PVD-grown antimicrobial thin films on PVDF substrates for sensors applications

摘要

Electroactive polymers are the most interesting class of polymers used as smart materials in various applications,such as the development of sensors and actuators for biomedical applications in areas as smart prosthesis,implantable biosensors and biomechanical signal monitoring, among others. For acquiring or applying theelectrical signal from/to the piezoelectric material, suitable electrodes can be produced from Ti based coatingswith tailored multifunctional properties, as conductivity and antibacterial characteristics, obtained by the inclusionof Ag. This work reports on Ti1-xAgx electrodes and Ag-TiNy electrodes deposited by d. c. and pulsed magnetronsputtering at room temperature on poly(vinylidene fluoride)(PVDF). In the first system (Ti1-xAgx electrodes),silver content was varied from 0-100 at. %. For the second system (Ag-TiNy electrodes), the nitrogen contentchanged between 0 to 40.3 at. % by increasing the nitrogen gas flow between 0 sccm and 15 sccm and the ratioTi/Ag changed from 13.4 to 2.2 being clearly the visible decrease on the Ti content in the reactive mode.The X-Ray Diffraction (XRD) results revealed that the deposition conditions preserve the polymer structure andsuggested the presence of crystalline Ti phase in pure titanium coating and fcc-Ag phase in pure silver coatingfor the Ti1-xAgx system. For the Ag-TiNy system it is possible to detect a fcc TiN structure and a fcc Ag phase.Sheet resistivity values show a typical behavior of a binary alloy system, varying between 0.12 and 28.5 /sq forthe Ti1-xAgx electrodes. For the second system the sheet resistivity decrease with the nitrogen content from 12.0/sq with 0 at. % to 2.8 /sq for 40.3 at. % of N. The piezoelectricity of the different samples show similarvalues, showing values from 19.6 to 27.6 pCN-1 for the Tix-1Agx system and 13.6 pCN-1 as minimum for the Ag-TiNy system, achieved for the highest N content. In order to assess the mechanical behavior of the as-sputteredfilms, the film/substrate system was loaded unidirectionally using a tensile machine. The stress-strain curves wereanalyzed and correlated with the structural data. Moreover, the antibacterial activity of the samples was assessedand it was verified that samples from the second series (Ag-TiNy) present antibacterial activity, in contrast of thefirst series (Ti1-xAgx).