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)

Fabrication and performance of Zinc-based biodegradable metals: From conventional processes to laser powder bed fusion

Zinc (Zn)-based biodegradable metals (BMs) fabricated through conventional manufacturing methods exhibit adequate mechanical strength, moderate degradation behavior, acceptable biocompatibility, and bioactive functions. Consequently, they are recognized as a new generation of bioactive metals and show promise in several applications. However, conventional manufacturing processes face formidable limitations for the fabrication of customized implants, such as porous scaffolds for tissue engineering, which are future direction towards precise medicine. As a metal additive manufacturing technology, laser powder bed fusion (L-PBF) has the advantages of design freedom and formation precision by using fine powder particles to reliably fabricate metallic implants with customized structures according to patient-specific needs. The combination of Zn-based BMs and L-PBF has become a prominent research focus in the fields of biomaterials as well as biofabrication. Substantial progresses have been made in this interdisciplinary field recently. This work reviewed the current research status of Zn-based BMs manufactured by L-PBF, covering critical issues including powder particles, structure design, processing optimization, chemical compositions, surface modification, microstructure, mechanical properties, degradation behaviors, biocompatibility, and bioactive functions, and meanwhile clarified the influence mechanism of powder particle composition, structure design, and surface modification on the biodegradable performance of L-PBF Zn-based BM implants. Eventually, it was closed with the future perspectives of L-PBF of Zn-based BMs, putting forward based on state-of-the-art development and practical clinical needs.

A Critical Review of Biodegradable Zinc Alloys toward Clinical Applications

Biodegradable zinc (Zn) alloys stand out as promising contenders for biomedical applications due to their favorable mechanical properties and appropriate degradation rates, offering the potential to mitigate the risks and expenses associated with secondary surgeries. While current research predominantly centers on the in vitro examination of Zn alloys, notable disparities often emerge between in vivo and in vitro findings. Consequently, conducting in vivo investigations on Zn alloys holds paramount significance in advancing their clinical application. Different element compositions and processing methods decide the mechanical properties and biological performance of Zn alloys, thus affecting their suitability for specific medical applications. This paper presents a comprehensive overview of recent strides in the development of biodegradable Zn alloys, with a focus on key aspects such as mechanical properties, toxicity, animal experiments, biological properties, and molecular mechanisms. By summarizing these advancements, the paper aims to broaden the scope of research directions and enhance the understanding of the clinical applications of biodegradable Zn alloys.

The effect of Silver addition and deformation parameters on mechanostructure, biodegradation, antimicrobial and mechanical properties of Zn-based biodegradable alloys

Although low mechanical properties, Zinc (Zn) alloy systems with Copper (Cu) and Silver (Ag) as alloying elements have strong biocompatibility and biodegradability characteristics. This study examined the effects of rolling parameters and Ag alloying on the mechanical, biodegradable, and final structure of an alloy based on Zn. Comparing treated and untreated specimens, the addition of Ag led to a considerable improvement in both hardness and compressive strength. The produced alloys with varying amounts of Ag (between 1 and 4 wt%) were cold rolled at 400-800 r/min and friction coefficients between 0.3 and 0.5. The alloys' ultimate strength rose with an increase in rolling speed for Zn1Cu4Ag, and hardness and compressive strengths rose to 80HV and 470 MPa, respectively. It was demonstrated that rolling force rose somewhat with Ag concentration but significantly increased with rolling speed and friction. E. Coli and S. aureus were used to assess the biodegradable alloys' antibacterial properties. For the Zn-1Cu-2Ag alloy, the inclusion of Ag resulted in a considerable (50%) rise in antibacterial activity that exceeded the effects seen in other alloy systems.

Structural and temporal dynamics analysis of zinc-based biomaterials: History, research hotspots and emerging trends

Objectives

To examine the 16-year developmental history, research hotspots, and emerging trends of zinc-based biodegradable metallic materials from the perspective of structural and temporal dynamics.

