Alloying design of biodegradable zinc as promising bone implants for load-bearing applications

Zechuan Zhang,Kerong Dai,Hongtao Yang,Yufeng Zheng,Donghui Zhu,Wenjiao Lin,Xinhua Qu,Bo Jia,Guannan Li

doi:10.1038/s41467-019-14153-7

Abstract

Magnesium-based biodegradable metals (BMs) as bone implants have better mechanical properties than biodegradable polymers, yet their strength is roughly less than 350 MPa. In this work, binary Zn alloys with alloying elements Mg, Ca, Sr, Li, Mn, Fe, Cu, and Ag respectively, are screened systemically by in vitro and in vivo studies. Li exhibits the most effective strengthening role in Zn, followed by Mg. Alloying leads to accelerated degradation, but adequate mechanical integrity can be expected for Zn alloys when considering bone fracture healing. Adding elements Mg, Ca, Sr and Li into Zn can improve the cytocompatibility, osteogenesis, and osseointegration. Further optimization of the ternary Zn-Li alloy system results in Zn-0.8Li-0.4Mg alloy with the ultimate tensile strength 646.69 ± 12.79 MPa and Zn-0.8Li-0.8Mn alloy with elongation 103.27 ± 20%. In summary, biocompatible Zn-based BMs with strength close to pure Ti are promising candidates in orthopedics for load-bearing applications.

Highlights

Magnesium-based biodegradable metals (BMs) as bone implants have better mechanical properties than biodegradable polymers, yet their strength is roughly less than 350 MPa
Bone screws made of Mg-Y-RE-Zr3 and Mg-Ca-Zn4 alloys have been approved by Conformité Européene (CE) and the Korea Food and Drug Administration (KFDA) in 2013 and 2015, respectively
The mechanical property, biodegradability, and biocompatibility are necessary and sufficient criteria for materials being regarded as biodegradable bone implants

Summary

Introduction

Magnesium-based biodegradable metals (BMs) as bone implants have better mechanical properties than biodegradable polymers, yet their strength is roughly less than 350 MPa. In this work, binary Zn alloys with alloying elements Mg, Ca, Sr, Li, Mn, Fe, Cu, and Ag respectively, are screened systemically by in vitro and in vivo studies. There is still a great gap between the mechanical strength of biodegradable materials like polymers[1,2] and Mg alloys[6] (UTS < 350 MPa) and traditional metallic materials like cobalt chromium alloys[7, 316] L stainless steel and titanium-based alloys[8] (UTS > 500 MPa). The alloying design strategy for Zn alloys as bone implants is proposed regarding the mechanical property, biodegradation, and biocompatibility. The present study may provide guidance on the future clinical prospects of Zn-based materials in orthopedic applications

Methods

Results

Conclusion