Appel 43.1 - Micro

when it defies gravity. Together laminar flow and capillary
forces allow for ideal dispersion and faster diffusion.
Using these principles, chemists and biologists developed
complex microfluidic circuits and measuring devices, like
blood glucose meters and pregnancy tests.
Unfortunately, many of these scientists were too preoccupied
with this microfluidic technology. They neglected
to produce research with commercial or practical applications.
Currently, microfluidics are experiencing a revival
thanks to a close collaboration between new generations
of scientists and engineers.
HOW MICROFLUIDICS CAN BE AP-
PLIED IN A SOFT ROBOT?
design, pressure opens and closes the gates. This controls
whether or not a microfluid can pass through.
This year researchers from the Chonnam National University,
South Korea, published a paper on a new concept
of a 3D slope valve which precisely controls fluid flow.
Through either improvement of functions or revision of
control of microfluidic circuits, researchers are now working
tirelessly to replicate functions of integrated electric
circuits (IECs) into integrated microfluidic circuits (IMCs).
Depending on the amount of programmable actions, soft
robots will be able to sense, move, and interact with their
surroundings.
CONTROL
A recent result of this collaboration has been an introduction
of microfluidics into some soft robotics devices.
In 2016, Harvard presented the first entirely autonomous
soft robotics device, an octopus shaped robot named Octobot.
Microfluidics powered, controlled, and actuated it.
Octobot did not look too phenomenal and its tentacles appeared
to rather twinge than produce a smooth motion,
but it was a start nevertheless.
A complete integration of fully microfluidic control is a
reason why this was such a prominent project. Microfluidics
and regular fluids are a good source for smooth and
compliant movement of a robot. For example changing
pressure can alter the shape of the silicon (or another soft
material), so there is nothing groundbreaking there. However,
prior to Cctobot, the traditional control of these
motions was done via hard electronics and batteries or
other external connections. Naturally, use of rigid electronics
significantly reduces the compliant behavior of
robots and, therefore, their effectiveness.
Beginning with fuel storage and ending with actuation, all
tasks are done via microfluidics within the Octobot. The
power comes from the chemical reaction which explodes
liquid fuel into a gas. This gas fills 3D printed cavities of
the silicon based body, which expands them, causing respective
twitching. The brain of Octobot is a microfluidic
logic circuit, and it controls when the chemical reaction
should take place. This microfluidic circuit functions similarly
to an electronic oscillator where the inductor and
capacitor exchange energy creating an alternating current.
The exchange continues until the robot runs out of
fuel, and friction within channels decreases the current
to zero. According to the Nature Magazine, one milliliter
of the liquid can support Octobot for around 8 minutes [6].
Research to increase and improve functions of a microfluidic
circuit, and thus expanding what it can actually do,
is an ongoing process.
Back in 2011, a group from the University of Michigan,
USA, proposed a design of an elastomeric valve based system
which functions as a self regulating circuit. In the
MANUFACTURING
Two years after the release of Octobot, the same team
from Harvard presented another eight legged silicon
creature, a peacock spider. This soft robot combined microfluidic
control with newly developed microfabrication
techniques to achieve a wider range of motion. Not an expanding
gas but dyed water allows it to squat and balance
on its eight colorful legs. With an increased amount of
channels and interwindings, degrees of freedom and complexity
of the movement increase, approaching the ideal
of a muscle.
But, the spider is still far from this ideal. Its body and legs
are made from twelve layers of stacked silicon allowing
for varying stiffness. The channels and their sizes merge
between different layers. Larger cavities span more layers,
for example. When fluid fills one of knee cavities, the
compliant layers expand under the pressure, thus forcing
the leg to bend. The group from Harvard calls this process
injection-induced self-folding. The control of bending the
eight legs allows for a variety of different motions.
There are different ways to create these patterns of cavities
and channels. The industry standard for many years
has been soft lithography. Simply put, this process transfers
the pattern on a photomask to the surface of a silicon
wafer using UV light. There are many steps and preparation
procedures in this process. The main steps are: (1)
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DE APPEL