Squishy Bio-Electronics Could Make Better Implants and Brain-Machine Interface Controls | Popular Science: A pair of grad students at North Carolina State University presented a paper last week describing a quasi-liquid diode whose electrodes are made of a gallium-indium alloy that is liquid at room temperature. Two hydrogel films are sandwiched between the electrodes — one is doped with an acid and the other holds an alkaline compound.
The interface between the electrodes develops a thin coating of gallium oxide, which creates resistance, as IEEE Spectrum explains. The electrode with the alkaline substance suppresses the formation of this skin. So, applying voltage changes the the thickness of this gallium oxide “skin” — negative voltage makes the oxide thinner, lowering the device’s resistance, and a positive voltage makes it thicker, producing greater resistance.