Living Bionics
Biologically based materials that leave no scar
Living bioelectronics: Bridging the interface between devices and tissues Project Objectives
Bionic devices like cochlear implants and bionic eyes are currently made using relatively stiff metals that the body recognises as foreign, which limits the effectiveness of these devices when they are implanted. We spoke to Dr Rylie Green about the work of the Living Bionics project in developing new, softer materials that can be integrated into the body more effectively. The vast majority of bionic devices like cochlear implants, pacemakers and bionic eyes currently include metallic electrodes, with a non-conductive polymer as the insulating component. These types of devices are not naturally compatible with the tissue with which they interface when they are introduced into the body, as Dr Rylie Green explains. “When these devices are introduced, the body recognises them as foreign. It responds by essentially putting up a wall of scar tissue over time, to stop what it sees as a threat from causing damage to the rest of the body,” she outlines. This leads to the formation of a scar tissue capsule, which impedes communication between a bionic device and the rest of the body. “Where you want to be communicating very efficiently with the nerve cells within a system, instead you’re communicating through a big wall of scar tissue, to try and stimulate cells - or record from cells - that have moved further away from the interface,” says Dr Green.
Image credit: Dr Aaron Gilmour, postdoctoral researcher.
Living bionics project An alternative option is to use biologically based materials in a bionic device that the body will respond to in a more natural way, a topic central to the work of the Living Bionics project, an ERC-backed initiative based at Imperial College in London. As the project’s Principal Investigator, Dr Green is working to develop biomaterials that can be integrated with tissue without the formation of scar tissue. “We are trying to make biosynthetic materials that can essentially trick the body into thinking that they are natural,” she explains. This can be done in a variety of different ways; one of the simplest is to make something that is softer than the metals currently used. “Nervous tissue is very soft, somewhere in the region of very low kilopascals down to pascals in terms of stiffness. Whereas the metals usually used in electrodes are over the gigapascal range,” says Dr Green. “So there’s a huge difference in stiffness between the metals that are used conventionally, and the actual tissue in which they implant devices.”
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The Bionic Man. © Control Publishing
Image credit: Dr Ulises Aregueta-Robles.
A lot of energy in research has been devoted to essentially softening up that interface by using materials that are also in the kilopascals range, so that the neighbouring cells feel something soft when a device is introduced. While the body still recognises that a device has been
made with synthetic materials, the mechanical properties do not cause physical damage. “There is a better response at the interface,” stresses Dr Green. Biological elements that are normally present in the environment around the cells, such as protein-type components, can also be added to these materials, making them ‘biosynthetic’. “The body then starts to interact with these components, and we see some positive interactions,” says Dr Green. “However, when we implant these softer, more biological devices, the body can still recognise that they’re foreign in some respects. Critically, there is still implant damage when you actually introduce the device. In Living Bionics, we see this as a window of opportunity to create a better connection between the device and the surrounding tissue.” The aim here is to add in some stem cells or progenitor cells that will grow out from the device to interact with the tissue. By essentially pushing the stem cells down a particular developmental line, Dr Green hopes to ensure that they develop into neural cell networks that are more compatible with the local environment. “We provide, within the device, the ingredients the stem cells need to become neural cells that will then target the tissue that we’re looking to interface with,” she explains. However, stem cells do not always differentiate into neural cell networks, which is one of the major challenges facing the project. “No matter what cues you provide stem cells with, you never get 100 percent of one particular cell type. We’re working to develop not just one cell type, but a ratio of different cells that are present within the brain, to make functional neural tissue,” continues Dr Green. “We don’t just want nerve cells on their own, that’s not sufficient. We need to also think about their supporting cells.”
Cell networks Researchers have developed a method that enables the introduction of cells that have already been differentiated, called astrocytes. These act as support cells to the nerve cells, and form part of a wider network. “Nerve cells don’t contact each other and create a conduit on their own, they need these other
EU Research
Living Bionics brings together concepts from tissue engineering with bionic device design to provide connections at the device-tissue interface on the cellular level, enabling natural modes of nerve tissue activation. Living Bionics will use stem cells embedded within neural implant devices to create a paradigm shift in medical electrode design, to improve implant integration with the body and ultimately patient benefit from devices.
Project Funding
The Living Bionics project is funded by an ERC Consolidator grant.
Contact Details
cells to guide them. We’re finding that you need to really address the immune cells first. Mature astrocytes provide the nerve cells with the nutrients they need and show them where to go,” explains Dr Green. These other cells are critical in establishing a functional contact between a device and the tissue that is being targeted; Dr Green and her colleagues in the project are focusing largely on the brain and the central nervous system. “We’re starting with the cortex level rather than the hindbrain or the hypothalamus, which have different ratios of different types of cells,” she says. “We want to start with just one tissue type, and show a proof-ofconcept. There’s a balance here, in the sense that you have to provide the right sorts of ingredients and cues.”
look towards applying new bionic devices to treat disease by effectively slowing their progression. “Some diseases have a degenerative state, and the natural environment within the brain continually causes cells to die,” continues Dr Green. “It has been theorised that controlling those cells, or stimulating them in some way, will help to slow down or halt a disease.” It is unclear whether those cells that are introduced as part of the device will still be subject to the factors that caused the original damage and if they will then become degenerate. However, even if the cells do degenerate, Dr Green says such a device would provide a solid basis for treatment. “We still have a soft device there that hasn’t formed scar tissue, so you should still have
When these devices are introduced, the body recognises them as foreign. It responds by essentially putting up a wall of scar tissue over time, to stop what it sees as a threat from causing damage to the rest of the body. This research is very much exploratory at this stage, so at the moment Dr Green is essentially putting all the building blocks together and building a deeper understanding of cell populations. The next stage would be to trial these devices within rodent brains, and assess their effectiveness in terms of communicating with the rest of the brain. “Success for us in a murine model would basically mean cell survival. For example, where we can visualise some of the cells that have been incorporated in our devices, and see that they are communicating with the cells in the animal’s brain,” outlines Dr Green. Beyond that, researchers could eventually
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Project Coordinator, Dr Rylie Green Faculty of Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ T: +44 (0)20 7594 0943 E: rylie.green@imperial.ac.uk W: https://www.imperial.ac.uk/people/rylie.green
Dr Rylie Green
Dr Rylie Green joined Bioengineering, Imperial College London in 2016. Dr Green’s research has been broadly focused on developing medical electrodes, with a specific focus on neuroprostheses. She seeks to bring together approaches from biomaterials and tissue engineering, with technology development in bionics and device design to provide disruptive solutions to the bioelectronics field.
a more effective interface for long-term electrical treatment,” she explains. This research is still at a very early stage however, and researchers are currently focused more on gaining fundamental knowledge than translational activity. “We’ve learnt a lot about what we need to provide our cells with, such that they not only survive within a device, but they also have the components to turn into the right sorts of cells to develop neural networks,” says Dr Green. “What cells need is more space, and topographical cues in that space that they can cling onto and create sort of mechanical connections, which allow them to change their shape and become part of wider networks.”
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