Design biodegradable Zn alloys: Second phases and their significant influences on alloy properties

Degradation Characteristics and Biocompatibility of Zinc Alloy in Advanced Biomedical Bone Implants

Biodegradable zinc-based alloys are regarded as a promising avenue of research for the development of bone fixation implants, offering potential solutions to clinical issues, such as stress shielding, secondary surgeries, and biocompatibility. In this study, a Zn-0.8Li-0.4Mg alloy was designed and fabricated and its potential for use as a clinical bone implant was evaluated. The alloy displays an ultimate tensile strength of 450 MPa and an elongation of 18%, thereby satisfying the requisite mechanical specifications for clinical bone implants. The results of the electrochemical and SBF in vitro corrosion tests indicate that the degradation mechanism evolves over time. The initial corrosion product layer is composed of a dense Li-containing corrosion product (LiOH/Li2CO3), which subsequently transforms into an Mg-containing corrosion product layer (MgO/Mg(OH)2) as corrosion progresses. Ultimately, due to the depletion of Li and the erosion by Cl-, it transitions to a corrosion product layer containing only the Zn and Ca/P layer. The overall degradation mechanism is jointly determined by the degree of local degradation and the corrosion resistance of the product layer. Cytotoxicity tests demonstrate that the Zn-0.8Li-0.4Mg alloy exhibits favorable biocompatibility.

Effect of Mn content on the corrosion behavior and biocompatibility of biodegradable Zn-Mn alloys

Zinc-based alloys have attracted increasing attention as biodegradable metals by virtue of their excellent mechanical, degradable and biocompatible properties. By introducing different levels of manganese (0.1, 0.3, 0.5 and 0.8 wt%), the properties of pure zinc were improved. The obtained zinc-manganese alloys consisted mainly of a zinc matrix and a MnZn13 phase, which led to a significant improvement of the mechanical properties with ultimate tensile strength (UTS), yield strength (YS) and elongation up to 117.3 MPa, 110.4 MPa, and 14%, respectively, and a Vickers hardness of 78 HV. After immersion in simulated body fluid (SBF), the addition of manganese slightly slowed down the corrosion rate of pure zinc, with an average corrosion rate of approximately 0.12 mm/y. Subsequent electrochemical tests and scanning Kelvin probe tests further confirmed this observation. In addition, the zinc-manganese alloys showed better resistance to E. coli and Staphylococcus aureus than pure zinc according to antimicrobial and in vitro cytotoxicity tests. Cell viability in the alloy extraction solution was higher than that of pure zinc and remained within acceptable limits (> 75%). In summary, Zn-Mn alloy has excellent performance, the promoting effect of Mn element on osteogenesis, and the excellent mechanical properties of the alloy itself, making it a potential biodegradable material for orthopedics.

Machine Learning Prediction of the Corrosion Rate of Zinc-Based Alloys Containing Copper, Lithium, Magnesium, and Silver

Implementation of machine learning (ML) techniques in materials science often requires large data sets. However, a proper choice of features and regression methods allows the construction of accurate ML models able to work with a relatively small data set. In this work, an extensive, although still limited, experimental data set of corrosion-related properties of Zn-based alloys used in biomedicine was created. On the basis of this data set, a robust and accurate model was built to predict the corrosion behavior of Zn-based alloys. This work highlights the effectiveness of ML methods for assessing the corrosion behavior of Zn-based alloys, which can facilitate their application in bioimplants.

Additively Manufactured Biodegradable Zn-Based Porous Scaffolds to Suppress Osteosarcoma and Promote Osteogenesis

Postoperative therapies for osteosarcoma present substantial challenges due to tumor recurrence and extensive bone defects. To tackle these challenges, laser powder bed fusion is utilized to fabricate biodegradable Zn-Li porous scaffolds that supress tumors and promote osteogenesis. After the structure design and composition selection, the Zn-0.8Li porous scaffold with Gyroid unit optimally balances the co-release of Zn2+ and Li+ during degradation, resulting in favorable antitumor and osteogenic effects. In vitro, the Zn-0.8Li scaffold significantly inhibits osteosarcoma progression by suppressing tumor cell proliferation, promoting apoptosis, alleviating migration, and simultaneously promotes osteogenic differentiation through the enhanced expression of osteogenic markers. In vivo, the Zn-0.8Li scaffold inhibits the malignant osteosarcoma behavior and facilitates bone regeneration in areas with bone defects. Transcriptomic analysis further reveals that the simultaneous release of Zn2+ and Li+ from the biodegradable Zn-0.8Li scaffold contributes to anti-osteosarcoma activity by downregulating PI3K/Akt signaling pathways. Taken together, the Zn-0.8Li porous scaffold fabricated using laser powder bed fusion with enhanced antitumor and osteogenic properties is a promising alternative for the postoperative management of osteosarcoma.

Biodegradable zinc alloys with high strength and suitable mechanical integrity as bone repair metals

Mechanical properties and integrity of biodegradable Zn alloys during degradation holds significant importance. In this study, a Zn-Mg-Mn alloy with tensile strength of 414 MPa and an elongation of 26% was developed. The strength contributions of as-extruded Zn alloy from grain boundary strengthening, precipitation strengthening, and second phase strengthening. Degradation of the Zn alloy in Hank's solution exhibited a decreasing trend with prolonged immersion, eventually stabilizing at 16 μm/year. Corrosion morphology analysis revealed that the corrosion modes transformed from pitting corrosion to severely localized corrosion with prolonged immersion time, eventually lead to formation of large holes. Although the tensile strength of the Zn alloys remained relatively unchanged following varied immersion time, a substantial decrease in elongation was observed. The decreased elongation primarily attributed to the formation of surface corrosion pits or holes, exacerbating crack propagation during tension. Biocompatibility assessments of Zn alloys demonstrated that a 50% concentration of Zn alloy leach solution cultured with C3H10 and RMSC cells yielded cellular activity exceeding 80%, indicating excellent cytocompatibility. Alkaline phosphatase (ALP) and alizarin red staining results further underscored the remarkable early and late osteogenic properties exhibited by Zn-Mg-Mn alloy.

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.

Fabrication and performance of Zinc-based biodegradable metals: From conventional processes to laser powder bed fusion

Zinc (Zn)-based biodegradable metals (BMs) fabricated through conventional manufacturing methods exhibit adequate mechanical strength, moderate degradation behavior, acceptable biocompatibility, and bioactive functions. Consequently, they are recognized as a new generation of bioactive metals and show promise in several applications. However, conventional manufacturing processes face formidable limitations for the fabrication of customized implants, such as porous scaffolds for tissue engineering, which are future direction towards precise medicine. As a metal additive manufacturing technology, laser powder bed fusion (L-PBF) has the advantages of design freedom and formation precision by using fine powder particles to reliably fabricate metallic implants with customized structures according to patient-specific needs. The combination of Zn-based BMs and L-PBF has become a prominent research focus in the fields of biomaterials as well as biofabrication. Substantial progresses have been made in this interdisciplinary field recently. This work reviewed the current research status of Zn-based BMs manufactured by L-PBF, covering critical issues including powder particles, structure design, processing optimization, chemical compositions, surface modification, microstructure, mechanical properties, degradation behaviors, biocompatibility, and bioactive functions, and meanwhile clarified the influence mechanism of powder particle composition, structure design, and surface modification on the biodegradable performance of L-PBF Zn-based BM implants. Eventually, it was closed with the future perspectives of L-PBF of Zn-based BMs, putting forward based on state-of-the-art development and practical clinical needs.

