Stéphanie P. Lacour

In 2003, Lacour published a paper looking at implementing thin gold stripes onto elastomeric substances to make electronic skins more flexible and stretchable.[5] She found that inducing micrometer long cracks in the gold made the stripes more stretchable, while inducing buckles in the gold made the stripes have lower resistance.[5] Lacour and Wagner further found that electrical continuity could be preserved in gold stripes with micro-fractures, even when stretched by 1% and strained by up to 22%.[6] The incredible degree of malleability and preserved electrical continuity that these thin gold films exhibit poised them to be essential in the future construction of 3D electronic circuits.[6] An alternative to inducing micro-fractures in gold to enhance stretchability, is inducing wave-like buckles by placing the gold films on pre-stretched elastomeric substrates.[7] Once these substrates relax, the gold creates surface waves which are repeatedly stretchable and can serve as interconnects for skin-like electronic circuits.[7]

After developing these elastic technologies at Princeton, Lacour implemented stretchable microelectrode arrays (SMEAs) into organotypic hippocampal slice culture models of traumatic brain injury (TBI) to measure neural activity prior to, during, and after a trauma-like event.[8] This tool will enable a better understanding of the biophysical changes during and resulting from injury to determine how neuronal dysfunction manifests in TBI.[8]

Once Lacour began her position as a Research Fellow at the University of Cambridge, she collaborated with surgeons and other medical professionals to explore the potential of using her stretchable circuits and electrodes for nerve repair after injury.[9] Since injured axons can be assisted in their regeneration through mechanical guidance, Lacour sought to design an implantable device to mechanically guide axon repair.[10] Using polyimide as the substrate, Lacour rolled 2D gold microelectrodes and microchannels into 3D channel bundles to fit around axons.[10] These 3D electrode channel devices fixed to polymer substrates not only provide an innovative tool for in vivo guided axon regeneration but also set the stage for in vivo electrode implants that can communicate with multiple groups of nerve fibers, one day possibly enabling effective communication between a prosthetic and the human body.[10]

Lacour later began to experiment with different substrates with which to build stretchable electronics that are more compatible with biological systems in vivo.[11] Instead of using rigid, inorganic materials, like silicon, Lacour tested the viability of using pulsed lasers to create diamond-like carbon microstructures on polydimethylsiloxane.[11] She found that human skin cells were able to coat the substrate, making the technology suitable for future incorporation in medical devices and prostheses.[11] To further explore the potential of creating efficient and biocompatible in vivo neural interfaces, Lacour and her colleagues focused their attention to making microelectrode arrays more mechanically compliant.[12] By embedding thin, gold microelectrodes in a polymer that can be rolled and flexed, Lacour and her team were able to create improved interfaces between the device and neural tissue.[12]

Another goal of Lacour's research in Cambridge was to apply her stretchable electronics to produce sensory e-skins, so she began to design technologies in this realm.[13] Lacour applied her thin, gold films onto silicone rubber and was able to create multifunctional, capacitative sensors that can detect and localize touch as well as record pressure and strain.[13] Merging this tool with commercial transducer electronics will enable the production of sensory e-skins.[13] The e-skins that Lacour was working towards developing could be merged with her in vivo stretchable electronic interfaces to enable people with prosthetic limbs to not only sense their environment with their prosthesis but also integrate it into their nervous system such that they have autonomous mental control over their own limbs.[9]

In 2010, Lacour was awarded a European Research Council Grant to support her initiative, ESKIN aimed at designing and improving current electronic systems to increase their stretchability to make them compatible with biological tissues while maintaining electrical functionality.[17] Shortly after, Lacour was invited to give a TEDx talk at CERN In 2011 where she discussed her current research applying soft, flexible electronic circuits in addressing hearing loss in humans.[18] Because her soft machines are able to integrate with human nerves, Lacour says that, “These machines will help us to continue to be human”.[18] For example, Lacour and her team designed auditory brainstem implants adhered to polyimide substrates that have specific and enhanced interfaces with auditory neurons.[19] These tiny, flexible electrodes are inserted into cochlea, and deliver electrical pulses along the nerve to transduce sound from the environment into signals that the brain can interpret.[19] By creating machines that have physical properties that are compatible with biological tissues, Lacour is able to establish a communication link between the external world, the device, and the brain to enhance the quality of life for people suffering from hearing loss.[19]

In 2012, Lacour gave a talk at TEDxHelvetia discussing the use of silicon rubber as a substrate for electronic circuit construction, and the trick of combining these flexible materials with typical electronic conductive materials to enable electrical function.[20] She deems this the “soft to hard challenge” - making electronic 3D structures that interface the most delicate tissues like nerves, spinal chords, and the brain.[20] To tackle this challenge, Lacour took a new approach, in an article published in 2013, where instead of using full and uniform elastomers, Lacour experimented with flexible, heterogeneous foams.[21] Since foam is a network of air bubbles, Lacour found that building metallic pathways between the bubbles kept the conductive materials intact and elasticity over 100% could be achieved.[22] With this enhanced flexibility and maintained conductivity, these new flexible circuits can be implemented in electrodes, sensors, and biocompatible connections.[21]

By 2015, Lacour and her team at EPFL had developed a groundbreaking technology called e-Dura, short for electronic dura mater.[23] In its mechanical properties, the e-Dura technology resembles biological dura mater, the thick protective coating around tissues of the central nervous system.[23] However, e-Dura integrates electrical and pharmacological stimulation to return spinal chord function and mobility in rodents.[23] The part of this technology that allows it to return function to the nervous system of a living animal, is the biocompatibility.[23] e-Dura accommodates deformations, since it is made from Lacour's stretchable, soft, electronic circuits, and this allows it to move with the body and prevent irritation and resistance that might lead to scarring and inflammation.[23] Further, this technology has a fluidic microchannel that enables delivery of neurotransmitters which help to pharmacologically regenerate nervous tissue.[23] Lacour and Grégoire Courtine, co-principal investigator in this research endeavour, tested their e-Dura technology on paralyzed rats and, incredibly, these rats were able to regain spinal chord and limb function, enabling them to walk again.[24]

Though e-Dura already substantially progressed the field towards effective neuroprosthetics, one major limiting factor that still remains is the ability to precisely record neural activity in order to seamlessly integrate the internal motivation and neural activity in an organism with the desired output of the prosthetic.[25] In a therapeutic setting, the desired output of a neuroprosthetic can encompass a range of things from motor activity, such as driving muscles to fire and limbs to move, to silencing pain in chronic pain patients, to enabling amputees with the sensation of touch again.[25] As such, Lacour and her team developed a “nerve-on-a-chip” platform that is able to stimulate and record neural activity in nerve fibers.[25] Astonishingly, their technology, consisting of microfabricated electrode arrays, is able to record up to hundreds of individual neurons with a resolution at the level of individual neurons.[26] This technology also enabled photothermic inhibition of neurons, a capability that might one day be adapted to treat chronic pain.[26] Lastly, Lacour and her team used the neural recordings to train an algorithm to discern motor neuron signals from sensory signals which will one day enable the technology to bi-directionally control sensation and motor function.[26]