The Effect of Ca on In Vitro Behavior of Biodegradable Zn-Fe Alloy in Simulated Physiological Environments

Highly plastic Zn-0.3Ca alloy for guided bone regeneration membrane: Breaking the trade-off between antibacterial ability and biocompatibility

A common problem for Zn alloys is the trade-off between antibacterial ability and biocompatibility. This paper proposes a strategy to solve this problem by increasing release ratio of Ca2+ ions, which is realized by significant refinement of CaZn13 particles through bottom circulating water-cooled casting (BCWC) and rolling. Compared with conventionally fabricated Zn-0.3Ca alloy, the BCWC-rolled alloy shows higher antibacterial abilities against E. coli and S. aureus, meanwhile much less toxicity to MC3T3-E1 cells. Additionally, plasticity, degradation uniformity, and ability to induce osteogenic differentiation in vitro of the alloy are improved. The elongation up to 49 %, which is the highest among Zn alloys with Ca, and is achieved since the sizes of CaZn13 particles and Zn grains are small and close. As a result, the long-standing problem of low formability of Zn alloys containing Ca has also been solved due to the elimination of large CaZn13 particles. The BCWC-rolled alloy is a promising candidate of making GBR membrane.

Methods for improving the properties of zinc for the application of biodegradable vascular stents

Biodegradable stents can support vessels for an extended period, maintain vascular patency, and progressively degrade once vascular remodeling is completed, thereby reducing the constraints of traditional metal stents. An ideal degradable stent must have good mechanical properties, degradation behavior, and biocompatibility. Zinc has become a new type of biodegradable metal after magnesium and iron, owing to its suitable degradation rate and good biocompatibility. However, zinc's poor strength and ductility make it unsuitable as a vascular stent material. Therefore, this paper reviewed the primary methods for improving the overall properties of zinc. By discussing the mechanical properties, degradation behavior, and biocompatibility of various improvement strategies, we found that alloying is the most common, simple, and effective method to improve mechanical properties. Deformation processing can further improve the mechanical properties by changing the microstructures of zinc alloys. Surface modification is an important means to improve the biological activity, blood compatibility and corrosion resistance of zinc alloys. Meanwhile, structural design can not only improve the mechanical properties of the vascular stents, but also endow the stents with special properties such as negative Poisson 's ratio. Manufacturing zinc alloys with excellent degradation properties, improved mechanical properties and strong biocompatibility and exploring their mechanism of interaction with the human body remain areas for future research.

Cytotoxicity of Biodegradable Zinc and Its Alloys: A Systematic Review

Zinc-based biodegradable metals (BMs) have been developed for biomedical implant materials. However, the cytotoxicity of Zn and its alloys has caused controversy. This work aims to investigate whether Zn and its alloys possess cytotoxic effects and the corresponding influence factors. According to the guidelines of the PRISMA statement, an electronic combined hand search was conducted to retrieve articles published in PubMed, Web of Science, and Scopus (2013.1-2023.2) following the PICOS strategy. Eighty-six eligible articles were included. The quality of the included toxicity studies was assessed utilizing the ToxRTool. Among the included articles, extract tests were performed in 83 studies, and direct contact tests were conducted in 18 studies. According to the results of this review, the cytotoxicity of Zn-based BMs is mainly determined by three factors, namely, Zn-based materials, tested cells, and test system. Notably, Zn and its alloys did not exhibit cytotoxic effects under certain test conditions, but significant heterogeneity existed in the implementation of the cytotoxicity evaluation. Furthermore, there is currently a relatively lower quality of current cytotoxicity evaluation in Zn-based BMs owing to the adoption of nonuniform standards. Establishing a standardized in vitro toxicity assessment system for Zn-based BMs is required for future investigations.

The Effect of Mn on the Mechanical Properties and In Vitro Behavior of Biodegradable Zn-2%Fe Alloy

The attractiveness of Zn-based alloys as structural materials for biodegradable implants mainly relates to their excellent biocompatibility, critical physiological roles in the human body and excellent antibacterial properties. Furthermore, in in vivo conditions, they do not tend to produce hydrogen gas (as occurs in the case of Mg-based alloys) or voluminous oxide (as occurs in Fe-based alloys). However, the main disadvantages of Zn-based alloys are their reduced mechanical properties and their tendency to provoke undesirable fibrous encapsulation due to their relatively high standard reduction potential. The issue of fibrous encapsulation was previously addressed by the authors via the development of the Zn-2%Fe alloy that was selected as the base alloy for this study. This development assumed that the addition of Fe to pure Zn can create a microgalvanic effect between the Delta phase (Zn11Fe) and the Zn-matrix that significantly increases the biodegradation rate of the alloy. The aim of the present study is to examine the effect of up to 0.8% Mn on the mechanical properties of biodegradable Zn-2%Fe alloy and to evaluate the corrosion behavior and cytotoxicity performance in in vitro conditions. The selection of Mn as an alloying element is related to its vital role in the synthesis of proteins and the activation of enzyme systems, as well as the fact that Mn is not considered to be a toxic element. Microstructure characterization was carried out by optical microscopy and scanning electron microscopy (SEM), while phase analysis was obtained by X-ray diffraction (XRD). Mechanical properties were examined in terms of hardness and tensile strength, while corrosion performance and electrochemical behavior were assessed by immersion tests, open circuit potential examination, potentiodynamic polarization analysis and impedance spectroscopy. All the in vitro corrosion testing was performed in a simulated physiological environment in the form of a phosphate-buffered saline (PBS) solution. The cytotoxicity performance was evaluated by indirect cell viability analysis, carried out according to the ISO 10993-5/12 standard using Mus musculus 4T1 cells. The obtained results clearly demonstrate the strengthening effect of the biodegradable Zn-2%Fe alloy due to Mn addition. The effect of Mn on in vitro corrosion degradation was insignificant, while in parallel Mn had a favorable effect on indirect cell viability.

