The Application of the Rare Earths to Magnesium and Titanium Metallurgy in Australia

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

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

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

The unique combination of biodegradability, biocompatibility, and functionality of zinc (Zn)-based alloys makes them highly desirable for a wide range of medical applications. However, a long-standing problem associated with this family of biodegradable alloys in the as-cast state is their limited mechanical strength and slow degradation rate. Here we report the development of Zn-xDy (x = 1, 3, and 5 wt.%) alloys with high strength, ductility, cytocompatibility, antibacterial ability, and appropriate degradation rate for biodegradable bone-implant applications. Our results indicate that the mechanical properties of Zn-xDy alloys were effectively improved with increasing Dy addition and hot-rolling due to the second-phase strengthening. The hot-rolled (HR) Zn-3Dy alloy showed the best combined mechanical performance with an ultimate tensile strength of 270.5 MPa, a yield strength of 214.8 MPa, an elongation of 55.1%, and Brinell hardness of 75.9 HB. The corrosion and degradation rates of HR Zn-xDy alloys in Hanks' solution gradually increased with increasing Dy addition due to the intensification of galvanic corrosion. The HR Zn-3Dy alloy showed high antibacterial ability against S. aureus and cytocompatibility toward MC3T3-E1 cells among all the HR alloys. Overall, the HR Zn-3Dy alloy can be considered a promising biodegradable material for bone implants. STATEMENT OF SIGNIFICANCE: This work reports on Zn-xDy (x = 1, 3, and 5%) alloys fabricated by Dy alloying followed by hot-rolling for biodegradable bone-implant applications. Our findings demonstrate that the hot-rolled (HR) Zn-3Dy alloy showed the best combined mechanical performance with an ultimate tensile strength of 270.5 MPa, a yield strength of 214.8 MPa, an elongation of 55.1%, and Brinell hardness of 75.9 HB. The corrosion and degradation rates of HR Zn-xDy alloys in Hanks' solution gradually increased with increasing Dy addition due to the intensification of galvanic corrosion. Furthermore, the HR Zn-3Dy alloy showed greater antibacterial ability against S. aureus and the best cytocompatibility toward MC3T3-E1 cells among all the HR alloys.

Design of single-phased magnesium alloys with typically high solubility rare earth elements for biomedical applications: Concept and proof

Rare earth elements (REEs) have been long applied in magnesium alloys, among which the mischmetal-containing WE43 alloy has already got the CE mark approval for clinical application. A considerable amount of REEs (7 wt%) is needed in that multi-phased alloy to achieve a good combination of mechanical strength and corrosion resistance. However, the high complex RE addition accompanied with multiple second phases may bring the concern of biological hazards. Single-phased Mg-RE alloys with simpler compositions were proposed to improve the overall performance, i.e., “Simpler alloy, better performance”. The single-phased microstructure can be successfully obtained with typical high-solubility REEs (Ho, Er or Lu) through traditional smelting, casting and extrusion in a wide compositional range. A good corrosion resistance with a macroscopically uniform corrosion mode was guaranteed by the homogeneously single-phased microstructure. The bimodal-grained structure with plenty of sub-grain microstructures allow us to minimize the RE addition to <1 wt%, without losing mechanical properties. The single-phased Mg-RE alloys show comparable mechanical properties to the clinically-proven Mg-based implants. They exhibited similar in-vitro and in-vivo performances (without local or systematic toxicity in SD-rats) compared to a high purity magnesium. In addition, metal elements in our single-phased alloys can be gradually excreted through the urinary system and digestive system, showing no consistent accumulation of RE in main organs, i.e., less burden on organs. The novel concept in this study focuses on the simplification of Mg-RE based alloys for biomedical purpose, and other biodegradable metals with single-phased microstructures are expected to be explored.

•

A concept of developing single-phased biodegradable magnesium alloys was proposed.

•

Single-phased magnesium alloys with bimodal-grained structures were obtained.

•

Good strength and corrosion resistance synergy was achieved in the alloys.

•

Significantly reduced rare earth addition is beneficial to the biocompatibility.

•

Simpler alloy helps to lower the possible biological risks of Mg related implants.

