The speed that neurons communicate, approximately 10 milliseconds, has proved incredibly difficult to replicate with microfluidics and other fluid transport systems. It is possible to use these technologies to mimic neural signaling, although achieving speeds greater than 50 ms appeared to be beyond the scope of current technologies.
If sufficiently high speeds of neurotransmitter release can be achieved to mimic synaptic function, researchers should be able to use the technology to develop next-generation therapies to restore or augment dysfunctional neural signaling.
Significant progress has recently been made by researchers at Sweden’s Linköping University. The researchers have developed an organic electronic ion pump (OEIP) capable of releasing neurotransmitters at speeds close to those seen in neurons. Not only have they managed to reach the 50 ms milestone, they have surpassed it, delivering neurotransmitters at speeds as fast as 45 ms.
Rather than trying to reinvent the wheel, the researchers used an older OEIP that had been developed at the university. The old device moved ions horizontally from the source to the target, although horizontal movement of charged particles using an electric field did not allow sufficiently high speed ion transfer. In fact, all too often the transfer speed needed to be measured in seconds rather than milliseconds.
By changing the design of the system, the researchers were able to achieve much higher transfer speeds. As with the original device, a neurotransmitter – in this case acetylcholine – was pushed through metal and polymer horizontal channels using an electric current. However, rather than simply travelling horizontally, there is a small outlet in the channel. If an electric current is applied, the particles are sent upwards through the outlet towards their destination.
Daniel Simon, researcher at the Laboratory of Organic Electronics and assistant professor at Linköping University, explained the updated OEIP saying, “Instead of going laterally through several millimeters of film, we’re using the thinness of the film—the same type of film—but going vertically through just a couple hundred nanometers.”
The new OEIP, which is just 2.5 cm long, contains six channels which were created on planar glass substrates using photolithographic patterning. Each of those channels can be activated separately.
In the tests, the researchers were able to deliver neurotransmitters to specific parts of a sample and activate only a small subset of neurons without disturbing other neurons. “We have demonstrated an electrically controlled chemical delivery circuit, where charged compounds can be released independently from several delivery points within tens of milliseconds,” says Simon.
While the rapid signaling of neurons has been replicated on 2D structures, Simon believes the OEIP could be adapted and used in a range of neuromodular applications.