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Interconnectivity is the key characteristic of bone tissue engineering scaffold modulating cell migration, blood vessels invasion and transport of nutrient and waste. However, efforts and understanding of the interconnectivity of porous Mg is limited due to the diverse architectures of pore struts and pore size distribution of Mg scaffold systems. In this work, biomimetic hierarchical porous Mg scaffolds with tailored interconnectivity as well as pore size distribution were prepared by template replication of infiltration casting. Mg scaffold with better interconnectivity showed lower mechanical strength. Enlarging interconnected pores would enhance the interconnectivity of the whole scaffold and reduce the change of ion concentration, pH value and osmolality of the degradation microenvironment due to the lower specific surface area. Nevertheless, the degradation rates of five tested Mg scaffolds were no different because of the same geometry of strut unit. Direct cell culture and evaluation of cell density at both sides of four typical Mg scaffolds indicated that cell migration through hierarchical porous Mg scaffolds could be enhanced by not only bigger interconnected pore size but also larger main pore size. In summary, design of interconnectivity in terms of pore size distribution could regulate mechanical strength, microenvironment in cell culture condition and cell migration potential, and beyond that it shows great potential for personalized therapy which could facilitate the regeneration process.

Zn alloys are promising materials for application in the fabrication of vascular stents because they have a desirable degradation rate and acceptable biocompatibility. However, the poor thermostability of Zn is one limitation that needs to be addressed in order to broaden their clinical applications. Suppression atomic diffusion is of practical significance when enhancing the thermostability of Zn alloys. The present study seeks to examine lattice diffusion associated with various alloy elements by calculating the diffusion activation energies for nineteen substitutional solutes via first-principles calculations combined with CINEB methods. The calculated activation energies depend strongly on the size and the number of d-electrons of the solute atoms. The trend to improve the thermostability and creep resistance of Zn alloys at ambient temperature can also be predicted using the Nabarro-Herring model. An anti-self-aging Zn-Cu alloy was prepared to verify our calculation results. Therefore, the present work has great significance for the design of biodegradable zinc alloys with improved thermostability. Graphic abstract

To develop a biodegradable membrane with guided bone regeneration (GBR), a Mg-2.0Zn-1.0Gd alloy (wt.%, MZG) membrane with Ca-P coating was designed and fabricated in this study. The microstructure, hydrophilicity, in vitro degradation, cytotoxicity, antibacterial effect and in vivo regenerative performance for the membrane with and without Ca-P coating were evaluated. After coating, the membrane exhibited an enhance hydrophilicity and corrosion resistance, showed good in vitro cytocompatibility upon MC3T3E-1 cells, and exhibited excellent antibacterial effect against E. coli, Staphylococcus epidermis and Staphylococcus aureus, simultaneously. In vivo experiment using the rabbit calvarial defect model confirmed that Ca-P coated MZG membrane underwent progressive degradation without inflammatory reaction and significantly improved the new bone formation at both 1.5 and 3 months after the surgery. All the results strongly indicate that MZG with Ca-P coating have great potential for clinical application as GBR membranes.

The grain size of Mg foams was innovatively refined without alteration of pore structure and relative density by subjecting multi-axial forging (MAF) process to Ti-Mg composite, an intermediary product of the fabrication process of Mg foams where the spherical Ti particles were utilized as the replication material. The feasibility of the MAF process and the grain size effect on the mechanical properties of Mg foams were discussed. The results showed that, with the appropriate strain of 0.24 applied in the MAF process, Ti-Mg composites returned to original physical appearance without generating micro-cracks. And complete recrystallization was achieved after heat treatment, with the grain size of the MAF-processed Mg foams two to three orders of magnitude smaller than that of as-cast foam. The mechanical properties of Mg foams were enhanced extensively after grain refinement with the yield strength and the plastic collapse strength increased by 147% and 50.7%, respectively. A revised model integrated by the Hall-Petch law and Gibson-Ashby model was proposed, which gave a good estimation of the yield strength and the plastic collapse strength of Mg foams from the compressive behavior of the corresponding parent material, though a knockdown factor of 0.45 was introduced for the yield strength.

