Biodegradable Zn-Dy binary alloys with high strength, ductility, cytocompatibility, and antibacterial ability for bone-implant applications

In situ phosphorus-modified Mg2Ge/Zn-Cu composite with improved mechanical, degradation, biotribological properties, and in vitro and in vivo osteogenesis and osteointegration performance for biodegradable bone-implant applications

Zinc (Zn)-based composites are promising biodegradable bone-implant materials because of their good biocompatibility, processability, and biodegradability. Nevertheless, the low interfacial bonding strength, coordinated deformation capacity, and mechanical strength of current Zn-based composites hinder their clinical application. In this study, we developed a biodegradable in situ 4Mg2Ge/Zn-0.3Cu-0.05P composite (denoted ZMGCP) via phosphorus (P) modification and hot-rolling for bone-implant applications. The mechanical properties, corrosion behavior, biotribological performance, in vitro cytocompatibility and osteogenic differentiation, and in vivo osteogenesis and osteointegration of the as-cast (AC) and hot-rolled (HR) ZMGCP samples were systematically evaluated and compared to those of 4Mg2Ge/Zn-0.3Cu (denoted ZMGC). The primary and eutectic reinforcement Mg2Ge phases formed during solidification were refined after P modification and hot-rolling. The HR ZMGCP exhibited the best tensile properties among all the samples with an ultimate tensile strength of 288.9 MPa, a yield strength of 194.5 MPa, and an elongation of 17.7 %. The HR ZMGCP showed the lowest corrosion rate of 336 μm/a, 186 μm/a, and 61.7 μm/a as measured by potentiodynamic polarization, electrochemical impedance spectroscopy, and immersion testing, respectively, among all the samples in Hanks' solution. The HR ZMGCP also showed higher biotribological resistance than its ZMGC counterpart. The HR ZMGCP exhibited the highest in vitro cytocompatibility, the best osteogenesis capability and angiogenesis property among the HR samples of pure Zn, ZMGC, and ZMGCP. Furthermore, the HR ZMGCP displayed complete in vivo biocompatibility, osteogenesis, osteointegration capability, and an appropriate degradation rate, showing significant potential for a biodegradable bone-implant material.

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.

Study on the Bioactivity Response of the Newly Developed Zn-Cu-Mn/Mg Alloys for Biodegradable Implant Application

Scaffolds play a crucial role in bone tissue engineering to support the defect area through bone regeneration and defect reconstruction. Promising tissue regeneration without negative repercussions and avoidance of the lifelong presence inside the body make bioresorbable metals prosper in the field of regenerative medicine. Recently, Zn and its alloys have emerged as promising biodegradable materials for their moderate degradation rate and satisfactory biocompatibility. Nevertheless, it is very challenging for cells to adhere and grow over the Zn surface alone, which influences the tissue-implant integration. In this study, an attempt has been made to systematically investigate the bioactivity responses in terms of in vitro hemocompatibility, cytotoxicity, antibacterial activity, and in vivo biocompatibility of newly developed Zn-2Cu-0.5Mn/Mg alloy scaffolds with different surface roughness. The rough surface of Zn-2Cu-0.5Mg shows the highest degradation rate of 0.16 mm/yr. The rough surface exhibits a prominent role in the adsorption of protein, further enhancing cell adhesion. Concentration-dependent alloy extract shows the highest cell proliferation for 12.5% of the extract with a maximum cell viability of 101% in Zn-2Cu-0.5Mn and 108% in Zn-2Cu-0.5Mg after 3 d. Acceptable hemolysis percentages (less than 5%) with promising anticoagulation properties are observed for all of the conditions. Enhanced antibacterial (Staphylococcus aureus and Escherichia coli) activity due to a significant effect of ions illustrates the maximum killing effect on the bacterial colony for the rough Zn-2Cu-0.5Mg alloy. In addition, it is observed that for rough Zn-2Cu-0.5Mn/Mg alloys, the inflammatory response is minimal after subcutaneous implantation, and neo-bone tissue forms in the defect areas of the rat femur with satisfactory biosafety response. The osseointegration property of the Zn-2Cu-0.5Mg alloy is comparable to that of the Zn-2Cu-0.5Mn alloy. Therefore, the rough surface of the Zn-2Cu-0.5Mg alloy has the potential to enhance biocompatibility and promote better osseointegration activity with host tissues for various biomedical applications.

