Now in preclinical trials, Mallarias’ electrodes could offer a huge leap in the quality of speech production. By placing them on the part of the brain cortex that deals with language and asking patients to imagine words, the resulting ECoG recordings can be processed by computer algorithms to predict the words and vocalise them through a speech synthesiser.īut with systems like Malliaras’ that use a mixed conductive polymer, the electrodes can be much smaller – just a couple of microns across – and can be precisely placed on the brain’s surface to capture individual neural signatures, which represents a new capability for ECoG. Such electrodes are used on patients with impaired speech, including those who have locked-in syndrome. If you implant a device into the brain, you’re now past the blood–brain barrierĮCoG usually uses millimetre-wide metal electrodes that record averaged signals arising from many neurons. As a member of BrainCom – an EU collaborative research project developing neuroprosthetic devices to restore communication in patients – Malliaras works on minimally invasive mixed conductor electrodes and transistors for decoding brain signals into speech using electrocorticography (ECoG). Malliaras’ group has developed devices with thin films of Pedot:PSS to find novel therapies and treatments for brain injuries and disease. The formation of an electric double layer at internal interfaces between ionic and electronic conductors essentially allows the signals to be coupled. The Pedot part provides the electrical conductivity of the conjugated polymer, while PSS allows ionic transport. One mixed conductor that has gained ground in recent years is a flexible, biocompatible conducting polymer called Pedot, or poly(3,4-ethylenedioxythiophene), doped with PSS, or poly(styrene sulfonate). Mixed conductor materials can do the translation and enable communication between the world of biology and the world of micro-electronics.’ ’We operate in a very foreign environment to electronics. ‘In a sense we want to teach electronics a foreign language: the language of ions,’ says George Malliaras, who investigates brain interface bioelectronics at the University of Cambridge, UK. So how are researchers going about bringing ions and electrons together? Brain waves Such technology could ultimately lead to anything from bionic soft robots, intelligent wearable sensors and cyborg tissues all the way to human–computer interfaces, electronic plants and digital control of biomolecules. Ionotronic materials can respond to environmental changes in life-like ways, which could be a crucial step in the integration of humans and machines. This means that functionalities could be attached to ions that influence optical characteristics, surface energy, or even bioactivity of a material.’Ī growing number of studies are revealing just how the world of ions and electrons can be integrated, offering tantalising glimpses into what merging living matter with machines could look like in years to come. ‘Nature has only one flavour of electron, but nearly an infinite number of ions. ![]() ‘Over the last two decades or so people have started to realise that ions offer opportunities for producing unconventional effects,’ says Ryan Hayward who investigates soft polymer materials at the University of Massachusetts in the US. ![]() Nature has only one flavour of electron, but nearly an infinite number of ions ![]() What’s new, however, is that ionic and electronic signals are increasingly being united with flexible and stretchy conducting polymers, known as ‘ionotronic’ materials. These all rely on ionic and electronic charges interconverting. But to an extent, ions and electrons have co-existed in certain devices for decades, such as batteries, supercapacitors and electrochemical cells. It would seem that ionic and electronic circuits and materials are worlds apart. When our senses are stimulated, ions are triggered into motion across cell membranes, precisely controlled by protein channels, generating an electrical current that fires signals along nerves to the brain.Ĭonversely, electronic devices – smart phones, computers, displays, you name it – rely on electricity produced by the interaction of negative electrons and positive holes along metal wires embedded in rigid materials. This electricity enables us to think, move and experience the world and it happens thanks to ions: atoms and molecules carrying positive or negative charge. ![]() Every second, electricity flows through the soft, flexible, water-filled cells of living organisms.
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