Adhesion and Scratch Testing of Antibiotic Loaded Poly-Lactic Acid Biocomposite Thin Films on Metallic Implants

Shock Wave-Activated Silver-Loaded Biopolymer Implant Coating Eliminates Staphylococcus epidermidis on the Surface and in the Surrounding of Implants

Bacterial biofilms on foreign surfaces are considered a primary cause of implant-related infections, which are challenging to treat. A new implant coating was developed, containing anti-infective silver within a biocompatible polymer carrier substance. In addition to its passive effect on the implant surface, highly concentrated anti-infective silver can be released as needed via the application of high-energy shock waves. This intervention could be applied transcutaneously in a clinical setting without the need for additional surgery. We investigated the inhibition of biofilm formation and the effectiveness of eradication after activation of the coating via shock waves in an in vitro biofilm model using Staphylococcus epidermidis RP62A. This was performed via scanning electron microscopy and quantitative microbiology. Additionally, we examined the cytotoxicity of the new coating on normal human fibroblasts and Saos-2 osteoblast-like cells, depending on the silver concentration. All studies were compared to uncoated titanium surfaces Ti6Al4V and a conventional electroplated silver coating. Cytotoxicity toward normal human fibroblasts and Saos-2 osteoblast-like cells increased with higher silver content but remained tolerable at 6%. Compared to uncoated Ti6Al4V and the electroplated silver coating, the new coating with a silver content of 4% and 6% exhibited a significant reduction in adherent bacteria by a factor of approximately 1000. This was also evident via microscopic examination of the surface morphology of the biofilms. Furthermore, following shock wave activation, no bacteria were detectable on either the implant or in the surrounding fluid after a 24 h period.

Mechanical and microbiological testing concept for activatable anti-infective biopolymer implant coatings

An anti-infective bilayer implant coating with selectively activatable properties was developed to prevent biofilm formation and to support the treatment of periprosthetic infection as a local adjunct to current treatment concepts. In a first step, Ti6Al4V discs were coated with a permanent layer of Poly(l-lactide) (PLLA) including silver ions. The PLLA could be optionally released by the application of extracorporeal shock waves. In a second step, a resorbable layer of triglyceride (TAG) with incorporated antibiotics was applied. The second layer is designed for resorption within weeks. Prior to approval and clinical application, a comprehensive evaluation process to determine mechanical/physical and microbiological properties is obligate. To date, none of the existing test standards covers both drug-releasing and activatable coatings for orthopedic implants. Therefore, a comprehensive test concept was developed to characterize the new coating in a pilot series. The coatings were homogeneously applied on the Ti6Al4V substrate, resulting in an adhesion strength sufficient for non-articulating surfaces for PLLA. Proof of the extracorporeal shockwave activation of PLLA was demonstrated both mechanically and microbiologically, with a simultaneous increase of biocompatibility compared to standard electroplated silver coating. Wettability was significantly reduced for both layers in comparison to the Ti6Al4V substrate. Thus, potentially inhibiting biofilm formation. Furthermore, the TAG coating promoted cell proliferation and bacterial eradication. In conclusion, the testing concept is applicable for similar biopolymer coating systems. Furthermore, the extracorporeal activation could represent a completely new supportive approach for the treatment of periprosthetic joint infections.