Recently magnesium and its alloys have been proposed as a promising next generation orthopedic implant material, whereas the poor corrosion behavior, potential cytotoxicity, and the lack of efficient drug delivery system have limited its further clinical application, especially for the local treatment of infections or musculoskeletal disorders and diseases. In this study, we designed and developed a multifunctional bilayer composite coating of poly(lactic acid)/brushite with high interfacial bonding strength on a Mg–Nd–Zn–Zr alloy, aiming to improve the biocorrosion resistance and biocompatibility of the magnesium-based substrate, as well as to further incorporate the biofunctionality of localized drug delivery. The composite coating consisted of an inner layer of poly(lactic acid) serving as a drug carrier and an outer layer composed of brushite generated through chemical solution deposition, where a facile pretreatment of UV irradiation was applied to the poly(lactic acid) coating to facilitate the heterogeneous nucleation of brushite. The in vitro degradation results of electrochemical measurements and immersion tests indicated a considerable reduction of magnesium degradation provided the composite coating. A systematic investigation of cellular response with cell viability, adhesion, and ALP assays confirmed the coated Mg alloy induced no toxicity to MC3T3-E1 osteoblastic cells but rather fostered cell attachment and proliferation and promoted osteogenic differentiation, revealing excellent biosafety and biocompatibility and enhanced osteoinductive potential. An in vitro drug release profile of paclitaxel from the composite coating was monitored with UV–vis spectroscopy, showing an alleviated initial burst release and a sustained and controlled release feature of the drug-loaded composite coating. These findings suggested that the bilayer poly(lactic acid)/brushite coating provided effective protection for Mg alloy, greatly enhanced cytocompatibility and bioactivity, and, moreover, possessed local drug delivery capability; hence magnesium alloy with poly(lactic acid)/brushite coating presents great potential in orthopedic clinical applications, especially for localized bone therapy.Keywords: biocompatibility; biocorrosion resistance; biodegradable magnesium alloy; composite coating; local drug delivery; orthopedic implants;

•More homogeneous microstructure was obtained with solution before extrusion.•The elongation was enhanced by 24% with solution before extrusion.•The corrosion resistance was improved by 20% with solution before extrusion.The microstructure, mechanical properties and corrosion of Mg-2.4Zn-0.8Gd (wt.%) alloy with and without solution treatment before extrusion were investigated in vitro. The volume of secondary phases decreased after solution treatment, leading to more homogeneous microstructure distribution of as-extruded samples. The solution treatment before extrusion contributed to an elongation increase by 24%, and corrosion resistance was improved by about 20% according to hydrogen evolution and weight loss test. Electrochemical test also confirmed the improvement of corrosion resistance. With solution treatment before extrusion, the corrosion morphology was transformed from localized pitting corrosion to uniform corrosion due to the more homogeneous microstructure.Download high-res image (254KB)Download full-size image

•The degradation of Mg-alloy substrate would improve the in vitro rapamycin release on a Mg alloy based drug-eluting system.•Quantitative analyzation distinguished that the improved drug release was mainly caused by H2 evolution, while pH played a trivial role.•Mg-based PLGA/RAPA drug-loading system exhibited more pronounced long-term inhibition for the proliferation of smooth muscle cells.To understand the possible influence of substrate degradation on the drug-loading system of magnesium alloy-based drug-eluting stents, a rapamycin drug-loading poly(lactic-co-glycolic acid) coating was prepared on Mg-Nd-Zn-Zr stents for a systematic investigation in a phosphate buffer system. Mg degradation accelerated the drug release kinetics prominently, which was mainly attributed to H2 evolution in the diffusion-controlled phase while thereafter to PLGA erosion. Although physiochemical stability of the released rapamycin was partially deteriorated by magnesium degradation, the drug-loading system on magnesium substrates exhibited a more potent long-term inhibition on smooth muscle cell proliferation in vitro as compared to drug-loaded stainless steel.Download high-res image (206KB)Download full-size image

•JDBM alloy shows less susceptibility to pitting corrosion and reduced corrosion rate in artificial plasma.•The corrosion products of JDBM show excellent cellular compatibility with HUVECs and primary human macrophages.•Animal experiment suggests long-term stability and structural integrity of the JDBM stent in the supported vessel.Biodegradable magnesium (Mg) alloy emerges as revolutionary biomaterial by meeting both engineering and medical requirements for implants. In this study, we report a Mg alloy Mg-2.5Nd-0.21Zn-0.44Zr (wt. %, denoted as JDBM) potential for vascular stent application due to its outstanding performance in corrosion behaviors and biocompatibility. The investigation of corrosion properties evaluated by immersion test and electrochemical measurement shows less susceptibility to pitting corrosion and lower corrosion rate of JDBM as compared with AZ31 alloy. The corrosion products of JDBM do not cause significant adverse effect on the cell viability and growth during in vitro cytotoxicity test of the Mg extract via human vascular endothelial cells (HUVECs). We also investigated macrophage response to the Mg extract and observed compromised foreign body reaction (FBR) determined by human peripheral blood derived macrophage fusion and inflammatory cytokine and chemokine secretion. At last, we performed in vivo degradation assessment via implantation of JDBM stent in an animal model, and confirmed long-term stability and structural integrity of the stent in blood vessel. Thus, the JDBM alloy with excellent biocompatibility and long-term stability and durability in vivo, represents a significant advance in the development of biodegradable implants.

