Modulating the elution of antibiotics from nanospongy titanium surfaces with a pH-sensitive coating

Abstract

Metals currently used for prosthetic reconstructions enjoy a relatively good success rate, but post-surgical infections still remain an important challenge. In addition, there are still no such metals that are able to respond to any deterioration of their relationship with the host tissue, in particular to an acidification of the local environment, an event associated to bone remodeling, tissue inflammation and bacterial infection. Distinctive from previous work that employed anodization of titanium to engender nanotubular structures, we exploited this technique to create a nanospongy surface that behaved as a non-eroding drug-eluting template for the extended release of vancomycin, a model antibiotic. Successively, as a proof of concept, we employed a chitosan–poly(ethylene glycol) (PEG) coating to provide pH-dependent release kinetics of vancomycin molecules stored in the underlying 3-dimensional network of nanometric pores. A physicochemical characterization of the polymeric blend by ATR-FTIR and DPFM-AFM unveiled its morphological and nanomechanical characteristics and permitted to link them to its stability and swelling behavior in aqueous solutions at three different pHs. This study demonstrates the ability of nanospongy titanium surfaces to provide extended elution of vancomycin, one of the most effective antibiotics against Gram-positive bacteria, for over one week, thus becoming a valid alternative to existing drug-eluting metallic platforms. In addition, our results show how the elution profiles can be modulated to respond to an acidification of the surrounding environment by exploiting uncross-linked and cross-linked chitosan–PEG coatings, ultimately paving the way for their broader use as a versatile coating for nanoporous drug-delivery platforms.