New prospects for medical textiles: Continuous sputter deposition on fibers

Despite the widespread use of silver (Ag) in medical textiles such as wound bandages, Ag-coated fibers in medical devices need to pass a cytotoxicity test where common conductive fibers fail. Therefore, smart textiles such as, e.g., electrocardiography (ECG) belts could not yet enter the medical sector.  We thus developed a reel-to-reel coating system for fibrous substrates enabling both metal and metal oxide coatings based on magnetron sputtering. In particular, we found that titanium-passivated Ag-coated fibers are suitable for medical applications such as embroidered body electrodes enabling long-term ECG measurements.

At first, pure silver is continuously deposited on the fiber to optimize electrical conductivity. The pure silver coated fibers, however, show the typical burst release of Ag ions when immersed in an aqueous environment yielding local cytotoxic conditions. While the ion release can be favourable for antibacterial properties, it needs to be limited for medical devices. A diffusion barrier is thus required maintaining the electrical and optical properties. Thus, continuous deposition of an ultrathin titanium adlayer that passivates by oxidation was investigated using XPS depth profiling. Ag release measurements show an efficient control over the release properties (initial burst and long term release) depending on the thickness of the Ti adlayer.