Living biohybrid systems via in vivo polymerization of thiophene oligomers

Abstract: Life is the result of a multitude of electrical signals which drives our nervous system but also accomplishes a cascade of electrochemical reactions. In the 18th century, Lucia Galeazzi and Luigi Galvani got the idea to stimulate frog legs with electrodes. This first step into the world of bioelectronics showed that electronic systems were able to communicate with living organisms through electrical stimulation, as well as by recording electrical signals from organisms. Until the end of the 20th century, the field of bioelectronics kept progressing using metal electrodes. This class of material inherently exhibits a high conductivity from their dispersed cloud of shared electrons. However, an obvious physical mismatch occurs when inserting metal electrodes inside a living organism. Since these materials are not as soft as living tissues, internal damage followed by an immune response impacts the impedance of such probes.In the late 80s', the large-scale commercialization of water processable conducting polymers brought a new paradigm in the choice of electronic material for bioelectronics devices. Compared to metals, conducting polymers are composed of semi-crystalline blocks that interact through electrostatic forces. These soft structures make these materials permeable to aqueous solutions, which allow the introduction of ionic species in the vicinity of the polymer backbone. Ions close to the polymer backbone can tune the conductivity of the material creating a unique ion/electron dialogue that increases the electronic signal resolution. Additionally, these soft structures considerably reduce scaring effects and therefore enable the devices to trigger lower immune responses. Conducting polymers could also be directly inserted within living tissues to create electronic platforms inside a host. Living organisms with new material properties could unravel new functions such as collecting electrophysiological data without surgery.Plants are living organisms that made their way out of the ocean and conquered most of the available land on earth. Saying that plants are good climate controllers is a euphemism since plants are legitimately the organisms that have settled the climate conditions for the development of more advanced life forms. Plant biohybrid is a new technological concept where plants are not only seen for their nutritious or environmental aspect but also as devices that can record and transfer information about their local environmental conditions. Such data could be used in a positive feedback loop to improve the production yield of crops or understand the underlying communication mechanism that occurs between plants or with plant micro-biomes. Most of the approaches toward plant biohybrids nowadays focus on nanomaterials that act as fluorescent probes in leaves and detect analytes from plants' local environment.In this thesis, we push forward a plant biohybrid strategy that instead uses conducting polymers as vectors to build conductors inside plants with the aim to build electrochemical platforms that could be used for applications such as energy storage, sensing, and energy production. Works developed in this thesis are going in an array of directions that aims for the better integration of electronic platforms in living systems with more focus on plants.We first identified a plant enzymatic mechanism that triggers the polymerization of a thiophene oligomer, namely ETE-S in vivo and in vitro. Such plant enzymatic pathways can then be reused to develop electronic systems in plantae without additional reagents. In the next work, we presented the synthesis of three new oligomers called ETE-N, EEE-S, and EEE-N that have a similar architecture compared to ETE-S but with different chemical moieties such as a different ionic side chain or an EDOT instead of thiophene in the middle position of the oligomer. We then demonstrated the effective enzymatic polymerization of these oligomers both in vivo and in vitro and how the resulting polymers' optoelectronic and tissue integrations properties differ. Towards even more versatility, we demonstrated that this electronic integration in vivo was also observed in the case of an animal: the freshwater hydra polyp. The polymerization was observed mostly in differentiated cells from the gastric column of the animal that normally secretes an adhesive used to fix the animal underwater. P(ETE-S) was incorporated in this glue that we managed to characterize using electrochemical methods. Lastly, we performed demonstrations of electrochemical applications with a plant root system. By dipping several roots in an ETE-S solution, we created a network of conducting roots that can effectively store charge as a capacitor with performance comparable to what is classically obtained with conducting polymers. In addition, we modified roots with two different surface modification concepts to make them specific to glucose oxidation: the first method uses a traditional redox hydrogel with a crosslinker and glucose oxidase. The second one uses the embedment of a glucosespecific enzyme inside the p(ETE-S) layer during its formation. These devices are presented as possible new solutions for environmental glucose sensors that could collect current from the environment and store it in neighbouring capacitive roots.Overall, this thesis shows that the enzymatic activity of living systems can be used from an engineering point of view as part of a deposition methods for the development of biohybrid applications.