RT/ New soft robot material to morph from ground to air vehicle using liquid metal
Robotics biweekly vol.45, 9th February — 23rd February
TL;DR
- Researchers have developed a new approach for shape-changing at the material level. They use rubber, metal, and temperature to morph materials and fix them into place with no motors or pulleys.
- Soft robots have received much attention recently due to their adaptability and safety. However, the fluidic systems used in these robots continue to use pumps that are large, heavy, and noisy. Now, researchers report a fluid pump driven by electrochemical reactions that are simple, lightweight, silent, and enable self-sensing actuation, with potential applications in wearable technology and touch display devices.
- Scientists have developed self-healing, biodegradable, 3D-printed materials that could be used in the development of realistic artificial hands and other soft robotics applications. The low-cost jelly-like materials, developed by researchers at the University of Cambridge, can sense strain, temperature and humidity. And unlike earlier self-healing robots, they can also partially repair themselves at room temperature.
- Researchers have shown that solar cells can be used to achieve underwater wireless optical communication with high data rates. The new approach — which used an array of series-connected solar cells as detectors — could offer a cost-effective, low-energy way to transmit data underwater.
- A new study could be a game-changer for users of prosthetic hands who have long-awaited advances in dexterity. Researchers examined if people could precisely control the grip forces applied to two different objects grasped simultaneously with a dexterous artificial hand. They designed a multichannel wearable soft robotic armband to convey artificial sensations of touch to the robotic hand users. Subjects were able to successfully grasp and transport two objects simultaneously with the dexterous artificial hand without breaking or dropping them, even when their vision of both objects was obstructed. The study is the first to show the feasibility of this complex simultaneous control task while integrating multiple channels of haptic/touch sensation feedback noninvasively.
- Researchers at the Max Planck Institute for Intelligent Systems (MPI-IS) have recently developed new light-driven microswimmers that could be more suited for navigating biological systems, including body fluids. These microswimmers, introduced in a paper published in Science Robotics, are simple microparticles based on the two-dimensional (2D) carbon nitride poly(heptazine imide) or PHI.
- A new robotic sensor that mimics the automatic human reaction to heat is being hailed as a world first. The device has been built by a team of experts from Liverpool Hope University, who say it’s the first sensor that can trigger this ‘sensory impulse’ that the robotics community has yet seen.
- Scientists are empowering small, humanoid-sensing robots to take a patient’s blood pressure — using only a simple touch.
- Researchers have made an android child named Nikola that successfully conveys six basic emotions — happiness, sadness, fear, anger, surprise, and disgust. Facial expressions are generated by moving ‘muscles’ in Nikola’s face. This is the first time that the quality of android-expressed emotion has been tested and verified for these six emotions.
- Boston Dynamics put together a behind-the-scenes video of sorts about the Super Bowl commercial they did in collaboration with some beer company or other.
- CMU RI Seminar video by Jessica Burgner-Kahrs from the University of Toronto, Mississauga, on continuum robots.
- Check out robotics upcoming events. And more!
Robotics market
The global market for robots is expected to grow at a compound annual growth rate (CAGR) of around 26 percent to reach just under 210 billion U.S. dollars by 2025.
Size of the global market for industrial and non-industrial robots between 2018 and 2025 (in billion U.S. dollars):
Size of the global market for industrial and non-industrial robots between 2018 and 2025 (in billion U.S. dollars). Source: Statista
Latest News & Research
Shape morphing mechanical metamaterials through reversible plasticity
by Dohgyu Hwang, Edward J. Barron, A. B. M. Tahidul Haque, Michael D. Bartlett in Science Robotics
Imagine a small autonomous vehicle that could drive over land, stop, and flatten itself into a quadcopter. The rotors start spinning, and the vehicle flies away. Looking at it more closely, what do you think you would see? What mechanisms have caused it to morph from a land vehicle into a flying quadcopter? You might imagine gears and belts, perhaps a series of tiny servo motors that pulled all its pieces into place.
If this mechanism was designed by a team at Virginia Tech led by Michael Bartlett, assistant professor in mechanical engineering, you would see a new approach for shape changing at the material level. These researchers use rubber, metal, and temperature to morph materials and fix them into place with no motors or pulleys. The team’s work has been published in Science Robotics. Co-authors of the paper include graduate students Dohgyu Hwang and Edward J. Barron III and postdoctoral researcher A. B. M. Tahidul Haque.
Nature is rich with organisms that change shape to perform different functions. The octopus dramatically reshapes to move, eat, and interact with its environment; humans flex muscles to support loads and hold shape; and plants move to capture sunlight throughout the day. How do you create a material that achieves these functions to enable new types of multifunctional, morphing robots?
“When we started the project, we wanted a material that could do three things: change shape, hold that shape, and then return to the original configuration, and to do this over many cycles,” said Bartlett. “One of the challenges was to create a material that was soft enough to dramatically change shape, yet rigid enough to create adaptable machines that can perform different functions.”
