Biomedical Engineering Reference
In-Depth Information
shapes, their properties can be engineered and they can potentially be integrated with microelec-
tromechanical system (MEMS) sensors to produce smart actuators. Unfortunately, the materials that
have been developed so far still exhibit low conversion efficiency and are not robust; besides there are
no standard commercial materials available for consideration in practical applications. To be able to
take these materials from the development phase to application as effective actuators, it is necessary
to adequately establish the field infrastructure (Bar-Cohen, 2004).
In recent years, significant progress has been made in the field of EAP towards making practical
actuators, and commercial products are beginning to emerge. The first milestone product, a
biomimetic device in the form of a fish-robot, was announced by Eamax, Japan, at the end of
2002. Moreover, a growing number of organizations are exploring potential applications for EAP
materials, and cooperation across disciplines is helping overcome related challenges. The mech-
anisms and devices that are being considered or developed are applicable to aerospace, automotive,
medical, robotics, exoskeletons, articulation mechanisms, entertainment, animation, toys, clothing,
haptic and tactile interfaces, noise control, transducers, power generators, and smart structures.
Some of the biologically inspired applications of EAP are discussed in the following section.
10.5.1
Artificial Organs and Other Medical Applications
Considering the use of EAP for artificial organs requires addressing a number of challenges. These
challenges include biological compatibility — avoiding rejection — and ability to meet the
stringent functional requirements to operate as organ replacements. Currently, electronic EAP
materials seem to be most applicable since they are highly robust and they generate the largest
actuation forces. However, the required voltage range — from hundreds to thousands of voltage —
presents concerns. Even though the electric current is relatively low, the use of high voltage levels
can cause such dangers as producing blood clots or injury due to potential voltage breakdown and
short circuits in the body. On the other hand, the ionic group of EAP materials is chemically
sensitive requiring careful protection. It is also difficult to maintain their static position, particularly
for the IPMC, because these materials involve chemical reaction and even DC voltage causes a
reaction.
Interfacing between human and machine to complement or substitute our senses may enable
important capabilities for medical applications. A number of such interfaces have been investigated
or considered. Of notable significance in this area is the ability to interface machines and the human
brain. A development by scientists at Duke University (Wessberg et al., 2000; Mussa-Ivaldi, 2000)
enabled this possibility where electrodes were connected to the brain of a monkey, and using brain
waves, the monkey operated a robotic arm, both locally and remotely via the Internet. Success in
developing EAP-actuated robotic arms with the strength and dexterity to win a wrestling match
against a human opponent (Bar-Cohen, 2004) can greatly benefit from this interface development by
neurologists. Using such a capability to control prosthetics would require feedback to allow the
human operator to ''feel'' the remote or virtual environment at the artificial limbs. Such feedback can
be provided with the aid of tactile sensors, haptic devices, and other interfacing mechanisms. Besides
providing feedback, sensors will allow users to protect the prosthetic from potential damage (heat,
pressure, impact, etc.) just as we do our biological limbs. The development of EAP materials that can
provide tactile sensing is currently under way as described in (Bar-Cohen, 2004).
The growing availability of EAP materials that exhibit high actuation displacement and force is
opening new avenues to bioengineering in terms of medical devices for diagnosis, treatment, and
assistance to humans in overcoming different forms of disability. Applications that are currently
being considered include catheter steering mechanism (Della Santa et al., 1996), vein connectors for
repair after surgery (Jager et al., 2000; http://www.micromuscle.com/1024.htm), smart prosthetics
(Herr and Kornbluh, 2004), Braille displays (Bar-Cohen, 2004), and others. Recent research at the
Sungkyunkwan University, Korea, has led to the development of a series of mechanisms and devices
that use dielectric elastomer EAP (Jung et al., 2004). These devices include a smart pill, a tube-like
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