•Mg2Zn11 phase newly forms and precipitates by adding Mg into Zn-Cu alloy.•Yield strength increases by 99.7% with 1 Mg addition, indicating obvious strengthening effect of Mg for Zn-3Cu alloy.•Ranging from 11.4 to 43.2 μm year-1, the degradation rates of Zn-3Cu-xMg alloys are more suitable for clinic application.•The cytocompatibility of Zn-3Cu is enhanced apparently by Mg addition.Zn-3Cu-xMg (x = 0, 0.1, 0.5 and 1.0 wt.%) alloys were developed as potential biodegradable metallic materials in this study. The mechanical properties, corrosion behavior and in vitro cytocompatibility of Zn-3Cu-xMg alloys were studied systematically to evaluate the feasibility as biodegradable implant materials. The secondary phase in as-cast and as-extruded Zn-3Cu alloy was CuZn5 phase. Mg2Zn11 phase newly formed and precipitated by Mg addition. The volume fraction of Mg2Zn11 phase increased gradually with increasing Mg concentration. As a result, yield strength was improved from 213.7 to 426.7 MPa and increased by 99.7% while elongation decreased from 47.1% to 0.9%. Besides, biocompatibility was improved apparently and in vitro corrosion rates increased from 11.4 to 43.2 μm year− 1, which is more suitable for clinic application. The present research indicated that the newly developed alloys could be promising candidates for biomedical use due to the proper mechanical properties, degradation rate and acceptable biocompatibility.Download high-res image (365KB)Download full-size image

•In vivo degradation of Mg-Nd-Zn-Zr (JDBM) DESs was reported in porcine coronary arteries in this work.•The JDBM DESs degraded slowly and kept most of the radial supporting strength post implantation for 3 months•The JDBM DESs showed favourable biosafety, biocompatibility and neointimal proliferation.In this work, rapamycin-eluting poly (d, l-lactic acid) coating (PDLLA/RAPA) was prepared on biodegradable Mg-Nd-Zn-Zr alloy (JDBM) for both in vitro and in vivo investigation of the degradation behaviors of the magnesium alloy stent platform. Electrochemical tests and hydrogen evolution test demonstrated significant in vitro protection of the polymeric coating against magnesium degradation both in short and long term. The 3-month in vivo study on the RAPA-eluting JDBM stent implanted into porcine coronary arteries confirmed its favorable safety, and in the meanwhile revealed similar neointima proliferation compared to the second generation DES Firebird 2 with no occurrence of adverse complications. Moreover, Micro-CT examination combined with IVUS and OCT detection indicated a remarkably lower degradation rate and prolonged radial supporting duration of the drug-eluting JDBM stent as compared to the bare, attributable to the protection of the coating in vivo. Hence, rapamycin-eluting JDBM stents exhibit great potential for clinical application.Download high-res image (130KB)Download full-size image

•Zn-3Cu-xFe (x = 0, 0.5 and 1 wt%) alloys are proposed for the first time as candidate biodegradable materials.•The YS, UTS, and elongation of Zn-3Cu-0.5Fe alloy are 232 MPa, 284 MPa and 33%, respectively.•The in vitro degradation rate in SBF was successfully increased by about 52% by 1 wt% Fe addition for Zn-3Cu.Zn and Zn-based alloys as biodegradable material have drawn more and more attention in recent years due to their good mechanical properties, lower degradation rate than Mg and acceptable biocompatibility. However, too low degradation rate is a challenge for future application of Zn-based alloys. In this study, Zn-3Cu-xFe (x = 0, 0.5 and 1 wt%) alloys were proposed as candidate biodegradable materials. The microstructure, mechanical and in vitro biodegradable properties were investigated systematically. The Zn-3Cu alloy was composed of Zn matrix and CuZn5 phase, while the FeZn13 phase was newly formed with the addition of Fe. Due to the micro-galvanic effect produced by FeZn13 as a cathodic phase to the Zn matrix, in vitro degradation rate in simulated body fluid solution (SBF) was greatly increased by about 52.1%, from 45.3 ± 8.22 for Zn-3Cu alloy to 68.9 ± 7.34 μm/year for Zn-3Cu-1Fe alloy. Although the mechanical properties were decreased slightly due to the introduction of hard and brittle FeZn13 secondary phase to the Zn matrix, Zn-3Cu-0.5Fe alloy still exhibits good combined mechanical properties and the YS, UTS and elongation are 232 MPa, 284 MPa and 33%, respectively. Taken together, the mechanical properties and in vitro degradation behavior of the Zn-3Cu-xFe alloys are more suitable than Zn-3Cu alloy as candidate biodegradable materials.Download high-res image (226KB)Download full-size image

•Zn-xCu alloys are newly developed as biodegradable materials.•Mechanical properties of Zn-xCu alloys are enhanced with Cu addition.•Zn-xCu alloys possess moderate corrosion rates and acceptable biocompatibility.•Zn-xCu alloys possess good antibacterial property.•Zn-xCu alloys are promising candidate for cardiovascular stent applications.Binary Zn-Cu alloy system is developed as potential biodegradable materials for cardiovascular implant application. The microstructure, tensile properties, in vitro corrosion behavior, cytotoxicity and antibacterial property of as-extruded Zn-xCu (x=1, 2, 3, and 4 wt%) alloys are investigated systematically. It shows that as Cu content increases more CuZn5 phase precipitates. After extrusion, the CuZn5 phases are broken and the grains of Zn-xCu alloys are refined. Tensile test shows that Cu addition could significantly improve the mechanical properties of Zn-xCu alloys. Particularly, the elongation of the Zn-4Cu reaches 50.6±2.8%, which could facilitate the micro-tubes processing for stent fabrication. The micro-tubes of 3 mm in outer diameter and 0.2 mm in thickness as well as vascular stents have been fabricated successfully using the Zn-Cu binary alloy. The degradation rates of Zn-xCu alloys in c-SBF solution are quite low, which vary from 22.1±4.7 to 33.0±1.0 μm year−1. With increasing Cu concentration, the corrosion rates of the Zn-xCu alloys generally exhibit a little increase compared with pure Zn, which show no significant difference among Zn-xCu alloys. In vitro test shows that Zn-xCu alloys exhibit acceptable cytotoxicity to human endothelial cells and the antibacterial property (S. aureus) is perfect when Cu concentration is higher than 2 wt%. Therefore, the newly developed Zn-xCu binary alloys could be promising candidates for biodegradable cardiovascular implant application due to their excellent combination of strength and ductility, low degradation rates, acceptable cytotoxicity and good antibacterial property.Download high-res image (131KB)Download full-size image

•Dislocation in I-phase embedded in Mg-based alloys was found.•Effects of deformation conditions on deformation behaviors of the I-phase were discussed.•Effects of deformation behavior of I-phase on mechanical properties were discussed.•The bonding between the I-phase and Mg matrix was also confirmed to be strong.We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg–3.5Zn–0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong.

