Implantable Optoelectronic Devices for Neurophysiology

Techniques for the generation and manipulation of light have developed rapidly in recent years, leading to the possibility of optical systems miniaturised to a size previously considered unattainable. At the forefront of these developments are plastics that allow the manufacturing of light sources and detectors with a flexibility in colour, shape, size and structure that pushes the limits of miniature optical systems even further.
We are barely beginning to understand the revolutionary impact of these technological advances on the medical field, as this requires a deep integration between physical and medical sciences. In this project, we will be exploring it by using miniature plastic light sources and detectors to build implantable devices, with the potential to transform the way we approach the understanding and the treatment of the nervous system.
By measuring the blood colour around nerve cells, it is possible to monitor in very fine detail how oxygen is used by the nervous tissue. This, in turn, tells us about the tissue activity level. It is also possible to modify the nerve cells so that they respond to light. By illuminating them with light of a given colour, the modified cells are activated, and by using a different colour, the activity is temporarily stopped.
Using light, we have therefore the capability to measure the activity of nerve cells, and to interact with such activity as needed. For this reason, miniaturized and implantable light manipulation devices have the potential to become invaluable tools in detecting how the nervous system works, and to implement corrections in its activity. Examples where this technology may offer solutions can be Parkinson?s Disease, epilepsy, or the augmentation of damaged parts of the nervous system.
For it to be effective in real-life applications, the development of such a technology goes well beyond the capabilities of a single research group. The project will therefore aim to establish a stable collaboration between physicists/engineers and neurosceintists/medical doctors
The collaborative research will start by developing plastic light sources and detectors tailored to the needs of nerve cell analysis and manipulation. We will then explore the suitability of such devices for long-term implants, by checking if they may cause damage to the nerve tissue structure or to the way the tissue works. Finally, we will demonstrate a simple application, in which the light sources and the detectors will be used to measure an actual nerve or brain signal.

Optical techniques are increasingly being applied in biology and medicine because of their high sensitivity, spatial and temporal resolution. Even simple optical devices, such as the pulse oxymeter can have major clinical impact. This project will explore exciting new opportunities arising from forefront research on organic (polymer) semiconductors which enables a new generation of compact light sources and detectors. These devices enable fine tuning of wavelengths, are compatible with miniaturization and allow simple processing on flexible substrates.

The purpose of this proposal is to bring together physicists and neuroscientists in a truly interdisciplinary activity, to explore the development of a technology that uses organic semiconductors for innovative implantable neural probes. This will combine advances in organic semiconductors with recent demonstrations that optical techniques can measure neural activity and even modify it. To develop the strong and stable collaboration required, we will train a skilled physicist/engineer to work in a neurophysiology team. The proposed collaboration promises new and potentially revolutionary tools to understand and to act upon the nervous system. These include a potential means to control the neural code and possibly restore it to normal in neurological disorders such as epilepsy and Parkinson?s disease.

Towards this vision, we will first approach the feasibility of novel implantable polymeric sources and detectors. This will involve the fabrication of such devices, to be tailored to neurophysiology in their major functional parameters. We will then address biocompatibility issues of such devices in an animal model, verifying at first, by histopathological techniques, that they do not cause structural damage to the biological tissue to which they are applied. As a conceptually separate issue, though approached mainly within the same experiments for animal number minimisation, the neural tissue will be examined by electrophysiological techniques to detect functional alterations. In a successive stage, ancillary external electronics will be applied to the sources and the detectors, to detect a simple hemodynamic signal of neurological relevance, such as a localised hemodynamic response to a stimulus. Finally, stimulation and inhibition of neural activity will be investigated.