Study on the Synergistic Effects of Cu and Sr on Biodegradable Zn Alloys

Bone defect repair and postoperative infections are among the most challenging issues faced by orthopedic surgeons. Thus, the antibacterial agent Cu and the osteogenic promoter Sr have been widely incorporated into biodegradable alloys separately. However, to the best of our knowledge, the synergistic effects of Cu and Sr on zinc alloys have not been investigated. Therefore, we have developed a series of novel Zn-4Cu-xSr (x = 0.05, 0.1, and 0.3 wt %) alloys. Our results showed that the addition of Cu and Sr significantly increased the strength of pure zinc while maintaining a certain level of ductility. Plastic deformation further enhanced the strength and ductility of the alloys. The tensile strength of HR Zn-4Cu-xSr alloys remains between 233.34 ± 1.31 MPa and 235.81 ± 3.0 MPa, with elongation values ranging from 45.7 ± 1.56% to 49.6 ± 6.22%. The HE Zn-4Cu-0.05Sr alloy exhibits a high elongation of 95.05 ± 11.1%. Furthermore, the HE Zn-4Cu-0.1Sr alloy demonstrates the best overall mechanical performance with ultimate tensile strength (σuts), yield strength (σys), and elongation (ε) values of 252.73 ± 0.12 MPa, 181.0 ± 0.79 MPa, and 42.8 ± 1.13%, respectively. The corrosion rate of HE Zn-4Cu-xSr alloys increases with an increase in Sr content. All samples exhibit satisfactory cytocompatibility with the cells displaying a healthy spindle-like morphology. In vitro antibacterial tests show that the HE Zn-4Cu-xSr alloys exhibit significant antibacterial effects against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), with the antibacterial properties strengthening as the Sr content increases. Therefore, this study demonstrates the tremendous potential application of Zn-4Cu-xSr alloys in biodegradable zinc alloys for bone fracture fixation and repair.

Nanoparticle-Enabled Zn-0.1Mg Alloy with Long-Term Stability, Refined Degradation, and Favorable Biocompatibility for Biodegradable Implant Devices

Zinc-based alloys, specifically Zn-Mg, have garnered considerable attention as promising materials for biodegradable implants due to their favorable mechanical strength, appropriate corrosion rate, and biocompatibility. Nevertheless, the alloy's lack of mechanical stability and integrity, resulting from ductility loss induced by age hardening at room temperature, hampers its practical bioapplication. In this study, ceramic nanoparticles have been successfully incorporated into the Zn-Mg alloy system, leading to a significant improvement in long-term stability as well as mechanical strength and ductility. In addition, this study represents the first investigation of Zn-based nanocomposites both in vitro and in vivo to comprehend the influence of nanoparticles on the degradation behavior and biocompatibility of the Zn system. The findings indicate that the incorporation of WC nanoparticles effectively refines and stabilizes the degradation behavior of Zn-Mg without negatively impacting the cytocompatibility of the alloy. The subcutaneous implantation and femoral implantation further prove the benefits of nanoparticle incorporation and found no negative effects. Collectively, Zn-Mg-WC nanocomposites yield great potential for implant usage.

Insights into the biocompatibility of biodegradable metallic molybdenum for cardiovascular applications-a critical review

Atherosclerotic cardiovascular disease (ACD) is the leading cause of death worldwide. The gold standard of treatment is the implantation of a permanent stent implant that is often associated with complications such as thrombus formation, vascular neointimal response, and stent fracture, which altogether decrease the long-term safety and efficacy of the stent. Biodegradable metallic materials have become an attractive alternative because of the ability to facilitate a more physiological healing response while the metal degrades. Recently, Molybdenum (Mo) has been considered as a potential candidate due to its excellent mechanical and medical imaging properties. Moreover, the biomedical research studies performed to date have shown minimal adverse effects in vitro and in vivo. However, there are still concerns of toxicity at high doses, and the impact of the biochemical mechanisms of Mo on material performance especially in pathophysiological environments are yet to be explored. Mo is an essential co factor for enzymes such as xanthine oxidoreductase (XOR) that plays a critical role in vascular homeostasis and ACD progression. Herein, this review will focus on the biochemistry of Mo, its physiological and pathological effects with an emphasis on cardiovascular disease as well as the recent studies on Mo for cardiovascular applications and its advantages over other biodegradable metals. The limitations of Mo research studies will also be discussed and concluded with an outlook to move this revolutionary metallic biomaterial from the bench to the bedside.

Development and characterization of ZnxCuyTizMo alloys for biomedical applications: A high-throughput gradient continuous casting approach

The limited mechanical properties of pure Zn, such as its low strength and ductility, hinder its application as a material for biodegradable implants. Addressing this challenge, the current study focuses on the development of biodegradable Zn-based alloys, employing innovative alloy design and processing strategies. Here, alloys with compositions ranging from 0.02 to 0.10 weight percent (wt%) Cu, 1.22 to 1.80 wt% Ti, and 0.04 to 0.06 wt% Mo were produced utilizing a high-throughput gradient continuous casting process. This study highlights three specific alloys: Zn1.82Cu0.10Ti0.05Mo (HR8), Zn0.08Cu1.86Ti0Mo (HR7), and Zn1.26Cu0.13Ti0.06Mo (HR6), which were extensively evaluated for their microstructure, mechanical properties, electrochemical performance, potential as bioimplants, and cytotoxicity. These alloys were found to exhibit enhanced mechanical strength, optimal degradation rates, and superior biocompatibility, evidenced by in-vivo experiments with SD rats, positioning them as promising candidates for medical implants. This research not only introduces a significant advancement in biodegradable alloy development but also proposes an efficient method for their production, marking a pivotal step forward in biomedical engineering. STATEMENT OF SIGNIFICANCE: The limited mechanical properties of pure Zn have hindered its application in biodegradable implants. Our research primarily focuses on the alloy design and process strategies of biodegradable Zn-based alloys. We explore the ZnCuxTixMox alloys. This study introduces a high-throughput experimental approach for efficient screening of multi-component alloy systems with optimal properties. The ZnCuxTixMox alloys were designed and processed through gradient continuous casting, followed by homogenization and hot rolling. Our findings indicate that the Zn1.82Cu0.10Ti0.05Mo alloy demonstrates superior tensile, mechanical, and corrosion properties post hot rolling. The study suggests that Zn0.13Cu1.26Ti0.06Mo, Zn0.08Cu1.86Ti0Mo, and Zn1.82Cu0.10Ti0.05Mo alloys hold significant potential as biodegradable materials.

Advances in biodegradable materials: Degradation mechanisms, mechanical properties, and biocompatibility for orthopedic applications

Mg-based and Zn-based biodegradable materials have the potential to become the next-generation implant materials to treat bone diseases, because of their desired degradation and mechanical properties. This article reviews the status of these implant materials. The required properties of biodegradable materials such as biodegradability, mechanical properties, and biocompatibility for performance evaluation were briefly discussed. The influence of fabrication techniques, microstructure, alloying elements, and post-processing techniques on the properties of Mg and Zn-based materials was addressed. The degradation mechanism by dissolution, oxidation, and interaction with human body cells was discussed. The biocompatibility of Mg and Zn-based biodegradable materials was analyzed. The significance of in vitro and in vivo biocompatibility testing was highlighted, emphasizing the superiority of in vivo results over cell line studies. This article identifies the many Mg and Zn-based biodegradable materials and summarizes the key findings.