•Zn-4 wt.%Cu is proposed as a biodegradable vascular stents material.•Zn-4Cu alloy shows good mechanical properties.•Zn-4Cu exhibits low and uniform corrosion behavior.•Zn-4Cu shows acceptable cytotoxicity and pronounced antibacterial effect.Zn-based alloys have been viewed as new potential materials for biodegradable implants, such as cardiovascular stents, mainly in consideration of their lower corrosion rate when compared with that of Mg alloys. In this study we developed a new Zinc-4 wt.%Copper (Zn-4Cu) alloy as a biodegradable material. Hot extrusion was applied to Zn-4Cu to refine the microstructure and consequently improve its mechanical properties and corrosion resistance. After extrusion, dendritic CuZn5 phases were broken and distributed along the extrusion direction. The grains were refined obviously due to dynamical recrystallization. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the as-extruded alloy are 250 ± 10 MPa, 270 ± 10 MPa and 51 ± 2%, respectively. The corrosion rate of the as-extruded alloy in Hank's solution is about 9.41(± 1.34) μm year− 1. In vitro evaluation shows that Zn-4Cu presents acceptable toxicity to human endothelial cells, and could effectively inhibit bacteria adhesion and biofilm formation. The present study indicates that the as-extruded Zn-4Cu alloy exhibits excellent strength and ductility, uniform and slow degradation, good biocompatibility and significant antibacterial effect, which make it an excellent candidate material for biodegradable implants, especially for cardiovascular stents application.

Magnesium (Mg) alloys have revolutionized the application of temporary load-bearing implants as they meet both engineering and medical requirements. However, rapid degradation of Mg alloys under physiological conditions remains the major obstacle hindering the wider use of Mg-based implants. Here we developed a simple method of preparing a nanoscale MgF2 film on Mg–Nd–Zn–Zr (denoted as JDBM) alloy, aiming to reduce the corrosion rate as well as improve the biological response. The corrosion rate of JDBM alloy exposed to artificial plasma is reduced by ∼20% from 0.337 ± 0.021 to 0.269 ± 0.043 mm·y–1 due to the protective effect of the MgF2 film with a uniform and dense physical structure. The in vitro cytocompatibility test of MgF2-coated JDBM using human umbilical vein endothelial cells indicates enhanced viability, growth, and proliferation as compared to the naked substrate, and the MgF2 film with a nanoscale flakelike feature of ∼200–300 nm presents a much more favorable environment for endothelial cell adhesion, proliferation, and alignment. Furthermore, the animal experiment via implantation of MgF2-coated JDBM stent to rabbit abdominal aorta confirms excellent tissue compatibility of the well re-endothelialized stent with no sign of thrombogenesis and restenosis in the stented vessel.Keywords: cytocompatibility; endothelialization; in vitro degradation; magnesium alloy; surface modification

•The effect of size and volume fraction of reinforcement on the deformation morphology of composite was studied.•The larger plastic strain was obtained in the composite with smaller reinforcement.•There is a significant brittle–ductile–brittle transition with the reinforcement increase.Bulk metallic glassy composites reinforced by ZrO2 with various volume fraction and particle size were fabricated successfully by spark plasma sintering. The compression test results indicate that mechanical property of composite is related to the particle size and volume fraction of ZrO2. Due to the stress concentration between the ZrO2 and the glassy matrix, both the plastic strain and fracture strength increase firstly and then decrease with the increase of volume fraction of ZrO2. The deformation morphologies of composites after compression reflect the ductile–brittle transition process.

•TiNb/Zr-based bulk metallic glassy composites with high plastic strain were fabricated by SPS.•The interface was studied by nanoindentation and the results show there is a good bonding.•FEM was adopted to study the initiation and propagation of the shear bands in BMGCs.In the present study TiNb/Zr55Cu30Al10Ni5 with various fraction additions were fabricated by spark plasma sintering successfully. The interface between the TiNb and the glassy matrix was investigated by nanoindentation. The results indicate that there is a good bonding between them. Therefore, the strength and plastic strain are improved due to introduction of TiNb. In order to study the improved plastic deformation of the composites, the FEM (Finite Element Method) was adopted. It is observed that more shear bands are formed around the TiNb particles. The shear bands form and propagate at the interface of the TiNb and the glassy matrix due to the misfit of their Young's modulus, therefore, the plastic strain is improved.