Degradability of bone tissue engineering scaffold that matching the regeneration rate could allow a complete replacement of host tissue. However, the porous structure of biodegradable Mg scaffolds certainly generated high specific surface area, and the three-dimensional interconnected pores provided fast pervasive invasion entrance for the corrosive medium, rising concern of the structural integrity during the degradation. To clarify the structural evolution of the three-dimensional (3D) porous structure, semi-static immersion tests were carried out to evaluate the degradation performance in our previous study. Nevertheless, dynamic immersion tests mimicking the in vivo circulatory fluid through the interconnected porous structure have yet been investigated. Moreover, the effects of dynamic flow rates on the degradation deposition behavior of 3D porous Mg scaffolds were rarely reported. In this study, Mg scaffolds degraded at three flow rates exhibited different degradation rates and deposition process. A flow rate of 0.5 mL/min introduced maximum drop of porosity by accumulated deposition products. The deposition products provided limited protection against the degradation process at a flow rate of 1.0 mL/min. The three-dimensional interconnected porous structure of Mg scaffold degraded at 2.0 mL/min well retained after 14 days showing the best interconnectivity resistance to the degradation deposition process. The dynamic immersion tests disclosed the reason for the different degradation rates on account of flow rates, which may bring insight into understanding of varied in vivo degradation rates related to implantation sites.

The solid solution strengthening of Li, Mg, Al, Mn, Cu and Ag in biodegradable Zn-based alloys is quantitatively investigated by first-principles calculations based on density functional theory. The alloying effect on lattice parameters and elastic constants is determined. Mn is found to have the greatest impact on the lattice parameters and shear modulus, while Mg and Al exhibit the least. According to the theories proposed by Fleischer and Labusch, the strengthening capability of selected elements can be ranked as Mn > Li > Cu, Ag > Mg > Al. The different strengthening effect of solutes can be attributed to their valence electron structure. Analysis on experimental results indicates that ternary Zn-based alloys may satisfy the clinical requirements on mechanical properties with less secondary phase and suppressed mechanical instability.

Nanoscale precipitations in deformed dilute alloying Mg-Zn-RE alloys usually play critical positive roles in mechanical properties, while characterizing them still poses a significant challenge due to their small size and low volume fraction. Here, we conduct a systematic structural analysis of the nanoscale secondary phase particles, including W phase, a small amount of I phase and a handful of Mg3Gd phase, in hot deformed dilute alloying Mg-Zn-Gd alloy by combining atomic-resolution transmission electron microscopy with first-principles calculations. The investigation of atomic structure of nanoscale W phase reveals that the stoichiometric composition of W phase is determined by the quantity of Mg atoms which are replaced by Zn at certain positions. Furthermore, nanoscale W phase, I phase and Mg3Gd phase particles could exhibit certain orientation relationships and coherent or semi-coherent interface with Mg matrix, which contributes to atomic bonding at their interfaces. We also identify a phase transition from Mg3Gd phase to W phase, which is further supported by first-principles calculations showing that Mg3Zn3Gd2 phase is energetically more favorable than Mg3Gd phase. The phase transition between W phase and I phase could also take place during hot deformation and is reversible by absorbing or releasing Zn atoms at the interfacial region.

Magnesium and its alloys have been recently used in biomedical applications such as orthopedic implants, whereas the weak corrosion resistance undermines their clinical efficacy. Herein, to address this critical challenge, the preparation of hierarchically structured hydroxyapatite-based coatings was proposed. Compact coatings were fabricated on a Mg alloy through a facile two-step method of chemical deposition of brushite precursor and subsequent hydrothermal conversion. A series of HA-based coatings were obtained with kinetic conversion process with formation mechanism revealed. The hydroxyapatite coating demonstrated the greatest corrosion resistance for Mg in electrochemical and long-term immersion tests, especially against pitting corrosion, attributable to its compact structure, alkaline degradation environment and self-induced growth capacity. The in vitro cytocompatibility and osteoinductivity were dictated. Additionally, anti-corrosion mechanisms were compared among different coating compositions and structures, along with their correlation with cellular response. Our study brings hints for a tailored surface design for resorbable biomedical device applications.

