Page 520 - Handbook of Biomechatronics

Bioinspired and Biomimetic Micro-Robotics for Therapeutic Applications 513

The ultimate task for these micro-devices is to perform inside the human
body, such as in the bloodstream where there will be a flow in the back-
ground with a possible sinusoidal velocity component because of the heart-
beat. Therefore, at this point, it is appropriate to mention a simulation-based
control study addressing this very scenario: Sadelli et al. (2017) devised a
control strategy to that effect, although the authors were only considering
a magnetic robot of a spherical body for sake of simplicity. However, authors
modeled magnetic forces, contact forces, gravitational attraction, viscous
drag, and electrostatic forces together to represent the problem as accurate
as possible. Blood flow was predicted by an observer and with the help of
biophysical properties of the flow based on prior knowledge. Trajectory
control was implemented with mean-value theorem based on the
backstepping controller scheme. Authors also provided the state-space rep-
resentation of such a system after some mathematical steps. The blood flow,
indeed, is not easy to predict online for control studies, although fluid flow
in confined spaces is expected to affect the resistance matrix (Happel and
Brenner, 1965) of micro-swimmers. Although details of position and veloc-
ity control of such systems are beyond the scope of this text, at this juncture,
the reader is urged to refer to “system dynamics and control” texts to be
familiarized with the necessary terms, for example, such as observers, con-
trollers, feedback and feed-forward loops, tuning, and state-space represen-
tations, if not experienced in the control theory and applications.
Finally, it is of utmost importance to strongly emphasize that the control
input should be generated while observing the patient’s safety at all times.
The second highest concern is to see to it that the robotic system remains
intact during operation as losing the micro-swimmer will probably not be
a desirable scenario. One cannot just apply any arbitrary control signal with-
out knowing the physical limits of the end-effector and the restrictions of the
environment. To that effect, especially, if the end-effector will be actuated
or steered by means of the external intervention of a computer- or human-
controlled scheme, the meticulous design of the entire robotic system
coupled with its surroundings will determine what can and what cannot
be done without putting the patient and the end-effector in a risky situation.

5 EPILOG: FUTURE DIRECTIONS
The ultimate goal of this intriguing field of mechatronics is to help
patients and medical doctors to improve the quality of medicine and quality
of life by providing an alternative and reliable therapeutic tool of highly