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.

Phase Field Study on the Spinodal Decomposition of ß Phase in Zr-Nb-Ti Alloys.

In this study, a phase field method based on the Cahn-Hilliard equation was used to simulate the spinodal decomposition in Zr-Nb-Ti alloys, and the effects of Ti concentration and aging temperature (800-925 K) on the spinodal structure of the alloys for 1000 min were investigated. It was found that the spinodal decomposition occurred in the Zr-40Nb-20Ti, Zr-40Nb-25Ti and Zr-33Nb-29Ti alloys aged at 900 K with the formation of the Ti-rich phases and Ti-poor phases. The spinodal phases in the Zr-40Nb-20Ti, Zr-40Nb-25Ti and Zr-33Nb-29Ti alloys aged at 900 K were in an interconnected non-oriented maze-like shape, a discrete droplet-like shape and a clustering sheet-like shape in the early aging period, respectively. With the increase in Ti concentration of the Zr-Nb-Ti alloys, the wavelength of the concentration modulation increased but amplitude decreased. The aging temperature had an important influence on the spinodal decomposition of the Zr-Nb-Ti alloy system. For the Zr-40Nb-25Ti alloy, with the increase in the aging temperature, the shape of the rich Zr phase changed from an interconnected non-oriented maze-like shape to a discrete droplet-like shape, and the wavelength of the concentration modulate increased quickly to a stable value, but the amplitude decreased in the alloy. As the aging temperature increased to 925 K, the spinodal decomposition did not occur in the Zr-40Nb-25Ti alloy.

Selective Laser Melted Magnesium Alloys: Fabrication, Microstructure and Property.

As the lightest metal structural material, magnesium and its alloys have the characteristics of low density, high specific strength and good biocompatibility, which gives magnesium alloys broad application prospects in fields of biomedicine, transportation, and aerospace. Laser selective melting technology has the advantages of manufacturing complex structural parts, high precision and high degree of freedom. However, due to some disadvantages of magnesium alloy, such as low boiling point and high vapor pressure, the application of it in laser selective melting was relatively undeveloped compared with other alloys. In this paper, the fabrication, microstructure, mechanical performance and corrosion resistance property of magnesium alloys were summarized, and the potential applications and the development direction of selective laser melting magnesium alloys in the future are prospected.

Orientation Control for Nickel-Based Single Crystal Superalloys: Grain Selection Method Assisted by Directional Columnar Grains.

The service performance of single crystal blades depends on the crystal orientation. A grain selection method assisted by directional columnar grains is studied to control the crystal orientation of Ni-based single crystal superalloys. The samples were produced by the Bridgman technique at withdrawal rates of 100 µm/s. During directional solidification, the directional columnar grains are partially melted, and a number of stray grains are formed in the transition zone just above the melt-back interface. The grain selected by this method was one that grew epitaxially along the un-melted directional columnar grains. Finally, the mechanism of selection grain and application prospect of this grain selection method assisted by directional columnar grains is discussed.

Effect of Rolling Treatment on Microstructure, Mechanical Properties, and Corrosion Properties of WE43 Alloy.

Magnesium alloys show broad application prospects as biodegradable implanting materials due to their good biocompatibility, mechanical compatibility, and degradability. However, the influence mechanism of microstructure evolution during forming on the mechanical properties and corrosion resistance of the magnesium alloy process is not clear. Here, the effects of rolling deformation, such as cold rolling, warm rolling, and hot rolling, on the microstructure, mechanical properties, and corrosion resistance of the WE43 magnesium alloy were systematically studied. After rolling treatment, the grains of the alloy were significantly refined. Moreover, the crystal plane texture strength and basal plane density decreased first and then increased with the increase in rolling temperature. Compared with the as-cast alloy, the strength of the alloy after rolling was significantly improved. Among them, the warm-rolled alloy exhibited the best mechanical properties, with a tensile strength of 346.7 MPa and an elongation of 8.9%. The electrochemical experiments and immersion test showed that the hot working process can greatly improve the corrosion resistance of the WE43 alloy. The hot-rolled alloy had the best corrosion resistance, and its corrosion resistance rate was 0.1556 ± 0.18 mm/year.

In vitro and in vivo assessment of the effect of biodegradable magnesium alloys on osteogenesis.

