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Page 18 of 35 Kulkarni et al. Soft Sci. 2025, 5, 12 https://dx.doi.org/10.20517/ss.2023.51

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frequency (RF)-based heating systems to achieve rapid actuation . The actuator also allows for feedback
using high-power wireless energy. The authors discuss how the WASER soft robot can also be used for
applications in enclosed spaces.

Usevitch et al. describe the development of an inflatable octahedron truss structured robot that can change
shape and move using roller modules while maintaining a constant volume, eliminating the need for an air
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supply . This helps maintain the compactness of the soft robot and achieve locomotion. Tolley et al.
describe the development of an untethered pneumatic actuator that achieves a jumping motion via
combustion of butane into pneumatic chambers . The robot can reach a height of 0.6 meters in less than a
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second. This soft body structure absorbs energy upon landing, increases its impact-bearing capability, and
reduces risks to human safety. Thus, the development of explosive-driven soft robotic devices could provide
new opportunities for soft robotic locomotion while avoiding obstructions in search and rescue
environments . In another study, Mazzolai et al. describe a tendon-driven soft robotic arm with suction
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cups for grabbing objects in confined environments. The soft robot mimics the motion of octopus tentacles
and can achieve bending and twisting motions [Figure 9, Octopus robot]. These soft robots have
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actuation systems that allow them to transform to different diameter sizes for travel through different-sized
pipes. For instance, the pneumatic axial elongation actuation of the worm-inspired soft robots impacts the
distance the soft robot can move . The radial expansion of the soft robot also allows it to expand to the
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size of the pipe it is traveling through . Similarly, the axial bending deformation, flexion, and extension
motion through the pneumatic actuation of the soft pipe robot enable travel through pipes with different
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diameter sizes by expansion . These examples suggest that using actuation mechanisms that allow for easy
and efficient robot size deformation is advantageous in constricted environments. Pneumatically actuated
soft robots seem to be more beneficial and versatile as they can change size simply by inflation or deflation
and are more controlled. Other actuation mechanisms of soft robots, such as tendon-based actuation, may
not be as easily deformable in terms of size and instead can only be built for a specific application.

Soft sensor designs used for search and rescue and confined space applications
Soft pressure and strain sensors were developed for monitoring and inspection operations in hazardous and
confined environments. Soft grippers with sensing capabilities can sense object orientations and
deformation when collecting specimens . These sensors include 3D strain sensing printed ionic
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conductive gels . The flexibility of the gel helps the sensor to be easily integrated within the soft gripper
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for accurate sensing. Other integrated sensing technologies are discussed in the literature review by Milana
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on soft robots for infrastructure protection .
Soft pressure sensors have also been developed using conductive elastomer composites that have conductive
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fillers with piezoresistive characteristics . Capacitor-based soft sensors can be used as self-healing pressure
sensors and can detect changes in external pressure applied by changes in the capacitance of the
material . Zhang et al. describe a capacitive-based pressure sensor using the self-healing material,
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polyacrylic acid/betaine, thus extending the sensor’s operating life. The sensor is developed using two
conductive fabrics with an ionotronic layer between them that is composed of self-healing material
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[Figure 10A]. When pressure is applied to the sensor, the change in the capacitance of the material can be
used to detect the changes in the pressure . Georgopoulou et al. also propose using self-healing
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piezoresistive strain sensor fiber composites (ShSFCs) as an electronic skin to detect deformation and
damage on a soft robot. The sensor was tested using a tendon-based soft actuator in which the electric signal
output of the sensor was recorded before damage, after damage, and after healing. The signal output
displayed that the sensor was able to regain its performance after healing [Figure 10B]. Other self-healing
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soft sensors are discussed in a literature review by Khatib et al. .
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