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Page 4 of 35 Kulkarni et al. Soft Sci. 2025, 5, 12 https://dx.doi.org/10.20517/ss.2023.51

Table 1. Summary of benefits of properties of soft materials over traditional rigid materials in devices for certain applications in
extreme environments
Property and Soft materials Rigid materials
desired quality
Flexibility and (Silicone elastomer, PDMS, rubber, low-density polyethylene) Metals or hard plastics
9
4
12
9
elasticity: Low E = 10 to 10 Pa [28] E = 10 to 10 Pa [28]
Young’s modulus
[29] [30]
Resistance to brittle Silicone rubber: 80% to 530% Al: 65%, Fe: 43%
failure: high ductility
3 3 3
Lightweight: low SR-1610, Douglas and Sturgess 1.15 g/cm ; Dragon skin, Smooth-On 1.08 Steel 7.8 g/cm , iron 7.9 g/cm , aluminum 2.7
3
3
3
3
density g/cm ; Ecoflex 00-10, Smooth-On 1.03 g/cm ; HS-IV, Dow Corning 1.11 g/cm , copper 8.9 g/cm , brass 8.5 g/cm 3[32]
3 3
g/cm ; Candle Gel, Endless Possibilities 0.98 g/cm ; Tin-Sil, US
3
3
Composites 1.07 g/cm ; Semicosil 921, Wacker Solution 1.10 g/cm ;
3
8116SS plastic, M-F Manufacturing 0.99 g/cm ; CF11, Nusil Technologies
1.04 g/cm 3[31]
[33]
Thermal insulation: Silicone rubber: 0.06 to 6.5 W/mK Al: 210 W/mK, Fe: 76.2 W/mK, high carbon
low conductivity steel: 19-52 W/mK, low carbon steel: 25.3-93
[34-38]
W/mK, stainless steel: 10-34.3 W/mK
[42]
Biocompatibility Natural protein-based materials such as gelatin can help with Ti alloys can be biocompatible . Generally,
[39]
biointegration and are absorbable . Coating surfaces with polymeric corrosion of metallic implants may jeopardize
[40]
biomaterials can enhance cellular attachment . Silicone rubber has the mechanical stability of the device and the
excellent biocompatibility [41] integrity of surrounding tissue. Metal traces
[42]
can disturb homeostasis
Self-healing ability Self-healing damages that occur during operation can extend service life -
by (a) creating reversible crosslinks in thermoplastics and (b) introducing
healing agents into cracks
PDMS: Polydimethylsiloxane.
agents added to a base material while intrinsic self-healing materials have inherent healing capabilities.
Materials with intrinsic healing characteristics have dynamic covalent interactions where covalent bonds
can break and reform . These covalent bonds are strong (150-550 kilojoules per mole). Due to high bond
[45]
strengths, these self-healing materials usually require external stimuli (heat or light) to activate their healing
characteristics . Self-healing polymers with mechano-reversible bonds can form after breakage by the
[45]
[45]
rebinding reactive functional groups . Other self-healing soft robots have been implemented using
polymer networks that employ a thermoreversible Diers-Alder reaction to re-form after damage due to
sharp objects or overloading . Cheng et al. proposed a self-healing dielectric elastomer actuator (DEA)-
[45]
driven soft robot that operates on land and in water . The ion-to-dipole interactions between the charge
[46]
carriers and the fluorinated polymer matrix within the ionic electrode of the DEA allow the electrode to
self-heal from damage in aqueous or dry land environments. Kashef Tabrizian et al. propose a soft actuator
that comprises shape memory alloy (SMA) wire reinforcements within a castor oil-based self-healing
polymer able to heal large incisions. Diers-Alder covalent bonds and weak hydrogen interactions relink and
enable the restoration of damaged material surfaces . The ability of soft robots to withstand impact from
[47]
external forces provides advantages that increase their operational life.
Soft robots can not only operate despite external disturbances but also use these conditions to their
advantage. The integration of soft materials to build robotic systems has enabled the development of new
actuation and sensing techniques that leverage environmental conditions to function. Environmental inputs
for soft robots range from pressure , chemical , electrical , and magnet-driven systems to
[51]
[49]
[50]
[48]
temperature , acoustics , and light [Table 2].
[54]
[52]
[53]
Recent developments in soft robotics have focused on design techniques that prioritize optimization and
[95]
efficiency. Several soft robot designs are implemented through bio-inspiration and bio-mimicry including
locomotion, such as crawling, jumping, aerial motion, and swimming. These actuation mechanisms are