3D Printing of a Porous Zn-1Mg-0.1Sr Alloy Scaffold: A Study on Mechanical Properties, Degradability, and Biosafety

In recent years, the use of zinc (Zn) alloys as degradable metal materials has attracted considerable attention in the field of biomedical bone implant materials. This study investigates the fabrication of porous scaffolds using a Zn-1Mg-0.1Sr alloy through a three-dimensional (3D) printing technique, selective laser melting (SLM). The results showed that the porous Zn-1Mg-0.1Sr alloy scaffold featured a microporous structure and exhibited a compressive strength (CS) of 33.71 ± 2.51 MPa, a yield strength (YS) of 27.88 ± 1.58 MPa, and an elastic modulus (E) of 2.3 ± 0.8 GPa. During the immersion experiments, the immersion solution showed a concentration of 2.14 ± 0.82 mg/L for Zn2+ and 0.34 ± 0.14 mg/L for Sr2+, with an average pH of 7.61 ± 0.09. The porous Zn-1Mg-0.1Sr alloy demonstrated a weight loss of 12.82 ± 0.55% and a corrosion degradation rate of 0.36 ± 0.01 mm/year in 14 days. The Cell Counting Kit-8 (CCK-8) assay was used to check the viability of the cells. The results showed that the 10% and 20% extracts significantly increased the activity of osteoblast precursor cells (MC3T3-E1), with a cytotoxicity grade of 0, which indicates safety and non-toxicity. In summary, the porous Zn-1Mg-0.1Sr alloy scaffold exhibits outstanding mechanical properties, an appropriate degradation rate, and favorable biosafety, making it an ideal candidate for degradable metal bone implants.

Zinc based biodegradable metals for bone repair and regeneration: Bioactivity and molecular mechanisms

Bone fractures and critical-size bone defects are significant public health issues, and clinical treatment outcomes are closely related to the intrinsic properties of the utilized implant materials. Zinc (Zn)-based biodegradable metals (BMs) have emerged as promising bioactive materials because of their exceptional biocompatibility, appropriate mechanical properties, and controllable biodegradation. This review summarizes the state of the art in terms of Zn-based metals for bone repair and regeneration, focusing on bridging the gap between biological mechanism and required bioactivity. The molecular mechanism underlying the release of Zn ions from Zn-based BMs in the improvement of bone repair and regeneration is elucidated. By integrating clinical considerations and the specific bioactivity required for implant materials, this review summarizes the current research status of Zn-based internal fixation materials for promoting fracture healing, Zn-based scaffolds for regenerating critical-size bone defects, and Zn-based barrier membranes for reconstituting alveolar bone defects. Considering the significant progress made in the research on Zn-based BMs for potential clinical applications, the challenges and promising research directions are proposed and discussed.

Fucoidan- and Ciprofloxacin-Doped Plasma-Activated Polymer Coatings on Biodegradable Zinc: Hemocompatibility and Drug Release

Blood-contacting medical devices such as biodegradable metallic bone implant materials are expected to show excellent hemocompatibility both in vitro and in vivo. Different approaches are being studied and used to modify biomaterial surfaces for enhanced biocompatibility and hemocompatibility. However, the composition of degradable biomaterial must address several drawbacks at once. Iron-reinforced zinc material was used as a metallic substrate with improved mechanical properties when compared with those of pure zinc. Poly(lactic) acid (PLA) or polyethylenimine (PEI) was selected as a polymeric matrix for further doping with antibiotic ciprofloxacin (CPR) and marine-sourced polysaccharide fucoidan (FU), which are known for their antibacterial and potential anticoagulant properties, respectively. Radiofrequency air plasma was employed to induce metallic/polymer-coated surface activation before further modification with FU/CPR. Sample surface morphology and composition were studied and evaluated (contact angle measurements, AFM, SEM, and FT-IR) along with the hemolysis ratio and platelet adhesion test. Successful doping of the polymer layer by FU/CRP was confirmed. While PEI induced severe hemolysis over 12%, the PLA-coated samples exhibited even lower hemolysis (∼2%) than uncoated samples while the uncoated samples showed the lowest platelet adhesion. Moreover, gradual antibiotic release from PLA determined by the electrochemical methods using screen-printed carbon electrodes was observed after 24, 48, and 72 h, making the PLA-coated zinc-based material an attractive candidate for biodegradable material design.

Development of Zn-2Cu-xMn/Mg Alloys for Orthopedic Applications: Mechanical Performance to In Vitro Degradation under Different Physiological Environments

Zinc (Zn) and its alloys are considered futuristic biodegradable materials for their acceptable mechanical properties, suitable corrosion rate, and good biocompatibility. In this study, we report newly developed biodegradable Zn-2Cu-xMn/Mg (x = 0, 0.1, and 0.5) alloys, aiming to achieve good mechanical strength with excellent elongation, desirable wear resistance, and suitable corrosion rate. The effect of Mn/Mg addition on the structural, mechanical, wear, and degradation behaviors of the Zn-2Cu-xMn/Mg alloys was thoroughly investigated. Degradation and tribological behaviors of the alloys were explored in the presence of simulated body fluid (SBF), Dulbecco's modified Eagle medium (DMEM), and DMEM with a 10% fetal bovine serum (FBS) solution. Alloy elements and hot rolling improve their mechanical properties significantly due to precipitation hardening, grain refinement, and solid solution strengthening owing to the formation of MnZn13 and Mg2Zn11 phases. Among all the alloys, the Zn-2Cu-0.5Mn alloy achieved the highest ultimate tensile strength (UTS) of ∼405 MPa and yield strength (YS) of ∼293 MPa with an excellent elongation of ∼51%. The corrosion behavior of the alloys as determined by a potentiodynamic polarization study under different solutions follows the sequence Zn-2Cu < Zn-2Cu-0.5Mn < Zn-2Cu-0.1Mn < Zn-2Cu-0.1Mg < Zn-2Cu-0.5Mg. The corrosion rate by immersion testing for 30 and 90 days also follows the same sequence. The corrosion rate in different solutions follows the order SBF > DMEM + 10%FBS > DMEM. The addition of Mn/Mg also improves the wear resistance and slows the wear rate under wet conditions. The bending test results also indicate the highest bending strength of ∼375 MPa for the Zn-2Cu-0.5Mn alloy, among all the alloys. The bending and tensile strengths deteriorate continuously after the immersion for 30 and 90 days in the solution of SBF, DMEM, and DMEM + 10%FBS. Therefore, the Zn-2Cu-xMn/Mg (x = 0.1 and 0.5) alloys can be considered potential biodegradable implant materials.