Inspired by the process of bone reconstruction, porous scaffolds with robust osteogenesis and biodegradability would provide an ideal bone substitute for clinical practice. In this study, a novel porous Mg–Nd–Zn–Zr (JDBM) alloy scaffold coated with brushite (i.e., DCPD), denoted as JDBM-DCPD, is fabricated using a special patent template technique, which forms the main spherical pores (400–450 μm) and smaller pores (150–250 μm) interconnected between the adjacent main pores, facilitating nutrient penetration and cell in-growth, exhibiting sufficient mechanical properties. In vitro results demonstrate that JDBM-DCPD scaffolds promote cell in-growth and osteogenic differentiation, which significantly enhance mineralization, osteogenesis and angiogenesis-related genes expression when cultured with bone marrow mesenchymal stem cells. After implanting in vivo, JDBM-DCPD scaffolds effectively stimulate angiogenesis, osteogenesis, and remodeling with the degradation of JDBM-DCPD, and perfectly repair large bone defect in rat and rabbit models. Results from the present study provide the solid evidence that porous biodegradable Mg-based scaffolds whose pore structure can be precisely regulated by a spacer-selection technique may be a promising tissue engineering scaffolds for large bone defect repair clinically, free from any extra growth factors and live cells, such advances will make scaffold-based bone tissue repair safer, more convenient and more cost-effective. Keywords: Biodegradable Mg–Nd–Zn–Zr alloy scaffold, DCPD coating, Osteogenesis, Angiogenesis, Bone tissue engineering

Zn and its alloys are considered as a new class of biodegradable metals due to their moderate degradation rates and acceptable biocompatibility. However, inadequate mechanical properties limit their further applications, especially for cardiovascular stents. In this study, a novel biodegradable Zn-1.5Cu-1.5Ag (wt%) alloy with excellent mechanical properties was developed, and then its in vitro degradation and cytotoxicity were characterized. Microstructural characterization showed that hot extrusion produced a bimodal distribution of grain size and much finer secondary phase precipitates. The as-extruded alloy exhibited a satisfactory combination of strength and plasticity (yield strength: 162.0 ± 2.94 MPa, ultimate tensile strength: 220.3 ± 1.70 MPa and elongation: 44.13 ± 1.09%). After being aged at room temperature for 8 months, its mechanical properties increased about 10%, implying its good anti-aging ability. The strain hardening exponent (n) calculated from true stress-strain curve showed that this alloy has evident strain hardening. Immersion tests in c-SBF solution revealed that this alloy has a moderate corrosion rate (48.6 ± 4.14 μm/year) and slightly localized corrosion behavior. Electrochemical tests showed that a weak passive film formed on surface during degradation, which has a limited protective effect. The cytotoxicity tests exhibited that this alloy possesses acceptable in vitro biocompatibility, which is comparable to pure Zn. According to the results of mechanical properties, corrosion behavior and cytotoxicity, the Zn-1.5Cu-1.5Ag alloy can be regarded as a potential candidate for cardiovascular stent applications.

Generalized stacking fault energies (GSFEs) associated with the basal planes of pure Zn and substitutional Zn47X (X = Li, Mg, Al, Ti, Mn, Fe, Cu or Ag) were investigated by first-principles calculations in combination with climbing-image nudged elastic band (CINEB) methods. The transition elements, including Ti, Mn and Fe, were found to have relatively strong ability to increase the stability of I2 stacking fault by forming strong interatomic bonding with surrounding Zn atoms. To develop biodegradable Zn-based alloys with superior mechanical properties, especially improved creep properties, Ti, Mn or Fe is recommended as a proper alloying element.

We prepare a new type of patented biodegradable biomedical Mg–Nd–Zn–Zr (JDBM) alloy system and impose double continuously extrusion (DCE) processing. The lowest processing temperature is 250 °C for JDBM-2.1Nd and 310 °C for JDBM-2.8Nd, which increases with the Nd concentration. The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250 °C and the elongation is about 3.7%. Moreover, the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing. However, when extruded under the same conditions, the alloy with a higher alloying contents exhibits better tensile properties. Keywords: Magnesium alloys, Microstructure, Mechanical properties, Double continuously extrusion

