Zn-0.8Mg-0.2Sr (wt.%) Absorbable Screws-An In-Vivo Biocompatibility and Degradation Pilot Study on a Rabbit Model

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.

A detailed mechanism of degradation behaviour of biodegradable as-ECAPed Zn-0.8Mg-0.2Sr with emphasis on localized corrosion attack

In this study, advanced techniques such as atom probe tomography, atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy were used to determine the corrosion mechanism of the as-ECAPed Zn-0.8Mg-0.2Sr alloy. The influence of microstructural and surface features on the corrosion mechanism was investigated. Despite its significance, the surface composition before exposure is often neglected by the scientific community. The analyses revealed the formation of thin ZnO, MgO, and MgCO₃ layers on the surface of the material before exposure. These layers participated in the formation of corrosion products, leading to the predominant occurrence of hydrozincite. In addition, the layers possessed different resistance to the environment, resulting in localized corrosion attacks. The segregation of Mg on the Zn grain boundaries with lower potential compared with the Zn-matrix was revealed by atom probe tomography and atomic force microscopy. The degradation process was initiated by the activity of micro-galvanic cells, specifically Zn - Mg₂Zn₁₁/SrZn₁₃. This process led to the activity of the crevice corrosion mechanism and subsequent attack to a depth of 250 μm. The corrosion rate of the alloy determined by the weight loss method was 0.36 mm·a^-1. Based on this detailed study, the degradation mechanism of the Zn-0.8Mg-0.2Sr alloy is proposed.

[Research status and development of biodegradable zinc alloy as orthopedics implant]

Znic (Zn) alloys with good cytocompatibility and suitable degradation rate have been a kind of biodegradable metal with great potential for clinical applications. This paper summarizes the biological role of degradable Zn alloy as bone implant materials, discusses the mechanical properties of different Zn alloys and their advantages and disadvantages as bone implant materials, and analyzes the influence of different processing strategies (such as alloying and additive manufacturing) on the mechanical properties of Zn alloys. This paper provides systematic design approaches for biodegradable Zn alloys as bone implant materials in terms of the material selection, product processing, structural topology optimization, and assesses their application prospects with a view to better serve the clinic.

Microstructural and Mechanical Characterization of Newly Developed Zn-Mg-CaO Composite

In this study, the Zn-0.8Mg-0.28CaO wt.% composite was successfully prepared using different conditions of ball milling (rotations and time) followed by a direct extrusion process. These materials were characterized from the point of view of microstructure and compressive properties, and the correlation between those characteristics was found. Microstructures of individual materials possessed differences in grain size, where the grain size decreased with the intensified conditions (milling speed and time). However, the mutual relation between grain size and compressive strength was not linear. This was caused by the effect of other factors, such as texture, intermetallic phases, and pores. Material texture affects the mechanical properties by a different activity ratio between basal and pyramidal <c + a> slips. The properties of intermetallic particles and pores were determined in material volume using micro-computed tomography (µCT), enhancing the precision of our assumptions compared with commonly applied methods. Based on that, and the analysis after the compressive tests, we were able to determine the influence of aspect ratio, feret diameters, and volume content of intermetallic phases and pores on mechanical behavior. The influence of the aspects on mechanical behavior is described and discussed.

Impact of gadolinium on mechanical properties, corrosion resistance, and biocompatibility of Zn-1Mg-xGd alloys for biodegradable bone-implant applications

Zinc (Zn) and its alloys are currently regarded as one of the promising families of biodegradable metals for implant applications owing to their suitable biodegradability and biofunctionality. However, the inadequate mechanical properties of as-cast (AC) pure Zn restricted the practical clinical bone-implant applications due to its coarse grain size and hexagon close-packed crystal structure. Here, the impact of gadolinium (Gd) on the mechanical properties, corrosion resistance, hemolysis percentage, anticoagulant activity, and cytotoxicity of AC and hot-rolled (HR) Zn-1Mg-xGd (x = 0.1, 0.2, and 0.3) (wt.%) alloys were investigated for biodegradable bone-implant applications. Tensile testing showed that the HR Zn-1Mg-0.3Gd alloy exhibited the highest tensile strength of 288.1 MPa, tensile yield strength of 250.9 MPa, and elongation of 13.2%. Electrochemical corrosion and immersion tests revealed that the corrosion rates of both AC and HR specimens increased with increasing Gd content in Hanks' solution, and the HR Zn-1Mg-xGd specimens exhibited higher corrosion rates compared to their AC counterparts. The HR Zn-1Mg-xGd specimens showed an increasing hemolysis percentages and decreasing activated partial thromboplastin time (APTT) values with increasing Gd addition. The alloy extracts of HR samples at ≤ 25% concentration exhibited no cytotoxicity toward MG-63 cells, and the HR Zn-1Mg-0.3Gd alloy displayed the highest cell viability among all three alloy extracts at 12.5% concentration. Overall, the HR Zn-1Mg-0.3Gd can be considered a promising biodegradable implant material for bone-implant materials owing to its high mechanical strength and ductility, suitable degradation rate, and satisfying biocompatibility. STATEMENT OF SIGNIFICANCE: In this work, Zn-1Mg-xGd (x = 0.1, 0.2, and 0.3 wt.%) alloys were developed by alloying with gadolinium (Gd) and hot-rolling, and their mechanical properties, corrosion behavior, hemolysis percentage, anticoagulant activity, and cytotoxicity were investigated for biodegradable implant application. Our findings demonstrated that the hot-rolled Zn-1Mg-0.3Gd alloy exhibit the highest ultimate tensile strength of 288.1 MPa, yield strength of 250.9 MPa, and elongation of 13.2%. Hot-rolled Zn-1Mg-xGd alloys show slowly increasing hemolysis percentages and decreasing activated partial thromboplastin time (APTT) values with increasing Gd addition. Extracts of hot-rolled Zn-1Mg-xGd alloys at a concentration of ≤ 25% show no cytotoxicity towards MG-63 cells, and Zn-1Mg-0.3Gd exhibit good cytocompatibility among all three alloys at a concentration of 12.5%.

A Complex Evaluation of the In-Vivo Biocompatibility and Degradation of an Extruded ZnMgSr Absorbable Alloy Implanted into Rabbit Bones for 360 Days

The increasing incidence of trauma in medicine brings with it new demands on the materials used for the surgical treatment of bone fractures. Titanium, its alloys, and steel are used worldwide in the treatment of skeletal injuries. These metallic materials, although inert, are often removed after the injured bone has healed. The second-stage procedure—the removal of the plates and screws—can overwhelm patients and overload healthcare systems. The development of suitable absorbable metallic materials would help us to overcome these issues. In this experimental study, we analyzed an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. From this alloy we developed screws which were implanted into the rabbit tibia. After 120, 240, and 360 days, we tested the toxicity at the site of implantation and also within the vital organs: the liver, kidneys, and brain. The results were compared with a control group, implanted with a Ti-based screw and sacrificed after 360 days. The samples were analyzed using X-ray, micro-CT, and a scanning electron microscope. Chemical analysis revealed only small concentrations of zinc, strontium, and magnesium in the liver, kidneys, and brain. Histologically, the alloy was verified to possess very good biocompatibility after 360 days, without any signs of toxicity at the site of implantation. We did not observe raised levels of Sr, Zn, or Mg in any of the vital organs when compared with the Ti group at 360 days. The material was found to slowly degrade in vivo, forming solid corrosion products on its surface.