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IntroductionIn general movement is an intrinsic property of living creatures. It occurs at different structural levels including ion transfer through membranes, separation of replicated chromosomes, beating of cilia and flagella or, the most common, contraction of muscles. Those contractions enable the organism to carry out organized and sophisticated movements such as walking, running, flying, swimming, breathing, digesting foods, etc., as well as generating mechanical energy.Great strides have been made during human evolution in developing biological systems. Among these, muscles are elegant devices developed through thousand of years of evolution to transform chemical energy into mechanical energy and heat. This transformation is triggered by an electric pulse arriving from the brain through nerves, which promotes an increase of Ca+ 2 inside the myofibrils from 10-7 to 10-3 mollI. The increase of the ionic concentration promotes conformational changes in the troponimtropomyosin system allowing muscle contraction [1]. The energy required for these conformational changes is generated by ATP hydrolysis, this being the bonding ion between myosin heads and actin filaments. ATP is restored from ADP through the glucose cycle. All those processes take place in aqueous media. A muscle can be considered as an electro-chemo-mechanical actuator.Thus macroscopic movements developed by a muscle are generated by molecular movements occurring in biological macromolecules, and several points can be stressed: -A muscle is a complex system where water, ions, macromolecules, and small organic molecules play important roles. -A nervous pulse promotes ionic interchanges between every myofibril and the surroundings in a few microseconds. -The free energy of ATP hydrolysis drives conformational changes in the myosin head, resulting in the net movement of myosin along the actin filament. -The movement occurs through the formation of complexes between two macromolecules (myosin and actin) and an ion,ATP, and the subsequent dissociation of those complexes with formation of ADP. -The high energetic content of ATP is restored from the ADP by transferring energy from glycolysis. -Muscles work at constant temperature and the heat generated during those transformations by entropic requirements has to be eliminated. Y. Osada et al. (eds.), Polymer Sensors and Actuators

Here we present the synthesis and characterization of two new conducting materials having a high electro-chemo-mechanical activity for possible applications as artificial muscles or soft smart actuators in biomimetic structures. Glucose-gelatin nanofiber scaffolds (CFS) were coated with polypyrrole (PPy) first by chemical polymerization followed by electrochemical polymerization doped with dodecylbenzensulfonate (DBS-) forming CFS-PPy/ DBS films, or with trifluoromethanesulfonate (CF 3 SO 3-, TF) giving CFS-PPy/TF films. The composition, electronic and ionic conductivity of the materials were determined using different techniques. The electro-chemo-mechanical characterization of the films was carried out by cyclic voltammetry and square wave potential steps in bis(trifluoromethane)sulfonimide lithium solutions of propylene carbonate (LiTFSI-PC). Linear actuation of the CFS-PPy/DBS material exhibited 20% of strain variation with a stress of 0.14 MPa, rather similar to skeletal muscles. After 1000 cycles, the creeping effect was as low as 0,2% having a good long-term stability showing a strain variation per cycle of-1.8% (after 1000 cycles). Those material properties are excellent for future technological applications as artificial muscles, batteries, smart membranes, and so on.

The nature of the electrochemical responses from carbon nanotubes (CNTs), capacitive (physical), or Faradaic (chemical, also named p-doping or n-doping) remain controversial. In this chapter, the literature is reviewed and discussed trying to elucidate if some of the two processes prevails, how the presence of chemical reactions can be elucidated and which properties, specific from the chemical processes, can be exploited. Different electrochemical responses and theories trying to explain those responses are discussed. The separation and quantification methodologies of the capacitive and Faradaic components involved in some electrochemical responses from CNTs are presented.

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Correction for ‘Metal-functionalized covalent organic frameworks as precursors of supercapacitive porous N-doped graphene’ by Jorge Romero et al., J. Mater. Chem. A, 2017, 5, 4343–4351.

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