To create a structure that could be morphed, the team turned to kirigami, the Japanese art of making shapes out of paper by cutting. (This method differs from origami, which uses folding.) By observing the strength of those kirigami patterns in rubbers and composites, the team was able to create a material architecture of a repeating geometric pattern.
Next, they needed a material that would hold shape but allow for that shape to be erased on demand. Here they introduced an endoskeleton made of a low melting point alloy (LMPA) embedded inside a rubber skin. Normally, when a metal is stretched too far, the metal becomes permanently bent, cracked, or stretched into a fixed, unusable shape. However, with this special metal embedded in rubber, the researchers turned this typical failure mechanism into a strength. When stretched, this composite would now hold a desired shape rapidly, perfect for soft morphing materials that can become instantly load bearing.
Finally, the material had to return the structure back to its original shape. Here, the team incorporated soft, tendril-like heaters next to the LMPA mesh. The heaters cause the metal to be converted to a liquid at 60 degrees Celsius (140 degrees Fahrenheit), or 10 percent of the melting temperature of aluminum. The elastomer skin keeps the melted metal contained and in place, and then pulls the material back into the original shape, reversing the stretching, giving the composite what the researchers call “reversible plasticity.” After the metal cools, it again contributes to holding the structure’s shape.
“These composites have a metal endoskeleton embedded into a rubber with soft heaters, where the kirigami-inspired cuts define an array of metal beams. These cuts combined with the unique properties of the materials were really important to morph, fix into shape rapidly, then return to the original shape,” Hwang said.
The researchers found that this kirigami-inspired composite design could create complex shapes, from cylinders to balls to the bumpy shape of the bottom of a pepper. Shape change could also be achieved quickly: After impact with a ball, the shape changed and fixed into place in less than 1/10 of a second. Also, if the material broke, it could be healed multiple times by melting and reforming the metal endoskeleton.
The applications for this technology are only starting to unfold. By combining this material with onboard power, control, and motors, the team created a functional drone that autonomously morphs from a ground to air vehicle. The team also created a small, deployable submarine, using the morphing and returning of the material to retrieve objects from an aquarium by scraping the belly of the sub along the bottom.
“We’re excited about the opportunities this material presents for multifunctional robots. These composites are strong enough to withstand the forces from motors or propulsion systems, yet can readily shape morph, which allows machines to adapt to their environment,” said Barron.
Looking forward, the researchers envision the morphing composites playing a role in the emerging field of soft robotics to create machines that can perform diverse functions, self-heal after being damaged to increase resilience, and spur different ideas in human-machine interfaces and wearable devices.
Series-connected solar array for high-speed underwater wireless optical links
by Zhijian Tong, Xingqi Yang, Hao Zhang, Yizhan Dai, Xiao Chen, Jing Xu in Optics Letters
Although solar cells are typically designed to turn light into power, researchers have shown that they can also be used to achieve underwater wireless optical communication with high data rates. The new approach — which used an array of series-connected solar cells as detectors — could offer a cost-effective, low-energy way to transmit data underwater.
“There is a critical need for efficient underwater communication to meet the increasing demands of underwater data exchange in worldwide ocean protection activities,” said research team leader Jing Xu from Zhejiang University in China. For example, in coral reef conservation efforts, data links are necessary to transmit data from divers, manned submarines, underwater sensors and unmanned autonomous underwater vehicles to surface ships supporting their work.
In the Optica Publishing Group journal Optics Letters, Xu and colleagues report on laboratory experiments in which they used an array of commercially available solar cells to create an optimized lens-free system for high-speed optical detection underwater. Solar cells offer a much larger detection area than the photodiodes traditionally used as detectors in wireless optical communication.
“To the best of our knowledge, we demonstrated the highest bandwidth ever achieved for a commercial silicon solar panel-based optical communication system with a large detection area,” said Xu. “This type of system could even allow data exchange and power generation with one device.”
Compared to using radio or acoustic waves, light-based underwater wireless communication exhibits higher speed, lower latency and requires less power. However, most long-distance high-speed optical systems are not practical for underwater implementation because they require strict alignment between the transmitter emitting the light and the receiver that detects the incoming light signal.
Because solar cells detect light from a large area and convert it to an electrical signal, using them as detectors can ease the transmitter-receiver alignment requirement in an underwater wireless communication system. However, it has been difficult to achieve high bandwidth because solar cells are optimized for energy harvesting rather than communication.
“Until now, achieving high-speed links using off-the-shelf silicon solar cells has required complex modulation schemes and algorithms, which need intense computing resources that use extra power and create a high processing latency,” said Xu. “Using modeling and simulation of connected solar cells, we optimized the peripheral circuit, which significantly improved the performance of our solar cell-based detector.”
The researchers tested the new design, which used a 3×3 solar array to create a detection area of 3.4 × 3.4 centimeters, in a 7-meter-long water tank that emulated an underwater channel. Mirrors were used to extend the pathlength of the optical signal, creating a transmission distance of 35 meters. The system showed reliable stability, low power consumption and high performance. As the size of the solar array increases from 1×1 to 3×3, the ?20-dB bandwidth increases from 4.4 MHz to 24.2 MHz.