•High-quality Mg alloy micro-tubes for biodegradable stents are fabricated.•Texture component and intensity vary in different Mg alloy micro-tubes.•Three Mg alloy micro-tubes show different fracture mechanisms.•How microstructures and textures affect mechanical properties of tubes is studied.In this study, through a combination of hot extrusion, cold rolling and drawing, three Mg alloys, Mg–Nd–Zn–Zr (abbr. JDBM), AZ31 and WE43, were successfully fabricated into the high-quality micro-tubes with 3.00 mm outer diameter and 180 μm thickness for biodegradable stents. This processing method overcame the shortcoming of the poor workability of Mg alloys and could be applied to fabricate sufficiently long tubes with low dimensional errors within 2.8%. Microstructure observation demonstrated that the as-annealed JDBM, AZ31 and WE43 micro-tubes had more uniformly distributed grains with an average size of 10.9 μm, 12.9 μm and 15.0 μm, respectively. Tensile mechanical test results showed that the as-annealed JDBM, AZ31 and WE43 micro-tubes respectively exhibited the yield strength of 123 MPa, 172 MPa and 113 MPa, and significantly different breaking elongation of 26%, 16% and 10%. The following SEM observation showed microvoid coalescence, quasi-cleavage and cleavage fracture, respectively. In addition, EBSD analyses revealed that the as-annealed AZ31 tubes had a strong texture component 21¯1¯0 with a low Schmid factor for basal slip, while JDBM and WE43 tubes respectively exhibited weak textures 101¯0 and 101¯0+202¯1 with a similarly high Schmid factor for basal slip.

To diminish incongruity between bone regeneration and biodegradation of implant magnesium alloy applied for mandibular bone repair, a brushite coating was deposited on a matrix of a Mg–Nd–Zn–Zr (hereafter, denoted as JDBM) alloy to control the degradation rate of the implant and enhance osteogenesis of the mandible bone. Both in vitro and in vivo evaluations were carried out in the present work. Viability and adhesion assays of rabbit bone marrow mesenchyal stem cells (rBM-MSCs) were applied to determine the biocompatibility of a brushite-coated JDBM alloy. Osteogenic gene expression was characterized by quantitative real-time polymerase chain reaction (RT-PCR). Brushite-coated JDBM screws were implanted into mandible bones of rabbits for 1, 4, and 7 months, respectively, using 316L stainless steel screws as a control group. In vivo biodegradation rate was determined by synchrotron radiation X-ray microtomography, and osteogenesis was observed and evaluated using Van Gieson’s picric acid-fuchsin. Both the naked JDBM and brushite-coated JDBM samples revealed adequate biosafety and biocompatibility as bone repair substitutes. In vitro results showed that brushite-coated JDBM considerably induced osteogenic differentiation of rBM-MSCs. And in vivo experiments indicated that brushite-coated JDBM screws presented advantages in osteoconductivity and osteogenesis of mandible bone of rabbits. Degradation rate was suppressed at a lower level at the initial stage of implantation when new bone tissue formed. Brushite, which can enhance oeteogenesis and partly control the degradation rate of an implant, is an appropriate coating for JDBM alloys used for mandibular repair. The Mg–Nd–Zn–Zr alloy with brushite coating possesses great potential for clinical applications for mandibular repair.Keywords: brushite coating; degradation control; mandibular repair; Mg−Nd−Zn−Zr alloy; synchrotron radiation

•Cells accelerate magnesium alloy corrosion rate.•Proteins slow down magnesium alloy corrosion rate.•Surface corrosion layer composition is studied.•Mechanisms how proteins and cells affect Mg alloy corrosion are proposed.The influence of proteins and primary human umbilical vein endothelial cells (HUVECs) coculture on in vitro corrosion of Mg–Nd–Zn–Zr alloy is investigated in this study. Protein supplemented in cell culture medium slows down the corrosion rate of magnesium alloy, while cell coculture accelerates it. Corrosion surface composition is studied using XPS. The Mg–Nd–Zn–Zr alloy shows no adverse effects on cell viability and apoptosis. The mechanisms how proteins and cells affect magnesium alloy corrosion are also discussed.

•Mg alloy is modified by C2H2 plasma immersion ion implantation and deposition.•The enhanced corrosion resistance is due to the formed diamond-like carbon film.•The corrosion mechanism is discussed from the perspective of random defects.Plasma immersion ion implantation and deposition (PIII&D) is conducted to modify the corrosion behavior of Mg–Nd–Zn–Zr alloy. A diamond-like carbon film (DLC) with a thickness of about 200 nm is formed on the surface after acetylene PIII&D and the resulting corrosion resistance in the 0.9 wt% NaCl solution is significantly improved. The corrosion mechanism is discussed from the perspective of random defects in the DLC film.

•The effect of the glassy matrix fracture toughness on the plasticity of composites was studied.•The larger plastic strain was obtained in the glassy matrix with higher toughness.•The formation of shear bands and micro-crack reduced the energy of crack for development.In the present study, two kinds of bulk metallic glasses (Zr55Cu30Al10Ni5 and Cu46Zr42Al7Y5) with high strength and no plastic strain were adopted as matrixes. Both of them were reinforced by ductile crystalline TiNb with the same volume fraction and particle size. The compression results showed that the plastic strain of TiNb/Zr55Cu30Al10Ni5 composite was higher 292% than that of TiNb/Cu46Zr42Al7Y5 composite. It should be related to the fracture toughness of the glassy matrix. For the glassy matrix with high toughness, the formation of shear bands and micro-crack at the front of the crack reduced the energy of main crack development. It resulted in a large plastic strain. On the other hand, for the brittle metallic glassy matrix, crack developed quickly through the cross section so that no more shear bands was formed. It resulted in the failure of the sample with smaller plastic strain.

A comprehensive transmission electron microscopy investigation was conducted to gain insights into how the secondary phases in Mg–1.50Zn–0.25Gd alloys are transformed during hot compression. It was found that needle-like Mg4Zn7 phases precipitate in Mg matrix, yet vanish during compression, forming nano-quasicrystals. These nano-quasicrystals are found to nucleate on the Mg4Zn7 phase with orientation relationships [112‾0]Mg‖[1‾07]Mg4Zn7|| [2-fold]I-phase, indicating that the crystal phase can transform to the quasicrystalline phase. The formation mechanism of the quasicrystals in Mg alloys at the nanoscale is also discussed.

