Stretchable polymer composites are a new group of materials with a wide range of application possibilities in wearable electronics. The purpose of this study was to fabricate stretchable electroluminescent (EL) structures using developed polymer compositions, based on multiple different nanomaterials: luminophore nanopowders, dielectric, carbon nanotubes, and conductive platelets. The multi-layered EL structures have been printed directly on textiles using screen printing technology. During research, the appropriate rheological properties of the developed composite pastes, and their suitability for printed electronics, have been confirmed. The structure that has been created from the developed materials has been tested in terms of its mechanical strength and resistance to washing or ironing.

The paper describes the investigations of pH-sensitive materials for screen printed flexible pH sensors. The sensors were fully printed and consisted of three layers, conductive made of low temperature-curable silver paste, insulating made of UV-curable dielectric paste, and pH-sensitive made of developed graphene/ruthenium oxide pastes. Graphene and ruthenium oxide composites were prepared with different proportions of graphene nanoplatelets paste and submicron ruthenium dioxide. To perform functional measurements, particular testing sensors were fabricated on flexible polyester foil. Afterwards electrochemical potential measurements of fabricated devices were carried out. Sensors were also exposed to cyclic bending and the change of pH sensitivity before and after bending was described. Eventually, percolation threshold concerning the amount of ruthenium oxide in the pH-sensitive layer was designated and UV influence on the sensitivity was observed that together allow for optimization of sensors’ fabrication costs.

Possible risks stemming from the employment of novel, micrometer-thin printed electrodes for direct current neural stimulation are discussed. To assess those risks, electrochemical methods are used, including cyclic voltammetry, squarewave voltammetry, and electrochemical impedance spectroscopy. Experiments were conducted in non-deoxidized phosphate-buffered saline to better emulate living organism conditions. Since preliminary results obtained have shown unexpected oxidation peaks in 0-0.4 V potential range, the source of those was further investigated. Hypothesized redox activity of printing paste components was disproven, supporting further development of proposed fabrication technology of stimulating electrodes. Finally, partial permeability and resulting electrochemical activity of underlying silverbased printed layers of the device were pointed as the source of potential tissue irritation or damage. Employing this information, electrodes with corrected design were investigated, yielding no undesired redox processes.

Novel printable composites based on high aspect ratio graphene nanoplatelets (GNPs), fabricated without using solvents, and at room temperature, that can be employed for flexible, standalone conducting lines for wearable electronics are presented. The percolation threshold of examined composites was determined to be as low as 0.147 vol% content of GNPs. Obtained sheet resistance values were as low as 6.1 Ω/sq. Stretching and bending tests are presented, proving suitability of the composite for flexible applications as the composite retains its conductivity even after 180° folding and 13.5% elongation.

No abstract