Even though a simple modulation scheme was used, the new system exhibited a much higher detection bandwidth — which leads to a higher data rate — than has been reported in other studies using commercial silicon solar cells with a large detection area as detectors. Applying a reverse bias voltage of 90 V boosted the bandwidth further, allowing them to achieve a ?20-dB bandwidth of 63.4 MHz. This bandwidth enabled a 35-m/150-Mbps underwater wireless optical link using the simplest form of amplitude-shift keying modulation.
“Because solar cells are mass produced, the proposed scheme is quite cost effective,” said Xu. “Beyond the underwater world, this type of detector could also be used in visible light communication, a type of wireless communication that uses visible light from LEDs and other sources to transmit data across distances.”
To optimize the system for real-world applications in underwater communication, the researchers plan to next study its performance with weak optical signals. This will show how well it works in muddy water and with movement. They are also working to make the system more practical by fine tuning key parameters like the number of solar cells in the array and the required reverse bias voltage.
Multichannel haptic feedback unlocks prosthetic hand dexterity
by Moaed A. Abd, Joseph Ingicco, Douglas T. Hutchinson, Emmanuelle Tognoli, Erik D. Engeberg in Scientific Reports
Typing on a keyboard, pressing buttons on a remote control or braiding a child’s hair has remained elusive for prosthetic hand users. With current myoelectric prosthetic hands, users can only control one grasp function at a time even though modern artificial hands are mechanically capable of individual control of all five digits.
A first-of-its-kind study using haptic/touch sensation feedback, electromyogram (EMG) control and an innovative wearable soft robotic armband could just be a game changer for users of prosthetic hands who have long awaited advances in dexterity. Findings from the study could catalyze a paradigm shift in the way current and future artificial hands are controlled by limb-absent people.
Researchers from Florida Atlantic University’s College of Engineering and Computer Science in collaboration with FAU’s Charles E. Schmidt College of Science investigated whether people could precisely control the grip forces applied to two different objects grasped simultaneously with a dexterous artificial hand.
For the study, they also explored the role that visual feedback played in this complex multitasking model by systematically blocking visual and haptic feedback in the experimental design. In addition, they studied the potential for time saving in a simultaneous object transportation experiment compared to a one-at-a-time approach. To accomplish these tasks, they designed a novel multichannel wearable soft robotic armband to convey artificial sensations of touch to the robotic hand users.
Results, published in Scientific Reports, showed that multiple channels of haptic feedback enabled subjects to successfully grasp and transport two objects simultaneously with the dexterous artificial hand without breaking or dropping them, even when their vision of both objects was obstructed.
In addition, the simultaneous control approach improved the time required to transport and deliver both objects compared to a one-at-a-time approach commonly used in prior studies. Of note for clinical translation, researchers did not find significant differences between the limb-absent subject and the other subjects for the key performance metrics in the tasks. Importantly, subjects qualitatively rated haptic feedback as considerably more important than visual feedback even when vision was available, because there was often little to no visually perceptible warning before grasped objects were broken or dropped.
“Our study is the first to demonstrate the feasibility of this complex simultaneous control task while integrating multiple channels of haptic feedback noninvasively,” said Erik Engeberg, Ph.D., corresponding author and a professor, FAU Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science, a member of FAU’s Center for Complex Systems and Brain Sciences, Charles E. Schmidt College of Science, and a member of I-SENSE and the FAU Stiles-Nicholson Brain Institute. “None of our study participants had significant prior use of EMG-controlled artificial hands, yet they were able to learn to harness this multitasking functionality after two short training sessions.”
To provide haptic feedback, Engeberg and the research team worked on the EMG control and design of the custom fabricated multichannel bimodal soft robotic armband with Emmanuelle Tognoli, Ph.D., co-author, a research professor, FAU Department of Psychology and Center for Complex Systems and Brain Sciences, and a member of the FAU Stiles-Nicholson Brain Institute.
The armband was fitted with soft actuators to convey a proportional sense of contact forces; vibrotactile stimulators were included to indicate if the grasped object(s) had been broken. The armband was designed for haptic feedback at three locations corresponding to the thumb, index, and little finger, a sufficient number to convey the amplitudes of the forces applied to both objects grasped by the hand. The armband has three air chambers, each of which proportionally corresponds to one of the three BioTacs equipped on the Shadow Hand fingertips. The armband also is equipped with three co-located vibrotactile actuators that would vibrate to alert the subject if the object(s) in the grasp(s) had been broken (if one or both force thresholds was/were exceeded).
“Examples of multifunction control demonstrated in our study included the proportional control of a card being pinched between the index and middle fingers at the same time that the thumb and little finger were used to unscrew the lid of a water bottle. Another simultaneous control demonstration was with a ball that was grasped with three fingers while the little finger was simultaneously used to toggle a light switch,” said Moaed A. Abd, first author and a Ph.D. student in FAU’s Department of Ocean and Mechanical Engineering.
