Antibacterial Inorganic Coating of Calcium Silicate Hydrate Substrates by Copper Incorporation.

Under environmental conditions, biofilms can oftentimes be found on different surfaces, accompanied by the structural degradation of the substrate. Since high-copper-content paints were banned in the EU, a solution for the protection of these surfaces has to be found. In addition to hydrophobation, making the surfaces inherently biofilm-repellent is a valid strategy. We want to accomplish this via the metal exchange in calcium silicate hydrate (CSH) substrates with transition metals. As has been shown with Europium, even small amounts of metal can have a great influence on the material properties. To effectively model CSH surfaces, ultrathin CSH films were grown on silicon wafers using Ca(OH)2 solutions. Subsequently, copper was incorporated as an active component via ion exchange. Biofilm development is quantified using a multiple-resistant Pseudomonas aeruginosa strain described as a strong biofilm former cultivated in the culture medium for 24 h. Comprehensive structural and chemical analyses of the substrates are done by environmental scanning electron microscopy (ESEM), transmission Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results do not show any structural deformation of the substrates by the incorporation of the Cu combined with three-dimensional (3D) homogeneous distribution. While the copper-free CSH phase shows a completely random distribution of the bacteria in biofilms, the samples with copper incorporation reveal lower bacterial colonization of the modified surfaces with an enhanced cluster formation.

Surface anchored metal-organic frameworks as stimulus responsive antifouling coatings.

Surface-anchored, crystalline and oriented metal organic frameworks (SURMOFs) have huge potential for biological applications due to their well-defined and highly-porous structure. In this work we describe a MOF-based, fully autonomous system, which combines sensing, a specific response, and the release of an antimicrobial agent. The Cu-containing SURMOF, Cu-SURMOF 2, is stable in artificial seawater and shows stimulus-responsive anti-fouling properties against marine bacteria. When Cobetia marina adheres on the SURMOF, the framework's response is lethal to the adhering microorganism. A thorough analysis reveals that this response is induced by agents secreted from the microbes after adhesion to the substrate, and includes a release of Cu ions resulting from a degradation of the SURMOF. The stimulus-responsive antifouling effect of Cu-SURMOF 2 demonstrates the first application of Cu-SURMOF 2 as autonomous system with great potential for further microbiological and cell culture applications.