Credit: Marc Miskin, University of
Pennsylvania
Researchers
at the University of Pennsylvania and University of Michigan have created the
world's smallest fully programmable, autonomous robots: microscopic swimming
machines that can independently sense and respond to their surroundings,
operate for months and cost just a penny each.
Barely visible to the naked eye, each
robot measures about 200 by 300 by 50 micrometers, smaller than a grain of
salt. Operating at the scale of many biological microorganisms, the robots
could advance medicine by monitoring the health of
individual cells and manufacturing by helping construct microscale devices.
Powered by light, the robots carry
microscopic computers and can be programmed to move in complex patterns, sense
local temperatures and adjust their paths accordingly.
Described in Science Robotics and Proceedings
of the National Academy of Sciences, the robots operate without tethers, magnetic fields
or joystick-like control from the outside, making them the first truly
autonomous, programmable robots at this scale.
"We've made autonomous robots
10,000 times smaller," says Marc Miskin, Assistant Professor in Electrical
and Systems Engineering at Penn Engineering and the papers' senior author.
"That opens up an entirely new scale for programmable robots."
Credit: Michael Simari, University of
Michigan
Breaking the sub-millimeter barrier
For decades, electronics have
gotten smaller and smaller, but robots have struggled to keep pace.
"Building robots that operate independently at sizes below one millimeter
is incredibly difficult," says Miskin. "The field has essentially been
stuck on this problem for 40 years."
The forces that dominate the human
world, like gravity and inertia, depend on volume. Shrink down to the size of a
cell, however, and forces tied to surface area, like drag and viscosity, take
over. "If you're small enough, pushing on water is like pushing through
tar," says Miskin.
In other words, at the microscale,
strategies that move larger robots, like limbs, rarely succeed. "Very tiny
legs and arms are easy to break," says Miskin. "They're also very
hard to build."
So the team had to design an
entirely new propulsion system, one that worked with—rather than against—the
unique physics of locomotion in the microscopic realm.
Credit: Lucas Hanson and William
Reinhardt, University of Pennsylvania
Making the robots swim
Large aquatic creatures, like fish,
move by pushing the water behind them. Thanks to Newton's Third Law, the water
exerts an equal and opposite force on the fish, propelling it forward.
The new robots, by contrast, don't
flex their bodies at all. Rather, they generate an electrical field that nudges
ions in the surrounding solution. Those ions, in turn, push on nearby water
molecules, animating the water around the robot's body.
"It's as if the robot is in a
moving river," says Miskin, "but the robot is also causing the river
to move."
The robots can adjust the
electrical field that causes the effect, allowing them to move in complex
patterns and even travel in coordinated groups, much like a school of fish, at
speeds of up to one body length per second.
And because the electrodes that
generate the field have no moving parts, the robots are extremely durable.
"You can repeatedly transfer these robots from one sample to another using
a micropipette without damaging them," says Miskin. Charged by the glow of
an LED, the robots can keep swimming for months on end.
Credit: Maya Lassiter, University of
Pennsylvania
Giving the robots brains
To be truly autonomous, a robot
needs a computer to make decisions, electronics to sense its surroundings and
control its propulsion, and tiny solar panels to power everything, and all that
needs to fit on a chip that is a fraction of a millimeter in size. This is
where David Blaauw's team at the University of Michigan came into action.
Blaauw's lab holds the record for
the world's smallest computer. When Miskin and Blaauw first met at a
presentation hosted by the Defense Advanced Research Projects Agency (DARPA)
five years ago, the pair immediately realized that their technologies were a
perfect match.
"We saw that Penn
Engineering's propulsion system and our tiny electronic computers were just
made for each other," says Blaauw. Still, it took five years of hard work
on both sides to deliver their first working robot.
The robot has a complete onboard
computer, which allows it to receive and follow instructions autonomously.
Credit: Miskin Lab, Penn Engineering; Blaauw Lab, University of Michigan
"The key challenge for the
electronics," says Blaauw, "is that the solar panels are tiny and
produce only 75 nanowatts of power. That is over 100,000 times less power than
what a smart watch consumes."
To run the robot's computer on such
little power, the Michigan team developed special circuits that operate at
extremely low voltages and bring down the computer's power consumption by more
than 1000 times.
Still, the solar panels occupy the
majority of the space on the robot. Therefore, the second challenge was to cram
the processor and memory to store a program in the little space that remained.
"We had to totally rethink the
computer program instructions," says Blaauw, "condensing what
conventionally would require many instructions for propulsion control into a
single, special instruction to shrink the program's length to fit in the
robot's tiny memory space."
Robots that sense, remember and react
What these innovations made
possible is the first sub-millimeter robot that can actually think. To the
researchers' knowledge, no one has previously put a true computer—processor,
memory and sensors—into a robot this small. That breakthrough makes these devices
the first microscopic robots that can sense and act for themselves.
The robots, each smaller than a grain of salt,
move by using an electrical field to manipulate the ions around them. They can
sense temperatures, and could potentially advance medicine by monitoring the
health of individual cells. Credit: Bella Ciervo, Penn Engineering
The robots have electronic sensors
that can detect the temperature to within a third of a degree Celsius. This
lets robots move towards areas of increasing temperature, or report the
temperature—a proxy for cellular activity—allowing them to monitor the health
of individual cells.
"To report their temperature
measurements, we designed a special computer instruction that encodes a value,
such as the measured temperature, in the wiggles of a little dance the robot
performs," says Blaauw. "We then look at this dance through a
microscope with a camera and decode from the wiggles what the robots are saying
to us. It's very similar to how honey bees communicate with each other."
The robots are programmed by pulses
of light that also power them. Each robot has a unique address that allows the
researchers to load different programs on each robot. "This opens up a
host of possibilities," adds Blaauw, "with each robot potentially
performing a different role in a larger, joint task."
Only the beginning
Future versions of the robots could
store more complex programs, move faster, integrate new sensors or operate in
more challenging environments. In essence, the current design is a general
platform: its propulsion system works seamlessly with electronics, its circuits
can be fabricated cheaply at scale and its design allows for adding new
capabilities.
"This is really just the first
chapter," says Miskin. "We've shown that you can put a brain, a
sensor and a motor into something almost too small to see, and have it survive
and work for months. Once you have that foundation, you can layer on all kinds
of intelligence and functionality. It opens the door to a whole new future for
robotics at the microscale."
Provided by University of Pennsylvania
by Ian Scheffler, University of Pennsylvania
edited
by Gaby
Clark, reviewed by Robert Egan
Source: Researchers
create world's smallest programmable, autonomous robots
