According to the proposed objectives, the research carried out during the project focused first on the development of low toxicity choline ILs and after that the prepared ILs were applied to prepare biocompatible IEAPs. The electro-chemo-mechanical performance of the materials was evaluated and compared with the benchmarked IEAP actuators.
A series of choline based ionic liquids and ionic liquid mixtures was synthesized and characterized (physico-chemical properties, thermal properties, toxicity). The choline cation was chosen due to its proven biocompatibility: choline salts have shown low toxicity towards various phyla of living organisms. Moreover, the choline salts have many biological functions in the human body and are vital for building up cell membranes and neurotransmitters. All the synthesised salts contained carboxylate anion, but the alkyl chain lengths, branching and number of carboxylic groups were varied. Toxicological properties of the ILs were evaluated using different bacteria (Escherichia coli, Staphylococcus aureus, Shewanella oneidensis MR-1) and cell-lines (HeLa, C2C12). Although all the tested ILs were found to have low toxicity, there were remarkable differences depending on the number of carboxylic groups in the anions. The synthesised ILs were further used for studying the possibilities to form eutectic mixtures. This approach is useful for fine-tuning the properties of electrolytes, especially the melting point and viscosity. Phase diagrams for the mixtures were constructed. The results are important for widening the knowledge about behaviour of IL mixtures. Although the various mixtures of imidazolium based ILs have been evaluated before, the data concerning choline ILs was lacking before the current study. Moreover, a computational method predicting the melting points for ionic liquids was developed. This helps to design ILs with required properties and decrease the experimental burden.
Following the developed ILs were used for preparation of biocompatible IEAPs. As electrode material PPy was chosen due to its proven biocompatibility (suitable substrate for cell growth, implantable). For membrane electrospun gelatin was compared with the widely used and medically approved PVdF. Performance of the choline IL electrolytes was tested against 1-ethyl-3-methylimidazolium trifluromethanesulfonate commonly used in the IEAPs. The electro-chemo-mechnical performance of the developed actuators was evaluated using different driving signals varying in frequencies and shapes. Obtained strain differences describing bending of the actuators were comparable with the benchmarked IEAPs. Computational methods such as MD and DFT simulations were used to shed light on the differences in the performance of the IEAPs depending on the applied electrolyte. The results revealed that clustering of the choline cations in the ILs strongly influences the actuation and strain difference of the IEAPs.
Results of the project were published in 4 peer-reviewed journal articles and disseminated to scientific community in conference presentation and to the broader audience through special events (art exhibitions, public lecture) and media releases.