A holistic approach for the recovery of rare earth elements and scandium from secondary sources under a circular economy framework - A review

Limited natural resources and a continuous increase in the demand for modern technological products, is creating a demand and supply gap for rare earth elements (REEs) and Sc. There is therefore a need to adopt the sustainable approach of the circular economy system (CE). In this review, we defined six steps required to close the loop and recover REEs, using a holistic approach. Recent statistics on REEs and Sc demand and the number of waste generations are reported and studies on more environmentally friendly, economic, and/or efficient recovery processes are summarized. Pilot-scale recovery facilities are described for several types of secondary sources. Finally, we identify obstacles to closing the REE loop in a circular economy and the reasons why secondary sources are not preferred over primary sources. Briefly, recovery from secondary sources should be environmentally and economically friendly and of an acceptable standard concerning final product quality. However, current technologies for recovery from for secondary sources are limiting and technology needs will vary depending on the source type. The quality/purity of the recovered metals should be proven so that they do not result in any adverse effects on the product quality, when they are being used as secondary raw material. In addition, for industrial-scale facilities, process improvements are required that consider environmental conditions.

Enhanced Electromagnetic Wave Absorption for Y2O3-Doped SiBCN Ceramics

Polymer-derived SiBCN ceramics (PDCs-SiBCN) are promising ultrahigh-temperature ceramics owing to their excellent high-temperature oxidation resistance and electromagnetic wave (EMW)-absorbing capability. In this paper, the microstructure evolutions, the dielectric properties, and EMW absorption properties of Y₂O₃-doped SiBCN ceramics were investigated. The results reveal that Y₂O₃ acting as a catalyst promotes the formation of SiC, BN(C), and graphite crystalline phases in the SiBCN ceramics, and these crystalline phases are constructed as conduction phases and polarization phases to enhance the EMW-adsorbing properties. The minimum reflection loss (RL_min) reaches -42.22 dB at 15.28 GHz, and the effective absorption bandwidth is 4.72 GHz (13.28-18.00 GHz). In addition, there is only 0.56 wt % mass loss for the Y₂O₃-doped SiBCN ceramics when they are heated from ambient temperature to 1500 °C in air, indicating that the Y₂O₃-doped SiBCN ceramics obtain excellent oxidation resistance at high temperature. We believe that rare metal oxidation is beneficial for the growth of crystalline phases in the PDCs, resulting in high EMW-absorbing properties and oxidation resistance. Thus, the research extends a novel method and design strategy for microstructure regulation and property enhancement of PDCs.

A Lysine-Modified Polyethersulfone (PES) Membrane for the Recovery of Lanthanides

Rare-earth elements (which include all lanthanides, scandium, and yttrium) play a key role in many fields including oil refining, metallurgy, electronics manufacturing, and other high-technology applications. Although the available lanthanide resources are enough for current levels of manufacturing, increased future demand for lanthanides will require new, efficient recovery methods to provide a sustainable supply. Membrane adsorbers are promising separation materials to recover lanthanides from high volumes of wastewater due to their tailorable surface chemistry, high binding capacity and high throughput. In this work, membrane adsorbers were synthesized by first using ultraviolet-initiated free radical polymerization to graft a poly(glycidyl methacrylate) (p-GMA) layer to the surface of polyethersulfone membranes. Then, the reactive epoxy groups of the grafted p-GMA were used for the covalent attachment of lysine molecules via a zinc perchlorate-catalyzed, epoxide ring-opening reaction at 35°C. Changes in membrane surface chemistry throughout the functionalization process were monitored with Fourier Transform Infrared Spectroscopy. The degree of grafting for the p-GMA film was quantified gravimetrically and increased with increasing polymerization time. Equilibrium adsorption experiments were performed for single specie solutions of La³⁺, Ce³⁺, Nd³⁺, Na⁺, Ca²⁺, and Mg²⁺ at pH 5.25 ± 0.25. Lysine-modified membranes showed negligible uptake of Na⁺, Ca²⁺, and Mg²⁺. The maximum capacities modeled by the Langmuir isotherm for La³⁺ and Ce³⁺ were 6.11 ± 0.58 and 6.45 ± 1.29 mg/g adsorbent, respectively. Nd³⁺ adsorbed to the membrane; however, the fit of the Langmuir model was not significant and it adsorbed to a lower extent than La³⁺ and Ce³⁺. Lower adsorption of the higher charge density species indicates that the primary binding mode is through the amine moieties of lysine and not the carboxylic acid. Dynamic adsorption experiments were conducted with 1 ppm La³⁺ feed solutions at different flow rates using either a single membrane or three membranes in series. The dynamic binding capacity at 50% breakthrough was independent of flowrate within the tested range. The low-temperature membrane functionalization methodology presented in this work can be used to immobilize biomolecules with even higher specificity, like engineered peptides or proteins, on membrane surfaces.