Mechanical properties, in vitro biodegradable behavior, biocompatibility and osteogenic ability of additively manufactured Zn-0.8Li-0.1Mg alloy scaffolds

Alloying and structural design provide flexibility to modulate performance of biodegradable porous implants manufactured by laser powder bed fusion (L-PBF). Herein, bulk Zn-0.8Li-0.1Mg was first fabricated to indicate the influence of the ternary alloy system on strengthening effect. Porous scaffolds with different porosities, including 60 % (P60), 70 % (P70) and 80 % (P80), were designed and fabricated to study the influence of porosity on mechanical properties, in vitro degradation behavior, biocompatibility and osteogenic ability. Pure Zn (Zn-P70) scaffolds with a porosity of 70 % were utilized for the comparison. The results showed Zn-0.8Li-0.1Mg bulks had an ultimate tensile strength of 460.78 ± 5.79 MPa, which was more than 3 times that of pure Zn ones and was the highest value ever reported for Zn alloys fabricated by L-PBF. The compressive strength (CS) and elastic modulus (E) of scaffolds decreased with increasing porosities. The CS of P70 scaffolds was 24.59 MPa, more than 2 times that of Zn-P70. The weight loss of scaffolds during in vitro immersion increased with increasing porosities. Compared with Zn-P70, a lower weight loss, better biocompatibility and improved osteogenic ability were observed for P70 scaffolds. P70 scaffolds also exhibited the best biocompatibility and osteogenic ability among all the used porosities. Influence mechanism of alloying elements and structural porosities on mechanical behaviors, in vitro biodegradation behavior, biocompatibility and osteogenic ability of scaffolds were discussed using finite element analysis and the characterization of degradation products. The results indicated that the proper design of alloying and porosity made Zn-0.8Li-0.1Mg scaffolds promising for biodegradable applications.

Mechanical properties, corrosion and degradation behaviors, and in vitro cytocompatibility of a biodegradable Zn-5La alloy for bone-implant applications

Zinc (Zn) and its alloys are used in bone-fixation devices as biodegradable bone-implant materials due to their good biosafety, biological function, biodegradability, and formability. Unfortunately, the clinical application of pure Zn is hindered by its insufficient mechanical properties and slow degradation rate. In this study, a Zn-5 wt.% lanthanum (Zn-5La) alloy with enhanced mechanical properties, suitable degradation rate, and cytocompatibility was developed through La alloying and hot extrusion. The hot-extruded (HE) Zn-5La alloy showed ultimate tensile strength of 286.3 MPa, tensile yield strength of 139.7 MPa, elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. The corrosion resistance of the HE Zn-5La in Hanks' and Dulbecco's modified Eagle medium (DMEM) solutions gradually increased with prolonged immersion time. Further, the HE Zn-5La exhibited an electrochemical corrosion rate of 36.7 μm/y in Hanks' solution and 11.4 μm/y in DMEM solution, and a degradation rate of 49.5 μm/y in Hanks' solution and 30.3 μm/y in DMEM solution, after 30 d of immersion. The corrosion resistance of both HE Zn and Zn-5La in DMEM solution was higher than in Hanks' solution. The 25% concentration extract of the HE Zn-5La showed a cell viability of 106.5%, indicating no cytotoxicity toward MG-63 cells. We recommend the HE Zn-5La alloy as a promising candidate material for biodegradable bone-implant applications. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion and degradation behaviors, in vitro cytocompatibility and antibacterial ability of biodegradable Zn-5La alloy for bone-implant applications. Our findings demonstrate that the hot-extruded (HE) Zn-5La alloy showed an ultimate tensile strength of 286.3 MPa, a yield strength of 139.7 MPa, an elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. HE Zn-5La exhibited appropriate degradation rates in Hanks' and DMEM solutions. Furthermore, the HE Zn-5La alloy showed good cytocompatibility toward MG-63 and MC3T3-E1 cells and greater antibacterial ability against S. aureus.

[Research status and development of biodegradable zinc alloy as orthopedics implant]

Znic (Zn) alloys with good cytocompatibility and suitable degradation rate have been a kind of biodegradable metal with great potential for clinical applications. This paper summarizes the biological role of degradable Zn alloy as bone implant materials, discusses the mechanical properties of different Zn alloys and their advantages and disadvantages as bone implant materials, and analyzes the influence of different processing strategies (such as alloying and additive manufacturing) on the mechanical properties of Zn alloys. This paper provides systematic design approaches for biodegradable Zn alloys as bone implant materials in terms of the material selection, product processing, structural topology optimization, and assesses their application prospects with a view to better serve the clinic.

Immunomodulatory zinc-based materials for tissue regeneration

Zinc(Zn)-based materials have contributed greatly to the rapid advancements in tissue engineering. The qualities they possess that make them so beneficial include their excellent biodegradability, biocompatibility, anti-bacterial activity, among and several others. Biomedical materials that act as a foreign body, will inevitably cause host immune response when introduced to the human body. As the osteoimmunology develops, the immunomodulatory characteristics of biomaterials have become an appealing concept to improve implant-tissue interaction and tissue restoration. Recently, Zn-based materials have also displayed immunomodulatory functions, especially macrophage polarization states. It can promote the transformation of M1 macrophages into M2 macrophages to enhance the tissue regeneration and reconstruction. This review covers mainly Zn-based materials and their characteristics, including metallic Zn alloys and Zn ceramics. We highlight the current advancements in the type of immune responses, as well as the mechanisms, that are induced by Zn-based biomaterials, most importantly the regulation of innate immunity and the mechanism of promoting tissue regeneration. To this end, we discuss their applications in biomedicine, and conclude with an outlook on future research challenges.

Development, Processing and Aging of Novel Zn-Ag-Cu Based Biodegradable Alloys

The use of biodegradable materials for implants is a promising strategy to overcome known long-term clinical complications related to permanent implants. Ideally, biodegradable implants support the damaged tissue for a certain period and then degrade, while the physiological function of the surrounding tissue is restored. Although Mg-based alloys nearly ideally lend themselves to biodegradable implants, a few critical shortcomings promoted the development of alternative alloy systems. Due to their reasonably good biocompatibility, moderate corrosion rate without hydrogen evolution and adequate mechanical properties, increasing attention has been paid to Zn alloys. In this work, precipitation-hardening alloys in the system Zn-Ag-Cu were developed relying on thermodynamic calculations. After casting the alloys, their microstructures were refined by thermomechanical treatment. The processing was tracked and directed, respectively, by routine investigations of the microstructure, associated with hardness assessments. Although microstructure refinement increased the hardness, the material proved to be susceptible to aging as the homologous temperature of zinc is at 0.43 T_m. Besides mechanical performance and corrosion rate, long-term mechanical stability is another crucial factor that must be taken into consideration to ensure the safety of the implant and thus requires a profound understanding of the aging process.

Three-Dimensional Printing of Poly-L-Lactic Acid Composite Scaffolds with Enhanced Bioactivity and Controllable Zn Ion Release Capability by Coupling with Carbon-ZnO

Poly-L-lactic acid (PLLA) has gained great popularity with researchers in regenerative medicine owing to its superior biocompatibility and biodegradability, although its inadequate bioactivity inhibits the further use of PLLA in the field of bone regeneration. Zinc oxide (ZnO) has been utilized to improve the biological performance of biopolymers because of its renowned osteogenic activity. However, ZnO nanoparticles tend to agglomerate in the polymer matrix due to high surface energy, which would lead to the burst release of the Zn ion and, thus, cytotoxicity. In this study, to address this problem, carbon–ZnO (C–ZnO) was first synthesized through the carbonization of ZIF-8. Then, C–ZnO was introduced to PLLA powder before it was manufactured as scaffolds (PLLA/C–ZnO) by a selective laser sintering 3D printing technique. The results showed that the PLLA/C–ZnO scaffold was able to continuously release Zn ions in a reasonable range, which can be attributed to the interaction of Zn–N bonding and the shielding action of the PLLA scaffold. The controlled release of Zn ions from the scaffold further facilitated cell adhesion and proliferation and improved the osteogenic differentiation ability at the same time. In addition, C–ZnO endowed the scaffold with favorable photodynamic antibacterial ability, which was manifested by an efficient antibacterial rate of over 95%.

