Interfacing biological and electrical systems has traditionally been done with metal electrodes, but something flexible can be more biocompatible. One possible option is 3D-printed bioelectric hydrogels.
Electrically conductive hydrogels based on conducting polymers have mechanical, electrical, and chemical stability properties in a fully organic package that makes them more biocompatible than other systems using metals, ionic salts, or carbon nanomaterials. Researchers have now found a way to formulate bi-continuous conducting polymer hydrogels (BC-CPH) that are a phase-separated system that can be used in a variety of manufacturing techniques including 3D printing.
To make the BC-CPH, a PEDOT:PSS electrical phase and a hydrophilic polyurethane mechanical phase are mixed with an ethanol/water solvent. Since the phase separation occurs in the ink before deposition, when the solvent is evaporated, the two phases remain continuous and interspersed, allowing for high mechanical stability and high electrical conductivity which had previously been properties at odds with each other. This opens up new avenues for printed all-hydrogel bioelectronic interfaces that are more robust and biocompatible than what is currently available.
If you want to try another kind of squishy electrode gel, try growing it.
Electrodermal activity, or galvanic skin response has a lot of practical applications. Everything from research into emotional states to significantly more off-the-wall applications like the E-meter use electrodermal activity. For his Hackaday Prize entry, [qquuiinn] is building a wearable biofeedback wristband that measures galvanic skin response that is perfect for treating anxiety or stress disorders by serving as a simple and convenient wearable device.
Detecting electrodermal activity has been within the capability of anyone with an ohmmeter for over a hundred years. [quin²] is doing something a little more complex than the most primitive modern means of measuring galvanic skin response and using a dual op-amp to sense the tiny changes in skin resistance. This data is fed into an ATMega328 which sends it out to a tiny LED display in the shape of an ‘x’.
Reading electrodermal activity is easy, but doing it reliably in a wearable device is not. There are issues with the skin contacts to work though, issues with the amplifier, and putting the whole thing in a convenient package. [qquuiinn] asked the community about these problems in group discussion on the hacker channel and got a lot of really good advice. That’s a great example of what a project on hackaday.io can do, and a great project for the Hackaday Prize.