Cancellous bone-like porous Fe@Zn scaffolds with core-shell-structured skeletons for biodegradable bone implants

Three-dimensional (3D) porous zinc (Zn) with a moderate degradation rate is a promising candidate for biodegradable bone scaffolds. However, fabrication of such scaffolds with adequate mechanical properties remains a challenge. Moreover, the composition, crystallography and microstructure of the in vivo degradation products formed at or near the implant-bone interface are still not precisely known. Here, we have fabricated porous Fe@Zn scaffolds with skeletons consisting of an inner core layer of Fe and an outer shell layer of Zn using template-assisted electrodeposition technique, and systematically evaluated their porous structure, mechanical properties, degradation mechanism, antibacterial ability and in vitro and in vivo biocompatibility. In situ site-specific focused ion beam micromilling and transmission electron microscopy were used to identify the in vivo degradation products at the nanometer scale. The 3D porous Fe@Zn scaffolds show similar structure and comparable mechanical properties to human cancellous bone. The degradation rates can be adjusted by varying the layer thickness of Zn and Fe. The antibacterial rates reach over 95% against S. aureus and almost 100% against E. coli. A threshold of released Zn ion concentration (similar to 0.3 mM) was found to determine the in vitro biocompatibility. Intense new bone formation and ingrowth were observed despite with a slight inflammatory response. The in vivo degradation products were identified to be equiaxed nanocrystalline zinc oxide with dispersed zinc carbonate. This study not only demonstrates the feasibility of porous Fe@Zn for biodegradable bone implants, but also provides significant insight into the degradation mechanism of porous Zn in physiological environment. Statement of significance Biodegradable porous Zn scaffold is a promising candidate for bone repair. To overcome the individual limitations of biodegradable Fe and Zn, we have fabricated cancellous bone-like porous Fe@Zn scaffolds with skeletons consisting of an inner core layer of Fe and an outer shell layer of Zn. The scaffolds show similar structure and mechanical properties to cancellous bone, controllable degradation rate, strong antibacterial ability and can promote new bone formation and ingrowth. The composition, crystallography and microstructure of the in vivo degradation products were revealed at the nanometer scale. This study thus not only demonstrates the feasibility of porous Fe@Zn for biodegradable bone implants, but also provides significant insight into the degradation mechanism of porous Zn in physiological environment. (c) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study presented the feasibility of porous Fe@Zn scaffolds for biodegradable bone implants with similar structure and mechanical properties to cancellous bone, controllable degradation rate, strong antibacterial ability, and promotion of new bone formation and ingrowth. The composition, crystallography, and microstructure of in vivo degradation products were revealed at the nanometer scale, providing significant insight into the degradation mechanism of porous Zn in a physiological environment.