Evolution of degradation mechanism and fixation strength of biodegradable Zn-Cu wire as sternum closure suture: An in vitro study

This work reports the first in vitro study on the in-situ biodegradation behaviour and the evolution of fixation strength of Zn-Cu alloy wires in a simulated sternum closure environment. Zn-Cu wires were used to reapproximate the partial bisected sternum models, and their fixation effect was compared with traditional surgical grade 316 L stainless steel (SS) wires in terms of fixation rigidity, critical load, first/ultimate failure characteristics. The metal sutures were then immersed in Hank's balanced salt solution for 12 weeks immersion period, and their corrosion behaviours assessed. Zn-Cu wires showed similar fixation rigidity at 70.89 ± 6.97 N/mm as SS, but the critical load, first failure and ultimate failure characteristics were inferior to SS. The key challenges that limited the fixation effect of the Zn-Cu wires were poor mechanical strength, short elastic region, and strain softening behaviours, which resulted in poor load-bearing capabilities and reduced the knot security of the sutures. The in-situ biodegradation of the Zn-Cu suture was accompanied by the early onset of localised corrosion within the twisted knot and the section located next to the incision line. Crevice corrosion and strain-induced corrosion were the dominant mechanisms in the observed localised corrosion. The localised corrosion on the Zn-Cu sutures did not lead to a significant shift in fixation rigidity, critical load and the first failure characteristics. The findings suggest that the Zn-based biodegradable metallic wires could be a promising sternum closure suture material once the limitations in mechanical characteristics are addressed.

In vitro cytocompatibility and antibacterial studies on biodegradable Zn alloys supplemented by a critical assessment of direct contact cytotoxicity assay

In vitro cytotoxicity assessment is indispensable in developing new biodegradable implant materials. Zn, which demonstrates an ideal corrosion rate between Mg- and Fe-based alloys, has been reported to have excellent in vivo biocompatibility. Therefore, modifications aimed at improving Zn's mechanical properties should not degrade its biological response. As sufficient strength, ductility and corrosion behavior required of load-bearing implants has been obtained in plastically deformed Zn-3Ag-0.5Mg, the effect of simultaneous Ag and Mg additions on in vitro cytocompatibility and antibacterial properties was studied, in relation to Zn and Zn-3Ag. Direct cell culture on samples and indirect extract-based tests showed almost no significant differences between the tested Zn-based materials. The diluted extracts of Zn, Zn-3Ag, and Zn-3Ag-0.5Mg showed no cytotoxicity toward MG-63 cells at a concentration of ≤12.5%. The cytotoxic effect was observed only at high Zn²⁺ ion concentrations and when in direct contact with metallic samples. The highest LD₅₀ (lethal dose killing 50% of cells) of 13.4 mg/L of Zn²⁺ ions were determined for the Zn-3Ag-0.5Mg. Similar antibacterial activity against Escherichia coli and Staphylococcus aureus was observed for Zn and Zn alloys, so the effect is attributed mainly to the released Zn²⁺ ions exhibiting bactericidal properties. Most importantly, our experiments indicated the limitations of water-soluble tetrazolium salt-based cytotoxicity assays for direct tests on Zn-based materials. The discrepancies between the WST-8 assay and SEM observations are attributed to the interference of Zn²⁺ ions with tetrazolium salt, therefore favoring its transformation into formazan, giving false cell viability quantitative results.

Systematic in vitro and in vivo study on biodegradable binary Zn-0.2 at% Rare Earth alloys (Zn-RE: Sc, Y, La-Nd, Sm-Lu)

Biomedical implants and devices for tissue engineering in clinics, mainly made of polymers and stiff metallic materials, require possibly secondary surgery or life-long medicine. Biodegradable metals for biomedical implants and devices exhibit huge potential to improve the prognosis of patients. In this work, we developed a new type of biodegradable binary zinc (Zn) alloys with 16 rare earth elements (REEs) including Sc, Y, La to Nd, and Sm to Lu, respectively. The effects of REEs on the alloy microstructure, mechanical properties, corrosion behavior and in vitro and in vivo biocompatibility of Zn were systematically investigated using pure Zn as control. All Zn-RE alloys generally exhibited improved mechanical properties, and biocompatibilities compared to pure Zn, especially the tensile strength and ductility of Zn-RE alloys were dramatically enhanced. Among the Zn-RE alloys, different REEs presented enhancement effects at varied extent. Y, Ho and Lu were the three elements displaying greatest improvements in majority of alloys properties, while Eu, Gd and Dy exhibited least improvement. Furthermore, the Zn-RE alloys were comparable with other Zn alloys and also exhibited superior properties to Mg-RE alloys. The in vivo experiment using Zn-La, Zn-Ce, and Zn-Nd alloys as tibia bone implants in rabbit demonstrated the excellent tissue biocompatibility and much more obvious osseointegration than the pure Zn control group. This work presented the significant potential of the developed Zn-RE binary alloys as novel degradable metal for biomedical implants and devices.

Recent Developments in Zn-Based Biodegradable Materials for Biomedical Applications

Zn-based biodegradable alloys or composites have the potential to be developed to next-generation orthopedic implants as alternatives to conventional implants to avoid revision surgeries and to reduce biocompatibility issues. This review summarizes the current research status on Zn-based biodegradable materials. The biological function of Zn, design criteria for orthopedic implants, and corrosion behavior of biodegradable materials are briefly discussed. The performance of many novel zinc-based biodegradable materials is evaluated in terms of biodegradation, biocompatibility, and mechanical properties. Zn-based materials perform a significant role in bone metabolism and the growth of new cells and show medium degradation without the release of excessive hydrogen. The addition of alloying elements such as Mg, Zr, Mn, Ca, and Li into pure Zn enhances the mechanical properties of Zn alloys. Grain refinement by the application of post-processing techniques is effective for the development of many suitable Zn-based biodegradable materials.

Microstructural and Mechanical Characterization of Newly Developed Zn-Mg-CaO Composite

In this study, the Zn-0.8Mg-0.28CaO wt.% composite was successfully prepared using different conditions of ball milling (rotations and time) followed by a direct extrusion process. These materials were characterized from the point of view of microstructure and compressive properties, and the correlation between those characteristics was found. Microstructures of individual materials possessed differences in grain size, where the grain size decreased with the intensified conditions (milling speed and time). However, the mutual relation between grain size and compressive strength was not linear. This was caused by the effect of other factors, such as texture, intermetallic phases, and pores. Material texture affects the mechanical properties by a different activity ratio between basal and pyramidal <c + a> slips. The properties of intermetallic particles and pores were determined in material volume using micro-computed tomography (µCT), enhancing the precision of our assumptions compared with commonly applied methods. Based on that, and the analysis after the compressive tests, we were able to determine the influence of aspect ratio, feret diameters, and volume content of intermetallic phases and pores on mechanical behavior. The influence of the aspects on mechanical behavior is described and discussed.