Designing Advanced Biomedical Biodegradable Mg Alloys: A Review

The increased demand for alloys that can serve as implantation devices with outstanding bio-properties has led to the development of numerous biomedical Mg-based alloys. These alloys have been extensively investigated for their performance in living tissue with mixed results. Hence, there are still major concerns regarding the use of magnesium alloys for such applications. Among the issues raised are elevated corrosion rates, hydrogen generation, and the maintenance of mechanical integrity for designated healing times. In addition, toxicity can arise from the addition of alloying elements that are intended to improve the mechanical integrity and corrosion resistance of Mg alloys. The current work reviews the recent advances in the development of Mg alloys for applications as bio-absorbable materials in living organic environments. In particular, it attempts to develop a roadmap of effective factors that can be utilized when designing Mg alloys. Among the factors reviewed are the effects of alloying additions and processing methods on the exhibited mechanical properties and corrosion rates in simulated bio-fluids used in biomedical applications.

Stress Corrosion Analysis and Direct Cell Viability of Biodegradable Zn-Fe-Ca Alloy in In-Vitro Conditions

Due to the excellent biocompatibility of Zn and Zn-based alloys, researchers have shown great interest in developing biodegradable implants based on zinc. Furthermore, zinc is an essential component of many enzymes and proteins. The human body requires ~15 mg of Zn per day, and there is minimal concern for systemic toxicity from a small zinc-based cardiovascular implant, such as an arterial stent. However, biodegradable Zn-based implants have been shown to provoke local fibrous encapsulation reactions that may isolate the implant from its surrounding environment and interfere with implant function. The development of biodegradable implants made from Zn-Fe-Ca alloy was designed to overcome the problem of fibrous encapsulation. In a previous study made by the authors, the Zn-Fe-Ca system demonstrated a suitable corrosion rate that was higher than that of pure Zn and Zn-Fe alloy. The Zn-Fe-Ca system also showed adequate mechanical properties and a unique microstructure that contained a secondary Ca-reach phase. This has raised the promise that the tested alloy could serve as a biodegradable implant metal. The present study was conducted to further evaluate this promising Zn alloy. Here, we assessed the material’s corrosion performance in terms of cyclic potentiodynamic polarization analysis and stress corrosion behavior in terms of slow strain rate testing (SSRT). We also assessed the ability of cells to survive on the alloy surface by direct cell culture test. The results indicate that the alloy develops pitting corrosion, but not stress corrosion under phosphate-buffered saline (PBS) and air environment. The direct cell viability test demonstrates the successful adherence and growth of cells on the alloy surface.

Limitation of Water-Soluble Tetrazolium Salt for the Cytocompatibility Evaluation of Zinc-Based Metals

Zinc (Zn) and its alloys have been regarded as promising biodegradable metals. The standardized cytotoxicity evaluation is a mandatory step to screen the biocompatibility of novel Zn and its alloys. Nevertheless, the suitability of the tetrazolium-based assay in the direct contact test for some metallic biomaterials (i.e., magnesium and manganese) is questionable. In this study, our results demonstrate an obvious inconsistency between qualitative observation via fluorescence staining and quantitative assessment using water-soluble tetrazolium salt (CCK-8). Subsequent experiments revealed that Zn and pre-treated Zn can directly convert tetrazolium salts to formazan, falsifying the cytotoxicity results. Therefore, we conclude that the CCK-8 assay is not suitable for evaluating the cytotoxicity of biodegradable Zn-based metals in the direct contact test.

In vitro behavior of bioactive hybrid implant composed of additively manufactured titanium alloy lattice infiltrated with Mg-based alloy

We have developed a novel bioactive hybrid metallic implant that integrates the beneficial characteristics of a permanent matrix and a biodegradable substance. Such a combination may generate a material system that evolves into a porous structure within weeks to months following implantation and can be used to form strong interfacial bonding and osseointegration for orthopedic and dental applications. Presently, traditional technologies such as casting, powder metallurgy and plastic forming have limited ability to produce the complex bioactive implant structures that are required in practical applications. The present study aimed to develop an innovative bioactive TiMg (BTiMg) hybrid system using a Ti-lattice (Ti-6Al-4 V) produced by an additive manufacturing (AM) process, in combination with a new Mg-based alloy (Mg-2.4%Nd -0.6%Y -0.3%Zr) as a biodegradable filling material. We evaluated the in-vitro behavior of the BTiMg system in a simulated physiological environment, along with cytotoxicity assessment. The microstructure was evaluated by scanning electron microscopy and X-ray diffraction, mechanical properties were examined in terms of compressive strength, environmental performance analysis was conducted by electrochemical testing using potentiodynamic polarization and impedance spectroscopy (EIS), and cytotoxicity characteristics were assessed by indirect cell viability analysis. The results demonstrated the feasibility to produce geometrically complex implants by AM technology, as well as the strength and non-cytotoxic effects of the BTiMg system. Benefits included a relatively high ultimate compressive strength (UCS) and a high yield point (YP), along with an adequate cell viability response in the range between 70 and 120%.