Information discovered from the study could be used in the future frameworks of highly complex bimanual operations, such as those required of surgeons and guitarists, with the goal of enabling upper limb-absent people to pursue career paths and recreational pursuits currently unattainable to them.
“Enabling refined dexterous control is a highly complex problem to solve and continues to be an active area of research because it necessitates not only the interpretation of human grasp control intentions, but also complementary haptic feedback of tactile sensations,” said Stella Batalama, Ph.D., dean, FAU College of Engineering and Computer Science. “With this innovative study, our researchers are addressing the loss of tactile sensations, which is currently a major roadblock in preventing upper limb-absent people from multitasking or using the full dexterity of their prosthetic hands.”
Electrochemical Dual Transducer for Fluidic Self-Sensing Actuation
by Yu Kuwajima, Yumeta Seki, Yuhei Yamada, Satoshi Awaki, Shota Kamiyauchi, Ardi Wiranata, Yuto Okuno, Hiroki Shigemune, Shingo Maeda in ACS Applied Materials & Interfaces
The word “robot” would probably conjure up images of hard metallic bodies that are invulnerable to attacks. In modern day-to-day life, however, robots are hardly needed for defending against enemy attacks. Instead, they are required to perform more mundane tasks such as handling delicate objects and interacting with humans. Unfortunately, conventional robots perform poorly at such seemingly simple tasks. Moreover, they’re heavy and often noisy.
This is where “soft” robots have the upper hand. Made of materials called “elastomers” (materials with high viscosity and elasticity), soft robots absorb shocks better, can adapt better to their environments, and are safer compared to conventional robots. This has allowed for a broad range of applications, including medicine and surgery, manipulation, and wearable technology. However, many of these soft robots rely on fluidic systems, which still use pumps operated by mechanical parts (motors and bearings). As a result, they are still heavy and noisy.
One way around this problem is to use chemical reactions to drive pumps. But while such systems are definitely lightweight and quiet, they don’t perform as well as conventional pumps. Is there a way to beat this trade-off? Turns out, the answer is yes. A team of researchers from Shibaura Institute of Technology (SIT), Japan, led by Prof. Shingo Maeda, introduced an “electrohydrodynamic” (EHD) pump that uses electrochemical reactions to drive pumps. The EHD pumps have all the advantages of pumps driven by chemical reactions and none of their issues.
Now, in a recent study, the team, including Prof. Maeda, Yu Kawajima, Dr. Yuhei Yamada (all from the Department of Engineering Science and Mechanics, SIT), and Associate Professor Hiroki Shigemune (Department of Electrical Engineering, SIT) has gone one step further, designing a “self-sensing” EHD pump that uses an electrochemical dual transducer (ECDT) to sense the fluid flow, which, in turn, activates electrochemical reactions and increases current.
“Self-sensing technology has attracted much attention recently for compactifying soft robots. Incorporating sensors in soft robots enhances their multifunctionality, but often make for complex wiring and bloating. Self-sensing actuation technology can help solve this issue and allow for miniaturization of soft robots,” explains Prof. Maeda.
The team based the ECDT design on the EHD pump they had previously designed. The pump consisted of a symmetrical arrangement of planar electrodes, which allowed an easy control of the flow direction by simply changing the voltage. Moreover, the arrangement enabled an obstruction-free flow and in the same amount in each direction owing to same strength of the electric field on either side.
The team evaluated sensing performance in terms of range of detectable flow, rate, sensitivity, response, and relaxation times, and also used mathematical modeling to understand the sensing mechanism.
“The ECDT can easily be integrated into a fluidic system without bloating or complexity,” says Yu Kuwajima, doctoral student at the Smart Materials Laboratory (SIT) and the first author of the study.
Additionally, the researchers tested its performance by using it to drive a suction cup to detect, grab, and release objects.
“The advantages of the ECDT are that it does not require any special equipment or complex processing for its fabrication. Moreover, it is small, lightweight, and demonstrates a wide range of sensitivity,” says Prof. Maeda.
3D printed leech-inspired origami dry electrodes for electrophysiology sensing robots
by Tae-Ho Kim, Chao Bao, Ziniu Chen, Woo Soo Kim in npj Flexible Electronics
Empowering small, humanoid-sensing robots to take a patient’s blood pressure — using only a simple touch — is Simon Fraser University researcher Woo Soo Kim’s latest health care technology development.
Based on the intricacies of origami — and inspired by the movements of nature’s leeches — his research is advancing how robots could carry out basic health care tasks in certain conditions, including in remote regions, or where minimal personal contact is needed, such as during pandemics. The research is published in the journal npj Flexible Electronics from Nature Publishing Group.