Fluoride treatment is a commonly used technique or pre-treatment to optimize the degradation kinetic and improve the biocompatibility of magnesium-based implant. The influence of changed surface properties and degradation kinetics on subsequent protein adsorption and cytocompatibility is critical to understand the biocompatibility of the implant. In this study, a patent magnesium alloy Mg–Nd–Zn–Zr alloy (JDBM) designed for cardiovascular stent application was treated by immersion in hydrofluoric acid. A 1.5 μm thick MgF2 layer was prepared. The surface roughness was increased slightly while the surface zeta potential was changed to a much more negative value after the treatment. Static contact angle test was performed, showing an increase in hydrophilicity and surface energy after the treatment. The MgF2 layer slowed down in vitro degradation rate, but lost the protection effect after 10 days. The treatment enhanced human albumin adsorption while no difference of human fibrinogen adsorption amount was observed. Direct cell adhesion test showed many more live HUVECs retained than bare magnesium alloy. Both treated and untreated JDBM showed no adverse effect on HUVEC viability and spreading morphology. The relationship between changed surface characteristics, degradation rate and protein adsorption, cytocompatibility was also discussed.

Biodegradable metal alloys emerge as a new class of biomaterials for tissue engineering and medical devices such as cardiovascular stents. Deploying biodegradable materials to fabricate stents not only obviates a second surgical intervention for implant removal but also circumvents the long-term foreign body effect of permanent implants. However, these materials for stents suffer from an un-controlled degradation rate, acute toxic responses, and rapid structural failure presumably due to a non-uniform, fast corrosion process. Here we report that highly uniform, nanophasic degradation is achieved in a new Mg alloy with unique interstitial alloying composition as the nominal formula Mg–2.5Nd–0.2Zn–0.4Zr (wt%, hereafter, denoted as JDBM). This material exhibits highly homogeneous nanophasic biodegradation patterns as compared to other biodegradable metal alloy materials. Consequently it has significantly reduced degradation rate determined by electrochemical characterization. The in vitro cytotoxicity test using human vascular endothelial cells indicates excellent biocompatibility and potentially minimal toxic effect on arterial vessel walls. Finally, we fabricated a cardiovascular stent using JDBM and performed in vivo long-term assessment via implantation of this stent in an animal model. The results confirmed the reduced degradation rate in vivo, excellent tissue compatibility and long-term structural and mechanical durability. Thus, this new Mg-alloy with highly uniform nanophasic biodegradation represents a major breakthrough in the field and a promising material for manufacturing the next generation biodegradable vascular stents.

•Mg–1.5Zn–0.25Gd alloy was successfully extruded at 373 K.•The grain size of the sample is smaller than 1 μm after extrusion at 373 K.•Tensile yield strength is up to about 395 MPa, UTS is 417 MPa and elongation is 8.3%.In this study, we have developed an excellent mechanical properties of an ultrafine-grained quasicrystalline strengthened magnesium alloys by conventional extruding as-casted Mg–1.5Zn–0.25Gd (at%) ingot at 373 K with an extrusion ratio of about 9:1. After extrusion, multi-modal microstructure was formed, i.e. exhibited large deformed grains surrounded by fine dynamical recrystallization grains and the mean grain sizes smaller than 1 μm. The extruded sample shows excellent tensile properties at ambient temperature with ultimate tensile strength of 417 MPa, 0.2% proof stress of 395 MPa and elongation to failure of 8.3%. The notable improvement in strength mainly attributed to the grain refinement, dense distribution of the fine precipitates inside the fine dynamical recrystallization grains and the high intensity of typical basal texture.

In this study, in vitro blood biocompatibility of Mg-Nd-Zn-Zr (JDBM) alloy was investigated to determine its suitability as a degradable medical biomaterial. Blood biocompatibility was assessed by blood cell aggregation, platelet adhesion, and protein adsorption. A titanium alloy was used as control. The results showed that the JDBM alloy did not induce significant blood cell aggregation, platelet adhesion, and protein adsorption comparison with the titanium alloy (P>0.05). Our data indicate that the JDBM alloy has excellent in vitro blood compatibility, and thus can be considered as a potential degradable biomaterial for medical applications with respect to hemocompatibility.

•A brushite coating was successfully developed on Mg–Nd–Zn–Zr alloy.•The hemolysis rate of JDBM alloy is significantly reduced from 48% to 0.68%.•Over 10 weeks in vivo degradation time for JDBM can be prolonged by the coating.To further improve the corrosion resistance and biocompatibility of Mg–Nd–Zn–Zr alloy (JDBM), a biodegradable calcium phosphate coating (Ca–P coating) with high bonding strength was developed using a novel chemical deposition method. The main composition of the Ca–P coating was brushite (CaHPO4·2H2O). The bonding strength between the coating and the JDBM substrate was measured to be over 10 MPa, and the thickness of the coating layer was about 10–30 μm. The in vitro corrosion tests indicated that the Ca–P treatment improved the corrosion resistance of JDBM alloy in Hank's solution. Ca–P treatment significantly reduced the hemolysis rate of JDBM alloy from 48% to 0.68%, and induced no toxicity to MC3T3-E1 cells. The in vivo implantation experiment in New Zealand's rabbit tibia showed that the degradation rate was reduced obviously by the Ca–P treatment and less gas was produced from Ca–P treated JDBM bone plates and screws in early stage of the implantation, and at least 10 weeks degradation time can be prolonged by the present coating techniques. Both Ca–P treated and untreated JDBM Mg alloy induced bone growth. The primary results indicate that the present Ca–P treatment is a promising technique for the degradable Mg-based biomaterials for orthopedic applications.

