Polymer Microactuators

Actuators that generate movements and forces, such as bending, expansion and contraction driven by stimulation of electrical, chemical, thermal and optical energies, are different from rotating machines such as electric motors and internal combustion engines. There are many sorts of soft actuators made of polymers [1-3], gels [4] and nanotubes [5]. Particularly, biomimetic actuators are interesting because of the application to artificial muscles that will be demanded for medical equipment, robotics and replacement of human muscle in the future. 

In fact, films, fibres or blocks of conducting polymer expand and contract upon electrochemical oxidation and reduction [1, 2, 11-16], respectively. This process is 

In this section, the behaviour of the electrolytic expansion in conducting polymers, especially polyaniline and poly(o-methoxyaniline) (PMAN) are described, with discussion of the basic redox reaction of polyaniline, the dependence of the expansion ratios on oxidation levels, the kind of anions, strain, the pH of the electrolyte and anisotropy. 

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E.W.H. Jager, O. Inganas, and I. Lundstrom, Perpendicular actuation with individually controlled polymer microactuators, Adv. Mater., 13 (1), 76-79 (2001). 

The fundamentals of electrolytic expansion in polyaniline films have been discussed. Ion insertion and exclusion by electrolytic oxidation and reduction are the primary mechanisms. However, it is also evident that the changes in molecular conformations, arising due to the delocalisation of 7t-electrons and the electrostatic repulsion between the polycations, are other mechanisms operating in a conducting polymer microactuator. By investigating the molecular structure and the higher order structure to optimise the electrolytic expansion, it should be possible to improve the expansion ratio and the force for practical usage. 

FIGURE 14.10 Conjugated polymer microactuator being hit by a macro-object top row). Actuator working normally afterward (bottom row). (From Smela, E., /. Micromech. Microeng., 9, 1, 1999. With permission.)... 

Conjugated polymer microactuator devices have been reviewed many times previously [120-122], and so this section will give only a brief. For further information, refer to those reviews and the publications referenced therein. 

Because polypyrrole operates in aqueous electrolytes at room temperature, the largest niche for conjugated polymer microactuators is biomedical applications. Commercialization efforts are underway for blood vessel coimectors, a valve to prevent urinary incontinence, and a Braille display [25,122,133]. One area that requires further research is the temperature-dependence of actuator metrics, because for biomedical applications the devices must be operated at 37°C. In PPy(DBS) microactuators, strain increases from room temperature to body temperature by 45%, and they are 250% faster, but the blocked force drops [126]. 

Actuators Current MEMS Actuator Principles Materials Selection Conjugated Polymer Microactuators 14-17... 

Maitland, D.J., Wilson, T., Metzger, M. and Schumann, D.L. (2002) Laser-activated shape memory polymer microactuators for treating stroke. Proceedings of SPIE (The International Society for Optical Engineering), 4626, 394—402. 

As mentioned previously, one of the most important and exciting advantages of conjugated polymer microactuators is the possibility of integrating them into more complex microsystems, such as the cell-based sensors described above. The actuators add the powerful capability of mechanical manipulation of biology on the microscale. This is enabled by their low voltage operation and room temperature microfabrication, and the wide variety of actuator configurations that are possible. 

Alici G, Devaud V, Renaud P, Spinks G (2009) Conducting polymer microactuators operating in air. J Micromech Microeng 19 025017... 

Jager EWH, Masurkar N, Nworah NF, Gaihre B, Alici G, Spinks GM (2013b) Patterning and electrical interfacing of individually controllable conducting polymer microactuators. Sens Actuators B 183 283-289... 

Maziz A et al (2014) Demonstrating kHz frequency actuation for conducting polymer microactuators. Adv Funct Mater 24(30) 4851-4859... 

Alici G, Huynh NN (2007) Performance quantification of conducting polymer actuators for real applications a microgripping system. lEEE/ASME Trans Mechatron 12 73-84 Alici G, Spinks G, Huynh NN, Sarmadi L, Minato R (2007) Establishment of a biomimetic device based on tri-layer polymer actuators - propulsion fins. Bioinspir Biomim 2 S18 Alici G, Devaud V, Renaud P, Spinks G (2009) Conducting polymer microactuators operating in air. J Micromech Microeng 19 025017... 

Martinez JG, Otero TF, Jager EWH (2014) Effect of the electrolyte concentration and substrate on conducting polymer actuators. Langmuir 30(13) 3894-3904. doi 10.1021/la404353z Maziz A et al (2014) Demonstrating kHz frequency actuation for conducting polymer microactuators. Adv Funct Mater p.n/a-n/a. Available at 10.1002/adfm.201400373. Accessed 30 May 2014... 

Small, W., Metzger, M. R, Wilson, T. S., Maitland, D. J. (2005a), Laser-activated shape memory polymer microactuator for thrombus removal following ischemic stroke Preliminary in vitro analysis, IEEE Journal of Selected Topics in Quantum Electronics, 11, 892-901. 

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