Together with PhD student Tae-Ho Kim and a team in SFU’s Additive Manufacturing Lab, Kim and researchers have replaced the traditional blood pressure procedure by replicated the folding mechanisms of the leech in their design of 3-D printable origami sensors. The leech-inspired origami (LIO) sensors can be integrated onto the fingertips of a humanoid-sensing robot.
“Our origami-inspired dry electrode has unique characteristics such as suction for grasping and foldability inspired by nature,” says Kim, a professor and associate director of SFU’s School of Mechatronic Systems Engineering. “In keeping with nature, we saw that in addition to the complex mechanisms of a leech’s adhesive feature, these creatures have an expandable posterior sucker and body, while its organs expand and shrink appropriately to maintain better adhesion to its victim. Incorporating this point of view, we found that origami can achieve similar motions and also be customized.”
The LIO sensors integrated onto the robot’s fingertips can be positioned on the patient’s chest. Blood pressure is monitored and estimated by combining data from electrocardiogram (ECG)and photoplethysmogram (PPG) readings, as recorded by sensors on the fingers of each hand respectively.
Using predetermined algorithms, the signals from the paired sensors can generate a patient’s systolic and diastolic blood pressure without using the traditional cuff-based digital sphygmomanometer.
Kim’s earlier work involved programming sensing robots to measure other human physiological signals, such as those from an electrocardiogram (which monitors heart rate), temperature and respiration rate.
“Robotics offers a promising method to mitigate risk and improve patient care effectiveness and quality as focused remote healthcare technology,” says Kim. The researchers plan further trials of their new process and are developing the next generation of sensors, which they hope will lead to its biomedically meaningful implementation.
“Blood pressure monitoring is an essential medical diagnostic tool for many chronic diseases and overall good health. The use of sensing robots in medical healthcare systems has substantial advantages because they can assist health care workers in monitoring patient vital signs while creating a friendly environment for those patients who may need to be isolated.”
Kim believes that robotics can provide a future platform or bridge between medical personnel and remote patients with “the potential to play an essential role in the new era of remote healthcare.”
An Android for Emotional Interaction: Spatiotemporal Validation of Its Facial Expressions
by Wataru Sato, Shushi Namba, Dongsheng Yang, Shin’ya Nishida, Carlos Ishi, Takashi Minato in Frontiers in Psychology
Researchers from the RIKEN Guardian Robot Project in Japan have made an android child named Nikola that successfully conveys six basic emotions. The new study, published in Frontiers in Psychology, tested how well people could identify six facial expressions — happiness, sadness, fear, anger, surprise, and disgust — which were generated by moving “muscles” in Nikola’s face. This is the first time that the quality of android-expressed emotion has been tested and verified for these six emotions.
Rosie the robot maid was considered science fiction when she debuted on the Jetson’s cartoon over 50 years ago. Although the reality of the helpful robot is currently more science and less fiction, there are still many challenges that need to be met, including being able to detect and express emotions. The recent study led by Wataru Sato from the RIKEN Guardian Robot Project focused on building a humanoid robot, or android, that can use its face to express a variety of emotions. The result is Nikola, an android head that looks like a hairless boy.
Inside Nikola’s face are 29 pneumatic actuators that control the movements of artificial muscles. Another 6 actuators control head and eyeball movements. Pneumatic actuators are controlled by air pressure, which makes the movements silent and smooth. The team placed the actuators based on the Facial Action Coding System (FACS), which has been used extensively to study facial expressions. Past research has identified numerous facial action units — such as ‘cheek raiser’ and ‘lip pucker’ — that comprise typical emotions such as happiness or disgust, and the researchers incorporated these action units in Nikola’s design.
Typically, studies of emotions, particularly how people react to emotions, have a problem. It is difficult to do a properly controlled experiment with live people interacting, but at the same time, looking at photos or videos of people is less natural, and reactions aren’t the same.
“The hope is that with androids like Nikola, we can have our cake and eat it too,” says Sato. “We can control every aspect of Nikola’s behavior, and at the same time study live interactions.” The first step was to see if Nikola’s facial expressions were understandable.
A person certified in FACS scoring was able to identify each facial action unit, indicating that Nikola’s facial movements accurately resemble those of a real human. A second test showed that everyday people could recognize the six prototypical emotions — happiness, sadness, fear, anger, surprise, and disgust — in Nikola’s face, albeit to varying accuracies. This is because Nikola’s silicone skin is less elastic than real human skin and cannot form wrinkles very well. Thus, emotions like disgust were harder to identify because the action unit for nose wrinkling could not be included.
“In the short term, androids like Nikola can be important research tools for social psychology or even social neuroscience,” says Sato. “Compared with human confederates, androids are good at controlling behaviors and can facilitate rigorous empirical investigation of human social interactions.”
As an example, the researchers asked people to rate the naturalness of Nikola’s emotions as the speed of his facial movements was systematically controlled. They researchers found that the most natural speed was slower for some emotions like sadness than it was for others like surprise.
While Nikola still lacks a body, the ultimate goal of the Guardian Robot Project is to build an android that can assist people, particularly those which physical needs who might live alone.
