Organic memristive devices towards biocompatible interfaces

The PhD dissertation of Angelica Cifarelli entitled “Organic memristive devices towards biocompatible interface” deals with two different topics, both related to develop the interfaces between memristive devices and biosystems and the study of their properties. The main task of this research is to develop a solid state electrochemical device able to integrate biological systems. To reach this goal, materials generally used in other sectors (pharmaceutical and food industry, for example) are employed as the interface between biological environment and not biocompatible polymeric film . A new architecture of organic memristive device with a structure of double-layered polyelectrolyte is proposed. In order to be able to implement biocompatible materials to electronic architectures as “bridging” materials, these systems should maintain suitable conditions for the survival of a biological organism without compromising the device operation. Water is the ideal medium for biological system and thus the methods of fabrication must embrace and drive any interactions in water. For this reason, we focus on hydrogel-based interfaces that should be introduced between biological systems and polymeric film as a polymeric host material able to capture and maintain the biological functionality. Many polymer systems are qualified as hydrogels because they incorporate and maintain an enormous amount of water, e.g., Chitosan, Alginates, Pectins. We chose polymers of natural origin, that have shown a high degree of bio-compatibility and solubility in dilute solutions of organic acids. So, while the biological side of this system is satisfied via the incorporation of water, the polymer system preserves the conductivity of polyaniline. In addition, these bio-materials support the “communication” and the ion- exchange process to allow the interconversion of biological and electronic signals. In particular, bio-polymers such as chitosans and pectins were studied in order to test their functioning as buffer layers, able to preserve the Langmuir-Schaefer polyaniline (PANI) film conductivity at neutral pH. The research is focused on the modification of electrochemical response of PANI layer using soft and cheap methods. An electrochemical model explaining the memristive properties of the devices was proposed, which takes into account all the electrochemically active species in the system. The results have demonstrated that the memristive properties of the devices are due to a synergy between polyaniline electrochemistry, the role of Cl- ion, the diffusion of silver as Ag+ with H2 evolution and the transport properties of bio-based solid polyelectrolyte. Finally, a bio-integrated system containing Physarum polycephalum as a model biological system was designed. In conclusion, this work demonstrates the possibility to integrate such a special alive cell working as solid-polyelectrolyte in memristor. The devices are characterized by means of cyclic voltage-current measurements, UV-Vis spectroscopy, SEM and EDX analysis. The possibility to couple electronic devises with biological objects or even with living organisms opens new perspectives in development of living technology devices, biocompatible non-silicon hardware for applications in integrated circuits, bioelectronics, and biosensing.