Recently, Zn-based alloys are attracting intensive interest as biodegradable biomaterials. Their moderate degradation rate makes them a better potential candidate for porous scaffolds than Mg-based alloys. In this study, hot press sintering (HPS) was employed to enhance the stacking density of NaCl templates. And then, pure Zn and Zn-3 wt%Cu scaffolds with different porosities were achieved by replicating the architecture of NaCl templates. The pore structure, compressive properties and degradation behavior of the scaffolds were investigated. The scaffolds with a higher porosity of about 75% showed enhanced interconnectivity and reduced surface area due to the formation of more interconnected pores and the enlarged size of them. The scaffolds with a lower porosity of about 68% exhibited higher yield strength on account of the earlier closure of the smaller interconnected pores during deformation. The corrosion rate was decreased with the increase of the porosity due to the reduction of specific surface area. The compressive properties (including yield strength and modulus) and corrosion rate of the Zn scaffolds were significantly enhanced by the addition of 3 wt% Cu because of the solution of Cu in Zn matrix and the precipitation of CuZn5 secondary phase. Moreover, the effect of porosity on corrosion was more distinguishable for Zn-3 wt%Cu scaffolds than pure Zn scaffolds due to the acceleration of galvanic corrosion effect.

Mg-based scaffolds have great potential of application for bone defect repair due to their biodegradability and the excellent osteoinductivity, yet currently the fabrication of Mg-based porous materials is still a challenge. In this study, a new fabrication method was proposed to produce porous Mg scaffolds, which could be achieved by three steps: (1) defectless NaCl open porous template with enhanced relative density was prepared with NaCl particles by hot press sintering (HPS) process; (2) green compact of Mg and the NaCl template was produced by infiltration casting; (3) open porous Mg scaffold was achieved after leaching out the template. By using spherical NaCl particles and irregular polyhedral NaCl particles, respectively, two different types of templates were prepared, and correspondingly Mg scaffolds with spherical and irregular pores were respectively fabricated. The irregular-pore scaffold (I-scaffold) exhibited higher yield strength, while the spherical-pore scaffold (S-scaffold) showed superior interconnectivity and more stable compressive deformability due to the uniform spatial structure. Keywords: Mg scaffold, Infiltration casting, NaCl template, Interconnectivity, Mechanical properties, Microstructural evolution

Double extrusion with a large plastic deformation was conducted to fabricate Mg-Nd-Zn-Zr (JDBM) micro-tubes (3.5 mm in outer diameter and 0.25 mm in thickness) with high plasticity for biodegradable vascular stents application. After double extrusion, the grain size was greatly decreased to one seventh of the original size and the basal texture intensity was enhanced slightly. The elongation increases from about 23% for the as-extruded JDBM alloy bar to about 48.8% for the as-extruded micro-tubes, which is a 112% increase by double extrusion. The high elongation is attributed to the enhanced activation of non-basal slips contributed by the significant grain refinement.

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.

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.

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.

Biomedical Mg alloy is promising for its widespread use clinically. In vitro and in vivo studies showed that the degradation products of biomedical Mg alloy were composed of O, P, Ca, Mg and other alloying elements. However, little is known about the metabolism of the degradation products. In this study, the in vitro macrophage phagocytosis of the degradation products of a biomedical Mg-Nd-Zn-Zr alloy was directly observed. This result affirms the necessity to investigate the long-term fate of Mg alloy degradation products in physiological environments. Besides, an electrochemical method was proposed to prepare enough amount of degradation products in vitro efficiently.

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. Keywords: Biodegradable, Zn-based alloy, Mechanical properties, Corrosion behavior, Cytocompatibility

The performance of biodegradable magnesium alloy stents (BMgS) requires special attention to non-uniform residual stress distribution and stress concentration, which can accelerate localized degradation after implantation. We now report on a novel concept in stent shape optimization using a finite element method (FEM) toolkit. A Mg-Nd-Zn-Zr alloy with uniform degradation behavior served as the basis of our BMgS. Comprehensive in vitro evaluations drove stent optimization, based on observed crimping and balloon inflation performance, measurement of radial strength, and stress condition validation via microarea-XRD. Moreover, a Rapamycin-eluting polymer coating was sprayed on the prototypical BMgS to improve the corrosion resistance and release anti-hyperplasia drugs. In vivo evaluation of the optimized coated BMgS was conducted in the iliac artery of New Zealand white rabbit with quantitative coronary angiography (QCA), optical coherence tomography (OCT) and micro-CT observation at 1, 3, 5-month follow-ups. Neither thrombus or early restenosis was observed, and the coated BMgS supported the vessel effectively prior to degradation and allowed for arterial healing thereafter. The proposed shape optimization framework based on FEM provides an novel concept in stent design and in-depth understanding of how deformation history affects the biomechanical performance of BMgS. Computational analysis tools can indeed promote the development of biodegradable magnesium stents., National Institutes of Health (Grant R01-GM49039)