“Androids that can emotionally communicate with us will be useful in a wide range of real-life situations, such as caring for older people, and can promote human wellbeing,” says Sato.
Light-driven carbon nitride microswimmers with propulsion in biological and ionic media and responsive on-demand drug delivery
by Varun Sridhar et al in Science Robotics
Researchers at the Max Planck Institute for Intelligent Systems (MPI-IS) have recently developed new light-driven microswimmers that could be more suited for navigating within biological systems, including body fluids. These microswimmers, introduced in a paper published in Science Robotics, are simple microparticles based on the two-dimensional (2D) carbon nitride poly(heptazine imide) or PHI .
In recent years, scientists have introduced a wide variety of robots of all shapes and sizes. Among these are microswimmers, carefully engineered microstructures that can move in water and other liquids.
Microswimmers could have numerous interesting applications, for instance allowing doctors to deliver drugs to targeted regions inside the human body, or scientists to introduce specific substances in water-based environments. While some of these robotic systems achieved remarkable results, most of them were found to be unable to efficiently move inside the human body.
“Our study came about due to the need for having a biocompatible organic material that can be used as light-driven microswimmers,” Varun Sridhar, one of the researchers who carried out the study, told TechXplore. “Our objective was to build a biocompatible organic microswimmer that can swim in a biological medium containing salts and could thus deliver drugs on demand in an intelligent manner.”
Sridhar previously conducted other studies exploring the potential of light-driven microswimmers (i.e., microswimmers that respond to visible light). In collaboration with Filip Podjaski, a researcher at the Max Planck Institute for Solid State Research, he started trying to validate and improve their propulsion mechanism, by using different materials to create them and then testing their performance.
Initially, the team at MPI-IS studied titanium dioxide and Cobalt monoxide, but then they tried using organic light conversion materials. They discovered that the latter were particularly promising and efficient, and started exploring the challenges impeding the performance of microswimmers in general, most of which are associated with the presence of ions hindering propulsion.
“Since the carbon nitride materials I worked on showed enhanced properties in the presence of ions, such as energy conversion catalysis being required for propulsion, ion pumping, and property changes going in hand with intrinsic charging assisted by ions, we decided to study them to overcome some limitations in the field, and it worked out super nicely,” Podjaski told TechXplore. “We then added different carbon nitride systems to the study, which have less pronounced interactions with ions, to better disentangle what is going here (i.e., what properties are given by pure porosity, with our microswimmer particles being effectively sponge structures) and what comes on top from intrinsic ‘ionic interactions’ (material interactions with salt ions, such as Na+ or K+, which are found in all biological fluids).”
The new, light-driven microswimmers developed by Sridhar, Podjaski and their colleagues are made of an organic-based material known as Carbon Nitride, which has photocatalytic properties. This means that when light is shone on the material, it is absorbed and produces electric charges that are used to drive chemical reactions.
“The charges react with the bio fluids and this reaction combined with the electric field around the particle makes the microswimmers swim,” Sridhar explained. “The carbon nitride PHI can also store charges when light shines on it, behaving like a solar battery, which can also be used to enhance their drug delivery properties.”
PHI, the material used by the researchers, can absorb light energy in a similar way to solar cells. This energy is then used to propel each particle, allowing it to move in fluids. Essentially, the propulsion of the particles relies on catalytic reactions occurring on their surface.
“The process called ‘photocatalysis’ is being studied and used to convert solar energy directly into chemical energy,” Podjaski said. “Carbon nitrides are very efficient photocatalysts, so they are also good light driven ‘swimmers.” In addition, their synthesis is very simple and cheap, as it is based on abundant organic precursors, such as urea (e.g., from urine.), making them very promising and widely accessible materials.”
To propel the particles, the researchers relied on a driving force (i.e., light enabling photocatalysis) and symmetry breaking, which pushes them in a specific direction. They thus used a torch light that illuminates one half of a sphere, leaving the other dark, producing a gradient of reactions on both sides. Finally, as the swimmers were designed to be introduced in liquids, the team ensured that the propulsion force was stronger than the ‘slowing down’ of a surrounding environment.
“Salt ions in water are a big problem, since they break down the propulsion force field around the particle,” Podjaski said. “We found that it is sufficient to enable an ion flow through the particle to overcome this strong ‘slow down’ in principle. And apparently, the intrinsic ionic interactions of our special carbon nitride PHI enhances this ion tolerance, as the flow through the particle is ‘accelerated.’”
In initial experiments, the researchers demonstrated the efficient movement of the microswimmers in liquids with low to medium , such as those inside biological organisms, as well as highly salted waters, such as those of the dead sea. These findings suggest that the swimmers could eventually be used to deliver drugs inside the human body and in other biological systems.
“The microswimmers are also sensitive to environmental conditions inside the body and can be triggered by light or pH changes to release drugs,” Sridhar said. “The light triggered release is also sensitive to oxygen deficient environments, such as those found around cancer cells. Thus, the microswimmers can release drugs more efficiently near cancer cells, eventually killing them efficiently.”
