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Page 10 of 35 Kulkarni et al. Soft Sci. 2025, 5, 12 https://dx.doi.org/10.20517/ss.2023.51

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surfaces, causing discomfort to patients . Additionally, common circuit components may result in poor
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transduction (i.e., signal mismatch) between the device and biological tissues . There exists a need to
explore soft, flexible sensors for monitoring body conditions to gather accurate data while preventing harm
or discomfort to patients.

Hydrogel-based materials have been investigated in biomedical sensor design because of their soft structure
[124]
and response to external stimuli . Hydrogels consist of polymer chain networks that can swell in aqueous
conditions. Environmentally responsive hydrogels can detect glucose levels and can be used for touch,
stress, stretch, and pH level sensing . Zhai et al. propose a glucose sensor comprising platinum
[124]
nanoparticles/polyaniline hydrogel hetero-structured electrodes which allow for physiologically relevant
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sensitivity and rapid response when detecting changes in glucose levels . Noninvasive methods of glucose
monitoring have been developed for diabetic patients to avoid anxiety and pain from traditional, invasive
fingerstick procedures . For instance, Lin et al. demonstrated how hydrogel-based patches with
[155]
electrochemical glucose sensing can be safely placed on a skin surface to detect changes in glucose levels
from sweat . This hydrogel strategy allows for accurate noninvasive sensing in a wearable sensor design.
[155]
Such sensors can be paired with actuating devices to deliver therapeutics in response to illness or disease.

Tactile sensors have also been developed for soft robotic biomedical applications. Qiu et al. describe the
application of force, pressure, and tactile sensors including haptic feedback for robot-assisted minimally
invasive surgery (RMIS) [Figure 4A]. Tactile sensing can detect tissue palpation to identify tumors,
[156]
[156]
lumps, vessels, or other abnormalities within the human body . Qasaimeh et al. describe the development
of a tactile sensor made of polyvinylidene fluoride (PVDF) for minimally invasive surgery applications to
sense the pulses of arteries . The PVDF material was used as it is a piezoelectric material and can be used
[157]
to sense a wide range of frequencies. Thus, the sensor can detect different loads by varying voltage levels
from the PVDF sensing elements. The sensor also features a tooth-like structure, enabling it to grasp and
hold soft tissues . Li et al. propose an implantable and degradable tactile soft sensor for intracranial
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pressure detection [Figure 4B]. The sensor is made of silk fibroin protein and is unaffected by
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temperature changes or tissue environments .
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Soft electronic sensors, or electronic skin sensors, are made from biocompatible and biodegradable
polymers to mimic the properties of human skin and can sense changes in strain, pressure, shear force,
temperature, and humidity . Elastomers integrated with inorganic, conductive fillers can be used as
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resistive strain sensors measuring signal changes with stretching to monitor cardiac rhythm, tendon
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rehabilitation, and physiological data . Kim et al. have developed silicone rubber cantilever sensors to
measure cardiac tissue contractility by detecting strain changes in cardiomyocytes cultured on the
cantilever [Figure 4C]. Polydimethylsiloxane (PDMS)-based soft sensors have been used as a dielectric
[161]
layer for capacitive-based pressure sensors . A tissue-adhesive piezoelectric soft sensor was developed to
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adhere to the surface of the biological tissue and monitor vitals including blood pressure, heart rate, and
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respiratory signals during surgery . However, soft electronic skin sensors usually rely on external power
sources which increases power consumption and design complexity. These examples demonstrate the wide
variety of biological signals that can be detected by soft material sensors to further enhance the performance
of implantable soft robots.

SOFT ROBOTS FOR MARINE ENVIRONMENTS
Robotic devices are being investigated for ocean exploration applications including inspection, offshore
operations, and biological sampling . Robots designed to perform operations in marine environments
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must withstand extreme conditions such as high hydrostatic pressure , and rough, uneven, and delicate
[105]