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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.

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.

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/Ag

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.

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.

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-4wt.%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±10MPa, 270±10MPa and 51±2%, respectively. The corrosion rate of the as-extruded alloy in Hank's solution is about 9.41(±1.34)μmyear(-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.

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 3.00mm outer diameter and 180μm 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 10.9μm, 12.9μm and 15.0μm, respectively. Tensile mechanical test results showed that the as-annealed JDBM, AZ31 and WE43 micro-tubes respectively exhibited the yield strength of 123MPa, 172MPa and 113MPa, 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.

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.