Electrospun polycaprolactone-chitosan nanofibers on a zinc mesh as biodegradable guided bone-regeneration membranes with enhanced mechanical, antibacterial, and osteogenic properties for alveolar bone-repair applications

Guided bone-regeneration membrane (GBRM) is commonly used in bone-repair surgery because it blocks fibroblast proliferation and provides spatial support in bone-defect spaces. However, the need for removal surgery and the lack of antibacterial properties of conventional GBRM limit its therapeutic applicability for alveolar bone defects. Here we developed a GBRM for alveolar bone-repair and -regeneration applications through double-sided electrospinning of polycaprolactone and chitosan layers on a Zn mesh surface (denoted DSZM). The DSZM showed a UTS of ∼25.6 MPa, elongation of ∼16.1%, strength-elongation product of ∼0.413 GPa%, and ultrahigh spatial maintenance ability, and the UTS was over 6 times higher than that of commercial Bio-Gide membrane. The DSZM exhibited a corrosion rate of ∼17 µm/y and a Zn ion concentration of ∼0.23 µg/ml after 1 month of immersion in Hanks' solution. The DSZM showed direct and indirect cytocompatibility with exceptional osteogenic differentiation and calcium deposition toward MC3T3-E1 cells. Further, the DSZM showed strongly sustained antibacterial activity against S. aureus and osteogenesis in a rat critical-sized maxillary defect model. Overall, the DSZM fits the requirements for alveolar bone-repair and -regeneration applications as a biodegradable GBRM material due to its spatial support, suitable degradability, cytocompatibility, and antibacterial and osteogenic capabilities. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, antibacterial ability and osteogenic properties of electrospun PCL-CS nanofiber on Zn mesh as biodegradable guided bone-regeneration membrane for alveolar bone-repair applications. Our findings demonstrate that the DSZM prepared by double-sided electrospinning of PCL-CS layers on Zn mesh showed a UTS of ∼25.6 MPa, elongation of ∼16.1%, strength-elongation product of ∼0.413 GPa%, and ultrahigh spatial maintenance ability, and the UTS was over 6 times greater than that of commercial Bio-Gide® membrane. The DSZM showed direct and indirect cytocompatibility with exceptional osteogenic differentiation and calcium deposition toward MC3T3-E1 cells. Further, the DSZM showed strongly sustained antibacterial activity against S. aureus and osteogenesis in a rat critical-sized maxillary defect model.

Preparation, Mechanical Properties, and Degradation Behavior of Zn-1Fe-xSr Alloys for Biomedical Applications

As biodegradable materials, zinc (Zn) and zinc-based alloys have attracted wide attention owing to their great potential in biomedical applications. However, the poor strength of pure Zn and binary Zn alloys limits their wide application. In this work, a stir casting method was used to prepare the Zn-1Fe-xSr (x = 0.5, 1, 1.5, 2 wt.%) ternary alloys, and the phase composition, microstructure, tensile properties, hardness, and degradation behavior were studied. The results indicated that the SrZn13 phase was generated in the Zn matrix when the Sr element was added, and the grain size of Zn-1Fe-xSr alloy decreased with the increase in Sr content. The ultimate tensile strength (UTS) and Brinell hardness increased with the increase in Sr content. The UTS and hardness of Zn-1Fe-2Sr alloy were 141.65 MPa and 87.69 HBW, which were 55.7% and 58.4% higher than those of Zn-1Fe alloy, respectively. As the Sr content increased, the corrosion current density of Zn-1Fe-xSr alloy increased, and the charge transfer resistance decreased significantly. Zn-1Fe-2Sr alloy had a degradation rate of 0.157 mg·cm-2·d-1, which was 118.1% higher than the degradation rate of Zn-1Fe alloy. Moreover, the degradation rate of Zn-1Fe-xSr alloy decreased significantly with the increase in immersion time.

