Systematic in vitro and in vivo study on biodegradable binary Zn-0.2 at% Rare Earth alloys (Zn-RE: Sc, Y, La-Nd, Sm-Lu).

Biomedical implants and devices for tissue engineering in clinics, mainly made of polymers and stiff metallic materials, require possibly secondary surgery or life-long medicine. Biodegradable metals for biomedical implants and devices exhibit huge potential to improve the prognosis of patients. In this work, we developed a new type of biodegradable binary zinc (Zn) alloys with 16 rare earth elements (REEs) including Sc, Y, La to Nd, and Sm to Lu, respectively. The effects of REEs on the alloy microstructure, mechanical properties, corrosion behavior and in vitro and in vivo biocompatibility of Zn were systematically investigated using pure Zn as control. All Zn-RE alloys generally exhibited improved mechanical properties, and biocompatibilities compared to pure Zn, especially the tensile strength and ductility of Zn-RE alloys were dramatically enhanced. Among the Zn-RE alloys, different REEs presented enhancement effects at varied extent. Y, Ho and Lu were the three elements displaying greatest improvements in majority of alloys properties, while Eu, Gd and Dy exhibited least improvement. Furthermore, the Zn-RE alloys were comparable with other Zn alloys and also exhibited superior properties to Mg-RE alloys. The in vivo experiment using Zn-La, Zn-Ce, and Zn-Nd alloys as tibia bone implants in rabbit demonstrated the excellent tissue biocompatibility and much more obvious osseointegration than the pure Zn control group. This work presented the significant potential of the developed Zn-RE binary alloys as novel degradable metal for biomedical implants and devices.

pH Stimuli-Responsive, Rapidly Self-healable Coatings Enhanced the Corrosion Resistance and Osteogenic Differentiation of Mg-1Ca Osteoimplant.

Mg-Ca alloys have emerged as a promising research direction for biomedical implants in the orthopedic field. However, their clinical use is deterred by their fast corrosion rate. In this work, a pH stimuli-responsive silk-halloysite (HNT)/phytic acid (PA) self-healing coating (Silk-HNT/PA) is constructed to slow down the corrosion rate of Mg-1Ca alloy and its cell viability and osteogenic differentiation ability are enhanced. The Silk-HNT/PA coating exhibits appealing active corrosion protection, by eliciting pH-triggerable self-healing effects, while simultaneously affording superior biocompatibility and osteogenic differentiation ability. Moreover, in vivo studies by histological analysis also demonstrate better osseointegration for the Silk-HNT/PA coated Mg-1Ca alloy. In summary, the Silk-HNT/PA coating in the present study has great potential in enhancing the biomedical utility of Mg alloys.

Additive manufacturing of Zn-Mg alloy porous scaffolds with enhanced osseointegration: In vitro and in vivo studies.

Biodegradable metals (BM) and additive manufacturing (AM) are regarded revolutionary biomaterials and biofabrication technologies for bone repairing metal implants, the combination of both, namely AM of BM, is thus expected to solve the dual technical difficulties including "conventional medical metals are biologically inert and exist in the human body permanently" and "conventional manufacturing processes are inadequate to fabricate personalized implants of complicated structure". This work additively manufactured biodegradable Zn-Mg alloy porous scaffolds by laser powder bed fusion (L-PBF). By using the pre-alloyed Zn-xMg (x = 1, 2 and 5 wt.%) powder and the optimized processing conditions, high fusion quality with the relative density greater than 99.5% was confirmed for the L-PBF parts. The influence of Mg content on microstructure, mechanical properties, in vitro corrosion, cytocompatibility, in vivo degradation, biocompatibility and osteogenic effect was investigated. Fine α-Zn grains and precipitation phases including Mg2Zn11 and MgZn2 were observed in the Zn-xMg L-PBF parts. The hardness increased, and the strength increases firstly and then decreased with increasing the Mg content. The compressive strength and elastic modulus of Zn-1Mg porous scaffolds reached the highest as 40.9 ± 0.4 MPa and 1.17 ± 0.11 GPa, respectively, equivalent to those of cancellous bone. The corrosion rate and cell viability slightly rose with increasing the Mg content. Histological analysis after 6-week and 12-week implantation in rabbit femurs showed enhanced bone formation around the Zn-1Mg porous scaffolds compared with pure Zn counterparts. In summary, Zn-1Mg porous scaffolds produced by L-PBF presented promising results to fulfill customized requirements of biodegradable bone implants. STATEMENT OF SIGNIFICANCE: Additive manufacturing of biodegradable metal porous scaffolds is expected to solve the dual challenges from customized structures and bioactive function required for bone implants. It was the first to present a systematic in vitro and in vivo investigation into the compositions, microstructure, mechanical properties, biodegradation, biocompatibility and osteogenic effect of additively manufactured Zn-Mg alloy porous scaffolds. Reliable formation quality and performance evaluation was achieved by using the pre-alloyed Zn-xMg (x = 1, 2 and 5 wt.%) powder and the optimized laser powder bed fusion process. Although the Zn-1Mg scaffolds exhibited promising mechanical strength, biocompatibility, and osteogenic effect, their degradation rate needs to be further accelerated compared with the term of bone reconstruction.