Muscles artificial

Chemically active plastics such as the polyelectrolytes have been used to make artificial muscle materials. This is an unusual type of mechanical power device that creates motion by the lengthening and shortening of fibers made from a chemically active plastic by changing the composition of the surrounding liquid medium, either directly or by the use of electrolytic chemical action. Obviously this form of mechanical power generation is no competitor to thermal energy sources, but it is potentially valuable in detector equipment that would be sensitive to the changing... 

By using direct mechanical action from the artificial muscle, it would be possible to produce reliable sensing and control devices without electrical and electronic equipment. Another interesting application would be to drive prosthetic devices where the action would be similar to the muscle reaction in the body. This unusual type of chemically induced motion should be an interesting one to explore for the solution of unusual problems where conventional approaches do not work. 

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

Figure 20. Artificial muscle under work. In reduction (A) electrons are injected into the polymer chains. Positive charges are annihilated. Counter-ions and water molecules are expelled. The polymer shrinks and compaction stress gradients appear at each point of the interface of the two polymers. The free end of the bilayer describes an angular movement toward the left side. (B) Opposite processes and movements occur under oxidation. (Reprinted from T. F. Otero and J. Rodriguez, in Intrinsically Conducting Polymers An Emerging Technology, M. Aldissi, ed., pp. 179-190, Figs. 1,2. Copyright 1993. Reprinted with kind permission of Kluwer Academic Publishers.)...

Figure 23. Artificial muscle formed by a three-layer polypyrrole-nonconducting tape-polypyrrole. The consumed charge works two times in this device when polypyrrole I is oxidized (anodic process), pushing the free end of the layer, polypyrrole II is reduced (cathodic process), trailing the layer. Stresses at the polymer/polymer interfaces are summarized in the box. (Reprinted from Handbook of Organic Conductive Molecules and Polymers, H. S.Nalwa,ed., Vol. 4,1997, Figs. 10.13,10.15a, 10.18,10.36. Reproducedwithpermission of John Wiley Sons, Ltd., Chichester, UK.)...

Figure 25. Movement rate of bilayer devices (along an angle of 90°) with different dimensions (different polypyrrole weights) versus applied electrical current per mass unit (mA mg ). (Reprinted fromT. F. Otero and J. M. Sansinana, Bilayerdimensions and movement of artificial muscles. Bioelectrochem. Bioener-genetics 47, 117, 1997, Fig. 4. Copyright 1997. Reprinted with permission from Elsevier Science.)...

We are able to construct mechanical arms that reproduce movements quite close to those performed by the human arm. The problem in implanting these arms is that movements have to be coordinated with all the other body movements under the brain s direction. There is one possibility for connecting the electronic systems of the artificial arm to the nervous signals (Fig. 33) coming from the brain in order to obtain coordinated movements separate those signals into different components and amplify every component to drive an artificial muscle or electric motor. 

Theoretical models available in the literature consider the electron loss, the counter-ion diffusion, or the nucleation process as the rate-limiting steps they follow traditional electrochemical models and avoid any structural treatment of the electrode. Our approach relies on the electro-chemically stimulated conformational relaxation control of the process. Although these conformational movements179 are present at any moment of the oxidation process (as proved by the experimental determination of the volume change or the continuous movements of artificial muscles), in order to be able to quantify them, we need to isolate them from either the electrons transfers, the counter-ion diffusion, or the solvent interchange we need electrochemical experiments in which the kinetics are under conformational relaxation control. Once the electrochemistry of these structural effects is quantified, we can again include the other components of the electrochemical reaction to obtain a complete description of electrochemical oxidation. 

In general, those properties of industrial interest that are related to the electrochemical rates change several orders of magnitude when the conditions of synthesis are improved and when a solvent suitable for the specific application is used to produce the polymeric gel. We found this to be the case in our laboratory between the first and second generation of artificial muscles, with electrochromic films, or with specific energies. 

Collagen fibers, three dimensional, their part in artificial muscles, (Kuhn et al), 359... 

Katchalsky and Flory, work on artificial muscles, 359 Kinetics... 

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

FIGURE 10.13 Basic mechanism of dielectric elastomer actuator (DEA) generator. (From Kombluh, R., Power from plastic How electroactive polymer artificial muscles will improve portable power generator in tbe 21st century military, Presented at TRI-Service Power Expo, Norfolk, Virginia, July 2003. With permission.)... 

Kombluh, R., Pelrine, R., Pei, Q., and Shastri, S.V. Electroactive Polymer (EAP) Actuators as Artificial Muscles. Reality, Potential and Challenges, First edition, SPIE— the International Society for Optical Engineering, Bellingham, Washington, 2001, Chapter 16. 

Larsen, P.S., Artificial muscles, demonstrated on the website http /www.risoe.dk/lys-artmus/MIC-ARTI. pdf... 

Kombluh, R.D., Flamm, D.S., Vujkovic-Civijin, P., Pelrine, R.E., and Huestis, D., Large fight weight mirrors control by dielectric elastomer artificial muscle, AAS 200 meeting, Albuquerque, NM, June 2002, Paper no. 63-06. 

Shahinpoor, M., Elastically-activated artificial muscles made with liquid crystal elastomers. Proceedings of SPIE 7th Annual International Symposium of Smart Structures and Materials, EAPAD Conf, 3987, pp. 187-192, 2000. 

M Suzuki, O Hirasa. An approach to artificial muscle using polymer gels formed by microphase separation. Adv Polym Sci 110 241-261, 1993. 

The model of electric field-controlled artificial muscles has been described in 1972 [5], Fragala et al. fabricated an electrically activated artificial muscle system which uses a weakly acidic contractile polymer gel sensitive to pH changes. The pH changes are produced through electrodialysis of a solution. The response of the muscle as a function of pH, solution concentration, compartment size, certain cations, and gel fabrication has been studied. The relative change in length was about 10%, and the tensile force was 1 g/0.0025 cm2 under an applied electric field of 1.8 V and 10 mA/cm2. It took 10 min for the gel to shrink. 

A new composite PVA hydrogel for an artificial muscle has been prepared by a freezing and thawing method [71]. The gel contained PAA and PAAm.HCl (poly-allylamine hydrochloride). The electrocontractile behavior of the composite gel in various solutions was studied. A large stroke and better controllability have been detected in a 10 mM NaOH/7 mM Ba(OH)2 system. 

In addition to their potential use as structural composites, these macroscopic assemblies of nanocarbons have shown promise as mechanical sensors [83], artificial muscles [84], capacitors [85], electrical wires [59], battery elements [85], dye-sensitized solar cells [86], transparent conductors [87], etc. What stands out is not only the wide range of properties of these type of materials but also the possibility of engineering them to produce such diverse structures, ranging from transparent films to woven fibers. This versatility derives from their hierarchical structure consisting of multiple nano building blocks that are assembled from bottom to top. 

---