Page 491 - Handbook of Biomechatronics

Bioinspired and Biomimetic Micro-Robotics for Therapeutic Applications 485

applications to conduct mechanical waves in certain directions, and for the
realization of stress preloading again as demonstrated in the previously dis-
cussed study. The reader is encouraged to refer to Microsystems Engineering
and Materials Science textbooks for further details of lattice directions and
MEMS manufacturing.
Another interesting MEMS manufacturing technique is demonstrated
by Ghosh and Fischer (2009). Authors used “glancing-angle deposition,”
that is, a method relying on changing the incident angle of the targetted
substrate, which is depicted in Fig. 8, during material deposition of sili-
cone dioxide (SiO 2 ) hence generating 3D helices perpendicular to the
Si-wafer. The resultant tails are only a few micrometers in length, thus
much smaller than an average blood cell. After, the tails are freed from
the surface by the method of sonication followed by cobalt deposition
by thermal evaporation. Hence, they have ferromagnetic property
required to be actuated by EM coil pairs generating rotating homoge-
neous magnetic field.
MEMS-based manufacturing is also used for generating elastic filaments
as demonstrated by Williams et al. (2014). Authors used capillary forces, that
is, “capillary draw,” to fill the high aspect-ratio mold, which is etched by pho-
tolithography on Si-wafer, with liquid PDMS. The dried filament can be

Fig. 8 Glancing angle deposition of source material on the target substrate. Ions are
removed from the source under vacuum or by excitation by inert gas molecules. The
required energy to remove ions from the surface of the source could be obtained from
a direct-current (DC) electric field or radio frequency (RF) power transmission. The mate-
rial will eventually deposit on the substrate. This method is generally known as
sputtering. Furthermore, if the target is rotated in one or more axes than the incident
ions will deposit on the substrate forming high aspect ratio geometries overtime, rather
than forming a homogenous layer of coating (Ghosh and Fischer, 2009).