Artificial Axon
In the neuron, two opposing gradients of sodium and potassium ions across the cell membrane lead to a non-equilibrium state which, in the presence of voltage gated ion channels, supports a kind of relaxation oscillation which is the action potential. The Artificial Axon consists of a 100 microns size supported bilayer with embedded voltage gated potassium ion channels. In the first version of this developing project, there is only one ionic gradient and one type of ion channel. The system is held off equilibrium by a special kind of voltage clamp with limited current output. This simplified system supports action potentials, that is, it fires in response to an above threshold stimulus. It displays the same basic electrophysiology as neurons, for example, a firing rate which increases with increasing input current.
Figure 1 at left: Spike train in an artificial axon obtained under constant input current conditions (100 pA).
Just like with other threshold devices, one can implement logic operations, such as AND, OR. However, this system inherently combines analog and digital characteristics. We believe this is the more interesting aspect. You can see a simple application by watching the movie (link). In this (practically rather complicated) demo, a system of two artificial axons is the “brain” which steers the remote control car towards the light source in the SW corner of the screen. The car starts from the NE corner.
Among the foreseeable directions this project might take is the development of breadboards for electrophysiology research. We conceive that suitable synthetic platforms which incorporate the biological components will one day replace higher animals and their neurons on the lab bench, at least for some studies. A second direction is the development of networks of artificial axons, with signal processing and event storage capabilities; in general, the development of large ionic networks. Yet another scope is the construction of mixed electronics – ionics networks. But of course, the most interesting direction of all will be the presently unforeseen!
Associated publications:
- A. Ariyaratne and G. Zocchi, "Toward a minimal artificial axon", J. Phys. Chem. B 120, 6255 (2016).
- H. G. Vasquez and G. Zocchi, "Coincidences with the artificial axon", EPL 119, 48003 (2017).