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Page 8 of 30 Kim et al. Soft Sci 2023;3:16 https://dx.doi.org/10.20517/ss.2023.07

adhered to PDMS. A frequency-reconfigurable small monopole antenna driven by a bistable substrate was
presented as an application. Humood et al. fabricated polymer-based kirigami microscale structures and
investigated the mechanical stability of various 3D architectures by confirming the resilient behavior for
[146]
cyclically applied compression under different forces [Figure 3E] . The mechanical response of the 3D
structures was confirmed to be stable and recoverable when compressed up to 50% of their initial height,
and permanent changes in internal stress and curvature occur under extreme compression of 100%. With a
deep understanding of the compressive behavior of kirigami-based soft MEMS devices, guidelines are
presented to eliminate crack growth, which is critical for the fabrication of MEMS devices, including
pressure and shear sensors. Liu et al. introduced a mechanically induced 3D assembly approach for the
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design and fabrication of high-quality meanderline-based hemispherical small antennas [Figure 3F] .
External tensile strains were applied to reshape the elastomeric substrates and reversibly tune the wide range
of center frequencies to adapt to changes in environmental conditions. The demonstration of a small
antenna system whose frequency is tunable over a wide range and capable of maintaining high levels of
mechanical strain suggests promising potential applications in many applications, including wireless
wearables and bio-integrated electronics. Finally, Bai et al. fabricated a multimodal antenna capable of
customizing distinct beamforming and discrete beam scanning [Figure 3G] . They demonstrated
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approximately 30 reconfigurable mesostructures with diverse geometric topologies by mechanically guiding
the simplest ribbon geometries. Reconfigurable single antennas can replace array antennas to realize
miniaturized and smart wireless devices and can be useful in cases with limited design space.

Light-emitting diode and photodetector
Optoelectronics aims to develop devices that enable the sourcing, detection, and control of light, and it
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shares its strategic importance by being interdependent with various fields such as electronics ,
information technology [149-152] , and computer technology . Accordingly, many efforts have been made to
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develop 2D flexible/stretchable optoelectronic devices with strict mechanical criteria to maintain electrical
and optical properties despite mechanical deformation under various conditions [5,7,154] . In addition to these
efforts, the construction of complex 3D optoelectronic systems has provided qualitatively improved
performance, and it is possible to realize an efficient and highly functional optoelectronic device by
designing an architecture similar to that of 3D systems commonly seen around, including biology or
organism. Several methodologies have been proposed to implement 3D optoelectronic devices, and
representative methods include buckling, which can expand the space between optoelectronic component
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pixels by stretching or shrinking elastomeric substrates , and the kirigami method, which can fold and
convert 2D structures into 3D structures . In this chapter, we introduce recent advances in the fabrication
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method and application of stretchable and flexible 3D optoelectronic devices [Figure 4].

Wang et al. fabricated a mechanically stable 3D wireless LED device using a shape memory polymer (SMP),
a means to achieve a robust 3D framework [Figure 4A] . The recovery capability and programmability of
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the SMP provide novel routes to design freestanding 3D mesostructures and programmable microdevices.
Furthermore, when the external force along the out-of-plane direction is applied to the LED device and
removed using tweezers, the original shape is restored without noticeable damage, exhibiting essential
mechanical robustness for various applications. Lee et al. demonstrated a mechanically assembled 3D
photodetection and optical imaging system that enabled the measurements of the direction, intensity, and
angular divergence properties of incident light [Figure 4B] . Based on the mechanics of ultra-thin
[158]
graphene and MoS2, MoS2/graphene photodetector arrays were realized with origami-inspired complex 3D
shapes such as an octagonal prism, an octagonal prismoid, and a hemisphere. The resulting system could
track the direction and intensity of incident light through a 3D architecture, and the atomically thin MoS2
and graphene could fabricate optically transparent devices to detect light passing through the device at two
sensing positions. Lee et al. demonstrated an origami/kirigami-inspired LED array that can preserve the