Research on a new type of ureteral stent material Zn-2Cu-0.5Fe-xMn with controllable degradation rate

The placement of ureteral stents plays a crucial role in the treatment of ureteral strictures, therefore requiring high material performance standards. In addition, depending on the etiology of ureteral strictures, there are significant differences in the retention time of ureteral stents, thus requiring different degradation rates for the stents. Therefore, it is crucial to develop stent materials with high performance and controllable degradation rates. This study explores the potential of Zn-2Cu-0.5Fe-xMn alloy as a ureteral stent material, utilizing the antibacterial effect of copper ions, the strengthening effect of Fe element on Zn-based alloys, and the accelerated degradation effect of Mn element. The research found that with the increase in Mn content, the average grain size of the alloy and the size of (Fe, Mn)Zn13 phase gradually increased, leading to a decrease in hardness. The corrosion rate of the alloy increased with the increase in Mn content, attributed to changes in grain size and standard electrode potential differences between elements. Due to the antibacterial effects of Zn ions and Cu ions, the Zn-2Cu-0.5Fe-xMn alloy exhibits good anti-stone formation capabilities. Furthermore, the alloy also demonstrates acceptable cytotoxicity. Therefore, the Zn-2Cu-0.5Fe-xMn alloy is expected to become an important implant material in urological surgery.

Mechanical properties, corrosion behavior, and in vitro and in vivo biocompatibility of hot-extruded Zn-5RE (RE = Y, Ho, and Er) alloys for biodegradable bone-fixation applications

Biodegradable Zn alloys have significant application potential for hard-tissue implantation devices owing to their suitable degradation behavior and favorable biocompatibility. Nonetheless, pure Zn and its alloys in the as-cast state are mechanically instable and low in strength, which restricts their clinical applicability. Here, we report the exceptional mechanical, corrosion, and biocompatibility properties of hot-extruded Zn-5RE (wt.%, RE = rare earth of Y; or Ho; or Er) alloys intended for use in biodegradable bone substitutes. The microstructural characteristics, mechanical behavior, corrosion resistance, cytocompatibility, osteogenic differentiation, and capacity of osteogenesis in vivo of the Zn-5RE alloys are comparatively investigated. The Zn-5Y alloy demonstrates the best tensile properties, encompassing a 138 MPa tensile yield strength, a 302 MPa ultimate tensile strength, and 63% elongation, while the Zn-5Ho alloy shows the highest compression yield strength of 260 MPa and Vickers hardness of 104 HV. The Zn-5Er alloy shows a 126 MPa tensile yield strength, a 279 MPa ultimate tensile strength, 52% elongation, a 196 MPa compression yield strength, and a 101 HV Vickers microhardness. Further, the Zn-5Er alloy has a 130 µm per year corrosion rate in electrochemical tests and a 26 µm per year degradation rate in immersion tests, which is the lowest among the tested alloys. It also has the best in vitro osteogenic differentiation ability and capacity for osteogenesis and osteointegration in vivo after implantation in rat femurs among the Zn-5RE alloys, indicating promising potential in load-bearing biodegradable internal bone-fixation applications. STATEMENT OF SIGNIFICANCE: This work reports the exceptional mechanical, corrosion, and biocompatibility properties of hot-extruded (HE) Zn-5 wt.%-rare earth (Zn-5RE) alloys using single yttrium (Y), holmium (Ho), and erbium (Er) alloying for biodegradable bone-implant applications. Our findings demonstrate that the HE Zn-5Er alloy showed σuts of 279 MPa, tensile yield strength of 126 MPa, elongation of 51.6%, compression yield strength of 196 MPa, and microhardness of 101.2 HV. Further, HE Zn-5Er showed the lowest electrochemical corrosion rate of 130 µm/y and lowest degradation rate of 26 µm/y, and the highest in vitro osteogenic differentiation ability, in vivo osteogenesis, and osteointegration ability after implantation in rat femurs among the Zn-5RE alloys, indicating promising potential in load-bearing biodegradable internal bone-fixation applications.

Material synthesis and design optimization of biomaterials for biomedical implant applications

Introduction

In the modern era, the use of biomaterials in orthopaedics has revolutionised the healthcare sector. Traditionally, some non-biodegradable materials such as titanium and stainless steel are used as biomaterials. However, issues such as toxicity, poor tissue adhesion, and stress-shielding effect can occur with non-biodegradable materials for bone fracture fixation. Several biodegradable materials have been developed to resolve these issues but have not yet been appropriately industrialized for implant applications. These substances can be classified into metals, ceramics, and polymers, which can be blended to create composites that enhance biocompatibility and biomechanical characteristics.

