biocompatibility of zinc-silver alloys containing 3.3 wt% silver (ZnAg3) was assessed by evaluating their cell viability, the proliferation rate, and the cell toxicity. Two alloys were investigated in which one was phosphated and the other was non-phosphated. The alloys were tested on human osteoblasts (hOb), which are, to a large extent, responsible for bone formation and healing processes. The performance of the phosphated alloy did not differ significantly from the non-phosphated alloy. The results showed a promising biocompatibility with hOb for both alloys equally in all conducted assays, qualifying ZnAg3 for further investigations such as in vivo studies.

Fixation Performance of Bioabsorbable Zn-6Ag Pins for Osteosynthesis.

Bioabsorbable implants have become the focus of the latest research for new bone implant materials. With favorable characteristics such as compatible mechanical characteristics, no long-term side effects, and even osteogenesis enhancing properties they seem to be the future of osteosynthesis. Besides these characteristics, they must perform on the same level as traditional implant materials regarding their mechanical support for bone healing. A particular focus in the research for bioabsorbable implants has been on metal alloys, as these have particularly good mechanical properties such as excellent maximum force and high stability. This study focused on the shear strength of new bioabsorbable zinc and magnesium pins in comparison to traditional implants such as K-wires and cancellous bone screws in bone-implant connections. During quasi-static and fatigue loading experiments, magnesium pins (MAGNEZIX, Syntellix AG, Hannover, Germany) and new zinc silver pins (Zn-6Ag) by Limedion (Limedion GmbH., Mannheim, Germany) were compared with conventional osteosynthetic materials. The pins made of the new bioabsorbable alloys withstood the cyclic loads to the same extent as the conventional osteosynthesis materials. In the quasi-static loading, it was shown that the novel Zn-6Ag from Limedion has the same shear strength as the magnesium pin from Syntellix, which is already in clinical use. In addition, the zinc pin showed significantly better shear strength compared to osteosynthesis with K-wires (p < 0.05).

Mechanical Analysis and Corrosion Analysis of Zinc Alloys for Bioabsorbable Implants for Osteosynthesis.

Zinc alloys have recently been researched intensely for their great properties as bioabsorbable implants for osteosynthesis. Pure zinc (Zn) itself has relatively poor strength, which makes it insufficient for most clinical use. Research has already proven that the mechanical strength of zinc can be enhanced significantly by alloying it with silver. This study evaluated zinc silver alloys (ZnAg) as well as novel zinc silver titanium alloys (ZnAgTi) regarding their mechanical properties for the use as bioabsorbable implants. Compared to pure zinc the mechanical strength was enhanced significantly for all tested zinc alloys. The elastic properties were only enhanced significantly for the zinc silver alloys ZnAg6 and ZnAg9. Regarding target values for orthopedic implants proposed in literature, the best mechanical properties were measured for the ZnAg3Ti1 alloy with an ultimate tensile strength of 262 MPa and an elongation at fracture of 16%. Besides the mechanical properties, the corrosion rates are important for bioabsorbable implants. This study tested the corrosion rates of zinc alloys in PBS solution (phosphate buffered solution) with electrochemical corrosion measurement. Zinc and its alloys showed favorable corrosion rates, especially in comparison to magnesium, which has a much lower degradation rate and no buildup of hydrogen gas pockets during the process. Altogether, this makes zinc alloys highly favorable for use as material for bioabsorbable implants for osteosynthesis.

Bioresorbable zinc stent with ultra-thin center struts attenuates stent jail in porcine femoral artery bifurcations.

