Ionic electroactive polymer for organs-on-chip applications

An organ-on-chip (OoC) is a microelectromechanical (MEMS) device that aims to recapitulate in-vitro the physiology of the smallest functional unit of an organ in order to perform drug analysis or study disease models. OoCs are very complex systems that require actuation and sensing capabilities within controlled and delicate environment. The research presented in this thesis focuses on a transductive material that offers promising properties for organ-on-chip. The objective of the thesis is to demonstrate the potential of using ion-based electroactive materials to tackle current OoC limitations. An ionic electroactive material, called ionic polymer metal composite (IPMC) is proposed, characterized and developed in order to increase the ease of use, integrability, and scalability of OoC. The IPMC consists of a soft polymer, doped with ions naturally present in standard culture media, flanked by platinum electrodes on opposite sides. This biocompatible material shows good actuation and sensing capabilities, requires low driving voltage and has been herein investigated as a potential transducer for several organ-on-chip applications. A first version of the IPMC with a thickness of 180 𝜇m (called thick IPMC) showing good actuation capabilities has been adopted to implement a micropump and a tissue stretcher. The cells strecher could exhibit biologically relevant strain (0.1 %) while showing no toxicity, and the micropump achieved biologically relevant wall shear stress (0.008 Pa) through liquid flow within microchannels. Furthermore, in this thesis, this moisture-sensitive material has been investigated in the context of wafer-level process flow using state-of-the-art microfabrication tools to demonstrate its compatibility with silicon-based technology. A second version of the IPMC has been developed based on a thinner polymer (50 𝜇m, called thin IPMC), as well as an adjusted manufacturing recipe in order to explore the material potential as a sensor for OoC. A comparative study has been performed between the manufacturing of thick and thin IPMC, evidencing different dynamics of the electroless deposition reaction depending on the thickness of the polymer used. The developed thin IPMC shows superior sensing capabilities by virtue of lower flexural rigidity and higher electrodes conductivity. The applications explored with the thin IPMC are microfluidics flow sensing and strain sensing. The microfluidic flow sensor exhibits good sensing capabilities with a sensitivity of 4.78 mV/(uL/s) and a linear behavior in the studied range. In addition, soft lithography and patterning of hydrogel have been investigated on top of the thin IPMC, to further assess the material as a smart substrate for tissue engineering. The present thesis anticipates a potentially significant impact of smart materials as a new tool to engineer multi-functional culture substrates for OoC as well as develop electronically-controllable flexible membranes for micro pumping.