Methods

This study began by contrasting the biocompatibility and mechanical compatibility among various alloys: biodegradable low entropy (BLE) alloys, biodegradable medium entropy (BME) alloys, biodegradable high entropy (BHE) alloys, and non-biodegradable medium entropy (NBME) alloys. Additionally, the design morphology of bio-implants like plates, screws, and others was inspected. Moreover, a meta-analysis was conducted to optimize the design of biomaterials, ensuring appropriate biocompatibility and degradation rate. A subsequent statistical analysis was executed to determine the optimal material concentration for bio-implant alloy creation.

Results

Initially, in this paper, the advantages of biodegradable materials over conventional non-biodegradable materials are discussed and bibliometric analysis is done to show recent research contributions in the field of biomedical implant application. Then compared biocompatibility and mechanical compatibility among BLE alloys, BME alloys, BHE alloys, NBME alloys. Furthermore, investigated the design morphology of bio-implants such as plates and screws. Also presented a meta-analysis for design optimization of biomaterials to meet suitable biocompatibility and biodegradation rates and presented a statistical analysis among them, which helps to select the appropriate material concentration for bio-implant alloy formation.

Conclusion

It was observed that in biodegradable materials, tensile strength is in the pattern of NBME > BHE > BME > BLE, and the degradation rate is in the pattern of BME > NBME > BHE > BLE. This study suggests that biodegradable materials (BLE and BME) are a much better choice than non-biodegradable materials in orthopaedic applications. It was also observed that a Biodegradable locking compression plate (BLCP) can provide the necessary strength and performance. Further, the systematic meta-analysis presented herein furnishes crucial data to researchers, guiding them in enhancing the efficiency of diverse biomaterials and optimizing their designs.

Synthesis, antimicrobial activity and application of polymers of praseodymium complexes based on pyridine nitrogen oxide

The traditional pyridine nitrogen oxide-based antimicrobial agents are often associated with health risks due to heavy metal enrichment. To mitigate this concern, we synthesized two novel complexes, Pr2(mpo)6(H2O)2 and Pr(hpo)(mpo)2(H2O)2, and integrated rare-earth salts, Hhpo (2-hydroxypyridine-N-oxide) and Nampo (2-mercapto-pyridine-N-oxide sodium salt). These complexes were characterized through infrared analysis, elemental analysis, thermogravimetric analysis, and X-ray crystallographic analysis. Our comparative analyses demonstrate that the synthesized rare-earth complexes exhibit stronger antimicrobial activity against Staphylococcus aureus (S. aureus ATCC6538) and Escherichia coli (E. coli ATCC25922) compared to the ligands and rare-earth salts alone. Quantitative results revealed the lowest inhibitory concentrations of the two complexes against S. aureus ATCC6538 and E. coli ATCC25922 at 3.125 μg mL-1, 6.25 μg mL-1, 3.125 μg mL-1 and 6.25 μg mL-1, respectively. Preliminary investigations indicated that the antibacterial mechanism of these complexes involved promoting intracellular substance exudation to achieve antibacterial effects. Incorporation of these complexes into polymeric antimicrobial films resulted in a potent antimicrobial effect, achieving a 100% inhibition rate against S. aureus ATCC6538 and E. coli ATCC25922 at a low addition level of 0.6 wt%. Our results suggest that nitrogen oxide-based praseodymium complexes have potential for various antimicrobial applications.

Enhanced Mechanical Properties, Corrosion Resistance, Cytocompatibility, Osteogenesis, and Antibacterial Performance of Biodegradable Mg-2Zn-0.5Ca-0.5Sr/Zr Alloys for Bone-Implant Application

Magnesium (Mg) alloys are widely used in bone fixation and bone repair as biodegradable bone-implant materials. However, their clinical application is limited due to their fast corrosion rate and poor mechanical stability. Here, the development of Mg-2Zn-0.5Ca-0.5Sr (MZCS) and Mg-2Zn-0.5Ca-0.5Zr (MZCZ) alloys with improved mechanical properties, corrosion resistance, cytocompatibility, osteogenesis performance, and antibacterial capability is reported. The hot-extruded (HE) MZCZ sample exhibits the highest ultimate tensile strength of 255.8 ± 2.4 MPa and the highest yield strength of 208.4 ± 2.8 MPa and an elongation of 15.7 ± 0.5%. The HE MZCS sample shows the highest corrosion resistance, with the lowest corrosion current density of 0.2 ± 0.1 µA cm-2 and the lowest corrosion rate of 4 ± 2 µm per year obtained from electrochemical testing, and a degradation rate of 368 µm per year and hydrogen evolution rate of 0.83 ± 0.03 mL cm-2 per day obtained from immersion testing. The MZCZ sample shows the highest cell viability in relation to MC3T3-E1 cells among all alloy extracts, indicating good cytocompatibility except at 25% concentration. Furthermore, the MZCZ alloy shows good antibacterial capability against Staphylococcus aureus.

