Ultrafine-Grained Materials With Antibacterial Properties: A Novel Approach to Reducing Spinal Implant-Associated Infections

Abstract

Background

Implant-associated infection remains a serious complication of instrumented spinal surgery. Since biofilm formation on the implant surface is a key factor in the pathogenesis of such infections, current preventive strategies include the use of implants with antibiotic coatings. However, these approaches raise concerns related to antibiotic resistance and cytotoxicity. Ultrafine-grained (UFG) stainless steel, characterized by nanoscale grain sizes, has demonstrated superior mechanical properties and potential antimicrobial effects. This study aimed to evaluate the antibacterial properties of UFG stainless steel implants against Staphylococcus aureus biofilm formation in both in vitro and in vivo models.

Methods

UFG and conventional SUS316L stainless steel wires were incubated with bioluminescent Staphylococcus aureus Xen36 for up to 7 days in vitro. Biofilm formation was assessed using crystal violet (CV) staining, colony-forming unit (CFU) counting, and quantitative PCR (qPCR) for 16S rRNA and luxA genes. In vivo antibacterial effects were evaluated using two mouse models: a subcutaneous pouch model and a postoperative spinal implant infection model. Wires were harvested at 1, 3, and 7 days post-infection and analyzed using the same assays.

Results

In vitro, UFG wires had significantly lower CFU counts than standard wires at 4 h (p = 0.0005), 1 day (p = 0.0001), and 3 days (p = 0.0314). In the subcutaneous pouch model, UFG wires showed significantly reduced bacterial load at Day 1 by CFU (p = 0.011). In the spinal implant model, CFU counts were significantly lower on UFG wires at Day 3 (p = 0.015).

Conclusions

UFG stainless steel implants demonstrated a significant reduction in early biofilm formation by Staphylococcus aureus in both in vitro and in vivo, suggesting a delay in the biofilm formation process. These findings support the potential of UFG materials as promising candidates for infection-resistant spinal implants.