- Feb 2021
The liquids can be colored with dyes or pigments and heated/cooled to change the color of the microfluidic networks in the visible and IR spectrum
To create blue or red dyes, researchers mixed chemical compounds, methylene blue or amaranth, with water. They also used watercolor paints to create other colors. These solutions helped to camouflage their device.
To change the temperature of the liquids, the researchers would heat or cool them inside an oven or refrigerator before pumping them into the device. This allowed researchers to adjust how the robot is viewed in the infrared spectrum (IR). The IR spectrum reflects the temperature of the emitting body.
pumping colored or temperature-controlled fluids through a network of microfluidic channels
The researchers pumped fluids through the microchannels, manually with syringes or with the use of syringe pumps.
Syringe pumps gradually administer, or withdraw, liquid solutions: https://www.chemyx.com/support/knowledge-base/technical-support/chemyx-syringe-pump-work/
By pumping fluids through the microchannels, researchers could change the color and display of the device.
closely packed microfluidic channels (Fig. 1) or combined microfluidic channels with wider (millimeters to centimeters) channels (fig. S1D) to create features that are indistinguishable from continuous color in the far field
The researchers created color layers with different sized microchannels to change the appearance of the soft robot. Wider microchannels allowed for larger blocks of color to be observed. Whereas smaller microchannels allow for many sharp edges and transitions to be created.
They want readers to realize that many different color-layered microchannel networks can be created to alter how the device may be perceived.
once filled, the color layers require no power, have low requirements for volume of fluid (~30 μL/cm2 of surface), and are lightweight (130 mg/cm2 of surface)
The total volume of the microchannels used in the color layers equates to 0.75 ml, which is similar to a large drop of water. Therefore, they do not require much water to be filled and are lightweight. Once the robot is filled with liquid, via syringe pumps, no further input is needed.
creating a color layer with periodic microfluidic channels filled with colors matched to that environment
Here, researchers filled only certain microfluidic channels up with a certain color, in order to mimic the background the robot was resting upon. This form of camouflage is called background mimicking. Researchers wanted to see if this soft robot was capable of background mimicking.
In anatomy, our devices could simulate fluid vessels and muscle motion for realistic modeling or training
Next Generation Science Standards Disciplinary Core Idea ETS2.B: Influence of Engineering, Technology, and Science on Society and the Natural World
"How do science, engineering, and the technologies that result from them affect the ways in which people live? How do they affect the natural world?" (page 212)
AP Physics 2 Learning Standard: "Essential Knowledge 2.C.1: "The magnitude of the electric force F exerted on an object with electric charge q by an electric field E is F = qE. The direction of the force is determined by the direction of the field and the sign of the charge, with positively charged objects accelerating in the direction of the field and negatively charged objects accelerating in the direction opposite the field. This should include a vector field map for positive point charges, negative point charges, spherically symmetric charge distributions, and uniformly charged parallel plates" (page 33).
AP Biology Essential knowledge 3.E.2: Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses.
AP Biology: Curriculum Framework 2012–2013, (page 62 and page 90): https://secure-media.collegeboard.org/digitalServices/pdf/ap/10b_2727_AP_Biology_CF_WEB_110128.pdf
In all demonstrations, the colored solutions were prepared manually by the operator
Researchers mixed different colored dyes together in order to create different colored solutions. Then, they would place these colored solutions into a pump to be administered into the color layer microchannels of the soft robot.
Using a pumping rate of 2.25 mL/min and neglecting the time necessary to fill the tether, a change in color required 30 s
Here, researchers are filling the color layers up with liquid using a pump. The rate at which liquid is being pumped into the microchannels is 2.25 milliliters (ml) per 1 minute (min). The researchers want to demonstrate that their device can change colors rather quickly and, therefore, show that their device is capable of being used for camouflage.
Although 2.25ml/min may seem like a slow pumping rate, the total volume of the microchannels used in the color layers equates to 0.75 ml, which is similar to a large drop of water. Therefore, it is very reasonable for the microchannels to be filled in 30 seconds (s) with a pumping rate of 2.25ml/min.
The authors excluded the time it took to fill the “tether” when performing this experiment. The tether is simply the tubing that connects the pump to the microchannel. Liquid travels from the pump, through the tether, and into the microfluidic channel.
Because researchers only wanted to know the time it took for the microchannels to change colors within the color layers, they excluded the time needed for the tether to fill with liquid.
soft robotic quadrupedal “walker”
A soft robotic quadrupedal is a type of soft robot that has four appendages. These appendages can be contracted using a pneumatic network to allow for maneuverability.
Thermoelectrics can change the IR signature, and electronic displays can change the visible color, but neither technology has control over both IR and visible coloration
Thermoelectrics convert heat into electrical energy. Electrical energy can be measured. Researchers can then use this information to decided how to change the IR signature. Electronic displays are devices that display images for visualization electronically, like a television. Each of these technologies, thermoelectrics and electronic displays, work independently. Electronic displays have no control over temperature. Meanwhile, thermoelectrics cannot display images.
Here, the author is demonstrating the novelty of his work. Rather than integrating both thermoelectrics and electronic displays onto the robot, a liquid network can do the work of each technology, greatly simplifying the soft robotic design.
The liquids used in the microfluidic channels of the device can be colored and heated (or cooled). Therefore, both temperature and color can be controlled simultaneously using one methodology.
mechanical actuation results from pneumatic pressurization and inflation of an independent network of microchannels (pneu-nets) embedded in highly extensible elastomers (6, 7)
Pneumatic networks, also known as PneuNets, are commonly used in soft robotics to illicit movement. Pneumatic simply means to operate by air or gas under pressure. PneuNets are networks of small channels embedded into soft robots that can be inflated or deflated with pressurized air to allow for maneuverability.
Here, researchers created two independent sets of microchannels inside of the robot. One set is filled with air and functions as the PneuNet, allowing the robot to move. The other set is filled with liquid and changes the color or temperature of the device; this set does not facilitate movement.
This link provides videos that demonstrate how a PneuNet functions: https://softroboticstoolkit.com/book/pneunets-bending-actuator