Magnesium (Mg) and some of its alloys are considered promising biodegradable metallic biomaterials for bone implant applications. The osteogenesis effect of Mg alloys is widely reported; however, the underlying mechanisms are still not clear. In this study, pure Mg, Mg-3Zn, and Mg-2Zn-1Mn were prepared, and their degradation behavior, biocompatibility, and osteogenesis effect were systematically assessed both in vitro and in vivo. Primary rat bone marrow-derived mesenchymal stem cells (BMSCs) were used to evaluate the biocompatibility of the prepared Mg alloys, and a rat femur fracture model was used to assess the stimulating effect of these alloys on bone-tissue formation. Mg-2Zn-1Mn showed higher corrosion resistance and more stable degradation behavior than pure Mg and Mg-3Zn. Extracts of the three materials showed significant stimulating effects on osteogenic differentiation of BMSCs along with non-cytotoxicity. Implantation of Mg-2Zn-1Mn wires into the femur of rats demonstrated superior histocompatibility, stable degradation, and notable promotion of osteogenesis without systemic toxicity. Moreover, the results of both in vitro and in vivo assessments demonstrated that bone morphogenetic proteins and fibroblast growth factor receptors are involved in the stimulating effect of Mg alloys. STATEMENT OF SIGNIFICANCE: This work reports the degradation behavior, biocompatibility, and osteogenic effect of pure Mg and Mg-3Zn and Mg-2Zn-1Mn alloys in both in vitro and in vivo conditions. Mg-2Zn-1Mn showed higher corrosion resistance and more stable degradation behavior than pure Mg and Mg-3Zn. The extracts of the three materials showed a significant stimulating effect on osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs) along with non-cytotoxicity. Mg-2Zn-1Mn wires implanted into the femur of rats showed good histocompatibility, stable degradation, and notable promotion of osteogenesis without systemic toxicity. The results of the present study suggest that bone morphogenetic proteins (BMPs) and fibroblast growth factor receptors (FGFRs) are involved in the stimulating effect of Mg alloys on osteogenesis.

Comparative analysis of the microbial community and nutritional quality of sufu.

Sufu is a type of fermented food with abundant nutrients and delicious taste. It is made from the fermentation of tofu by various microorganisms. In this study, three types of sufu were prepared through natural fermentation: (NF), single-strain fermentation (SF), and mixed-strain fermentation (MF). Microbial species, amino acids, and fatty acids were identified to investigate dynamic changes in nutritional quality and microbial flora in sufu. The results showed that the number of microbial species in NF sufu was the highest (n = 284), whereas that in SF sufu was the lowest (n = 194). Overall, 153 microbial species were found in all three types of sufu. Relative abundance analysis also revealed that Tetragonococcus, Bacillus, Acinetobacter, and Staphylococcus were the main bacteria in sufu. However, there was a large number of harmful bacteria such as Enterococcaceae in NF sufu. The levels of various nutrients were low in SF sufu, whereas the contents of protein and soy isoflavones were higher in NF and MF sufu. Seventeen kinds of amino acids were detected, comprising seven essential amino acids and ten other amino acids. The contents of essential amino acids and essential fatty acids were higher in MF sufu than the other two types, resulting in its high nutritional value. The sufu produced through the three fermentation methods differed significantly (p < .05) in terms of microbial flora and nutritional quality.

Impact of scandium on mechanical properties, corrosion behavior, friction and wear performance, and cytotoxicity of a ß-type Ti-24Nb-38Zr-2Mo alloy for orthopedic applications.