Systematic review of the osteogenic effect of rare earth nanomaterials and the underlying mechanisms

Rare earth nanomaterials (RE NMs), which are based on rare earth elements, have emerged as remarkable biomaterials for use in bone regeneration. The effects of RE NMs on osteogenesis, such as promoting the osteogenic differentiation of mesenchymal stem cells, have been investigated. However, the contributions of the properties of RE NMs to bone regeneration and their interactions with various cell types during osteogenesis have not been reviewed. Here, we review the crucial roles of the physicochemical and biological properties of RE NMs and focus on their osteogenic mechanisms. RE NMs directly promote the proliferation, adhesion, migration, and osteogenic differentiation of mesenchymal stem cells. They also increase collagen secretion and mineralization to accelerate osteogenesis. Furthermore, RE NMs inhibit osteoclast formation and regulate the immune environment by modulating macrophages and promote angiogenesis by inducing hypoxia in endothelial cells. These effects create a microenvironment that is conducive to bone formation. This review will help researchers overcome current limitations to take full advantage of the osteogenic benefits of RE NMs and will suggest a potential approach for further osteogenesis research.

Biodegradable Zn-5Dy Alloy with Enhanced Osteo/Angio-Genic Activity and Osteointegration Effect via Regulation of SIRT4-Dependent Mitochondrial Function

Zinc (Zn)-dysprosium (Dy) binary alloys are promising biodegradable bone fracture fixation implants owing to their attractive biodegradability and mechanical properties. However, their clinical application is a challenge for bone fracture healing, due to the lack of Zn-Dy alloys with tailored proper bio-mechanical and osteointegration properties for bone regeneration. A Zn-5Dy alloy with high strength and ductility and a degradation rate aligned with the bone remodeling cycle is developed. Here, mechanical stability is further confirmed, proving that Zn-5Dy alloy can resist aging in the degradation process, thus meeting the mechanical requirements of fracture fixation. In vitro cellular experiments reveal that the Zn-5Dy alloy enhances osteogenesis and angiogenesis by elevating SIRT4-mediated mitochondrial function. In vivo Micro-CT, SEM-EDS, and immunohistochemistry analyses further indicate good biosafety, suitable biodegradation rate, and great osteointegration of Zn-5Dy alloy during bone healing, which also depends on the upregulation of SIRT4-mediated mitochondrial events. Overall, the study is the first to report a Zn-5Dy alloy that exerts remarkable osteointegration properties and has a strong potential to promote bone healing. Furthermore, the results highlight the importance of mitochondrial modulation and shall guide the future development of mitochondria-targeting materials in enhancing bone fracture healing.

A biodegradable Zn-5Gd alloy with biomechanical compatibility, cytocompatibility, antibacterial ability, and in vitro and in vivo osteogenesis for orthopedic applications

Zinc (Zn) and some of its alloys are recognized as promising biodegradable implant materials due to their acceptable biocompatibility, facile processability, and moderate degradation rate. Nevertheless, the limited mechanical properties and stability of as-cast Zn alloys hinder their clinical application. In this work, hot-rolled (HR) and hot-extruded (HE) Zn-5 wt.% gadolinium (Zn-5Gd) samples were prepared by casting and respectively combining with hot rolling and hot extrusion for bone-implant applications. Their microstructure evolution, mechanical properties, corrosion behavior, cytotoxicity, antibacterial ability, and in vitro and in vivo osteogenesis were systematically evaluated. The HR and HE Zn-5Gd exhibited significantly improved mechanical properties compared with those of their pure Zn counterparts and the HR Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%, all of which are greater than the mechanical properties required for bone-implant materials. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks' solution and the HE Zn-5Gd had the lowest corrosion rate of 155 µm/y measured by electrochemical corrosion and degradation rate of 26.9 µm/y measured by immersion testing. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, high antibacterial effects against S. aureus, and better in vitro osteogenic activity than their pure Zn counterparts. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion behaviors, cytocompatibility, antibacterial ability, in vitro and in vivo osteogenesis of biodegradable Zn-Gd alloy for bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn-5Gd showed a unique combination of tensile properties with an ultimate tensile strength of ∼311.6 MPa, yield strength of ∼236.5 MPa, and elongation of ∼40.6%. The HR and HE Zn-5Gd showed higher corrosion resistance than their pure Zn counterpart in Hanks' solution. The HR and HE Zn-5Gd showed high cytocompatibility toward MC3T3-E1 and MG-63 cells, good antibacterial effects against S. aureus, and better in vitro osteogenic activity. Furthermore, the HE Zn-5Gd exhibited better in vivo biocompatibility, osteogenesis, and osteointegration ability than pure Zn and pure Ti.