Zinc and its alloys have received increasing attention due to their potential to be applied as biodegradable implants. However, the distinct tension-compression yield asymmetry of zinc and its alloys after plastic forming is undesirable. Here we identify the strong tension-compression yield asymmetry in as-extruded pure zinc and reveal that higher { 10 1 ¯ 2 } 〈 1 ¯ 011 〉 twinning activity under tension is the underlying reason. Based on the finding, weakening texture and refining grains are put forward as effective strategies to reduce the tension-compression yield asymmetry.

Zn-Cu-based alloys are an important alloy series and show promising application prospect for biodegradable cardiovascular stents due to their excellent anti-self-aging property and combination of strength and ductility as well as good biocompatibility. Generally, nano-precipitates are an effective way to strengthen these alloys. In Zn-Cu-based alloys, only the second phases with submicron or micron size were observed in previous investigations. Here nanosized precipitates in an as-extruded Zn-2.0wt.%Cu alloy were first characterized using transmission electron microscopy, and identified as the e (CuZn4) phase enriched Cu element with a hexagonal structure, which present with a rod shape and are symmetrically distributed along the [ 02 2 ¯ 1 ] η direction at a specific angle with the basal plane of the matrix. The nano-precipitates exhibit an approximately coherent interface with the matrix. The shape and orientation relationship with the matrix of these nano-precipitates were analyzed based on free energy minimization.

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.

Electrospun fiber scaffolds, due to their mimicry of bone extracellular matrix (ECM), have become an important biomaterial widely applied in bone tissue engineering in recent years. While topographic cues of electrospun membranes such as alignment and diameter played vital roles in determining cellular behaviors. Yet few researches about the effects of these two significant parameters on osteogenesis have been reported. Thus, the present work explored the influence of aligned and random poly (L-lactic acid) (PLLA) fiber matrices with diameters of nanoscale (0.6 μm) and microscale (1.2 μm), respectively, on cellular responses of bone marrow mesenchymal stem cells (BMSCs), such as cell adhesion, migration, proliferation and osteogenesis. Our results revealed that aligned nanofibers (AN) could affect cell morphology and promote the migration of BMSCs after 24 h of cell culturing. Besides, AN group was observed to possess excellent biocompatibility and have significantly improved cell growth comparing with random nanofibers. More importantly, in vitro osteogenesis researches including ALP and Alizarin Red S staining, qRT-PCR and immunofluorescence staining demonstrated that BMSCs culturing on AN group exhibited higher osteogenic induction proficiency than that on aligned microfibers (AM) and random fiber substrates (RN and RM). Accordingly, aligned nanofiber scaffolds have greater application potential in bone tissue engineering.

In the present study, the effects of Zn-3Cu-xFe (x = 0, 0.2, 0.5 wt%) alloys on endothelial cells (EA.hy926) and smooth muscle cells (A7r5), the hemocompatibility and antibacterial properties were also evaluated. The cell viability of EA.hy926 cells and A7r5 cells decreased with the increasing of extract concentration. At the same Zn2+ concentration (over 6 ppm), the cell viability of EA.hy926 cells increased with the addition of Cu or Cu and Fe content, but no significant effect on A7r5 cells was observed. The hemolysis rate of Zn-3Cu-xFe alloys samples was about 1%, and there was no adversely affected on platelets adhering to the surface of the Zn alloys. As Fe content increases in the Zn-Cu-Fe alloys, the antibacterial lower concentrations against Staphylococcus aureus and Escherichia coli was improved due to the higher degradation rate and more Zn2+ and Cu2+ released. Our previous study already showed that the Zn-Cu-Fe alloy exhibited excellent mechanical properties and moderate degradation rate. Based on the above results, the in vitro biocompatibilities and antibacterial properties of Zn-3Cu alloy are significantly improved by the alloying of trace Fe, and the hemocompatibility is not adversely affected, which indicated that Zn-Cu-Fe alloy is a promising vascular stents candidate material.