INTRODUCTION: An ultra-thin, fracture-resistant and bioresorbable stent may be advantageous for provisional stenting in vessel bifurcations, if catheter passage and side-branch post-dilatation is facilitated to prevent a 'stent jail' by struts obstructing the orifice of a major side branch. MATERIAL AND METHODS: We studied a highly radiopaque, slowly bioresorbable zinc alloy stent characterized by a novel design of a radiopaque-marked region of ultra-thin struts in the center of the stent. The stent is characterized by an extended range flexibility and high fracture resistance. Zn-stents and Zn-drug eluting stents (DES) were implanted opposite to rigid Nitinol stents into both femoral artery bifurcations of 21 juvenile pigs, followed for one and three months and studied by angiography and histomorphometry.Results and conclusion: Bare Zn-stents with thinner stent struts showed less neointimal hyperplasia compared to Zn-stents with thicker struts. Neointimal formation was further reduced by 12% in Zn-alloy DES. Both, bare Zn-stents and Zn-DES, can be precisely positioned into the femoral artery bifurcation, allowing easy balloon catheter passage through the very thin strut mesh. Side branch orifices remained open after Zn-stent deployment without stent jailing. No stent fractures or particles emboli occurred after the deployment. A Zn-stent with ultra-thin center struts may be useful for provisional stenting in vessel bifurcations.

Zn-alloy provides a novel platform for mechanically stable bioresorbable vascular stents.

Metallic Zn alloys have recently gained interest as potential candidates for developing platforms of bioresorbable vascular stents (BVS). Previous studies revealed that Mg alloys used for BVS can degrade too early, whereas PLLA materials may fail to provide effective scaffolding properties. Here we report on results of a new bioresorbable, metallic stent made from a Zn-Ag alloy studied in a porcine animal model of thrombosis and restenosis. While the tensile strength (MPa) of Zn-3Ag was higher than that of PLLA and resembled Mg's (WE43), fracture elongation (%) of Zn-3Ag was much greater (18-fold) than the PLLA's or Mg alloy's (WE43). Zn-3Ag exposed to HAoSMC culture medium for 30 days revealed degradation elements consisting of Zn, O, N, C, P, and Na at a 6 nm surface depth. Platelet adhesion rates and blood biocompatibility did not differ between Zn-3Ag, PLLA, Mg (WE43), and non-resorbable Nitinol (NiTi) stent materials. Balloon-expandable Zn-3Ag alloy BVS implanted into iliofemoral arteries of 15 juvenile domestic pigs were easily visible fluoroscopically at implantation, and their bioresorption was readily detectable via X-ray over time. Histologically, arteries with Zn-3Ag BVS were completely endothelialized, covered with neointima, and were patent at 1, 3, and 6 months follow-up with no signs of stent thrombosis. Zn-3Ag alloy appears to be a promising material platform for the fabrication of a new generation of bioresorbable vascular stents.

Biocompatibility of a novel zinc stent with a closed-cell-design.

Biomaterials made of zinc have been widely described to be antioxidative, hypothrombogenic, antiinflammatory and antiproliferative. Additionally in vivo zinc is toxic only in high concentrations and can completely be metabolized in vivo. Due to these properties zinc based vascular stents might be able to reduce the rate of restenosis in comparison to bare metal stents and zinc stents might be also able to limit the foreign body reaction. In the presented study we tested the biocompatibility and degradability of a stent made of zinc and characterized by a closed-cell-design to achieve high opening force and to increase stent stiffness. After 100 days of enzymatic and hydrolytic degradation in 15 ml blood serum (fetal calf serum) a significant loss of weight (1.72 wt% ) was measured. Zinc was compared to other metals in terms of degradation rates. After six weeks of incubation in physiologic sodium chloride solution zinc showed the slowest degradation time, 6 times less than stainless steel and 4 times less than magnesium. In the tests for cytotoxic effects the degraded zinc stent caused no changes in the LDH-release and cell membrane integrity (3T3 cells, mouse fibroblasts) respectively, in the cell activity/proliferation (MTS assay) and in the morphological characteristics of the cells and cell layers in comparison to the control material (polystyrene). Based on these results the tested zinc stent proved to be non-cytotoxic and to be characterized by degradation characteristics which might be advantageous in comparison to magnesium and stainless steel.