Mg–1.5Zn–0.25Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) were fabricated to investigate the effect of heat treatment on the microstructure, mechanical properties and anisotropy of the as-extruded alloys. The results show that compared with the samples extruded without homogenized annealing, the samples extruded after homogenized annealing show larger grains, lower strength and elongation, which can be attributed to the secondary-phase particles precipitated in the matrix after homogenized annealing and to the fact that only a few volume fraction of nano-scale I-phase is precipitated in the matrix during extrusion. Moreover, the anisotropy is mitigated in the alloys extruded at as-cast condition because of the grain refinement and the I-phase precipitation. We also find that after annealing at 473 K or 673 K, yield strength decreases while the elongation increases slightly, indicating that annealing has a small effect on the improvement of room-temperature strength, especially the one at relatively higher temperature. The choice of appropriate annealing temperature only imposes a little impact on the ductility enhancement of the extruded samples.

In this paper, Mg–Nd–Zn–Zr alloy (denoted as JDBM) coated with hydrofluoric acid (HF) chemical conversion film (MgF2) was researched as a potential biodegradable cardiovascular stent material. The microstructures, in vitro degradation and biocompatibility were investigated. The field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) showed that a compact MgF2 film was formed on the surface of JDBM. The corrosion rate decreased in artificial plasma from 0.337 to 0.253 mm·y− 1 and the electrochemical measurement demonstrated that the corrosion resistance of JDBM alloy could be obviously improved due to the protective MgF2 film on the surface of the substrate. Meanwhile, the hemolysis ratio of JDBM decreased from 52.0% to 10.1% and the cytotoxicity met the requirement of cellular application after HF treatment. In addition, JDBM and MgF2 film showed good anti-platelet adhesion, which is a very favorable property for implant material in contact with blood directly.Highlights► We have prepared a uniform and dense MgF2 film on JDBM alloy. ► The corrosion rate of JDBM can be decreased by HF treatment. ► The biocompatibility of JDBM can be improved by HF treatment. ► JDBM showed uniform corrosion in artificial plasma.

Recently, commercial magnesium (Mg) alloys containing Al (such as AZ31 and AZ91) or Y (such as WE43) have been studied extensively for biomedical applications. However, these Mg alloys were developed as structural materials, not as biomaterials. In this study, a patented Mg–Nd–Zn–Zr (denoted as JDBM) alloy was investigated as a biomedical material. The microstructure, mechanical properties, biocorrosion behavior, and cytotoxicity of the alloy extruded at 320 °C with extrusion ratios of 8 and 25 were studied. The results show that the lower extrusion ratio results in finer grains and higher strength, but lower elongation, while the higher extrusion ratio results in coarser grains and lower strength, but higher elongation. The biocorrosion behavior of the alloy was investigated by hydrogen evolution and mass loss tests in simulated body fluid (SBF). The results show that the alloy extruded with lower extrusion ratio exhibits better corrosion resistance. The corrosion mode of the alloy is uniform corrosion, which is favorable for biomedical applications. Aging treatment on the as-extruded alloy improves the strength and decreases the elongation at room temperature, and has a small positive influence on the corrosion resistance in SBF. The cytotoxicity test indicates that the as-extruded JDBM alloy meets the requirement of cell toxicity.Highlights► The Mg–Nd–Zn–Zr (JDBM) alloy produced with lower extrusion ratio showed higher strength. ► The corrosion rate of the JDBM alloy slowed down significantly after extrusion. ► The JDBM alloy showed a uniform corrosion mode in SBF. ► The JDBM alloy meets the requirement of cell toxicity for biomaterials.

Mechanical properties at room temperature and biocorrosion behaviors in simulated body fluid (SBF) at 37 °C of a new type of patented Mg–3Nd–0.2Zn–0.4Zr (hereafter, denoted as JDBM) alloy prepared at different extrusion temperatures, as well as heat treatment, were studied. The mechanical properties of this magnesium alloy at room temperature were improved significantly after extrusion and heat treatment compared to an as-cast alloy. The results of mechanical properties show that the yield strength (YS) decreases with increasing extrusion temperature. The tensile elongation decreases a little while the ultimate tensile strength (UTS) has no obvious difference. The yield strength and ultimate tensile strength were improved clearly after heat treatment at 200 °C for 10 h compared with that at the extrusion state, which can be mainly contributed to the precipitation strengthening. The biocorrosion behaviors of the JDBM alloy were studied using immersion tests and electrochemical tests. The results reveal that the extruded JDBM alloy and the aging treatment on the extruded alloy show much better biocorrosion resistance than that at solid solution state (T4 treatment), and the JDBM exhibited favorable uniform corrosion mode in SBF.Highlights► A new type of patented Mg–2.0–4.0Nd–0.1–0.5Zn–0.3–0.6Zr (JDBM) alloy was designed for biomedical applications, avoiding potential risk caused by Al or heavy rare earth elements. ► The JDBM alloy exhibits good strength, excellent elongation and corrosion resistance after hot extrusion and heat treatment. ► The corrosion mode of the JDBM alloy is uniform corrosion, different from the serious local pitting mode of other commercial Mg alloys, such as AZ91.

The Mg-3.5Zn-0.6Gd (at. %) alloy was prepared and homogenized at 673 K for 8 h, and then extruded at 523 K with an extrusion ratio of 9:1. The microstructure and mechanical properties of the extruded alloy have been investigated. Icosahedral quasicrystalline phase (I-phase) existed in extruded Mg–Zn–Gd-based alloys in two morphologies: (1) micron-scale I-phase formed in the solidification, (2) nano-scale ellipsoid-shape I-phase particles precipitated in the extrusion process. A definite orientation relationship and good atomic match between I-phase and α-Mg matrix were directly observed by conventional and high-resolution transmission electron microscopy (HRTEM), which contribute to the high tensile strength of 308 MPa and the large plasticity of 16.4%.Highlights► I-phase existed in extruded alloys in two morphologies: micron-scale and nano-scale. ► The relationship between I-phase and α-Mg in Mg-3.5Zn-0.6Gd alloy was identified. ► The interface region between of I-phase and α-Mg was directly observed by HRTEM. ► Revealed strengthening & toughening mechanisms of Mg-Zn-Gd alloys containing I-phase.