ß-type titanium (Ti) alloys have been extensively investigated as orthopedic implant materials due to their unique combination of low elastic modulus, high specific strength, corrosion resistance, and biocompatibility. In this study the mechanical properties, corrosion behavior, friction and wear performance, and cytotoxicity of ß-type Ti-24Nb-38Zr-2Mo (TNZM) and Ti-24Nb-38Zr-2Mo-0.1Sc (TNZMS) have been comparatively investigated for orthopedic applications. Cold-rolling (CR) and cold-rolling plus solution-treatment (CR+ST) were performed on the as-cast (AC) alloys and their microstructures and material properties were characterized. The impact of Sc addition on the mechanical and corrosion properties, friction and wear behavior, and in vitro cytocompatibility of the TNZMS alloy was assessed. The CR+ST TNZMS alloy exhibited the best combination of properties among all the alloy samples, with a yield strength of 780 MPa, ultimate strength of 809 MPa, elongation of 19%, Young's modulus of 65.4 GPa, and hardness of 265 HV. Electrochemical testing in Hanks' Solution indicated that the CR+ST TNZMS sample also showed the highest corrosion resistance with a corrosion potential of -0.234 V, corrosion current density of 0.07 µA/cm2, and corrosion rate of 1.2 µm/y. Friction and wear testing revealed that the TNZMS alloy showed higher wear resistance compared to the TNZM alloy and the wear resistance of the different samples was ranked CR > CR+ST > AC. Finally, both the CR+ST TNZM and TNZMS showed no-cytotoxicity towards MG-63 cells and the TNZMS exhibited slightly higher cytocompatibility than the TNZM alloy. STATEMENT OF SIGNIFICANCE: This work reports the ß-type Ti-24Nb-38Zr-2Mo (TNZM) and Ti-24Nb-38Zr-2Mo-0.1Sc (TNZMS) alloys fabricated by as-cast (AC), cold-rolling (CR), and cold-rolling plus solution-treatment (CR+ST) for potential orthopedic applications. The experimental results showed that the TNZMS alloy exhibited significantly enhanced mechanical, wear, and corrosion properties than those of TNZM alloy; and the CR+ST TNZMS possess a unique combination of the best mechanical and corrosion properties including a yield strength of 780 MPa, ultimate strength of 809 MPa, elongation of 19%, Young's modulus of 65.4 GPa, and corrosion rate of 1.2 µm/y in Hanks' Solution. Both the CR+ST TNZM and TNZMS alloys exhibited non-cytotoxicity towards MG-63 cells and TNZMS showed a higher cytocompatibility than that of TNZM.

Mg(OH)2 nanoparticles enhance the antibacterial activities of macrophages by activating the reactive oxygen species.

Infection often causes disastrous consequences in all fields of clinical medicine, especially orthopedics. Hence, critical efforts are being made to engineer novel nanomaterials for the treatment of orthopedic infections due to the high biocompatibility and antibacterial properties they possess. The purpose of this study was to investigate the antibacterial effects of magnesium hydroxide (Mg(OH)2 ) nanoparticles (NPs) in vitro and determine their possible mechanisms of action. In this study, Escherichia coli was selected as the pathogenic bacteria and it was found that Mg(OH)2 NPs significantly inhibited the growth of E. coli by promoting nucleic acid leakage, inhibiting protein synthesis, and suppressing the metabolic activity. The minimum inhibitory concentration for these bacteria was determined to be 4.4 µg/ml. In vitro flow cytometry and immunofluorescence tests indicated that Mg(OH)2 NPs induced the macrophages to generate reactive oxygen species to kill the bacteria. To understand the mechanisms involved in this process, western blotting was performed and it was found that Mg(OH)2 NPs activated the phosphatidylinositol-3-kinase/serine-threonine kinase (PI3K/Akt) signaling pathway of macrophages to enhance their phagocytosis with no obvious cytotoxicity. Thus, Mg(OH)2 NPs are a suitable choice to develop promising agents or coating materials for the treatment of clinically widespread infections in view of their safety, biocompatibility, and powerful antibacterial properties.

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.

Microstructure, mechanical properties, degradation behavior, and biocompatibility of porous Fe-Mn alloys fabricated by sponge impregnation and sintering techniques.

