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

Current biodegradable bone scaffolds face limitations in mechanical strength and predictable degradation. While zinc (Zn) has shown promise due to its moderate degradation rate, its structural stability remains a challenge. Prior research has established Zn as a candidate material, but gaps remain in understanding its degradation products and mechanical behavior in vivo. The need for scaffolds that mimic cancellous bone structure is clear, yet few studies have addressed this systematically. The composition and crystallography of degradation products at the implant-bone interface remain poorly characterized. This gap motivated the investigation of a core-shell structure to enhance mechanical and biodegradable properties. No prior work had resolved the in vivo degradation products of Zn scaffolds at the nanoscale. This uncertainty drove the development of a novel fabrication method to better control degradation rates and improve biocompatibility.

The aim of this study was to fabricate and evaluate a novel biodegradable bone scaffold with a core-shell structure. The specific problem addressed is the lack of mechanical stability and predictable degradation in pure Zn scaffolds. The motivation stems from the need for implants that degrade at a controlled rate while supporting bone regeneration. The study focused on combining iron (Fe) and Zn in a porous structure to improve mechanical properties. The core-shell design was chosen to regulate degradation by varying layer thicknesses. The researchers sought to understand how this structure influences in vivo degradation and biocompatibility. They also aimed to identify the nanoscale degradation products formed at the implant-bone interface. This approach may improve the clinical viability of Zn-based scaffolds for bone repair.

The scaffolds were fabricated using template-assisted electrodeposition to create a core-shell structure with Fe as the inner core and Zn as the outer shell. The porous structure was evaluated using mechanical testing to assess strength and stability. In vitro degradation experiments were conducted to measure the rate of Zn release and its effect on biocompatibility. Antibacterial activity was tested against S. aureus and E. coli to evaluate antimicrobial properties. In vivo biocompatibility was assessed by observing new bone formation and inflammatory response in animal models. Transmission electron microscopy and focused ion beam micromilling were used to analyze degradation products at the nanoscale. The crystallography and morphology of these products were characterized to understand degradation mechanisms. The study combined structural, mechanical, and biological evaluations to provide a comprehensive analysis of the scaffold's performance.

The 3D porous Fe@Zn scaffolds exhibited mechanical properties comparable to human cancellous bone. The degradation rate was tunable by adjusting the thickness of the Zn and Fe layers. Antibacterial testing showed over 95% inhibition of S. aureus and nearly 100% inhibition of E. coli. In vitro biocompatibility was influenced by a threshold Zn ion concentration of approximately 0.3 mM. In vivo testing revealed new bone formation and ingrowth despite a mild inflammatory response. The degradation products were identified as equiaxed nanocrystalline zinc oxide with dispersed zinc carbonate. These findings suggest that the core-shell structure effectively controls degradation while maintaining mechanical integrity. The study provides detailed insights into the degradation mechanism of Zn scaffolds in physiological environments.

The study demonstrates that Fe@Zn scaffolds with a core-shell structure are a feasible option for biodegradable bone implants. The mechanical properties of these scaffolds match those of cancellous bone, making them suitable for load-bearing applications. The tunable degradation rate allows for customization based on clinical needs. The antibacterial properties observed suggest potential benefits in reducing implant-related infections. The in vivo results indicate that the scaffolds support new bone formation and ingrowth. The identified degradation products provide a clearer understanding of the Zn scaffold's behavior in physiological conditions. These findings may inform future scaffold design by highlighting the importance of structure and composition in controlling degradation. The study contributes to the development of biodegradable implants with improved performance and predictability.