Multifunctional Nanocomposite Plasma Coatings: Enabling New Biomaterials Applications

Abstract

Due to the increasing prevalence of resistance of bacteria to antibiotics and antiseptic methods, new strategies to prevent colonization of biomaterials are needed. Due to its high antimicrobial activity and relatively low toxicity to human cells, we are evaluating silver (Ag) releasing plasma polymers as a strategy to prevent bacterial colonization. Such Ag/plasma polymer nanocomposite materials, consisting of nano-scaled metal clusters embedded within a plasma-polymer matrix can be deposited using a mixed, plasma polymerization /sputtering process. For example, Ag containing plasma polymer nanocomposites are deposited employing an Ag cathode, an appropriate monomer to yield the desired material properties of the matrix (biocompatibility) and an asymmetric reactor design. The focus of this paper is a new development at Empa: a multi-functional Ag/amino-hydrocarbon (Ag/a-C:H:N) nanocomposite that can enhance cell growth and simultaneously prevent bacterial colonization at surfaces. Ag/a-C:H:N coatings containing 4.0% Ag have been demonstrated to reduce bacterial adhesion of E. coli by up to 95%, as compared to an external polyester fabric control in a static assay. Likewise, these coatings demonstrated a bacterial toxic effect both at the surface and in the surrounding media due to the release of Ag ions. XPS characterization of various nanocomposites has shown that the Ag quantity and matrix characteristics of the films can be tailored to specific requirements by altering deposition parameters such as power input, pressure and gas feed ratio. Although the surface chemistry has been characterized, open questions remain to the amount and the kinetics of the release of Ag and the subsequent effect on bacteria and cells. Since Ag release profiles will ultimately determine the antimicrobial efficacy of the coatings, as well as duration of the effect, these dosing issues must be quantified and clarified. Ag release kinetics of the various Ag/a-C:H:N as measured by atomic absorption spectroscopy has been evaluated and the relationships to biological assays, including bacterial and cellular adhesion are clarified. A range of Ag/a-C:H:N coatings having various Ag content are tested in two biological assays, bacterial toxicity and cytoxicity. Bacterial growth tests using the pathogen, P. aeruginosa wild type (PAO1), were performed according to the method of Tiller et al. The method is based on the bacterial deposition from aerosols, thus, it mimics bacterial exposure through airways such as intubation tubes. Secondly, cytotoxicity assays of the nanocomposites has been performed using a murine fibroblast cell line 3T3 testing protocol, and the proliferation of the cultures was measured taking the DNA amount per well as an index (Bruinink 2001). We will answer questions regarding what is the fundamental Ag content and Ag release profile under static bacterial testing environments which allow a maximum bacterial-toxic effect with a minimum amount of Ag.