Antimicrobial Efficacy of Surface-Coated External Fixation Pins

Abstract

In clinical applications, colonization of metal implants by adhesive and biofilm-forming bacteria not only prolong healing but create additional healthcare costs for implant revision and antimicrobial treatment. An in vitro assay was established investigating the antimicrobial surface activity of external fixation pins intended for use in bone fractures and deformities. Test articles made out of stainless steel and coated with a polymer-containing nanoparticulate silver were compared to non-coated reference controls out of stainless steel, copper and titanium. Staphylococcus epidermidis, known as a predominant cause for implant-related infections was used as test organism. Test pins and bacteria were incubated for a period of 20 h found to be sufficient for initiating biofilm formation. After removing non- and low-adherent bacteria by rinsing, two methods were used to isolate high-adherent (sessile) bacteria from the implant surfaces. Besides shaking the implants in a solution containing small glass beads, a cytobrush technique was used to mechanically harvest viable bacteria. Finally, the amount of detached bacteria was determined by plate counts. Several parameters identified to be critical within the different removal procedures such as the inoculum concentration and the shaking time in the presence of glass beads as well as time of the cytobrush treatment were analysed. The final test scheme resulted in the use of an inoculum of 10(5) colony forming units (CFU) per millilitre, ten rinsing steps for the removal of low adherent bacteria and 5 min of shaking in the presence of glass beads, detaching the high-adherent bacteria. Due to subjective variations impacting the outcome of the procedure, the cytobrush technique was not favoured and finally rejected. Using the in vitro assay developed, it could be demonstrated that fixation pins coated with silver show a 3 log step reduction in the number of biofilm-forming bacteria compared to a non-coated stainless steel or titanium implant. Pins made out of copper showed the highest antimicrobial efficacy, as the number of detached bacteria was found to be below the detection limit, they served as a positive control within this test.

Silver nanoparticles and their orthopaedic applications

“…It was demonstrated that fixation pins with a coating of nanoparticulate silver showed a 3-log step reduction in biofilmforming bacteria compared with non-coated stainless steel or titanium implants. 34 These findings are supported by in vitro work by Wassall et al, 35 who examined the antimicrobial effect of conventional silver and showed a significant reduction in adhesion for E. coli, Pseudomonas aeriginosa and S. aureus when silver coated pins were compared with stainless steel pins. Collinge et al 36 reported on the potential benefit of silver coating on external fixator pins inoculated with S. aureus inserted into the iliac crest of sheep.…”

The Role of Bacterial Biofilms in Device-Associated Infection

“…Modifying the surface of implants with antibacterial coatings, biologic membranes, and alterations of physical characteristics has had varying success. 85,94,95 The use of any drug-related coatings, however, would require regulatory scrutiny and approval, as the implant becomes a potential drug-delivery device. Anti-sense molecules and quorum sense inhibitors are compounds that disrupt bacterial communication.…”

Improving tribological and anti-bacterial properties of titanium external fixation pins through surface ceramic conversion

“…For instance, pure Ag has been used to coat stainless steel surfaces. However, it has been reported that no statistically significant difference in the clinical outcomes of Ag-coated and uncoated steel fixation pins could be observed [7]. Some attempts have also been made to develop Ag-containing nanocomposite coatings with increased hardness [5].…”