Polymer-based Silver Nanoparticle Coated Pedicle Screws Inhibits Biofilm Formation-a Novel Experimental Model in Rabbits

Abstract

Introduction Infection in spinal implant is of great concern. Anti-infection strategies must be tested in relevant animal models that will lead to appropriate clinical studies. A novel spine implant model was designed to study the antimicrobial effect of a modified Titanium (Ti) pedicle screws with methiciline resistant Staphyloccoccus Aerous (MRSA) in multiple surgical sites in the lumbar spine of a rabbit. Material and Methods Twenty two New Zealand White rabbits were divided into two groups: group 1: infected unmodified Ti screw group ( n = 10), group 2: infected polyethylene glycol grafted polypropylene based Silver nanoparticle (PP-g-PEG-Ag) covered Ti screw group ( n = 10), and two rabbits as control-sterile group. In all groups left L4- right L6 vertebra levels were exposed and screws were drilled to transverse processes after contamination of burr holes with 0.1 ml of 106 CFU MRSA solutions in group 1 and 2. After 21 days, samples were collected and infection was analyzed via light and scanning electron microscopy and culturing. Silver nanoparticles (Ag-NP) on the screws and tissues were assayed pre and postoperatively. Results The bacterial colony count for modified-Ti screw group was lower compared with unmodified Ti screw (17,2 vs 200 × 103 CFU/mL, p = 0,029) with less biofilm formation. There was no difference in duration of surgery among groups and within the surgical sites. Ag-NPs were detected on the screw surface postoperatively. Conclusion This novel experimental design of implantation in rabbits is easy to apply and resembles human stabilization technique. Modified Ti screws were shown to have antimicrobial effect with especially inhibiting the biofilm formation. This anchored Ag NPs which remained after 21st day of implantation shows that it is resistant to tapping forces of the screw.