Magnesium and Mg-based alloys are promising biomaterials for orthopedic implants because of their degradability, osteogenic effects, and biocompatibility. However, the drawbacks of these materials include high hydrogen gas production, unexpected corrosion resistance, and insufficient mechanical strength duration. Surface modification can protect these biomaterials and induce osteogenesis. In this work, a SrHPO4 coating was developed for our patented biodegradable Mg-Nd-Zn-Zr alloy (abbr. JDBM) through a chemical deposition method. The coating was characterized by in vitro immersion, ion release, and cytotoxicity tests, which showed a slower corrosion behavior and excellent cell viability. RNA sequencing of MC3T3E1 cells treated with SrHPO4-coated JDBM ion release test extract showed increased Tlr4, followed by the activation of the downstream PI3K/Akt signaling pathway, causing proliferation and growth of pre-osteoblasts. An intramedullary nail (IMN) was implanted in a femoral fracture rat model. Mechanical test, radiological and histological analysis suggested that SrHPO4-coated JDBM has superior mechanical properties, induces more bone formation, and decreases the degradation rate compared with uncoated JDBM and the administration of TLR4 inhibitor attenuated the new bone formation for fracture healing. SrHPO4 is a promising coating for JDBM implants, particularly for long-bone fractures.

Development of bone graft substitutes with appropriate integration of mechanical, biodegradable, and biofunctional properties, which promote bone formation while simultaneously preventing implant-associated infections, remains a great challenge. Herein we designed and synthesized a brushite/Ag3PO4-coated Mg-Nd-Zn-Zr scaffolds through chemical solution deposition of a composite coating onto the fluorinated Mg-based scaffolds generated with template replication method. The coated Mg-based open-porous scaffolds exhibit hierarchically-structured surface with cube-shaped Ag3PO4 nanoparticles uniformly distributed on top of microsized brushite grains. Immersion test reveals that the initial degradation rate of the coated scaffolds could be reduced by ~81% compared to the original scaffolds. The mean corrosion rate in 4 weeks falls into 0.10–0.15 mm/year to meet clinical requirements. The compatibility and ALP activity of cells grown in the extracts from the coated Mg-based scaffolds were increased compared with Ti control and original scaffolds, mainly due to the favorable microenvironment generated by Mg biodegradation. Besides, the coated Mg-based scaffold demonstrated potent antimicrobial activity via the synergistic actions of alkaline degradation products of Mg and the Ag species in the coating, achieving >99.5% antibacterial rate against both gram-positive and gram-negative bacteria with relatively low silver content. Taken together, this study presents a new candidate of brushite/Ag3PO4-coated Mg-based scaffold with appropriate degradation characteristics, cytocompatibility, and antimicrobial activities for bone tissue engineering applications.

Zn-based alloys as biodegradable materials for cardiovascular stents have drawn more and more attention in recent years. However, the hot plastic deformation of Zn-based alloys does not get enough attention. In this study, Zn-3Cu-0.5Fe alloy was prepared and then hot extruded at 140, 180, 220 and 260 °C. Effects of extrusion temperature on the microstructure, mechanical properties and degradation behavior were investigated. Nano-scaled particles precipitated during extrusion and the quantity decreased with the increasing of extrusion temperature. As the extrusion temperature increased from 140 to 260 °C, the grain size increased from 1.15 to 4.38 μm, the yield strength and ultimate tensile strength increased from 203 ± 3.23 and 221 ± 1.56 MPa to 269 ± 2.65 and 302 ± 8.01 MPa, increased by 32.5% and 45%, while the degradation rate was decreased gradually from 62.8 ± 0.72 μm/year to 49.9 ± 3.35 μm/year, decreased by 20.5%. In addition, the degradation behavior changes from a relatively uniform degradation mode to a localized degradation mode with the increase of the grain size. Dislocation gliding is replaced by grain-boundary movement and dynamic recrystallization (DRX) in the room temperature tensile deformation process. Lower extrusion temperature is beneficial for higher elongation and degradation rate as well as relatively uniform degradation mode, which is better suitable for the clinical application of cardiovascular stents.

