One of the main challenges in endoprosthesis surgeries are implant-associated infections and aseptic-loosenings, caused by wear debris. To combat these problems, the requirements to surfaces of endoprostheses are wear-resistance, low cytotoxicity and antimicrobial efficacy. We here present antimicrobial coatings with a smart, adaptive release of metal ions in case of infection, based on ZnO-nanoparticles embedded in diamond-like carbon (DLC). The Zn2+ ion release of these coatings in aqueous environments reacts and adapts smartly on inflammations accompanied by acidosis. Moreover, we show that this increased ion release comes along with an increased toxicity to fibroblastic cells (L929) and bacteria (Staphylococcus aureus subsp. aureus, resistant to methicillin and oxacillin. (ATCC 43300, MRSA) and Staphylococcus epidermidis (ATCC 35984, S. epidermidis). Interestingly, the antimicrobial effect and the cytotoxicity of the coatings increase with a reduction of the pH value from 7.4 to 6.4, but not further to pH 5.4.

An approach to enhance the durability of artificial joint replacements is to modify the surface of their polymeric bearing material to diamond-like carbon (DLC) by ion-induced polymer-to-DLC-transformation in a plasma immersion ion implantation process. Due to the dielectric character of the polymer and thus the impossibility of direct application of high voltage pulses to the component, this process requires an additional accelerator electrode above the surface. We here present two useful tools to optimize the geometry of such electrodes. First, we simulate the ions' trajectories for various electrode geometries and receive the resulting fluence distribution across the surface of the treated part. Second, we introduce a novel optical method to determine non-destructively the local ratio of sp(2) hybridized carbon atoms and thus the locally implanted fluence utilizing changes in reflectivity. Combining both tools, we here optimize, by way of example, the geometry of a grid electrode to obtain a homogeneous DLC-modification of a typical hip replacement inlay.

Diamond-like carbon (DLC) is known to be a versatile coating material, being found in a wide variety of surface engineering applications. In this study, we produced DLC coatings by ion irradiation and thus reconstruction of a thin polymer film. This procedure leads to a thin diamond-like carbon layer which is characterized by its high hardness. Due to the finite ion range during implantation, however, the maximum thickness of such coatings is limited. Nevertheless, several applications for DLC coatings demand a larger thickness. We thus increased the thickness of such DLC coatings by repeatedly applying the deposition and transformation process, thus creating thicker multilayers. We show that their physical and mechanical properties like roughness, nano-hardness, sp3 fraction as well as the very important adhesion of thick DLC films produced this way are very well suited for the desired applications. Although we find a small decrease in hardness and a little bit less sp3 fraction with increasing coating thickness, our results exhibit a typical hardness as well as sp3 fraction for a-C:H even for the largest coating thicknesses produced so far.

The aim of this study was the synthesis of hard and low-abrasive novel implant materials with built-in time-dependent antibacterial properties, which can be tailored by a well-defined time-dependent and finite release of metal ions. We were able to synthesize such smart implant surfaces employing ECR (electron cyclotron resonance)-plasma on typical titanium implant material by transforming a polymer film into diamond-like carbon (DLC) which contains metal nanoparticles as reservoirs for controlled metal ion release. We found that the amount of released antibacterial metal ions is a biexponential function of time with a high release rate during the first few hours followed by a decreased ion release rate within the following days. To describe our experimental findings, we developed a kinetic model assuming that both nanoparticles near the surface and nanoparticles in the DLC bulk contribute to the total amount of ions released with different time constants.

For an optimal implementation of materials, such as, e.g. medical implants in living environments, a thorough characterization of cell adhesion, kinetics and strength is required, as well as a prerequisite e.g. for bone integration. Here we present a miniaturized (~100 μl) lab-on-a-chip implant hybrid system which allows quantification of cell adhesion under dynamic conditions mimicking those of physiological relevance. Surface acoustic waves are excited and used on optical transparent chips to induce micro acoustic streaming and to create a microfluidic shear spectrum ranging from 0 to ~35 s(-1). We demonstrate its potential for a time-efficient, dynamic screening test of new implant materials using a model of an osseointegration with SAOS-2 cells. The upside-down orientation also allows utilization of the micro reactor on non-transparent materials like titanium and diamond-like-carbon (DLC).