Methods

The literature on zinc-based biodegradable metallic materials in WoSCC was searched. Historical characteristics, the evolution of active topics and development trends in the field of zinc-based biodegradable metallic materials were analyzed using the bibliometric tools CiteSpace and HistCite.

Results

Over the past 16 years, the field of zinc-based biodegradable metal materials has remained in a hotspot stage, with extensive scientific collaboration. In addition, there are 45 subject categories and 51 keywords in different research periods, and 80 papers experience citation bursts. Keyword clustering anchored 3 emerging research subfields, namely, #1 plastic deformation #4 additive manufacturing #5 surface modification. The keyword alluvial map shows that the longest-lasting research concepts in the field are mechanical property, microstructure, corrosion behavior, etc., and emerging keywords are additive manufacturing, surface modification, dynamic recrystallization, etc. The most recent research on reference clustering has six subfields. Namely, #0 microstructure, #2 sem, #3 additive manufacturing, #4 laser powder bed fusion, #5 implant, and #7 Zn-1Mg.

Conclusion

The results of the bibliometric study provide the current status and trends of research on zinc-based biodegradable metallic materials, which can help researchers identify hot spots and explore new research directions in the field.

Zinc based biodegradable metals for bone repair and regeneration: Bioactivity and molecular mechanisms

Bone fractures and critical-size bone defects are significant public health issues, and clinical treatment outcomes are closely related to the intrinsic properties of the utilized implant materials. Zinc (Zn)-based biodegradable metals (BMs) have emerged as promising bioactive materials because of their exceptional biocompatibility, appropriate mechanical properties, and controllable biodegradation. This review summarizes the state of the art in terms of Zn-based metals for bone repair and regeneration, focusing on bridging the gap between biological mechanism and required bioactivity. The molecular mechanism underlying the release of Zn ions from Zn-based BMs in the improvement of bone repair and regeneration is elucidated. By integrating clinical considerations and the specific bioactivity required for implant materials, this review summarizes the current research status of Zn-based internal fixation materials for promoting fracture healing, Zn-based scaffolds for regenerating critical-size bone defects, and Zn-based barrier membranes for reconstituting alveolar bone defects. Considering the significant progress made in the research on Zn-based BMs for potential clinical applications, the challenges and promising research directions are proposed and discussed.

Photoelectrons Sequentially Regulate Antibacterial Activity and Osseointegration of Titanium Implants

Titanium implants are widely used ; however, implantation occasionally fails due to infections during the surgery or poor osseointegration after the surgery. To solve the problem, an intelligent functional surface on titanium implant that can sequentially eradicate bacteria biofilm at the initial period and promote osseointegration at the late period of post-surgery time is designed. Such surfaces can be excited by near infrared light (NIR), with rare earth nanoparticles to upconvert the NIR light to visible range and adsorb by Au nanoparticles, supported by titanium oxide porous film on titanium implants. Under NIR irradiation, the implant converts the energy of phonon to hot electrons and lattice vibrations, while the former flows directly to the contact substance or partially reacts with the surrounding to generate reactive oxygen species, and the latter leads to the local temperature increase. The biofilm or microbes on the implant surface can be eradicated by NIR treatment in vitro and in vivo. Additionally, the surface exhibits superior biocompatibility for cell survival, adhesion, proliferation, and osteogenic differentiation, which provides the foundation for osseointegration. In vivo implantation experiments demonstrate osseointegration is also promoted. This work thus demonstrates NIR-generated electrons can sequentially eradicate biofilms and regulate the osteogenic process, providing new solutions to fabricate efficient implant surfaces.