Mg–1.50Zn–0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and then subjected to cyclic extrusion and compression (CEC) at 250, 300, 350 and 400 °C, respectively. The effects of CEC parameters including passes and temperatures on microstructure evolution and room temperature tensile mechanical properties were characterized and discussed. The results show that more passes are beneficial for secondary phase precipitation, grain refinement and basal texture weakening; while moderate temperature is beneficial for secondary phase precipitation and basal texture weakening by particle stimulated recrystallization nucleation (PSN), and lower temperature is beneficial for grain refinement. The alloy has the highest yield strength after CEC at 250 °C because of grain refinement and basal texture strengthening, while it has the highest elongation after being processed with 8 passes of CEC due to grain refinement and basal texture weakening. The processing passes have more important effects on microstructure evolution and mechanical properties than that of temperature during CEC. Keywords: Magnesium alloys, Cyclic extrusion and compression (CEC), Microstructure, Texture weakening, Mechanical properties

The secondary phases in quasicrystal-reinforced Mg–Zn–Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [11 2 ¯ 0]Mg ∥[2-fold]I-phase and (0001)Mg ∥(5-fold)I-phase. We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [ 1 ¯ 101]Mg ∥[mirror 2-fold]I-phase and (0 1 ¯ 11)Mg ∥(5-fold)I-phase are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys.

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.

Mg–1.5Zn–0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and subjected to cyclic extrusion and compression (CEC) at 350 °C to investigate the microstructure evolution during CEC and its effect on the mechanical properties. It is observed that, during CEC, the microstructure of the alloy was greatly refined by dynamic recrystallization (DRX), large numbers of I-phase particles precipitated and then grew up, the texture of the alloy was obviously weakened. These changes in microstructure improved the mechanical properties of the alloy significantly and the alloy processed by 8 passes CEC exhibited outstanding plasticity of 31.4% and moderate yield strength of 161 MPa.

In this work, the in vivo biocompatibility and biodegradation behavior of Mg-Nd-Zn-Zr alloy (denoted as JDBM) screws were studied using a goat femoral condyle fracture model. Blood analysis indicates that the liver and kidney functions of goats were not affected by JDBM, JDBM coated with brushite (denoted as JDBM-DCPD) and PLA implants. Radiographic analysis shows that JDBM-DCPD screw has lower degradation rate than JDBM. Histological images show that compared with PLA, JDBM and JDBM-DCPD show superior effect to promote more new bone formation. JDBM-DCPD group has more new bone formation than JDBM group, indicating good osteoinductivity of DCPD coating. JDBM group show higher osteogenic factors level (BMP2, ALP and OC) in peri-implant callus tissue than PLA group. Long-term (18months) in vivo implants Micro-CT result shows that the degradation of JDBM-DCPD screw may be slower than desirable, and the thickness of DCPD coating could be further adjusted to match the degradation to the bone recovery.

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.

We have performed a systematic transmission electron microscopy study of precipitated particles in Mg–Zn–Gd-based alloys after annealing. We find that the Mg–Zn phases and ellipsoidal-shaped icosahedral quasicrystal phases (I-phase) are precipitated and distributed by partition in the grains, which can be attributed to the composition segregation of the alloying elements in the as-cast alloys. The content of alloying element is found to be crucial to the precipitation of nanoscale I-phase. The nanoscale I-phase ranges in size from a few to dozens of nanometers, revealing that the precipitation process satisfies the classical nucleation and growth theory.

In recent years, bulk metallic glasses (BMGs) have received considerable attention due to their unique mechanical properties. However, the deformation of BMGs is highly localized in a few shear bands so that many of them exhibit poor plasticity. As such, more and more researchers have focused on improving the plasticity by in-situ or ex-situ introducing of nanoor micro-scale crystalline phases into the metallic glassy matrix in order to formation of multiple shear bands.

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 Mg 4 Zn 7 phases precipitate in Mg matrix, yet vanish during compression, forming nano-quasicrystals. These nano-quasicrystals are found to nucleate on the Mg 4 Zn 7 phase with orientation relationships [ 1 1 2 ‾ 0 ] Mg ‖ [ 1 ‾ 0 7 ] Mg 4 Zn 7 || [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.

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 (CaHPO 4 ·2H 2 O). 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 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.