Development of biodegradable Zn-Mn-Li and CaP coatings on Zn-Mn-Li alloys and cytocompatibility evaluation for bone graft

Zn-based alloys are considered as new kind of potential biodegradable implanted biomaterials recently. The difficulty of metal implanted biomaterials and bone tissue integration seriously affects the applications of metal implanted scaffolds in bone tissue-related fields. Herein, we self-designed Zn0.8Mn and Zn0.8Mn0.1Li alloys and CaP coated Zn0.8Mn and Zn0.8Mn0.1Li alloys, then evaluated the degradation property and cytocompatibility. The results demonstrated that the Zn0.8Mn0.1Li alloys had profoundly modified the degradation property and cytocompatibility, but Zn0.8Mn0.1Li alloys had particularly adverse effects on the surface morphology of osteoblasts. The results furtherly showed that the CaP-coated Zn0.8Mn and Zn0.8Mn0.1Li alloys scaffold had better biocompatibility, which would further guarantee the biosafety of this new kind of biodegradable Zn-based alloys implants for future clinical applications.

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.

Influence of Copper on the Microstructural, Mechanical, and Biological Properties of Commercially Pure Zn-Based Alloys for a Potential Biodegradable Implant

Three Zn-based alloys (Zn1Cu, Zn2Cu, and Zn3Cu) were developed by the addition of Cu (1, 2, and 3 wt %) into commercially pure Zn. This report systematically investigates the potential for these newly developed Zn-based alloys as biodegradable materials. Microstructural studies reveal the presence of spherical-shaped nanosized precipitates of ε-CuZn₄ in the Zn1Cu alloy, whereas Zn2Cu and Zn3Cu alloys exhibit the presence of both micron- and nanosized precipitates of ε-CuZn₄. The mechanical properties such as hardness, tensile and compressive strengths improve significantly with an increase in the amount of Cu in the alloy. The Zn3Cu alloy exhibits the highest yield strength (225 ± 9 MPa) and ultimate tensile strength (330 ± 12 MPa) among all of the alloys, which are ∼2.7 and 2 times higher than those of pure Zn. In vitro degradation behavior is evaluated by the potentiodynamic polarization study and immersion testing in Hank's solution for 20 and 75 days. The corrosion rate after both polarization and immersion testing follows the order of pure Zn < Zn1Cu < Zn3Cu < Zn2Cu. An electrochemical impedance spectroscopy (EIS) study also concludes that Zn2Cu shows the lowest corrosion resistance. The % cell viability values of 3T3 fibroblasts cells after 5 days of culture in a 50% diluted extract of pure Zn, Zn2Cu, and Zn3Cu alloys are 76 ± 0.024, 86.18 ± 0.033, and 92.9 ± 0.026%, respectively, establishing the improved cytocompatibility of the alloys as compared to pure Zn. Furthermore, an antibacterial study also reveals that the Zn3Cu alloy exhibits 80, 67, and 100% increases in the zone of inhibition (ZOI) for Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa bacteria, respectively, as compared to that of pure Zn.

In Vitro Corrosion Behavior of Zn3Mg0.7Y Biodegradable Alloy in Simulated Body Fluid (SBF)

Biodegradable metallic materials represent a new class of biocompatible materials for medical applications based on numerous advantages. Among them, those based on zinc have a rate of degradation close to the healing period required by many clinical problems, which makes them more suitable than those based on magnesium or iron. The poor mechanical properties of Zn could be significantly improved by the addition of Mg and Y. In this research, we analyze the electro-chemical and mechanical behavior of a new alloy based on Zn3Mg0.7Y compared with pure Zn and Zn3Mg materials. Microstructure and chemical composition were investigated by electron microscopy and energy dispersive spectroscopy. The electrochemical corrosion was analyzed by linear polarization (LP), cyclic polarization (CP) and electrochemical impedance spectroscopy (EIS). For hardness and scratch resistance, a microhardness tester and a scratch module were used. Findings revealed that the mechanical properties of Zn improved through the addition of Mg and Y. Zn, Zn-Mg and Zn-Mg-Y alloys in this study showed highly active behavior in SBF with uniform corrosion. Zinc metals and their alloys with magnesium and yttrium showed a moderate degradation rate and can be considered as promising biodegradable materials for orthopedic application.

Zinc-nutrient element based alloys for absorbable wound closure devices fabrication: Current status, challenges, and future prospects

The need for the development of load-bearing, absorbable wound closure devices is driving the research for novel materials that possess both good biodegradability and superior mechanical characteristics. Biodegradable metals (BMs), namely: magnesium (Mg), zinc (Zn) and iron (Fe), which are currently being investigated for absorbable vascular stent and orthopaedic implant applications, are slowly gaining research interest for the fabrication of wound closure devices. The current review presents an overview of the traditional and novel BM-based intracutaneous and transcutaneous wound closure devices, and identifies Zn as a promising substitute for the traditional materials used in the fabrication of absorbable load-bearing sutures, internal staples, and subcuticular staples. In order to further strengthen Zn to be used in highly stressed situations, nutrient elements (NEs), including calcium (Ca), Mg, Fe, and copper (Cu), are identified as promising alloying elements for the strengthening of Zn-based wound closure device material that simultaneously provide potential therapeutic benefit to the wound healing process during implant biodegradation process. The influence of NEs on the fundamental characteristics of biodegradable Zn are reviewed and critically assessed with regard to the mechanical properties and biodegradability requirements of different wound closure devices. The opportunities and challenges in the development of Zn-based wound closure device materials are presented to inspire future research on this rapidly growing field.

Rivet-Inspired Modification of Carbon Nanotubes by In Situ-Reduced Ag Nanoparticles To Enhance the Strength and Ductility of Zn Implants

Zinc shows promise for bone repair applications, while its strength and ductility require to be improved. Carbon nanotubes (CNTs) are exceptional reinforcements due to their superior strength, ultrahigh Young's modulus, and large aspect ratio. However, their strong agglomeration and weak interfacial bonding with the matrix are key bottleneck problems restricting the reinforcing effect. In this study, Ag nanoparticles were in situ reduced on CNTs and then the CNT@Ag powders were used to prepare Zn-CNT@Ag implants by laser powder bed fusion. Results showed that Ag reacted with Zn to form a "knot"-like AgZn₃ phase. It had the same lattice structure (HCP) with Zn, which indicated a good lattice matching with the matrix, thus improving the dispersion of CNTs. More significantly, the knot played a "rivet" role and enhanced the load transfer capacity, which advantaged the CNT strengthening effects by assisting in transferring the load. Moreover, it enhanced the heterogeneous nucleation effects during solidification, which weakened the texture strength of the matrix and thus increased the ductility by improving the sliding capacity. The compressive yield strength, ultimate tensile strength, and elongation of the Zn-CNT@Ag implant were increased by 22, 26, and 17% in comparison to Zn-CNTs. Moreover, the Zn-CNT@Ag implant exhibited favorable antibacterial activity with a bacterial inhibition rate of 87.79%. Additionally, it also exhibited a suitable degradation rate and acceptable biocompatibility.

