Silicone Rubber: Bio-inspired soft robots are coming

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Robotics designs have diversified from rigid to flexible, in a bid to make a new breed of agile robots that mimic the locomotion mechanisms of soft bodies such as earthworms, snakes, sea animals and insects. Called soft robots, they are built using easily deformable compliant materials such as rubbers, fluids, gels, and elastomers to enable soft structures and smooth movements, says Angelica Buan in this article.

Soft robots present advantages over traditional rigid robots in terms of their elasticity and flexibility as they are designed to be used effectively even in intricate spaces and for various tasks, which traditional robots are not fit to do. These features demonstrate the potentials of soft robots for use in a range of functions such as in invasive surgeries; in patient rehabilitative treatments; for explorations and monitoring; or for performing automation tasks in manufacturing set-ups where precision and accuracy as well as flexibility are required.

Currently, liquid silicone rubber (LSR) is commonly used for the soft bodies because it is versatile, lightweight, and can be moulded into any shape. It is also mould and germ-resistant as well as can enable hardware and circuits to be embedded directly into it. For the flexible electronics component of the soft robots, inkjet-printed liquid metal is commonly used.

Soft robots in use

Soft robots are able to explore environments, like underwater, that may be challenging to work around.

Tackling the challenge of underwater research, the Massachusetts Institute of Technology (MIT) developed a soft robotic fish that can swim for more than half hour, reaching depths of 50 ft. Equipped with a fisheye lens, SoFi was able to take high resolution images and videos during its test dive at the Fiji Reef. The back half of SoFi is made up of flexible plastic and silicone rubber; its other parts, like the head, which encases all of the fish’s electronics, are 3D printed.


Snake-like soft robots have real-life use such as in search and rescue missions. This is the goal of Worcester Polytechnic Institute (WPI) researchers that have started developing a soft crawler. The team was awarded in 2017 by the National Science Foundation with US$400,000 to create a robot that can steer through inaccessible and confined spaces in disaster-challenged areas; and to relay critical information and images to search-and-rescue teams. Here again, the segmented robot, constructed with LSR, features connected modules, each with its own tubing, valves, pneumatic actuators, integrated sensing, and control units.

Meanwhile, the Japanese cut paper art of kirigami inspired the design for the soft robot developed by researchers from Wyss Institute at Harvard University and the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). The snake-like design will enable the robot to crawl in between spaces as it mimics the friction-assisted locomotion of a snake. This invention is seen as an aid in exploring devastated areas; or potentially to perform some delicate medical procedures like laparoscopic surgery and other minimally invasive surgeries.


Soft crawlers for future medical applications

A pill-sized robot that can do multiple movements – walk, crawl, roll, climb, and carry cargo; and is able to navigate its way through uneven and complex spaces, is a breakthrough from scientists at the Max Planck Institute for Intelligent Systems in Germany. The soft robot‘s design is fashioned after the beetle larvae, caterpillar, spermatozoid, and jellyfish; made of LSR and embedded with magnetic particles. It is controlled via an external magnetic controller.

The researchers said that to allow it inside the human body, parts of the millirobot, such as the magnetic particles, first have to be modified to ensure that they are biocompatible, biodegradable and non-toxic. Moreover, its size at 4 mm long by 1 mm width is relatively “large” for such purposes, so it still has to be further downscaled to at least 8 micrometres, the approximate size of a human capillary.


In other news, breakthrough options for cardiac patients will soon be within reach with new soft robots targeted to assist in heart treatment.

One such robot has been developed by Harvard University and Boston Children’s Hospital researchers. It fits around the heart and helps it beat, in sync with a beating heart, augmenting cardiovascular functions weakened by heart failure. It also does not directly contact blood, and thus, reduces the risk of clotting and eliminates the need for a patient to take potentially dangerous blood thinner medications. The device may one day be able to bridge a patient to transplant or help in cardiac rehabilitation and recovery, the researchers stated.


The SEAS and Wyss Institute engineers collaborated with surgeons at Boston Children’s Hospital to develop the device and determine the best ways to implant and test it on animal models. Accordingly, more research needs to be done before the sleeve can be implanted in humans.

Touchy-feely robot assistants

A soft robot that can pick up, manipulate and sense objects is the brainchild of a team of engineers at the University of California San Diego. The robotic gripper’s fingers are constructed of soft flexible pneumatic chambers, which move when air pressure is applied. Each finger is also covered with a smart sensing skin that is made of LSR embedded with carbon nanotube sensors.


The sensors gather data of the object it is coming in contact with or is manipulating, with information relayed to a control board, which processes the information to create a 3D model of that object. The team is enhancing the features of the gripper, such as its capability to identify the objects it is manipulating.

The grippers can advance the touching capability of current robots, making them more sensitive and more efficient in gathering information in their surroundings.

Advancements are also underway to utilise grippers as assisting devices in a range of sectors – from medical and research to carpentry and agriculture.

One such example comes from scientists at the University of Plymouth who are developing a robot that could assist fruit and vegetable growers in harvesting crops. The GummiArm “can vary its stiffness by co-contracting its rubbery tendons, and is quite robust to impacts in the relaxed state. A broken piece can be redesigned, reprinted, and assembled in minutes via 3D printing”

Under the hood of the £10million-funded Automated Brassica harvesting in Cornwall (ABC) project, the tiny mobile robots are fitted with cameras as well as sensors in its gripper to assist in generating real-time 3D models of the crop by assessing the “information” it assimilates, allowing it to recognise which parts to collect and which to leave.

With such robots recording images and touch-data from all over a field in real-time, they also bring the possibility of gathering information that could be used in a variety of ways, potentially extending their application to beyond harvesting season.

In the coming years, and as R&D in soft robotics advances, it is expected that more of these soft, tiny helpers will make their way into laboratories, theatre tables, and industrial floors taking on gargantuan tasks to make human lives better.


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