Mechanical properties, corrosion behavior, and cytotoxicity of biodegradable Zn/Mg multilayered composites prepared by accumulative roll bonding process

Zinc (Zn), magnesium (Mg), and their respective alloys have attracted great attention as biodegradable bone-implant materials due to their excellent biocompatibility and biodegradability. However, the poor mechanical strength of Zn alloys and the rapid degradation rate of Mg alloys limit their clinical application. The manufacture of Zn and Mg bimetals may be a promising way to improve their mechanical and degradation properties. Here we report on Zn/Mg multilayered composites prepared via an accumulative roll bonding (ARB) process. With an increase in the number of ARB cycles, the thicknesses of the Zn layer and the Mg layer were reduced, while a large number of heterogeneous interfaces were introduced into the Zn/Mg multilayered composites. The composite samples after 14 ARB cycles showed the highest yield strength of 411±3 MPa and highest ultimate tensile strength of 501±3 MPa among all the ARB processed samples, significantly higher than those of the Zn/Zn and Mg/Mg multilayered samples. The Zn and Mg layers remained continuous in the Zn/Mg composite samples after annealing at 150 °C for 10 min, resulting in a decrease in yield strength from 411±3 MPa to 349±3 MPa but an increase in elongation from 8±1% to 28±1%. The degradation rate of the Zn/Mg multilayered composite samples in Hanks' solution was ranged from 127±18 µm/y to 6±1 µm/y. The Zn/Mg multilayered composites showed over 100% cell viability with their 25% and 12.5% extracts in relation to MG-63 cells after culturing for 3 d, indicating excellent cytocompatibility. STATEMENT OF SIGNIFICANCE: This work reports a biodegradable Zn/Mg multilayered composite prepared by accumulative roll bonding (ARB) process. The yield and ultimate tensile strength of the Zn/Mg multilayered composites were improved due to grain refinement and the introduction of a large number of heterogeneous interfaces. The composite samples after 14 ARB cycles showed the highest yield strength of 411±3 MPa and highest ultimate tensile strength of 501±3 MPa among all the ARB processed samples. The degradation rate of the Zn/Mg multilayered composite meets the required degradation rate for biodegradable bone-implant materials. The results demonstrated that it is a very promising approach to improve the strength and biocompatibility of biodegradable Zn-based alloys.

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.

Bioactivity Features of a Zn-1%Mg-0.1%Dy Alloy Strengthened by Equal-Channel Angular Pressing

The structure, phase composition, corrosion and mechanical properties, as well as aspects of biocompatibility in vitro and in vivo, of a Zn-1%Mg-0.1%Dy alloy after equal-channel angular pressing (ECAP) were studied. The structure refinement after ECAP leads to the formation of elongated α-Zn grains with a width of ~10 µm and of Mg- and Dy-containing phases. In addition, X-ray diffraction analysis demonstrated that ECAP resulted in the formation of the basal texture in the alloy. These changes in the microstructure and texture lead to an increase in ultimate tensile strength up to 262 ± 7 MPa and ductility up to 5.7 ± 0.2%. ECAP slows down the degradation process, apparently due to the formation of a more homogeneous microstructure. It was found that the alloy degradation rate in vivo after subcutaneous implantation in mice is significantly lower than in vitro ones. ECAP does not impair biocompatibility in vitro and in vivo of the Zn-1%Mg-0.1%Dy alloy. No signs of suppuration, allergic reactions, the formation of visible seals or skin ulcerations were observed after implantation of the alloy. This may indicate the absence of an acute reaction of the animal body to the Zn-1%Mg-0.1%Dy alloy in both states.

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.