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Xiao et al. Soft Sci 2023;3:11 https://dx.doi.org/10.20517/ss.2023.03 Page 17 of 26

color change of the cholesteric LCE could also be achieved by the volume expansion of the helix director
[49]
induced by the temperature or humidity change . A photonic flower-like sensor based on the cholesteric
LCE was developed, which shifted the color from colorless to light blue, and then to bright green, with
[49]
decreasing temperature or increasing humidity [Figure 9F] .

Biomedical devices
In addition to excellent actuation and sensing capabilities, specially designed LCEs also offer good
biocompatibility, thereby holding potential for biomedical applications. For example, Figure 10A shows 3D
biodegradable and highly regular foamlike cell scaffolds fabricated based on biocompatible porous
side-chain LCEs . The SEM images show that the cell scaffolds have similar architectures of vascular
[51]
networks in tissue. Fluorescence confocal microscopy images of myoblast cells proved the biocompatibility
of the LCEs. Such scaffolds show four times higher cell proliferation capability compared to conventional
[51]
porous template films . Figure 10B illustrates an artificial intervertebral disc based on the monodomain
LCE around the exterior and polydomain LCE in the center . Such intervertebral disc possesses similar
[153]
mechanical properties (e.g., modulus and anisotropy) to an actual one, which could be used as an
implantable device for tissue growth.

Aside from biocompatibility, LCEs also possess muscle-like actuation capabilities. By optimizing the
[52]
actuation performances, Wu et al. developed a breathable, shrinkable, hemostatic patch, which consists of
a LCE metamaterial layer with a low actuation temperature (~46 °C) and a waterproof dressing layer to offer
combined physical and chemical treatments [Figure 10C]. Such a patch could provide a suitable biaxial
contraction (~10 kPa; close to the tensile of the in vivo skin) and biaxial actuation strain (~23%) when
heated from 25 °C to 46 °C. By this noninvasive means, skin regeneration can be accelerated while avoiding
scar and keloid generation. Figure 10D illustrates an implanted LCE-based device with IR-absorbing carbon
black (CB) particles . The LCE-CB composites can change shape in response to temperature increase
[50]
induced by the transcutaneous IR light. This device could be implanted as an artificial cuff or sphincter
around the bladder neck to control the urine flow by the contraction forces induced by IR light, with the
potential to treat stress urinary incontinence.

Other applications
Excluding the above promising applications, the LCEs could also be used for energy absorption, flexible
display, liquid controlling, and smart textiles. By harnessing the soft elasticity of the LCEs, Traugutt et al.
[12]
fabricated various 3D porous LCE lattices for efficient energy absorption [Figure 11A]. Compared with the
elastomer (TangoBlack) lattice, the LCE lattice offers 12 times higher rate-dependency and 27 times higher
strain energy density. Based on the optomechanical responses of cholesteric LCEs, a highly stretchable
[154]
cholesteric LCE film was fabricated by Hussain et al. [Figure 11B] . When the film is stretched, the film
could reflect both left- and right-handed circular polarized lights with blue-shifted color. By controlling the
applied strain, polarized light, or temperature, the film could display or vanish the patterns, which could be
used in flexible displays and data encryption. In Figure 11C, Q. Liu et al. fabricated tubular LCE
[53]
microactuators whose shapes could be changed by the gradient of light . As a result, the liquid in the tube
could be driven into the narrow end. Using this technique, the velocity and direction of liquids could be
well remotely controlled by light over a long distance. In Figure 11D, the LCE fibers with reversible thermal
[54]
actuation were knit, sewn, and woven to fabricate smart textiles . Together with woven conductive fibers,
the LCE fibers could be sewn into a shirt, which could create proper pores to reduce users’ body
temperature on a hot day.