In the future, the researchers plan to test the microswimmers they created in real biological environments, such as in cell cultures, body fluids or sea water. To create microswimmers that could move in these environments, researchers previously had to introduce toxic additives to fuel the propulsion. The ability to naturally move around in sea water and bodily fluids could thus make these microswimmers truly revolutionary.
“While we only tested them outside of living organisms so far, our carbon nitride particles are biocompatible and do not appear to create immune responses,” Podjaski said. “Moreover, they retain all their properties when illuminated by visible light and do not degrade. This was not engineered, it was apparently a natural outcome from taking an organic based material that is very stable by itself (i.e., does not allow for spontaneous chemical interactions with cells body components).”
While many studies investigated carbon nitrites in the past, Sridhar, Podjaski and their colleagues are among the first to demonstrate their potential as microswimmers operating within living systems. In addition, the particles they used have a sponge-like structure, containing many pores and voids, which means that they could easily be soaked in drugs with large amounts. Remarkably, the team found that the chemotherapy drug Doxorubicin remains strongly bound to the particles, yet it could easily be released in targeted locations, simply by changing the pH or shining a light on the particles. This could also apply to other drugs.
“For our inherently porous particles without any special encapsulation, this does not happen at all by itself,” Podjaski said. “The cancer drug Doxorubicin stays bound for over a month. For the delivery of drugs that target a single spot and work at a desired time, this is fundamental, and a very novel observation.”
Microswimmers for drug delivery introduced in the past relied on ‘artificial capsules,” which were meant to be filled with drugs and delivered to specific locations in the body. Creating these capsules, however, could be both complex and expensive. In contrast, the particles used by the researchers are cheap, organic, and spongy by design, binding directly to drugs or other substances. This means that they could be easier to implement on a large-scale. Remarkably, they can also be loaded with more drugs (i.e., 185% of their own mass) than other materials used in the past.
“These mechanisms were already used before and they are useful, but only partially, since really aidic conditions are only found in the stomach and light is also required for propulsion, so the drug then is released all the way, which is not super controlled,” Podjaski said. “The really amazing thing we found and anticipated is that our microswimmers can intrinsically sense or diagnose oxygen poor environments (a scenario that cancer cells naturally create, called hypoxicity) — and then boost the release of the loaded drug under illumination.”
The microswimmers created by this team of researchers are ‘theanostic,” meaning that they could simultaneously have both diagnostic and therapeutic functions. Their operation mechanism mimics that of neurons, which sense their environment and convey messages to other parts of the body.
“All of the properties we demonstrated are possible using one material, without modifying it, tailoring its source functions to make it biocompatible, without adding artificial capsules for drugs and without sensing parts that look on pH or oxygen content,” Podjaski added. “Engineering this on a micrometer scale (1/1000 of a mm, 1/100 of a hair) would technically be impossible currently, as it is both expensive and complicated. I think the true beauty of our work is that with our microswimmers this happens naturally, using a very cheap material that is easy to prepare.”
Ultimately, this recent study could inspire the development of more affordable microrobots that can navigate in biological environments. The swimmers could be particularly valuable to deliver drugs or intervene in specific parts of the body that can be reached by light, such as the skin, transparent tissues, or inside the eye. Combinations of these novel, porous and organic materials with traditionally inorganic microrobots could also enable new functions.
Self-healing ionic gelatin/glycerol hydrogels for strain sensing applications
by David Hardman et al in NPG Asia Materials
Researchers have developed self-healing, biodegradable, 3D-printed materials that could be used in the development of realistic artificial hands and other soft robotics applications. The low-cost jelly-like materials, developed by researchers at the University of Cambridge, can sense strain, temperature and humidity. And unlike earlier self-healing robots, they can also partially repair themselves at room temperature.
Soft sensing technologies could transform robotics, tactile interfaces and wearable devices, among other applications. However, most soft sensing technologies aren’t durable and consume high amounts of energy.
“Incorporating soft sensors into robotics allows us to get a lot more information from them, like how strain on our muscles allows our brains to get information about the state of our bodies,” said David Hardman from Cambridge’s Department of Engineering, the paper’s first author.
These low-cost jelly-like materials, developed by researchers at the University of Cambridge, can sense strain, temperature and humidity. And unlike earlier self-healing robots, they can also partially repair themselves at room temperature. Credit: University of Cambridge
As part of the EU-funded SHERO project, Hardman and his colleagues have been working to develop soft sensing, self-healing materials for robotic hands and arms. These materials can detect when they are damaged, take the necessary steps to temporarily heal themselves and then resume work — all without the need for human interaction.
“We’ve been working with self-healing materials for several years, but now we’re looking into faster and cheaper ways to make self-healing robots,” said co-author Dr. Thomas George-Thuruthel, also from the Department of Engineering.
Earlier versions of the self-healing robots needed to be heated in order to heal, but the Cambridge researchers are now developing materials that can heal at room temperature, which would make them more useful for real-world applications.