Cu46Zr42Al7Y5 metallic glass with nearly 100% relative density was obtained by spark plasma sintering (SPS) with a diameter of 15 mm, which was larger than the largest size of 10 mm for the as-cast specimen. The fracture strength of the sintered specimen reached 2044 MPa, which was 15% higher than that of the as-cast Cu46Zr42Al7Y5 glassy specimen. The densification and compressive properties of the sintered specimens were related to sintering temperature. Structural changes of the specimens sintered at various sintering temperatures resulted in the difference of macro-mechanical properties.Highlights► The largest size of Cu46Zr42Al7Y5 with a diameter of 15 mm was fabricated successfully. ► The highest of strength of sintered specimen is higher than that of as-cast specimen. ► The sintering process was investigated.

A new type of patented biodegradable biomedical magnesium alloy Mg–Nd–Zn–Zr (hereafter, denoted as JDBM) was prepared in this study. The biocorrosion properties of the as-extruded JDBM alloy were investigated in simulated body fluid (SBF) by hydrogen evolution, mass loss and electrochemical tests. The biocorrosion properties of as-extruded AZ31 and as-extruded WE43 alloys as well as the mechanical properties at room temperature were also studied in order to compare with the novel JDBM biodegradable biomedical magnesium alloy. The results show that the as-extruded JDBM alloy not only owns much better mechanical properties at room temperature but also exhibits much better biocorrosion properties in SBF.Highlights► Mg–Nd–Zn–Zr (JDBM) alloy was designed for biomedical applications. ► The JDBM exhibits better strength than AZ31 and WE43 under the same parameters. ► The JDBM shows much better biocorrosion resistance in SBF than AZ31 and WE43.

Magnesium alloys have been currently investigated as potential biodegradable implant materials. In this study, a patent Mg alloy Mg–Nd–Zn–Zr (Jiao Da BioMg, hereafter, denoted as JDBM) was researched as a potential biodegradable stent material in comparison with the clinical trial Mg alloy WE43. The corrosion behaviors of the as-extruded JDBM and WE43 were investigated in artificial plasma by in vitro degradation measurements and cyclic polarization tests. The results showed that the corrosion rate of JDBM was much lower than that of WE43 alloy. Most importantly, the JDBM alloy showed a uniform corrosion behavior in artificial plasma, which could avoid stress concentration as well as a rapid reduction in the mechanical integrity. The investigations indicated that the as-extruded JDBM alloy may be a promising implant material suitable for stent applications.Highlights► Mg–Nd–Zn–Zr alloy (denoted as JDBM) showed lower corrosion resistance compared with WE43 ► JDBM showed very favorable uniform corrosion behavior in artificial plasma. ► The uniform corrosion mechanism was discussed from an electrochemical viewpoint.

The main challenge for the application of magnesium and its alloy as degradable biomaterials lies in their high degradation rates in physiological environment. In the present work, the biodegradable behavior of a patent magnesium alloy Mg–Nd–Zn–Zr (JDBM) and a reference alloy AZ31 was systematically investigated in Hank's physiological solution. The corrosion rate of JDBM (0.28 mm/year) was much slower than that of AZ31 (1.02 mm/year) in Hank's solution for 240 h. After corrosion products were removed, smooth surface of the JDBM was observed by SEM observation compared to many deep pits on the surface of AZ31. Open-circuit potential and potentiodynamic polarization results manifested that pitting corrosion did not occurred on the surface of JDBM at the early period of immersion time due to the formation of a more protective and compact film layer suggested by electrochemical impedance spectroscopy study. The corrosion rate of magnesium alloys was found to slow down in dynamic corrosion in comparison with that in the static corrosion. This provided the basis for scientific evaluation of in vitro and in vivo corrosion behavior for degradable biomagnesium alloy. The present results suggest that the new patent magnesium alloy JDBM is a promising candidate as degradable biomaterials and is worthwhile for further investigation in vivo corrosive environment.

In this study, in vitro degradation and biocompatibility of Mg-Nd-Zn-Zr (NZK) alloy were investigated to determine its suitability as a degradable medical biomaterial. Its corrosion properties were evaluated by static immersion test, electrochemical corrosion test, scanning electron microscopy (SEM), and energy dispersive spectroscopic (EDS) analysis, and in vitro biocompatibilities were assessed by hemolysis and cytotoxicity tests. Pure magnesium was used as control. The results of static immersion test and electrochemical corrosion test in simulated body fluid (SBF) demonstrated that the addition of alloying elements could improve the corrosion resistance. The hemolysis test found that the hemolysis rate of calcium phosphate coated NZK alloy was 4.8%, which was lower than the safe value of 5%. The cytotoxicity test indicated that NZK alloy extracts did not significantly reduce MC3T3-E1 cell viability. Hemolysis test and cytotoxicity test display excellent hemocompatibility and cytocompatibility of NZK alloy in vitro. Our data indicate that NZK alloy has excellent biocompatibility and thus can be considered as a potential degradable medical biomaterial for orthopedic applications.

