New insight into the behaviour of materials for bioelectronics

In science, it is easiest to tell the story of materials that perform more efficiently, last longer, and enable increasingly better performance of the devices in which they are used. It is much more difficult to attract attention to findings that show the opposite - that a widely used material has a significant limitation, undergoes degradation, or behaves differently from what was previously assumed. Yet observations of this kind can be of fundamental importance, particularly in bioelectronics, where materials are designed to operate in direct contact with living tissue.

P3HT, or poly(3-hexylthiophene), is one of the best-studied semiconducting polymers. It absorbs visible light, conducts electrical charges, and can be used both in the form of thin films and nanoparticles. Its unique properties have also led to its use in bioelectronics, including for the photostimulation of neural cells and the retina. The development of such devices is progressing rapidly and, in some areas, may be advancing faster than our full understanding of the chemical stability and degradation mechanisms of the materials they employ.

This was the focus of a team of researchers from the Warsaw University of Technology, Cardinal Stefan Wyszyński University, and CEITEC in the Czech Republic. The researchers examined the behaviour of P3HT under conditions resembling those in which the material would operate in the body - in an aqueous environment, in the presence of oxygen, and under light exposure. They demonstrated that hydrogen peroxide is generated when the material is illuminated and that this process is accompanied by the degradation of the polymer itself. This means that, in this system, P3HT does not act solely as a photocatalytic material, but is itself gradually consumed in the process.

"At first glance, demonstrating that a material undergoes degradation may be seen as an unfavourable finding from the perspective of its potential applications. This does not, however, make the result any less scientifically significant. From the perspective of materials engineering, observations of this kind are extremely important. If we want to use organic semiconductors safely in bioelectronics, we need to understand not only their electrical and optical properties, but also the chemical transformations that occur while a device is operating in the environment in which the material is ultimately intended to function," says Roman Gańczarczyk, MSc, from the Faculty of Chemistry at the Warsaw University of Technology.

In conventional organic electronics, material evaluation focuses primarily on the analysis of electrical and optical properties. In bioelectronics, and particularly in photostimulation applications, the criteria need to be broader. Materials used in such devices may remain in an aqueous environment for extended periods, come into contact with cells, and be exposed to light repeatedly. Therefore, not only the effectiveness of the device matters, but also the chemical stability of the materials used in it.

"If we know how and under what conditions a material degrades, we can begin to design solutions that limit this process. This may involve modifying its chemical structure, morphology, or processing method, but also changing the architecture of the entire device in order to reduce undesirable reactions. Therefore, understanding when a material begins to lose its properties and what causes this is just as important as demonstrating that the material works in the first place," emphasises Prof. Renata Rybakiewicz-Sekita from Cardinal Stefan Wyszyński University.

The findings demonstrate that an apparently “negative” observation can be an important step towards the responsible development of new technologies. This is particularly relevant in bioelectronics. A material intended to operate in contact with living tissue should be evaluated not only in terms of whether it performs its intended function, but also whether it is stable and safe.

The research findings have been published in Chemistry - A European Journal in an article entitled "Photoinduced ROS Production by Poly(3-hexylthiophene) (P3HT) is due to Autoxidation Rather Than Catalysis".

The research was co-financed by the National Science Centre (NCN) under the PRELUDIUM project (2024/53/N/ST5/02771) and the SONATA project (2024/55/D/ST5/02837).