12 Chemical Robots

A wide variety of soft actuators have been studied with the progress of the intelligent materials. Especially, stimuli-responsive polymers and gels which swell or shrink in response to the environmental changes such as temperature (Hirokawa & Tanaka, 1984), electric field (Tanaka et al., 1984), light (Suzuki & Tanaka, 1990)], etc have been applied to the actuation devices. In previous decades, researchers have demonstrated an energy conversion system transforming chemical energy into mechanical energy using collagen fibers (Tanaka et al., 1950). And also, since volume phase transition of gels was found, many kinds of applications such as, robotic hands (Hu et al., 1995), and matter transporting device (Yeghiazarian et al., 2005), have been studied in various fields. The phase transition of polymer gel is induced by hydrogen bonds, coulomb, hydrophobic and van der Waals interactions. Thus, by changing the external physicochemical conditions, these applications can be realized. For major example, poly(N-isopropylacrylamide) (PNIPAAm) is wellknown to a thermo-sensitive polymer gel and exhibits a discontinuous volume change. In application, a microfluidic device using MEMS technology and PNIPAAm, could adsorb proteins from solution and release them due to the adsorption change of PNIPAAm by controlling resistive heating (Huber et al, 2003). Recently, there are numbers of studies on robotics with intelligent materials (Otake et al, 2002). However, these systems need complex and fabricated circuits or external control devices because the function of the polymer gel is driven by on-off switchings of external physicochemical signals. On the other hand, in biological systems, there are several autonomic phenomena exhibiting spontaneous motion without any on-off switching of external stimuli such as peristaltic motion, heartbeat, brain waves, etc. If such system is to be achieved in an artificial system, a novel actuation device which does not depend on external control would be expected. Therefore, this novel system is a kind of molecular computing and which we call “Chemical Robotics.” There is no need for the conventional mechanical assembly, wiring, and the electric source because the system is a self-organized system, which performs a chemical signal processing to control a chemomehcanical body like a biological system. However, there are few reports realizing such autonomous systems. As an attempt using cardiac muscle cells and synthetic polymers, researchers have demonstrated a self-walking bioactuator driven by the ATP solution (Feinberg et al, 2007). Although utilization of biopolymer or cell system is one possible way, our aim is to realize a completely artificial system.