In this study, porous iron (Fe)-manganese (Mn) alloys with high porosity were successfully prepared by sponge impregnation and sintering (SIS). The compositions of the porous Fe-Mn alloys were strongly dependent on the sintering temperature, and the Mn content was ~44, 30, and 12 wt.% for alloys sintered at 1100, 1150, and 1200 °C, respectively. The porous Fe-Mn alloys exhibited a well-interconnected porous structure with ~85% porosity and average pore size ranging from 375 to 500 um. The porous Fe-44Mn and Fe-30Mn alloys were mainly composed of a γ-austenite phase, while the porous Fe-12Mn was composed of an α-ferrite phase. The yield strength and elastic modulus of the porous Fe-Mn alloys ranged from 6 to 10 MPa and from 0.12 to 0.37 GPa, respectively, similar to those of cancellous bone. The degradation rate of the porous Fe-Mn alloys decreased over time during immersion in simulated body fluid (SBF), and was 1.0 mm/year for Fe-44Mn, 0.81 mm/year for Fe-30Mn, 0.41 mm/year for Fe-12Mn, and 0.33 mm/year for pure Fe after 14 d SBF immersion. Moreover, the porous Fe-Mn alloys exhibited good biocompatibility with clearly enhanced cell proliferation after direct culturing of osteoblastic MC3T3-E1 cells for 7 d. Thus, these porous Fe-Mn alloys can be anticipated to be promising biodegradable implant materials. STATEMENT OF SIGNIFICANCE: This work reports on porous Fe-Mn alloys with high porosity, suitable mechanical properties and degradation rate, and good biocompatibility. The porous alloys prepared by sponge impregnation and sintering exhibited a well-interconnected porous structure with ~85% porosity and average pore size ranging from 375 to 500 um. The yield strength and elastic modulus of the porous alloys ranged from 6 to 10 MPa and from 0.12 to 0.37 GPa, respectively, similar to those of cancellous bone. The degradation rates in simulated body fluid (SBF) were ~1.0 mm/year for Fe-44Mn, 0.81 mm/year for Fe-30Mn, and 0.41 mm/year for Fe-12Mn, respectively. Moreover, the porous Fe-Mn alloys exhibited good biocompatibility with enhanced cell proliferation after direct culturing of osteoblastic MC3T3-E1 cells.

LOC103691336/miR-138-5p/BMPR2 axis modulates Mg-mediated osteogenic differentiation in rat femoral fracture model and rat primary bone marrow stromal cells.

Intramedullary stabilization is frequently used to treat long bone fractures. Since implant removal can become technically very challenging with the potential to cause further tissue damage, biodegradable materials are emerging as alternative options. Magnesium (Mg)-based biodegradable implants have a controllable degradation rate and good tissue compatibility, which makes them attractive for musculoskeletal research. Herein, the degradation of Mg and steel implants, the pathological characteristics and osteoblast differentiation in mice femora were examined. To investigate the molecular mechanism, we analyzed the differentially expressed long noncoding RNAs (lncRNAs) and messenger RNAs (mRNAs) in Mg-implanted or stain-steel-implanted callus tissues. lncRNA LOC103691336 was upregulated in Mg-implanted tissues and most relevant to BMPR2, a kinase receptor of BMPs with an established role in osteogenesis. The knockdown of LOC103691336 attenuated Mg-mediated osteogenic differentiation. Furthermore, miR-138-5p, previously reported to inhibit osteogenic differentiation, could bind to LOC103691336 and BMPR2 in bone marrow stromal cells (BMSCs). LOC103691336 competed with BMPR2 for miR-138-5p binding in BMSCs to attenuate the inhibitory effect of miR-138-5p on BMPR2 expression. Finally, the effect of LOC103691336 knockdown on Mg-mediated osteogenic differentiation could be attenuated by miR-138-5p inhibition. In conclusion, we provided a novel mechanism of Mg implants mediating the osteogenesis differentiation and demonstrated that Mg implants may be promising for improving fracture healing.

Mg-Zn-Mn alloy extract induces the angiogenesis of human umbilical vein endothelial cells via FGF/FGFR signaling pathway.

Magnesium (Mg) and its alloys as a type of different biodegradable materials have been used in the musculoskeletal field because of their excellent biocompatibility, biodegradability and mechanical properties similar to bone; besides, Mg could promote osteoblast differentiation in vitro and induce the formation of new bone in vivo. In the present study, we prepared the extracts of Mg-Zn-Mn alloy and examined their effects on the angiogenesis of human umbilical vein endothelial cells (HUVECs). In the present study, we prepared Mg-Zn-Mn alloy extracts of different concentrations and cultured HUVECs with these extracts. The DNA synthesis capacity, the cell viability, and the tube formation capacity of HUVECs could be significantly induced by 6.25% Mg alloy extract. In the meantime, the ratios of p-FGFR/FGFR, p-PI3K/PI3K, and p-AKT/AKT were significantly increased by 6.25% Mg alloy extract treatment, while decreased by FGFR/FGFR signaling pathway inhibitor BFJ398, indicating that 6.25% Mg alloy extract could promote the angiogenesis of HUVECs via activating FGF/FGFR signaling pathway. In conclusion, these data indicate that 6.25% Mg-Zn-Mn alloy extract induces the angiogenesis of HUVECs via FGF signaling pathway. Further in vivo experiments are needed to further confirm the present in vitro findings.

