A biodegradable in situ Zn-Mg2Ge composite for bone-implant applications

Advances in biodegradable materials: Degradation mechanisms, mechanical properties, and biocompatibility for orthopedic applications

Mg-based and Zn-based biodegradable materials have the potential to become the next-generation implant materials to treat bone diseases, because of their desired degradation and mechanical properties. This article reviews the status of these implant materials. The required properties of biodegradable materials such as biodegradability, mechanical properties, and biocompatibility for performance evaluation were briefly discussed. The influence of fabrication techniques, microstructure, alloying elements, and post-processing techniques on the properties of Mg and Zn-based materials was addressed. The degradation mechanism by dissolution, oxidation, and interaction with human body cells was discussed. The biocompatibility of Mg and Zn-based biodegradable materials was analyzed. The significance of in vitro and in vivo biocompatibility testing was highlighted, emphasizing the superiority of in vivo results over cell line studies. This article identifies the many Mg and Zn-based biodegradable materials and summarizes the key findings.

Biodegradable Zn-5Dy Alloy with Enhanced Osteo/Angio-Genic Activity and Osteointegration Effect via Regulation of SIRT4-Dependent Mitochondrial Function

Zinc (Zn)-dysprosium (Dy) binary alloys are promising biodegradable bone fracture fixation implants owing to their attractive biodegradability and mechanical properties. However, their clinical application is a challenge for bone fracture healing, due to the lack of Zn-Dy alloys with tailored proper bio-mechanical and osteointegration properties for bone regeneration. A Zn-5Dy alloy with high strength and ductility and a degradation rate aligned with the bone remodeling cycle is developed. Here, mechanical stability is further confirmed, proving that Zn-5Dy alloy can resist aging in the degradation process, thus meeting the mechanical requirements of fracture fixation. In vitro cellular experiments reveal that the Zn-5Dy alloy enhances osteogenesis and angiogenesis by elevating SIRT4-mediated mitochondrial function. In vivo Micro-CT, SEM-EDS, and immunohistochemistry analyses further indicate good biosafety, suitable biodegradation rate, and great osteointegration of Zn-5Dy alloy during bone healing, which also depends on the upregulation of SIRT4-mediated mitochondrial events. Overall, the study is the first to report a Zn-5Dy alloy that exerts remarkable osteointegration properties and has a strong potential to promote bone healing. Furthermore, the results highlight the importance of mitochondrial modulation and shall guide the future development of mitochondria-targeting materials in enhancing bone fracture healing.

Biodegradable Implants for Internal Fixation of Fractures and Accelerated Bone Regeneration

Bone fractures have always been a burden to patients due to their common occurrence and severe complications. Traditionally, operative treatments have been widely used in the clinic for implanting, despite the fact that they can only achieve bone fixation with limited stability and pose no effect on promoting tissue growth. In addition, the nondegradable implants usually need a secondary surgery for implant removal, otherwise they may block the regeneration of bones resulting in bone nonunion. To overcome the low degradability of implants and avoid multiple surgeries, tissue engineers have investigated various biodegradable materials for bone regeneration, whereas the significance of stability of long-term bone fixation tends to be neglected during this process. Combining the traditional orthopedic implantation surgeries and emerging tissue engineering, we believe that both bone fixation and bone regeneration are indispensable factors for a successful bone repair. Herein, we define such a novel idea as bone regenerative fixation (BRF), which should be the main future development trend of biodegradable materials.

Comparative Study of Porous Iron Foams for Biodegradable Implants: Structural Analysis and In Vitro Assessment

Biodegradable metal systems are the future of modern implantology. This publication describes the preparation of porous iron-based materials using a simple, affordable replica method on a polymeric template. We obtained two iron-based materials with different pore sizes for potential application in cardiac surgery implants. The materials were compared in terms of their corrosion rate (using immersion and electrochemical methods) and their cytotoxic activity (indirect test on three cell lines: mouse L929 fibroblasts, human aortic smooth muscle cells (HAMSC), and human umbilical vein endothelial cells (HUVEC)). Our research proved that the material being too porous might have a toxic effect on cell lines due to rapid corrosion.

Recent Developments in Zn-Based Biodegradable Materials for Biomedical Applications

Zn-based biodegradable alloys or composites have the potential to be developed to next-generation orthopedic implants as alternatives to conventional implants to avoid revision surgeries and to reduce biocompatibility issues. This review summarizes the current research status on Zn-based biodegradable materials. The biological function of Zn, design criteria for orthopedic implants, and corrosion behavior of biodegradable materials are briefly discussed. The performance of many novel zinc-based biodegradable materials is evaluated in terms of biodegradation, biocompatibility, and mechanical properties. Zn-based materials perform a significant role in bone metabolism and the growth of new cells and show medium degradation without the release of excessive hydrogen. The addition of alloying elements such as Mg, Zr, Mn, Ca, and Li into pure Zn enhances the mechanical properties of Zn alloys. Grain refinement by the application of post-processing techniques is effective for the development of many suitable Zn-based biodegradable materials.

Modulation of Osteogenesis and Angiogenesis Activities Based on Ionic Release from Zn-Mg Alloys

The enhancement of osteogenesis and angiogenesis remains a great challenge for the successful regeneration of engineered tissue. Biodegradable Mg and Zn alloys have received increasing interest as potential biodegradable metallic materials, partially due to the biological functions of Mg²⁺ and Zn²⁺ with regard to osteogenesis and angiogenesis, respectively. In the present study, novel biodegradable Zn-xMg (x = 0.2, 0.5, 1.0 wt.%) alloys were designed and fabricated, and the effects of adding different amounts of Mg to the Zn matrix were investigated. The osteogenesis and angiogenesis beneficial effects of Zn²⁺ and Mg²⁺ release during the biodegradation were characterized, demonstrating coordination with the bone regeneration process in a dose-dependent manner. The results show that increased Mg content leads to a higher amount of released Mg²⁺ while decreasing the Zn²⁺ concentration in the extract. The osteogenesis of pre-osteoblasts was promoted in Zn-0.5Mg and Zn-1Mg due to the higher concentration of Mg²⁺. Moreover, pure Zn extract presented the highest activity in angiogenesis, owing to the highest concentration of Zn²⁺ release (6.415 μg/mL); the proliferation of osteoblast cells was, however, inhibited under such a high Zn²⁺ concentration. Although the concentration of Zn ion was decreased in Zn-0.5Mg and Zn-1Mg compared with pure Zn, the angiogenesis was not influenced when the concentration of Mg in the extract was sufficiently increased. Hence, Mg²⁺ and Zn²⁺ in Zn-Mg alloys show a dual modulation effect. The Zn-0.5Mg alloy was indicated to be a promising implant candidate due to demonstrating the appropriate activity in regulating osteogenesis and angiogenesis. The present work evaluates the effect of the Mg content in Zn-based alloys on biological activities, and the results provide guidance regarding the Zn-Mg composition in designs for orthopedic application.