Bench Talk

Flexible Machines for the Future

(Source: Niki / stock.adobe.com)

Meet soft robotics. Rather than use steel and graphite, soft robotics encompasses flexible robots built from materials such as silicone, rubber, and gel, affording them a range and style of motion that is nearly impossible for a traditional machine. Because they move and behave uniquely, these robots enjoy several advantages over their steel-clad kin, including improved collision resistance and an enhanced capacity for complex motion.

In this blog, we’ll explore how soft robotics came to be as we highlight its advantages—along with some disadvantages—and the new applications currently being explored.

A Brief History of Soft Robotic

The first real-world application of soft robotics occurred with the McKibben artificial muscle, developed in 1950.^[1] Also known as McKibben air muscles, the device consisted of a flexible pneumatic tube shielded by braided mesh.^[2]  Although originally developed for orthotics, the pneumatic muscle has been employed in multiple robot designs since its development. McKibben’s work also inspired several technologies that laid the groundwork for modern soft robotics.

The years that followed would see a multitude of new technologies and innovations, including manipulators modeled after tentacles and elephant trunks, artificial muscles comprised of electrostrictive polymer and fluidic actuators, eventually leading to more sophisticated developments in the 21^st century.

Anatomy of a Soft Robot

Soft robots are typically comprised of flexible matter such as fluids, elastomers, or gels and use a process known as compliance matching to ensure even load distribution and minimize stress. Additionally, soft robotics may utilize one or more of the following systems for actuation:^[3]

• Compressed air
• Fluids such as oil or water
• Materials that change shape when exposed to heat
• A combination of electrodes, insulating polymers, and conducting polymers
• Magnetic fields
• Materials that change shape when exposed to light^[4]

The most common process for fabricating and manufacturing soft robotics—known as soft lithographic molding—consists of the following steps:

1. Manufacturing the internal components, commonly done either traditionally, through 3D printing, or via casting.
2. Modeling the flexible outer layer of the robot after the desired form factor by casting and curing silicon rubber or similar material in a purpose-built mold.
3. Joining the different layers together via uncured elastomer. After re-curing, the finished actuator is removed from the mold.

The Benefits and Drawbacks of Being Soft

Although soft robotics has many advantages compared to traditionally rigid robotics, they are not without their weaknesses—nor are they suitable for every application.^[5] See Table 1 for a comparison of the benefits and drawbacks of soft robotics.

Table 1:Strengths and weaknesses of soft robotics. (Source: Soft Gripping)^[6]

Exploring the Applications of Soft Robotics

There is incredible variety in the potential use cases for soft robotics, and new applications are constantly being explored. In healthcare, for example, soft robotics can be used for: 

• Complex soft prosthetics capable of complex motion and sensing touch,
• Soft exosuits for patients with limited motion,
• Wearable rehabilitation devices,
• Sophisticated and minimally invasive surgical procedures,
• Medication delivery,
• Targeted treatment of diseases such as cancer,
• Replacement muscles and organs, and
• Robotic assistants for mobility-restricted patients and elders.

The potential applications of soft robotic technology are equally exciting outside the healthcare space. For first responders and industrial workers, soft exoskeletons such as the Wyss Institute Exosuit^[7] could provide additional strength and protection. Soft robotics may also prove invaluable for search and rescue scenarios because they can reach and explore spaces far too small for humans.^[8]

Soft robotics capable of growth^[9] and self-repair^[10] could be used for scientific research into evolutionary biology, ecosystem restoration, construction, crop management, and even terraforming distant planets. Other potential applications of soft robotics include autonomous construction, education, and personal assistance.

The Future of Soft Robotics

Most near-term developments in soft robotics involve intelligence, efficiency, and flexibility.^[11] The growing sophistication of artificial intelligence already takes care of the former. As for the latter, potential measures include removing electronic components, more efficient energy storage and generation, and developing robots that imitate a biological organism's lifecycle.

When most people think of machines, they think of hard steel and rigid components. They don’t consider organic bodies or plants. However, these are perfect machines in their own right, so it’s only natural that soft robotics should try to emulate them. It is reasonable to assume that soft robotics will become more lifelike and indistinguishable from organic beings as they develop further.

As these flexible robots evolve with technology and progressively attain greater realism, their seamless integration with organic entities will create new use cases and applications that hold great promise for the field of robotics.

Sources

[1] Falk Tauber et al., “Perspectives for soft robotics: the field’s past and future,” Bioinspiration & Biomimetics, 18 (2023), https://iopscience.iop.org/article/10.1088/1748-3190/acbb48/pdf.
[2] Ellen Roche, “Pneumatic Artificial Muscles,” Soft Robotics Toolkit, https://softroboticstoolkit.com/book/pneumatic-artificial-muscles.
[3] Ravi Rao, “Powering Soft Robotics: A Deeper Look at Soft Robotics Actuators,” Wevolver, March 13, 2023, https://www.wevolver.com/article/powering-soft-robotics-a-deeper-look-at-soft-robotics-actuators.
[4] Wilfried Sire and Guilhem Velvé Casquillas, “Soft Robot: A Review,” Elveflow, https://www.elveflow.com/microfluidic-reviews/general-microfluidics/soft-robot/.
[5] Nora Bradford, “Soft Robots Take Steps toward Independence,” Scientific American, March 1, 2023, https://www.scientificamerican.com/article/soft-robots-take-steps-toward-independence/.
[6] Alexey Stepanyuk, “Soft Robotics vs. Hard Robotics – Comparative Insights and Analysis,” Soft Gripping, https://soft-gripping.com/discover/soft-robotics-vs-hard-robotics/.
[7] Conor Walsh, “Soft Exosuits for Lower Extremity Mobility,” Wyss Institute, https://wyss.harvard.edu/technology/soft-exosuits-for-lower-extremity-mobility/.
[8] Kyle Maxey, “A Growing Soft Robot to the Rescue,” Engineering.com, July 27, 2017, https://www.engineering.com/story/a-growing-soft-robot-to-the-rescue.
[9] Dario Floreano and Nicola Nosengo, “The Plant-Inspired Robots That Could Colonize Mars,” The MIT Press, https://thereader.mitpress.mit.edu/the-plant-inspired-robots-that-could-colonize-mars/.
[10] Scarlett Evans, “Self-Healing Robot Unveiled,” IOT World Today, December 15, 2022, https://www.iotworldtoday.com/robotics/self-healing-robot-unveiled-.
[11] Falk J. Tauber and Viacheslav Slesarenko, “Early career scientists converse on the future of soft robotics,” Frontiers in Robotics and AI, February 22, 2023, https://www.frontiersin.org/articles/10.3389/frobt.2023.1129827/full.