Investigation on the microstructure, mechanical properties, in vitro degradation behavior and biocompatibility of newly developed Zn-0.8%Li-(Mg, Ag) alloys for guided bone regeneration.

In order to develop a biodegradable guided bone regeneration membrane with the required mechanical properties and high corrosion resistance, Zn-0.8%Li(wt), Zn-0.8%Li-0.2%Mg(wt), and Zn-0.8%Li-0.2%Ag(wt) alloys were cast and hot rolled into 0.1-mm thick sheets. The main secondary phase in Zn-0.8%Li-(Mg, Ag) alloys was the LiZn4 nanoprecipitate. Following the addition of minimal amounts of Mg, the tensile strength of the Zn-0.8%Li-0.2%Mg alloy improved, albeit with a greatly reduced elongation and corrosion resistance. The addition of minimal amounts of Ag refined the microstructure, producing fine equiaxed grains (2.3 µm) in the Zn-0.8%Li-0.2%Ag alloy, and promoted a uniform distribution of LiZn4 nanoprecipitates with increased density and refined size. Therefore, the Zn-0.8%Li-0.2%Ag alloy exhibited optimal tensile strength and the highest corrosion resistance, with its elongation reaching 97.9 ±â€¯8.7%. The corrosion products of Zn-0.8%Li-(Mg, Ag) alloys immersed in Ringer's solution for 35 days mainly consisted of zinc oxide and zinc carbonate. In addition, the cytotoxicity test using L929 cells and the evaluation of bone marrow mesenchymal stem cell proliferation indicated that the Zn-0.8%Li-0.2%Ag alloy had good biocompatibility.

Evaluation of the mechanisms and effects of Mg-Ag-Y alloy on the tumor growth and metastasis of the MG63 osteosarcoma cell line.

Osteosarcoma is a malignant primary bone tumor, which often associates with pulmonary metastasis. The radical surgery of osteosarcoma often requires internal orthopedic implants. Therefore, implants with antitumor properties should be developed. Magnesium (Mg) and its alloys possess great potential as orthopedic materials, given their biodegradable properties, superior osteogenesis performance, and antitumor features. However, problems arise with their uncontrolled degradation rates and their unknown antitumor mechanisms. In our study, when compared with pure Mg, the rare element silver alloyed with yttrium (Ag-Y) could extremely enhance the corrosion resistance of these elements, giving the Ex-Mg-1Ag-1Y alloy better anticorrosion rates. Here, we implanted the Ex-Mg-1Ag-1Y alloy and pure Mg and Ti alloy in vivo around tumors in nude mice (BALB/c). Notably, the local tumor weight in Mg alloy and pure Mg groups were much smaller than that in Ti alloy group in 36 days after surgery (6.59 ± 0.70, 6.76 ± 0.62, and 8.54 ± 0.56 g), while the general scores of lung metastasis in Mg alloy and pure Mg groups were also lower than Ti alloy group (64.50 ± 7.64, 62.73 ± 7.84, and 87.60 ± 9.43). Therefore, the Mg and Ex-Mg-1Ag-1Y alloy, both demonstrated resisting effects against local tumor growth and pulmonary metastasis, which could be performed by changing the extracellular acidosis microenvironment, elevating the Mg concentration, suppressing C-X-C chemokine receptor type 4 (CXCR4) levels, and increasing prostacyclin (PGI2 ) synthesis. Our work revealed that the Ex-Mg-1Ag-1Y alloy may be a promising orthopedic implant for treating osteosarcoma due to its better corrosion resistance and antitumor attributes. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2537-2548, 2019.

In vitro and in vivo evaluation of novel biodegradable Mg-Ag-Y alloys for use as resorbable bone fixation implant.

