Abstract
Unlike the native surface of the implant material (Ti6Al4V), oxidation with H2O2 leads to increased binding of the effective antimicrobial agent poly(hexamethylene) biguanide [PHMB]. However, treating with NaOH instead results in an even higher PHMB mass coverage. After oxidation with H2O2, strong differences in the PHMB adsorption capability between polished and corundum-blasted surfaces appear, indicating a roughness dependence. After NaOH treatment, no such effect was observed. The wetting properties of specimens treated with either H2O2 or NaOH prior to PHMB exposure clearly varied. To unravel the nature of this interaction, widespread in silico and in vitro experiments were performed. Methods: By X-ray photoelectron spectroscopy, scanning electron microscopy, water contact angle measurements and MD simulations, we characterized the interplay between the polycationic antimicrobial agent and the implant surface. A theoretical model for PHMB micelles is tested for its wetting properties and compared to carbon contaminated TiO2. In addition, quantitation of anionic functional group equivalents, the binding properties of PHMB with blocked amino end-group, and the ability to bind chlorhexidine digluconate (CHG) were investigated. Ultimately, the capability of osteoblasts to build calcium apatite, and the activity of alkaline phosphatase on PHMB coated specimens, were determined. Results: Simulated water contact angles on carbon contaminated TiO2 surfaces and PHMB micelle models reveal little influence of PHMB on the wetting properties and point out the major influence of remaining and recovering contamination from ambient air. Testing PHMB adsorption beyond the critical micelle concentration and subsequent staining reveals an island-like pattern with H2O2 as compared to an evenly modified surface with NaOH. Both CHG and PHMB, with blocked amino end groups, were adsorbed on the treated surfaces, thus negating the significant influence of PHMB’s terminal groups. The ability of osteoblasts to produce calcium apatite and alkaline phosphatase is not negatively impaired for PHMB mass coverages up to 8 μg/specimen. Conclusion: Differences in PHMB adsorption are triggered by the number of anionic groups and carbon contaminants, both of which depend on the specimen pre-treatment. With more PHMB covering, the implant surface is protected against the capture of new contamination from the ambient air, thus building a robust antimicrobial and biocompatible surface coating.
Highlights
While titanium implants become more and more popular in surgical care, implantassociated infections are rising
We investigated the wetting properties of pure poly(hexamethylene) biguanide (PHMB) interfaces, and of contaminated models, for the Ti6Al4V-specimen by means of simulated contact angles
That a treatment of the Ti6Al4V surface with either NaOH or H2 O2 is essential for the generation of anionic groups and for the removal of carbon contamination, enabling adsorption of PHMB
Summary
While titanium implants become more and more popular in surgical care, implantassociated infections are rising. Titanium and titanium-based materials like Ti6Al4V alloys readily build oxidation layers upon air exposure, which are dominated by the TiO2 form of the crystal [1,2]. TiO2 is the relevant interface of implants based on. Ti6Al4V alloys that need to be investigated. Nearly every XPS measurement on TiO2 reveals a significant carbon content associated with the contamination by volatile hydrocarbons from ambient air [3,4]. While water contact angles on freshly cleaned TiO2 are usually reported in the range of 15◦ –30◦ or below, air-exposed and untreated samples can give readings in the range of 40◦ –
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