Novel Biodegradable Zn Alloy with Exceptional Mechanical and In Vitro Corrosion Properties for Biomedical Applications

A series of quaternary Zn-Al-Cu-Li alloys with different weight fractions of Cu, Al, and Li were developed and investigated for potential application in high load bearing bioresorbable implants. The developed alloys provided various fractions of binary and ternary intermetallic structures, which resulted in formation of multiphase microstructures containing a zinc-rich η-phase and LiZn₄ and CuZn₄ phases. The intermetallic phases promoted grain refinement and a good combination of mechanical properties. The developed Zn-2Al-4Cu-0.6Li alloy showed strength and ductility close to commercially pure Ti alloys with a UTS value of ∼535 MPa and elongation of 37%. The examination of in vitro corrosion behavior of the developed alloys in the modified Hanks' solution revealed suitable corrosion rates (∼38.5 μm/year). The moderate corrosion rate was controlled by the formation of a homogeneous layer of stable corrosion products that protected the alloys from the corrosive environment, particularly in the late stages of immersion. The developed alloys with the most promising mechanical and corrosion properties appeared to be biocompatible to mouse fibroblast cells and human umbilical mesenchymal stem cells, making them suitable candidates for implant applications.

Dynamic Recrystallization and Its Effect on Superior Plasticity of Cold-Rolled Bioabsorbable Zinc-Copper Alloys

High plasticity of bioabsorbable stents, either cardiac or ureteral, is of great importance in terms of implants’ fabrication and positioning. Zn-Cu constitutes a promising group of materials in terms of feasible deformation since the superplastic effect has been observed in them, yet its origin remains poorly understood. Therefore, it is crucial to inspect the microstructural evolution of processed material to gain an insight into the mechanisms leading to such an extraordinary property. Within the present study, cold-rolled Zn-Cu alloys, i.e., Zn with addition of 1 wt.% and 5 wt.% of Cu, have been extensively investigated using scanning electron microscopy as well as transmission electron microscopy, so as to find out the possible explanation of superior plasticity of the Zn-Cu alloys. It has been stated that the continuous dynamic recrystallization has a tremendous impact on superior plasticity reported for Zn-1Cu alloy processed by rolling to 90% of reduction rate. The effect might be supported by static recrystallization, provoking grain growth and thereby yielding non-homogeneous microstructures. Such heterogeneous microstructure enables better formability since it increases the mean free path for dislocation movement.

Zinc alloy-based bone internal fixation screw with antibacterial and anti-osteolytic properties

There is no targeted effective treatment for patients undergoing internal fixation surgery/two-stage total joint revision surgery with a high risk of postoperative infection and osteolysis, while the rate of reoperation due to infection and osteolysis remains high. In this study, we report a pioneering application of implants made of biodegradable Zn–Ag alloy with active antibacterial and anti-osteolytic properties in three classical animal models, illustrating antibacterial, anti-osteolysis, and internal fixation for fractures. The antibacterial activity of the Zn–2Ag alloy was verified in a rat femur osteomyelitis prevention model, while the anti-osteolytic properties were evaluated using a mouse cranial osteolysis model. Moreover, the Zn–2Ag based screws showed similar performance in bone fracture fixation compared to the Ti–6Al–4V counterpart. The fracture healed completely after 3 months in the rabbit femoral condyle fracture model. Furthermore, the underlying antibacterial mechanism may include inhibition of biofilm formation, autolysis-related pathways, and antibiotic resistance pathways. Osseointegration mechanisms may include inhibition of osteoclast-associated protein expression, no effect on osteogenic protein expression, and no activation of related inflammatory protein expression. The empirical findings here reveal the great potential of Zn–Ag-based alloys for degradable biomaterials in internal fixation surgery/two-stage total joint revision surgery for patients with a high risk of postoperative infection and osteolysis.

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Zn–2Ag alloy is designed for orthopedic applications.

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Zn–2Ag alloy exhibit outstanding antibacterial properties in a rat femur osteomyelitis prevention model.

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Zn–2Ag alloy exhibit outstanding anti-osteolytic properties in a mouse cranial osteolysis model.

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Zn-2Ag based screws showed reliable performance in bone fracture fixation in the rabbit femoral condyle fracture model.

The influence of Ca and Cu additions on the microstructure, mechanical and degradation properties of Zn-Ca-Cu alloys for absorbable wound closure device applications

Novel ternary Zn-Ca-Cu alloys were studied for the development of absorbable wound closure device material due to Ca and Cu's therapeutic values to wound healing. The influence of Ca and Cu on the microstructure, mechanical and degradation properties of Zn were investigated in the as-cast state to establish the fundamental understanding on the Zn-Ca-Cu alloy system. The microstructure of Zn-0.5Ca-0.5Cu, Zn-1.0Ca-0.5Cu, and Zn0.5Ca-1.0Cu is composed of intermetallic phase CaZn13 distributed within the Zn-Cu solid solution. The presence of CaZn13 phase and Cu as solute within the Zn matrix, on the one hand, exhibited a synergistic effect on the grain refinement of Zn, reducing the grain size of pure Zn by 96%; on the other hand, improved the mechanical properties of the ternary alloys through solid solution strengthening, second phase strengthening, and grain refinement. The degradation properties of Zn-Ca-Cu alloys are primarily influenced by the micro-galvanic corrosion between Zn-Cu matrix and CaZn13 phase, where the 0.5% and 1.0% Ca addition increased the corrosion rate of Zn from 11.5 μm/y to 19.8 μm/y and 29.6 μm/y during 4 weeks immersion test.

Fine-tuning of mechanical properties in a Zn-Ag-Mg alloy via cold plastic deformation process and post-deformation annealing

In recent years, Zn-based materials have been extensively investigated as potential candidates for biodegradable implant applications. The introduction of alloying elements providing solid-solution strengthening and second phase strengthening seems crucial to provide a suitable platform for the thermo-mechanical strengthening of Zn alloys. In this study, a systematic investigation of the microstructure, crystallographic texture, phase composition, and mechanical properties of a Zn-3Ag-0.5Mg (wt%) alloy processed through combined hot extrusion (HE) and cold rolling (CR), followed by short-time heat treatment (CR + HT) at 200 °C was conducted. Besides, the influence of different annealing temperatures on the microstructure and mechanical properties was studied. An adequate combination of processing conditions during CR and HT successfully addressed brittleness obtained in the high-strength HE Zn-3Ag-0.5Mg alloy. By controlling the microstructure, the most promising results were obtained in the sample subjected to 50% CR reduction and 5-min annealing, which were: ultimate tensile strength of 432 MPa, yield strength of 385 MPa, total elongation to failure of 34%, and Vickers microhardness of 125 HV0.3. The obtained properties clearly exceed the mechanical benchmarks for biodegradable implant materials. Based on the conducted investigation, brittle multi-phase Zn alloys' mechanical performance can be substantially enhanced to provide sufficient plasticity by grain refinement through cold deformation process, followed by short-time annealing to restore proper strength.

Development of a high-strength Zn-Mn-Mg alloy for ligament reconstruction fixation

Although various biodegradable materials have been investigated for ligament reconstruction fixation in the past decades, only few of them possess a combination of high mechanical properties, appropriate degradation rate, good biocompatibility, and osteogenic effect, thus limiting their clinical applications. A high-strength Zn-0.8Mn-0.4Mg alloy (i.e., Zn08Mn04Mg) with yield strength of 317 MPa was developed to address this issue. The alloy showed good biocompatibility and promising osteogenic effect in vitro. The degradation effects of Zn08Mn04Mg interference screws on the interface between soft tissue and bone were investigated in anterior cruciate ligament (ACL) reconstruction in rabbits. Compared to Ti6Al4V, the Zn alloy screws significantly accelerated the formation of new bone and further induced partial tendon mineralization, which promoted tendon-bone integration. The newly developed screws are believed to facilitate early joint function recovery and rehabilitation training and also avoid screw breakage during insertion, thereby contributing to an extensive clinical prospect.

