The cooperative actuation of multistep electrochemical molecular machines senses the working temperature: voltammetric study

Reaction Induced Conformational Change in Polyindole: Polyindole/PVA Film as Biomimetic Sensors of Temperature and Electrical Energetic Conditions

Conducting polymers can mimic the sensing characteristics of biological muscles through utilizing their unique electrochemical reactions. As these reactions occur, alterations in composition prompt changes in biomimetic properties, such as shifts in volume, brought about by the insertion of anions and solvent molecules, resulting in conformational movements. Similar to biological muscles, these electrochemical reaction senses the working variables affecting the reaction rate, through the same two connecting wires. The influence of working temperature and electrical energetic condition on the conformational movements of polyindole manifested as the cooperative actuation of the polymer chain is verified here using a polyindole-coated polyvinyl alcohol (PIN/PVA) film. Cyclic voltammetric (CV) studies revealed that the extent of reaction of polyindole varies linearly with temperature and scan rate. The logarithmic dependence of redox charge obtained from coulovoltammogram with inverse of temperature further proved the temperature sensing characteristics and the influence of temperature on the cooperative actuation of the film. The conformational relaxation increases as the temperature increases through hosting higher number of counter anions with the solvent molecule. The extension of the redox reaction was found to decrease as the scan rate increases. The double logarithmic relation between the consumed redox charge and the scan rate has proved that the electrical energetic condition can influence the conformational movement in a reversible manner. It is also verified from Chronopotentiometric (CP) studies that the consumed electrical energy during the reaction varies linearly with the change in temperature. The results suggest that the PIN/PVA film can act as a biomimetic macro molecular sensor of working temperature and electrical energetic condition as biological muscles do.

Bioinspired polypyrrole based fibrillary artificial muscle with actuation and intrinsic sensing capabilities

A non-conventional, bioinspired device based on polypyrrole coated electrospun fibrous microstructures, which simultaneously works as artificial muscle and mechanical sensor is reported. Fibrous morphology is preferred due to its high active surface which can improve the actuation/sensing properties, its preparation still being challenging. Thus, a simple fabrication algorithm based on electrospinning, sputtering deposition and electrochemical polymerization produced electroactive aligned ribbon meshes with analogous characteristics as natural muscle fibers. These can simultaneously generate a movement (by applying an electric current/potential) and sense the effort of holding weights (by measuring the potential/current while holding objects up to 21.1 mg). Electroactivity was consisting in a fast bending/curling motion, depending on the fiber strip width. The amplitude of the movement decreases by increasing the load, a behavior similar with natural muscles. Moreover, when different weights were hung on the device, it senses the load modification, demonstrating a sensitivity of about 7 mV/mg for oxidation and - 4 mV/mg for reduction. These results are important since simultaneous actuation and sensitivity are essential for complex activity. Such devices with multiple functionalities can open new possibilities of applications as e.g. smart prosthesis or lifelike robots.

Flexible hybrid film of polypyrrole incorporated chitosan as a biomimetic multistep electrochemical sensor of working temperature: a potentiodynamic study

A flexible polypyrrole/hydrogel hybrid film composed of macromolecular electrochemical machines is considered as a model material of the intracellular matrix of ectothermic muscle cells capable of sensing ambient thermal energy.

Electroactive macromolecular motors as model materials of ectotherm muscles

The electrochemical reaction in liquid electrolytes of conducting polymers, carbon nanotubes, graphenes, among other materials, replicates the active components (macromolecular electro-chemical motors, ions and solvent) and volume variation of the sarcomere in any natural muscles during actuation, allowing the development of electro-chemo-mechanical artificial muscles. Materials, reactions and artificial muscles have been used as model materials, model reactions and model devices of the muscles from ectotherm animals. We present in this perspective the experimental results and a quantitative description of the thermal influence on the reaction extension and energetic achievements of those muscular models using different experimental methodologies. By raising the temperature for 40 °C keeping the extension of the muscular movement the cooperative actuation of the macromolecular motors harvest, saving chemical energy, up to 60% of the reaction energy from the thermal environment. The synergic thermal influence on either, the reaction rate (Arrhenius), the conformational movement rates of the motors (ESCR model) and the diffusion coefficients of ions across polymer matrix (WLF equation) can support the physical chemical foundations for the selection by nature of ectotherm muscles. Macromolecular motors act, simultaneously, as electro-chemo-mechanical and thermo-mechanical transducers. Technological and biological perspectives are presented.