A Cu(â ¡)-eluting coating through silk fibroin film on ZE21B alloy designed for in situ endotheliazation biofunction.

In the cardiovascular field, coating containing copper used to catalyze NO (nitric oxide) production on non-degradable metal surfaces have shown unparalleled expected performance, but there are few studies on biodegradable metal surfaces. Magnesium-based biodegradable metals have been applied in cardiovascular field in large-scale because of their excellent properties. In this study, the coating of copper loaded in silk fibroin is fabricated on biodegradable ZE21B alloy. Importantly, the different content of copper is set to investigate the effects of on the degradation performance and cell behavior of magnesium alloy. Through electrochemical and immersion experiments, it is found that high content of copper will accelerate the corrosion of magnesium alloy. The reason is the spontaneous micro-batteries between copper and magnesium with the different standard electrode potentials, that is, the galvanic corrosion accelerates the corrosion of magnesium alloy. Moreover, the coating formed through silk fibroin by the right amount copper not only have a protective effect on the ZE21B alloy substrate, but also promotes the adhesion and proliferation of endothelial cells in blood vessel micro-environment. The production of NO catalyzed by copper ions makes this trend more significant, and inhibits the excessive proliferation of smooth muscle cells. These findings can provide guidance for the amount of copper in the coating on the surface of biodegradable magnesium alloy used for cardiovascular stent purpose.

Effect of HA Content on Microstructure and Properties of Ti-27Nb-17Ta-8Zr/HA Composite.

In this paper, Ti-27Nb-17Ta-8Zr/HA series composite materials were prepared by spark plasma sintering (SPS) technology. The medical titanium alloy (Ti-27Nb-17Ta-8Zr) with good mechanical properties, wear resistance, and corrosion resistance was combined with the hydroxyapatite (HA) bioactive ceramic with high biological activity and bone-binding ability. Moreover, the density, microstructure evolution, metal/ceramic reaction, mechanical behavior, in vitro bioactivity, and influencing mechanisms of composite materials with different HA contents were studied. The research results indicate that all biological composite materials are composed of ß-Ti solution, α-Ti, and ceramic phases (Ti2O, CaTiO3, CaO, TixPy). With the increase of HA content, the compressive strength and yield strength of the composite material show a trend of first increasing, then decreasing, and then slowly increasing. After soaking in SBF artificial simulated body fluid for 5 days, the deposition of elements such as Ca and P on the surface significantly increased, while elements such as Ti, Nb, Ta, and Zr were evenly distributed in the matrix, demonstrating good in vitro mineralization ability and facilitating the attachment and growth of osteoblasts.

Design of single-phased magnesium alloys with typically high solubility rare earth elements for biomedical applications: Concept and proof.

Rare earth elements (REEs) have been long applied in magnesium alloys, among which the mischmetal-containing WE43 alloy has already got the CE mark approval for clinical application. A considerable amount of REEs (7 wt%) is needed in that multi-phased alloy to achieve a good combination of mechanical strength and corrosion resistance. However, the high complex RE addition accompanied with multiple second phases may bring the concern of biological hazards. Single-phased Mg-RE alloys with simpler compositions were proposed to improve the overall performance, i.e., "Simpler alloy, better performance". The single-phased microstructure can be successfully obtained with typical high-solubility REEs (Ho, Er or Lu) through traditional smelting, casting and extrusion in a wide compositional range. A good corrosion resistance with a macroscopically uniform corrosion mode was guaranteed by the homogeneously single-phased microstructure. The bimodal-grained structure with plenty of sub-grain microstructures allow us to minimize the RE addition to <1 wt%, without losing mechanical properties. The single-phased Mg-RE alloys show comparable mechanical properties to the clinically-proven Mg-based implants. They exhibited similar in-vitro and in-vivo performances (without local or systematic toxicity in SD-rats) compared to a high purity magnesium. In addition, metal elements in our single-phased alloys can be gradually excreted through the urinary system and digestive system, showing no consistent accumulation of RE in main organs, i.e., less burden on organs. The novel concept in this study focuses on the simplification of Mg-RE based alloys for biomedical purpose, and other biodegradable metals with single-phased microstructures are expected to be explored.

Recent advances on the mechanical behavior of zinc based biodegradable metals focusing on the strain softening phenomenon.

Zinc based biodegradable metals (BMs) show great potential to be used in various biomedical applications, owing to their superior biodegradability and biocompatibility. Some high-strength (ultimate tensile strength > 600 MPa) Zn based BMs have already been developed through alloying and plastic working, making their use in load-bearing environments becomes a reality. However, different from Mg and Fe based BMs, Zn based BMs exhibit significant "strain-softening" effect that leads to limited uniform deformation. Non-uniform deformation is detrimental to Zn based devices or implants, which will possibly lead to unexpected failure. People might be misled by the considerable fracture elongation of Zn based BMs. Thus, it is important to specify uniform elongation as a term of mechanical requirements for Zn based BMs. In this review, recent advances on the mechanical properties of Zn based BMs have been comprehensively summarized, especially focusing on the strain softening phenomenon. At first, the origin and evaluation criteria of strain softening were introduced. Secondly, the effects of alloying elements (including element type, single or multiple addition, and alloying content) and microstructural characteristics (grain size, constituent phase, phase distribution, etc.) on mechanical properties (especially for uniform elongation) of Zn based BMs were summarized. Finally, how to get a good balance between strength and uniform elongation was generally discussed based on the service environment. In addition, possible ways to minimize or eliminate the strain softening effect were also proposed, such as controlling of twins, solute clusters, and grain boundary characteristics. All these items above would be helpful to understand the mechanical instability of Zn based BMs, and to make the full usage of them in the future medical device design. STATEMENT OF SIGNIFICANCE: Biodegradable metals (BMs) is a hotspot in the field of metallic biomaterials. Fracture elongation is normally adopted to quantify the deformability of Mg and Fe based BMs owing to their negligible necking strain, yet the strain softening would occur in Zn based BMs, which is extremely detrimental to performance of their medical device. In this review paper, a better understanding the mechanical performance of Zn-based BMs with the term "uniform elongation" instead of "fracture elongation" was depicted, and possible ways to minimize or eliminate the strain softening effect were also proposed, such as twins, solute clusters, self-stable dislocation network, and grain boundary characteristics. It would be helpful to understand the mechanical instability of Zn based BMs and making full usage of it in the future medical device design.