Our research focuses on three core areas:
- Bio-Interfacial Engineering for Neuroprosthetics
- Polymer based Bioelectronics
- Biomaterials for Regenerative Medicine
Over the past 30 years implantable bionic devices such as cochlear implants and pacemakers, have used a small number of metal electrodes to restore sensory perception or muscle control to patients following disease or injury of excitable tissues. With the miniaturisation of electronics, bionic devices are now being developed to treat a wide variety of neural disorders. Of particular interest are high-resolution devices that require smaller, more densely packed electrodes. Due to poor integration with living tissue, conventional metallic electrodes cannot meet these small size requirements and are limited in their ability to safely deliver charge at therapeutic levels. A core activity of the Green research group is the development of conducting polymer-based coatings and materials such as conductive hydrogels and elastomers. These polymeric technologies can create high quality neural interfaces by reducing the strain mismatch between hard devices and soft tissue, decreasing interfacial impedance, and enabling biofunctionalization strategies to influence the tissue response upon implantation. This research led to a patent on conductive hydrogels (CHs) (US Patent 9,299,476). The promising results in this area initiated a number of industry collaborations including Galvani Bioelectronics, Boston Scientific, the Bionics Institute (Aus) and Cochlear Ltd.
Building on this expertise, we are now investigating combinatorial approaches to the development of next-generation bionic devices & regenerative therapies such as bionic nerve guidance conduits, minimally invasive deep brain stimulation, and living electrode technologies.
Pioneered by our group, the living bioelectronics research track is a unique approach to creating high quality neural interfaces for bionic devices such as neural probes, cardiac patches and nerve guidance conduits. The concept of living bioelectronics is based on developing tissue engineered electrodes which form biological synapses with native tissue upon implantation to avoid the performance issues associated with the formation of scar tissue around implanted devices.. This approach builds on our conductive hydrogel coatings by applying a neuroprogenitor-laden degradable hydrogel layer on top of the conductive hydrogel coating. This project was originally funded as part of the DARPA Brain initiative and is currently funded through an ERC Consolidator Grant.
Preclinical testing of bioelectronic technologies commonly involves evaluating devices using saline to simulate bodily fluids before progressing to in vivo testing. This often leads to significant changes in electrode performance when moving from from in vitro to in vivo test environments. This research track challenges the accepted standard for device testing and advocates testing in biologically relevant solutions and ex vivo models under implant-specific stimulation regimes. The models developed in this track are used to assess clinically relevant devices as well as our novel electrode materials. This research has resulted in on-going collaboration with Galvani Bioelectronics, Cochlear Ltd, and researchers at the Bionics Institute, Melbourne.
Native neural tissue is incredibly complex and cannot be adequately replicated using two-dimensional, single cell-type cultures. This research track aims to create long-term, three-dimensional, primary mixed cell models of neural tissue to better equip researchers with the in vitro tools needed to assess device-tissue interactions in CNS. By doing so we hope to bridge the divide between traditional in vitro and in vivo techniques. New approaches to combining stem and neuroprogenitor cells have been developed as models of brain tissues. Current directions focus on translation to 3D constructs for modelling implantations. Most notably, this project has facilitated development of a range of microscopy techniques using 2-photon intravital microscopy within 3D cell culture constructs.
This research track is aimed at producing bioelectronics such as electrode arrays that are fully polymeric with no metal components. This is intended to produce soft, flexible, stretchable, and MRI compatible devices that are less susceptible to mechanical failure and cause less adverse tissue response upon chronic implantation. The development of solid metal-free electronics is funded through an EPSRC Healthcare Technology Challenge Award (HTCA). This research involves the design of fully polymeric electrode arrays that can be processed via conventional microfabrication techniques with the aim to develop flexible high-density bioelectronics. Ongoing collaborations with industry partners and alignment with MHRA processes ensure alignment to the pathways through which these technologies can be brought to the clinic. The other focus of this track is the creation of injectable electrode materials allowing for the in-situ formation of neural electrodes via electrochemical polymerisation of conducting hydrogels inside the brain.
Funded as part of the EPSRC IRC on hard-to-treat cancers, this research track aims to produce a new therapeutic option for patients with inoperable brain tumours. Combining conducting polymer technologies with ionic drug delivery the developed implant uses the application of electrical potential to release chemotherapeutics deep inside the tumour in a controlled fashion. Extensive drug delivery testing through both two- and three-dimensional cell culture models are being established to quantify the effect of increased chemotherapeutic bioavailability. Frequent clinical input via collaborations at Charing Cross Hospital and the BARTS Cancer Centre ensure that this technology is being developed in a form that can be directly translatable to clinical practices.