Investigating the stress corrosion cracking of a biodegradable Zn-0.8 wt%Li alloy in simulated body fluid

Stress corrosion cracking (SCC) may lead to brittle, unexpected failure of medical devices. However, available researches are limited to Mg-based biodegradable metals (BM) and pure Zn. The stress corrosion behaviors of newly-developed Zn alloys remain unclear. In the present work, we conducted slow strain rate testing (SSRT) and constant-load immersion test on a promising Zn-0.8 wt%Li alloy in order to investigate its SCC susceptibility and examine its feasibility as BM with pure Zn as control group. We observed that Zn-0.8 wt%Li alloy exhibited low SCC susceptibility. This was attributed to variations in microstructure and deformation mechanism after alloying with Li. In addition, both pure Zn and Zn-0.8 wt%Li alloy did not fracture over a period of 28 days during constant-load immersion test. The magnitude of applied stress was close to physiological condition and thus, we proved the feasibility of both materials as BM.

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The deformation mechanisms of pure Zn and Zn-0.8 wt%Li alloy were different.

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For pure Zn, surface curvatures provided sites for SCC initiation.

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Only shallow cracks on corrosion layer were observed for Zn-0.8 wt%Li alloy.

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Both materials did not fracture after constant-load immersion test.

Development of biodegradable Zn-1Mg-0.1RE (RE = Er, Dy, and Ho) alloys for biomedical applications

Zinc (Zn) and its alloys are receiving great attention as promising biodegradable materials due to their suitable corrosion resistance, good biocompatibility, and highly desirable biofunctionality. Nevertheless, the low mechanical strength of pure Zn impedes its practical clinical application and there have been calls for further research into the Zn alloys and thermomechanical processes to enhance their mechanical properties and biocompatibility. Here, we report on the alloying efficacy of rare earth elements (REEs) including erbium (Er), dysprosium (Dy), and holmium (Ho) on the microstructure, mechanical properties, corrosion and wear behavior, and in vitro biological properties of Zn-1Mg-0.1RE alloys. Microstructural characterization revealed that the addition of 0.1 wt.% REEs had a significant refining effect on the grain size of the α-Zn matrix and the second phases of the alloys. Alloying of the REEs and hot-rolling effectively improved the mechanical properties due to both precipitation strengthening of the second phases of ErZn₅, DyZn₅, and Ho₂Zn₁₇ and grain-refinement strengthening. The highest ultimate tensile strength of 259.4 MPa and yield strength of 234.8 MPa with elongation of 16.8% were achieved in the hot-rolled Zn-1Mg-0.1Ho. Alloying of REEs also improved the wear and corrosion resistance, and slowed down the degradation rate in Hanks' solution. Zn-1Mg-0.1Er showed the highest cytocompatibility of MC3T3-E1 cells cultured directly on the alloy surface and of MG-63 cells cultured in the alloy extract. Zn-1Mg-0.1Dy showed the best anticoagulant property among all the alloys. Overall, these Zn-1Mg-0.1RE (Er, Dy, and Ho) alloys can be considered promising biodegradable metallic materials for orthopedic applications.

Appropriately adapted properties of hot-extruded Zn-0.5Cu-xFe alloys aimed for biodegradable guided bone regeneration membrane application

Appropriately adapted comprehensive mechanical properties, degradation behavior and biocompatibility are prerequisites for the application of Zn-based biodegradable implants. In this study, hot-extruded Zn-0.5Cu-xFe (x = 0.1, 0.2 and 0.4 wt%) alloys were fabricated as candidates for biodegradable materials for guided bone regeneration (GBR) membranes. The hot-extrusion process and Cu alloying were expected mostly to enhance the mechanical properties, and the Fe alloying was added mainly for regulating the degradation. The microstructure, mechanical properties and in vitro degradation behavior were systematically investigated. The ZnCuFe alloys were composed of a Zn matrix and FeZn₁₃ phase. With increasing Fe content, a higher FeZn₁₃ phase precipitation with larger particles was observed. Since elongation declined significantly until fracture with increasing Fe content up to 0.4 wt%, the ZnCuFe (0.2 wt%) alloy achieved a good balance between mechanical strength and ductility, with an ultimate tensile strength of 202.3 MPa and elongation at fracture of 41.2%. Moreover, the addition of Fe successfully accelerated the degradation of ZnCuFe alloys. The ZnCuFe (0.2 wt%) alloy showed relatively uniform corrosion in the long-term degradation test. Furthermore, extracts of the ZnCuFe (0.2 wt%) alloy showed no apparent cytotoxic effects against L929 fibroblasts, Saos-2 osteoblasts or TAg periosteal cells. The ZnCuFe (0.2 wt%) alloy exhibited the potential to inhibit bacterial adhesion of Streptococcus gordonii and mixed oral bacteria. Our study provides evidence that the ZnCuFe (0.2 wt%) alloy can represent a promising material for the application as a suitable GBR membrane.

Structural and mechanical aspects of hypoeutectic Zn-Mg binary alloys for biodegradable vascular stent applications

The study is concerned with the mechanical properties of Zn and three Zn–Mg double alloys with Mg concentrations: 0.5%, 1.0% and 1.5% in the form of rods with a diameter of 5 mm as potential materials for use in biodegradable medical implants, such as vascular stents. The materials were cast, next conventionally hot extruded at 250 °C and finally, hydrostatically extruded (HE) at ambient temperature. Occasionally HE process was carried at liquid nitrogen temperature or in combination with the ECAP process. After HE, the microstructure of the alloys was made up of fine-grained αZn of mean grain size ~1 μm in a 2-phase coat of 50–200 nm nano-grains of the fine αZn + Mg₂Zn₁₁ eutectic. The 3 to 4-fold reduction of grain size as a result of HE allowed an increase in yield strength from 100% to over 200%, elongation to fracture from 100% to thirty fold and hardness over 50% compared to the best literature results for similar alloys. Exceptions accounted for elongation to fracture in case of Zn-0.5 Mg alloy and hardness in case of Zn-1.5 Mg alloy, both of which fell by 20%. For the Zn-0.5 Mg and Zn–1Mg alloys, after immersion tests, no corrosive degradation of plasticity was observed. Achieving these properties was the result of generating large plastic deformations at ambient temperature due to the application of high pressure forming with the cumulative HE method. The results showed that Zn–Mg binary alloys after HE have mechanical and corrosive characteristics, qualifying them for applications in biodegradable implants, including vascular stents.

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Forming under high pressure allows to generate severe deformation in Zn–Mg alloys.

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HE reduces grain size of Zn alloys by 3–4 times in comparison to hot extrusion.

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HE increases YS by 200%, ε_f by 300% and HV by 50% in comparison to literature data.

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In Zn with 0.5 and 1% Mg no ductility reduction after the corrosion test was observed.

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Mechanical and corrosion properties qualify Zn alloys after HE for vascular stents.