A step toward fully 3D-printed active electronics

While mentally stimulating, this sounds practically not very useful. They're using a copper-doped polymer for printing, which probably has way worse properties anything we make PCB traces out of.

And the 3D part is gimmicky. We have built electronic systems of monstrous complexity just with planar printers.

Wake me up when someone build a system that can reliably make PCBs at home, with placing components, and doesn't cost an arm and a leg, and is cheap and easy to run.

It would be nice to pattern diodes and semiconductors on PCB without components as follows: etch circuit layout of a copper layer, mask the traces so they don't oxidize, then heat the PCB to have unmasked copper turn into Cu2O (cuprous oxide, a semiconductor).

Anyone seriously attempting this should make sure they understand solid state physics, and at a minimum understand diffusion length of charge carriers and the different type of contacts: Ohmic, Schottky ( for example https://lampz.tugraz.at/~hadley/psd/lectures20/contacts.pdf )

Performance will be horrible, but in some situations constructing and inspecting the device oneself can be paramount ( bootstrapping a secure computational platform, implementing formal verifier associated to a cryptocurrency, ... )