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Figure 10. Soft sensors for search and rescue environments. (A) Self-healing polyacrylic acid/betaine pressure sensor material
composition and capacitance variations based on different pressure level loads, response time at a loading pressure of 0.36 kPa, and
dynamic loading and unloading at different pressure levels [218] ; (B) ShSFC-based electronic skin sensor that is attached to a tendon-
based soft robotic actuator. The electrical signal of the sensor recorded before damage, after damage, and after healing is also
displayed [219] . [All images (A and B) are licensed under CC BY 4.0. http://creativecommons.org/licenses/by/4.0/.] ShSFC: Self-healing
piezoresistive strain sensor fiber composite.

EXPANDING THE USE OF SOFT ROBOTS IN EXTREME ENVIRONMENTS
So far, this paper has explored the benefits of soft robots in extreme environmental conditions because of
their material composition, actuation mechanisms, and adaptability. However, challenges and limitations to
using soft robots persist. Topology optimization tools may be used to strengthen the design and function of
these robots to expand their usage. Special considerations for soft robots in terms of control systems and the
extreme environments described should also be considered. Finally, as the field develops and prototypes
become commercial products, it will benefit these efforts to address challenges for end users during early
research.

Soft actuator limitations for use in extreme environments
Soft actuators have advantages and limitations that are important to understand when designing soft robots
for extreme environments. Some soft actuators have drawbacks, such as tendon-driven actuators which may
undergo fatigue, nonlinear friction, backlash hysteresis, and other transmitted forces . Flexible fluidic
[44]
actuators including PAMs and McKibben actuators require external power sources for actuation, making it
difficult to build untethered systems for biomedical devices and other applications in enclosed spaces. Soft
[44]
pneumatic actuators also usually suffer from low actuation response speeds . Soft robots have
[137]
unpredictable and complex behaviors resulting in nonlinearities that make them difficult to model and
[220]
control . Therefore, matching actuation mechanisms to applications that achieve desired performance
levels may help develop soft robots that are favorable in their operating environments. For example, Zaidi
et al. describe how cable-driven soft actuators, despite their low response speed, can support high
payloads . In contrast, electro-active polymers have poor payload performance, but exhibit faster response
[137]
speeds and efficient power consumption. SMAs usually have low noise and high force-to-weight ratios but
lower response speeds and poor power consumption performance. In contrast, pneumatic actuators usually
[137]
have high payloads and adequate power but suffer from noise and poor power consumption . Future
improvements to building soft robots may include building multi-actuator systems to leverage the
advantages of different components for enhanced composite performance.