Magnesium (Mg) alloy is gaining more interest because of its degradability and osteogenic potential. Still, it has some deficiencies, such as its rapid degradation rate, insufficient mechanical property. This research aimed to design a novel biodegradable Mg-argentum (Ag)-yttrium (Y) alloy, and Y was added to improve degradable and mechanical property. Mg-Ag-Y alloys were characterized for mechanical features, practicabilities in vitro and in vivo. The mechanical features results shown that this novel component was similar to native bone tissue in elastic moduli, tensile, and compressive stress. Then mesenchymal stem cells (MSCs) were seeded in alloys to assess cell toxicity in vitro. The results showed that its aqueous extract was suitable for MSCs adhesion and proliferation. Then the alloy was evaluated for biomedical applications in nonfractured distal femora of Sprague Dawley rats for 6 weeks, compared with those of pure-Mg and stainless steel groups. All rats survived, and hematological and histological evaluation showed no abnormal physiology 6 weeks postimplantation, and measurements of serum Mg2+ concentration were within normal levels. X-ray scanning, microcomputed tomography, and histological examinations were performed to evaluate the degradability and osteogenic potential. The results indicated that the degradation rate of alloy was 0.91 mm per year, (range 0.77-1.22 mm), and pure-Mg 1.80 mm per year (1.43-2.26 mm). The new bone quantity was 3.18 mm3 (1.46-4.44 mm3 ) in Mg-Ag-Y alloys group, 1.39 mm3 (0.54-2.32 mm3 ) in pure-Mg group, and none in stainless steel group. These promising results suggest potential clinical application of Mg-Ag-Y alloys for use as resorbable bone fixation implant. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2059-2069, 2018.

Improvement of the mechanical properties and corrosion resistance of biodegradable ß-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy: the adding ß-Ca3(PO4)2, hot extrusion and aging treatment.

In this study, 10%ß-Ca3(PO4)2/Mg-6%Zn (wt.%) composites with Mg-6%Zn alloy as control were prepared by powder metallurgy. After hot extrusion, the as-extruded composites were aged for 72h at 150°C. The effects of the adding ß-Ca3(PO4)2, hot extrusion and aging treatment on their microstructure, mechanical properties and corrosion resistance were investigated. The XRD results identified α-Mg, MgZn phase and ß-Ca3(PO4)2 phase in these composites. After hot extrusion, grains were significantly refined, and the larger-sized ß-Ca3(PO4)2 particles and coarse MgZn phases were broken into linear-distributed ß-Ca3(PO4)2 and MgZn phases along the extrusion direction. After aging treatment, the elements of Zn, Ca, P and O presented a more homogeneous distribution. The compressive strengths of the ß-Ca3(PO4)2/Mg-Zn composites were approximately double those of natural bone, and their densities and elastic moduli matched those of natural bone. The immersion tests and electrochemical tests revealed that the adding ß-Ca3(PO4)2, hot extrusion and aging treatment could promote the formation of protective corrosion product layer on the sample surface in Ringer's solution, which improved corrosion resistance of the ß-Ca3(PO4)2/Mg-Zn composites. The XRD results indicated that the corrosion product layer contained Mg(OH)2, ß-Ca3(PO4)2 and hydroxyapatite (HA). The cytotoxicity assessments showed the as-extruded ß-Ca3(PO4)2/Mg-Zn composite aged for 72h was harmless to L-929 cells. These results suggested that the ß-Ca3(PO4)2/Mg-Zn composites prepared by powder metallurgy were promising to be used for bone tissue engineering.

Biodegradation performance of a chitosan coated magnesium-zinc-tricalcium phosphate composite as an implant.

A Mg-Zn-tricalcium phosphate composite with a chitosan coating was prepared in this investigation to study its biodegradation performance both in vitro and in vivo conditions. The in vitro test results show that the immersion corrosion rate, the pH values of the simulated body fluids and the released metal ion concentration of the chitosan coated composite are all lower than those of the uncoated composite. The in vitro cytotoxicity test shows that the chitosan coated specimens is safe for cellular applications. When the chitosan coated composite is tested in vivo, the concentration of metal ions from the composite observed in the venous blood of Zelanian rabbits is less than the uncoated composite specimens. The chitosan coating slows down the in vivo degradation of the composite after surgery. In vivo testing also indicates that the chitosan coated composite is harmless to important visceral organs, including the heart, kidneys, and liver of the rabbits. The new bone formation surrounding the chitosan coated composite implant shows that the composite improves the concrescence of the bone tissues. The chitosan coating is an effective corrosion resistant layer that reduces the hydrogen release of the implant composite, thereby decreasing the subcutaneous gas bubbles formed.