Mechanical properties, in vitro biodegradable behavior, biocompatibility and osteogenic ability of additively manufactured Zn-0.8Li-0.1Mg alloy scaffolds

Alloying and structural design provide flexibility to modulate performance of biodegradable porous implants manufactured by laser powder bed fusion (L-PBF). Herein, bulk Zn-0.8Li-0.1Mg was first fabricated to indicate the influence of the ternary alloy system on strengthening effect. Porous scaffolds with different porosities, including 60 % (P60), 70 % (P70) and 80 % (P80), were designed and fabricated to study the influence of porosity on mechanical properties, in vitro degradation behavior, biocompatibility and osteogenic ability. Pure Zn (Zn-P70) scaffolds with a porosity of 70 % were utilized for the comparison. The results showed Zn-0.8Li-0.1Mg bulks had an ultimate tensile strength of 460.78 ± 5.79 MPa, which was more than 3 times that of pure Zn ones and was the highest value ever reported for Zn alloys fabricated by L-PBF. The compressive strength (CS) and elastic modulus (E) of scaffolds decreased with increasing porosities. The CS of P70 scaffolds was 24.59 MPa, more than 2 times that of Zn-P70. The weight loss of scaffolds during in vitro immersion increased with increasing porosities. Compared with Zn-P70, a lower weight loss, better biocompatibility and improved osteogenic ability were observed for P70 scaffolds. P70 scaffolds also exhibited the best biocompatibility and osteogenic ability among all the used porosities. Influence mechanism of alloying elements and structural porosities on mechanical behaviors, in vitro biodegradation behavior, biocompatibility and osteogenic ability of scaffolds were discussed using finite element analysis and the characterization of degradation products. The results indicated that the proper design of alloying and porosity made Zn-0.8Li-0.1Mg scaffolds promising for biodegradable applications.

Mechanical properties, corrosion and degradation behaviors, and in vitro cytocompatibility of a biodegradable Zn-5La alloy for bone-implant applications

Zinc (Zn) and its alloys are used in bone-fixation devices as biodegradable bone-implant materials due to their good biosafety, biological function, biodegradability, and formability. Unfortunately, the clinical application of pure Zn is hindered by its insufficient mechanical properties and slow degradation rate. In this study, a Zn-5 wt.% lanthanum (Zn-5La) alloy with enhanced mechanical properties, suitable degradation rate, and cytocompatibility was developed through La alloying and hot extrusion. The hot-extruded (HE) Zn-5La alloy showed ultimate tensile strength of 286.3 MPa, tensile yield strength of 139.7 MPa, elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. The corrosion resistance of the HE Zn-5La in Hanks' and Dulbecco's modified Eagle medium (DMEM) solutions gradually increased with prolonged immersion time. Further, the HE Zn-5La exhibited an electrochemical corrosion rate of 36.7 μm/y in Hanks' solution and 11.4 μm/y in DMEM solution, and a degradation rate of 49.5 μm/y in Hanks' solution and 30.3 μm/y in DMEM solution, after 30 d of immersion. The corrosion resistance of both HE Zn and Zn-5La in DMEM solution was higher than in Hanks' solution. The 25% concentration extract of the HE Zn-5La showed a cell viability of 106.5%, indicating no cytotoxicity toward MG-63 cells. We recommend the HE Zn-5La alloy as a promising candidate material for biodegradable bone-implant applications. STATEMENT OF SIGNIFICANCE: This work reports the mechanical properties, corrosion and degradation behaviors, in vitro cytocompatibility and antibacterial ability of biodegradable Zn-5La alloy for bone-implant applications. Our findings demonstrate that the hot-extruded (HE) Zn-5La alloy showed an ultimate tensile strength of 286.3 MPa, a yield strength of 139.7 MPa, an elongation of 35.7%, compressive yield strength of 262.7 MPa, and microhardness of 109.7 HV. HE Zn-5La exhibited appropriate degradation rates in Hanks' and DMEM solutions. Furthermore, the HE Zn-5La alloy showed good cytocompatibility toward MG-63 and MC3T3-E1 cells and greater antibacterial ability against S. aureus.