Mg–10Gd–3Y–1.8Zn–0.5Zr (wt.%) (GWZ1032K) alloys are prepared by permanent mold casting at cooling rate of 5 K/s, or further prepared by melt spinning at cooling rate of 104 K/s, or by slow solidification at different cooling rates (0.5 K/s, 0.1 K/s, 0.01 K/s and 0.005 K/s). (Mg,Zn)3RE phase and 14H-LPSO structure in alloys under different conditions are measured by XRD and observed under electron microscope. It shows there is no LPSO structure in the alloy prepared by melt spinning at cooling rate of 104 K/s. In the alloy prepared by permanent mold casting at cooling rate of 5 K/s, fine lamellar 14H-LPSO structure appears in the matrix nearby grain boundaries. With the cooling rates slowing down from 0.5 K/s to 0.005 K/s, (Mg,Zn)3RE phase is gradually replaced by 14H-LPSO phase at grain boundaries, and lamellar 14H-LPSO structure also propagates in α-Mg matrix. Both (Mg,Zn)3RE phase and 14H-LPSO phase are present at grain boundaries in the alloys solidified at cooling rates of 0.5 K/s and 0.1 K/s. When the cooling rate is very slow (0.005 K/s), lamellar 14H-LPSO structure penetrates throughout the matrix grain. It suggests the cooling rate is an important factor for the formation of 14H-LPSO structure in as-cast GWZ1032K alloys. The orientation relationship between (Mg,Zn)3RE phase and 14H-LPSO phase is determined by the composite SAED patterns, which is expressed as (1 1 0)(Mg,Zn)3RE//(0 0 1 4)14H-LPSO phase, [3¯ 3 2](Mg,Zn)3RE//[1 1 0]14H-LPSO phase and [1¯ 1 2](Mg,Zn)3RE//[2 1 0]14H-LPSO phase.Research highlights▶ Six GWZ1032K alloys are prepared at different condition. ▶ Morphology and microstructure in alloys are observed by XRD, SEM and TEM. ▶ (Mg,Zn)3RE phase decreases and 14H-LPSO structure increases gradually with the cooling rate slowing down. ▶ The orientation relationship between (Mg,Zn)3RE phase and 14H-LPSO phase is confirmed.

The crystallization behaviors of Mg65Cu25Gd10, Mg65Cu20Ag5Gd10 and Mg65Cu20Ni5Gd10 metallic glasses were compared with respect to the continuous heating and the isothermal annealing. The results showed that both the partial substitution Ag and Ni for Cu in the Mg65Cu25Gd10 glass can increase the activation energy for the first crystallization and however decrease the thermal stability and the crystal growth rate during the isothermal annealing. The difference in the influence on the crystallization behaviors between Ag addition and Ni addition was analyzed in details. The examination of the crystallization product after the isothermal annealing revealed that Ag addition can effectively suppress the formation of the Mg2Cu crystalline phase of Mg65Cu25Gd10 glass while Ni addition can promote the Mg2Cu formation, which is well consistent with the larger glass-forming ability (GFA) of the Mg65Cu20Ag5Gd10 alloy than that of the Mg65Cu20Ni5Gd10 alloy. In addition, the possible relation between the crystallization features with the GFA was discussed.

Microstructural evolution including the stability of icosahedral phase (I-phase) in Mg95.9Zn3.5Gd0.6 alloy, before and after extrusion, has been investigated. The results indicate that the I-phase in Mg95.9Zn3.5Gd0.6 alloy is a face-centered icosahedral quasicrystal with stoichiometric composition of Mg42Zn50Gd8 and that this I-phase has excellent thermal stability up to 713 K. The W-phase and W′-phase, which are considered approximate crystalline equivalents of I-phase, have also been observed in the as-extruded alloy.

The structural relaxation and glass-forming ability (GFA) of Mg–Cu–Gd-based glassy alloys and the effect of Ni addition on the glass-forming ability, structural relaxation and mechanical properties were studied by thermal analysis, X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The medium-range order (MRO) zones of about 1–2 nm size were observed in the Mg65Cu25Gd10 glassy alloy after structural relaxation caused by annealing for 180 s at 305 K. The structural relaxation resistance increased with decreasing Cu content, although the GFA also decreased in Mg–Cu–Gd-based alloys. Appropriate substitution of Cu by Ni in Mg75Cu15Gd10-based alloy not only improved the glass-forming ability and mechanical properties, but also increased the stability against structural relaxation.

ObjectiveTo explore the effect ofβ-TCP/PLLA scaffold in repairing rabbit radial bone defects.MethodsThirty New Zealand rabbits were divided into β-TCP /PLLA group (group A), pure PLLA group (group B) and contrast group (group C) randomly. The rabbits were sacrificed respectively after 4, 8, 12, 24 weeks and the X-ray film was performed at the same time to evaluate the repair effect in different groups.ResultsX-ray film showed there was uneven low density bone callus development in defect region after 4 weeks in group A. The defect region was filled with neonate osseous tissue completely during 12-24 weeks. X-ray score revealed that repair of bone defect results significantly better than group B and group C.ConclusionsThe β-TCP /PLLA composite is capable of repairing radial bone bone defects. β-TCP/PLLA scaffold is significant because of rapid degradation ability, good histocompatibility and osteogenic action.

•The long-term degradation of Mg-Nd-Zn-Zr alloy screws in mandible bone of rabbits is investigated.•At 18 months, the screw volume has been reduced by ∼90 %, and the averaged corrosion rate is 0.122 ± 0.042 mm/year.•The degradation products show two-layer structure, and the outer layer shows similar composition with new bone tissue.In this work, the long-term degradation of Mg-Nd-Zn-Zr screws in the rabbit mandible is studied. At 18 months, the screw volume has been reduced by ∼90% according to the micro-computed tomography analysis, and the averaged corrosion rate is 0.122 ± 0.042 mm/year. The bone-implant interface analysis reveals good osteointegration. The corrosion products show two-layer structure with Ca and P elements concentrated in the out layer, and the Mg12Nd particles has degraded by Mg element dissolution. Our findings contribute to a better understanding of the in vivo degradation mechanism of Mg-based implants.