Materials for Bioelectronic Applications

Bioelectronics concerns the use of electronic devices in biological systems. Importance is placed on interfacing electronic signals and biological tissue, to provide information about the intercellular communication which occurs in a living organism. A possible application of such as system would be within spinal cord injuries (SCIs). According to the World Health Organisation, there are between 250,000 and 500,000 spinal cord injuries per year. Most of which cause chronic pain or paralysis. In a paralysed patient the brain is unable to communicate efficiently with the paralysed area of the body. Currently physiotherapy can offer treatments in the form of pain relief or ease of numbness but there is no reverse for paralysis. Bioelectronics could offer a solution. For those with SCIs, a bioelectronic device could be a way of passing electrical signals across the site of injury, essentially bridging the gap where communication could not pass. This communication can be mimicked using bioelectronic devices in the form of biological scaffolds and transistors. Therefore, a bioelectronic device which offers appropriate mechanical properties to the spinal cord could be used to restore some communication beyond the site of injury.
The brain communicates with the body by passing an action potential through the neurons which make up the central nervous system. To function in a way which replicates the passage of an action potential a bioelectronic device would need to have two states so it can be either 'on' or 'off' and therefore only able to pass a potential when triggered as part of a neural response. Organic electrochemical transistors (OECTs) can achieve this and are also appropriate for physiological environments.
The ability of an OECT to transduce both ionic and electronic currents makes them ideal for a system such as the nervous system. In this project poly(3,4-ethylenedioxythiophene) (PEDOT) will be used an active layer within an OECT. Although used as the semiconducting layer, PEDOT itself does not display appropriate mechanical properties and neither is it biodegradable. Therefore, to effectively function as a transistor for application in the spinal cord it must be doped. The doping agent effects the potential of the system, when in doped state the charge on the doping agent is balanced with the charges associated with PEDOT. However, when a potential bias is applied PEDOT is de-doped altering the potential of the system.
The doping agent in this project will need to be biocompatible, biodegradable and mechanically appropriate, therefore compounds which are naturally occurring within the body are ideal.
The creation of a biodegradable device with the right mechanical properties can be addressed by producing a biodegradable anionic hydrogen scaffold, using materials which are also GAGs. In order to quantify the mechanical properties of the device the elastic modulus can be measured. This quantity describes the extent to which a material deforms elastically and can be compared to components making up the spinal cord.
The aim of this project is to produce a biocompatible and biodegradable organic electrochemical transistor, using poly(3,4-ethylenedioxythiophene) doped with glycosaminoglycans and hydrogels prepared from the same, that offer compatibility with the spinal cord.