Researchers have used printed transistors to emulate the neurons and synapses of the biological system for artificial organic neuron

In 2018, researchers at the Linköping University developed complementary and printable organic electrochemical circuits having both n-type and p-type polymers, which conducted negative and positive charges. This made it possible to build printed complementary organic electrochemical transistors. Since then, the group has subsequently optimised the organic transistors for manufacturing in printing presses on thin plastic foil. Thousands of transistors can be printed on a single plastic substrate.
Now, these researchers together with those in Lund and Gothenburg have used the printed transistors to emulate the neurons and synapses of the biological system.
“For the first time, we’re using the transistor’s ability to switch based on ion concentration to modulate the spiking frequency”, says Padinhare Cholakkal Harikesh, post-doctoral researcher at the Laboratory of Organic Electronics, Linköping University.
The spiking frequency gives the signal that causes the biological system to react.
To demonstrate an artificial organic neuron, a nerve cell was integrated with a living plant and an artificial organic synapse. Both the neuron and the synapse were made from printed organic electrochemical transistors.
On connecting to the carnivorous Venus flytrap, the electrical pulses from the artificial nerve cell resulted in the plant’s leaves shutting – even though no-fly entered the trap. Organic semiconductors can conduct both electrons and ions, thus helping mimic the ion-based mechanism of pulse (action potential) generation in plants. In this case, the small electric pulse of less than 0.6 V can induce action potentials in the plant, which in turn causes the leaves to close.
“We chose the Venus flytrap so we could clearly show how we can steer the biological system with the artificial organic system and get them to communicate in the same language”, says Simone Fabiano, associate professor and principal investigator in organic nanoelectronics at the Laboratory of Organic Electronics, Linköping University, Campus Norrköping.
Organic semiconductors have numerous advantages – they’re biocompatible, biodegradable, soft and formable. They only require low voltage to operate, which is completely harmless to both plants and vertebrates. On that note, ion-based neurons can be connected to biological systems.
“We’ve also shown that the connection between the neuron and the synapse has a learning behaviour, called Hebbian learning. Information is stored in the synapse, which makes the signalling more and more effective”, says Simone Fabiano.
The hope is that artificial nerve cells can be used for sensitive human prostheses, implantable systems for relieving neurological diseases, and soft intelligent robotics.
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