A significant enhancement of yield strength and large plasticity was obtained in TiNb/Zr55Cu30Al10Ni5 composite by cyclic compression at the yield point. This phenomenon resulted from the cooperation of the metallic crystalline alloy TiNb and metallic glassy matrix Zr55Cu30Al10Ni5 in the composite. It was found that a large dislocation density of TiNb was produced during cyclic compression, which resulted in the increase of the strength. Meanwhile, the improvement of plasticity of the composite benefited from the propagation of excess shear bands in the glassy matrix, which were produced during the cyclic compression process. Hence, the collective effect of both resulted in the improved yield strength and large plasticity of the composite.

Biodegradable magnesium alloy with proper yield strength, high ultimate strength and elongation is a potential candidate for cardiovascular stent. Nevertheless, magnesium alloy with high ultimate tensile strength always exhibits high yield strength, which is not suitable for the plastic deformation of cardiovascular stent during implantation. Solution treatment was conducted on the as extruded Mg–2·7Nd–0·2Zn–0·4Zr alloy in order to reduce the high yield ratio, and the biocorrosion behaviour of the alloy was also evaluated in artificial plasma. The results show that the grains of the alloy grow, and the second phase reduces with increasing solution treatment temperature. The yield strength decreases gradually, and the ultimate tensile strength still keeps a high level due to the remarkable workhardening. The yield ratio of the alloy reduces from 92 to 57%. The corrosion resistance of the alloy after solution treatment is improved slightly when the temperature is

We have fabricated three types of Mg-Zn-Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) to investigate how volume fraction of the I-phase and extrusion ratio can have an impact on the microstructure, mechanical properties, and anisotropy of the as-extruded alloys. We find that grains are refined and that the ultimate tensile strength and elongation are improved as either the volume fraction of I-phase or the extrusion ratio is increased, which can be attributed to the secondary phase particle stimulate recrystallization nucleation and restrained grain boundary motion. Moreover, anisotropy is mitigated in all of the alloys as either the I-phase fraction or the extrusion ratio is increased owing to the coeffect of texture weakening and grain refinement as well as to the effect of I-phase on twinning. We also find that with the increase in the amount of the I-phase, the yield strength (YS) is decreased for the alloys extruded at a low ratio owing to the texture weakening, yet it is increased for the alloys extruded at high ratio owing to the strengthening originating from the I-phase and refined grains. The mechanical properties are improved for the alloys extruded at high ratio, which is due to their fine grains and uniform microstructure.

Double continuous extrusion (DCE) is proposed here as a novel thermomechanical process which means that the sample is continuously extruded twice by one process. The microstructures and mechanical properties of Mg 98 Zn 1.92 Gd 0.08 (at%, Alloy 1) and Mg 96.83 Zn 2.7 Gd 0.47 (at%, Alloy 2) after conventional extrusion and DCE at 373 K were investigated. The results show that the major secondary phase in Alloy 1 is Mg 2 Zn 3 and that in Alloy 2 is icosahedral quasicrystals phase (I-phase). After DCE, the microstructure is refined, and the average grain sizes of the both alloys are smaller than 1 μm, and this further improves the mechanical properties. Both the alloys exhibit excellent mechanical properties, and the ultimate tensile strength, yield strength and elongation to failure are 434 MPa, 410 MPa and 14.6%, respectively, for Alloy 1; and 444 MPa, 417 MPa and 13.1%, respectively, for Alloy 2. The possible strengthening mechanisms were discussed and it was found that DCE is an effective method for Mg-based alloys strengthening by grain refinement and secondary phase dispersion.

The Mg–3?08Nd–0?27Zn–0?46Zr (wt-%) alloy was hot extruded with different extrusion ratios to refine microstructure and to optimise mechanical properties and corrosion resistance as a biodegradable magnesium alloy. The microstructure was observed by optical microscopy, the mechanical properties were tested at room temperature and the corrosion resistance was evaluated in Hanks’ solution. The results show that the microstructure becomes more and more homogeneous with increasing the extrusion ratio. The mechanical properties of the as extruded alloy are much better than those of the as cast one. Higher strength is obtained with the extrusion ratio of 18, and better elongation is obtained with the extrusion ratio of 25. Corrosion results show that corrosion resistance of the as extruded alloy immersed in Hanks’ solution is better than that of the as cast one, and higher extrusion ratio results in better corrosion resistance. Both the as cast and the as extruded alloys exhibit uniform corrosion, which was interpreted by cyclic polarisation test.