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262 Biomimetics: Biologically Inspired Technologies

strategies must also be devised to control the force and power output of muscle, in the context of
robotic systems, through the modulation of electrical pulses to the muscle cell. Also, for the
development of controllable, adaptive and robust biomechatronic systems, feedback control sys-
tems that monitor and adapt the mechanical, electrical, and chemical environment of muscle
actuators are of critical importance.

9.12 CONCLUDING REMARKS

Muscle tissue as a mechanical actuator has great, though as-yet unrealized potential for use
in engineered systems. Synthetic technologies such as electroactive polymers are rapidly emerging
as quantitatively functional equivalents to muscle tissue, and it is likely that the technological
evolution of EAP muscles will soon out-pace the natural functional evolution of living muscle
tissue. This means that the quantitative performance advantages that muscle tissue has over some
forms of synthetic actuators in terms of efficiency, power density, and so forth are not likely to
remain the case for very much longer. One then invariably must ask why it is advantageous to even
consider the use of living muscle tissue as a mechanical actuator. It is easy to point out that the
many disadvantages of muscle outweigh the few performance advantages it may have. The answer
lies chiefly in the qualitative differences between muscle and competing synthetic actuator tech-
nologies, among these are those qualities that arise from muscle being a living tissue: its ability to
functionally adapt and to potentially integrate seamlessly with other living structures. So it is likely
that living muscle actuators will only be employed in practical systems where their qualitative
advantages as living tissue can be exploited to maximum benefit, such as in hybrid biomechatronic
prosthetic systems and implants, and perhaps in bioreactors where their biological products (such as
edible proteins) are of primary importance. Certainly though, living muscle tissue serves as the
explicit benchmark against which the performance of synthetic actuator technologies will be
evaluated for many decades to come.

FURTHER READING

The following list of papers and book chapters comprises a set of useful references for further work in this area.
These were not referenced directly in the text, but have been included because the authors have found them to
be useful during the course of the development of the technology discussed in this chapter.

Agoram, B. and Barocas, V.H. Coupled macroscopic and microscopic scale modeling of fibrillar tissues and
tissue equivalents. J. Biomech. Eng. 2001, 123(4): 362–369.
Askew, G.N., Marsh, R.L. et al. The mechanical power output of the flight muscles of blue-breasted quail
(Coturnix chinensis) during take-off. J. Exp. Biol. 2001, 204: 3601–3619.
Barrett, S. Propulsive Efficiency of a Flexible Hull Underwater Vehicle. PhD Thesis, Massachusetts Institute
of Technology, Cambridge, Massachusetts, 1996.
Biewener, A.A., Dial, K.P. et al. Pectoralis muscle force and power output during flight in the starling. J. Exp.
Biol. 1992, 164: 1–18.
Broadie, K.S. Development of electrical properities and synaptic transmission at the embryonic neuromuscular
junction. Neuromuscular Junctions Drosophila 1999, 43: 45–67.
Brown, K.J. et al. A novel in vitro assay for human angiogenesis. Lab. Invest. 1996, 75(4): 539–555.
Calve, S., Arruda, E., Dennis, R.G., and Grosh, K. Influence of mechanics on tendon and muscle development.
WCCM Abstracts, 2002.
Campbell, P.G., Durham, S.K., Hayes, J.D., Suwanichkul, A., and Powell, D.R.. Insulin-like growth factor-
binding protein–3 binds fibrinogen and fibrin. J. Biol. Chem. 1999, 274(42): 30215–30221.
Cederna, P.S., Kalliainen, L.K., Urbanchek, M.G., Rovak, J.M., and Kuzon, W.M. ‘‘Donor’’ muscle structure
and function following end-to-side neurorrhaphy. Plast. Reconstr. Surg. 2001, 107: 789–796.