“We started with a stretchy, gelatine-based material which is cheap, biodegradable and biocompatible and carried out different tests on how to incorporate sensors into the material by adding in lots of conductive components,” said Hardman.
The researchers found that printing sensors containing sodium chloride — salt — instead of carbon ink resulted in a material with the properties they were looking for. Since salt is soluble in the water-filled hydrogel, it provides a uniform channel for ionic conduction — the movement of ions.
When measuring the electrical resistance of the printed materials, the researchers found that changes in strain resulted in a highly linear response, which they could use to calculate the deformations of the material. Adding salt also enabled sensing of stretches of more than three times the sensor’s original length, so that the material can be incorporated into flexible and stretchable robotic devices.
The self-healing materials are cheap and easy to make, either by 3D printing or casting. They are preferable to many existing alternatives since they show long-term strength and stability without drying out, and they are made entirely from widely available, food-safe, materials.
“It’s a really good sensor considering how cheap and easy it is to make,” said George-Thuruthel. “We could make a whole robot out of gelatine and print the sensors wherever we need them.”
The self-healing hydrogels bond well with a range of different materials, meaning they can easily be incorporated with other types of robotics. For example, much of the research in the Bio-Inspired Robotics Laboratory, where the researchers are based, is focused on the development of artificial hands. Although this material is a proof-of-concept, if developed further, it could be incorporated into artificial skins and custom-made wearable and biodegradable sensors.
HaptiTemp: A Next-Generation Thermosensitive GelSight-Like Visuotactile Sensor
Alexander C. Abad et al in IEEE Sensors Journal
A new robotic sensor that mimics the automatic human reaction to heat is being hailed as a world first. The device has been built by a team of experts from Liverpool Hope University, who say it’s the first sensor that can trigger this ‘sensory impulse’ that the robotics community has yet seen.
Lead author Alexander Co Abad, of Hope’s School of Mathematics, Computer Science and Engineering, says the system is so robust it can measure temperature changes of 30 degrees C per second — similar to how someone might quickly pull their hand away from the threat of being burned.
He says the wireless, Wi-Fi enabled sensor could have numerous real-world applications, from space exploration to surgical procedures — and even creating “thermo-sensitive soft robots in the near future.”
Abad adds: “This feature could be useful for soft robots to act equivalent to humans’ withdrawal reflex in touching hot surfaces in search and rescue, industrial applications, and space explorations.”
And in giving robots a real sense of touch, it makes them even more adept in complex environments.
Ph.D. student Abad says, “Although psychologists often state that vision is the main way humans obtain information from the environment, when visual perception is impaired, haptic perception is the natural recourse. Even if vision is not impaired, the sense of touch often works in conjunction with visual perception.”
At the heart of the work is what’s called a GelSight sensor, first invented by experts at the Massachusetts Institute of Technology (MIT) in 2009, and which provides a highly detailed visual 3D topography of any surface by processing touch information. It provides digital feedback according to what it touches by way of a sensor and camera.
Previous studies have shown how a GelSight sensor can help a robotic arm to grip objects more efficiently — something that could prove crucial when it comes to robot-assisted surgery.
Abad and his Hope colleagues, including Professor David Reid and Dr. Anuradha Ranasinghe, created their own, ultra low-cost version of a GelSight sensor using a simple £1 cosmetic pad — the sort used to apply make-up — which means the tech is highly accessible to a whole host of different fields.
Crucially, it’s also extremely affordable. And this new research focused on adapting the GelSight sensor to react to extreme heat. It did so through use of so-called thermochromic paint, which changes color in response to temperature changes but reverts back to normal once exposure to varying temperatures has been removed.
And not only that, but this new sensor was improved to the point where it could detect all three “Haptic Primary Colors” — ie, force, temperature and vibration — such as being able to record someone’s pulse.
Abad explains: “Moreover, we demonstrated that we could easily sense temperature using the hue value by using different colors and layers of thermochromic pigments with varying thresholds of temperature on the reflective coating.”
Describing how the sensor can mimic the rapid temperature changes equivalent to the withdrawal reflex of humans, Abad says, “This thermosensitive visuotactile sensor is the first monolithic elastomer temperature sensor and can be used to infer tactile forces based on the mechanical deformation of the gel.”
The sensor quickly changed color when exposed to heat greater than 50 degrees Celsius.
Abad says, “We were able to measure a response time of 643 ms for cold-to-hot and hot-to-cold. The rapid temperature response of our visuotactile sensor is comparable to the less than one second time withdrawal reflex response of the human autonomic system to extreme heat. Our sensor might give robots the ability to react as humans and create thermosensitive soft robots in the near future.”
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MISC
- Boston Dynamics put together a behind-the-scenes video of sorts about the Super Bowl commercial they did in collaboration with some beer company or other.
- CMU RI Seminar video by Jessica Burgner-Kahrs from theUniversity of Toronto, Mississauga, on continuum robots.
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