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Lee et al. Soft Sci 2024;4:38 https://dx.doi.org/10.20517/ss.2024.36 Page 25 of 31

stretchable elastomer substrates. The review also explores how to maximize these approaches in various
environments through careful selection of substrate materials and strain designs tailored to specific
applications. Initially, promising buckling and Kirigami structures are examined, with an analysis of the
tensile deformation characteristics of structured plastic substrates under different design conditions.
Specifically, the review addresses deformation characteristics of buckling structures based on shape, size,
and isotropy, and explores Kirigami structures by systematically analyzing the effects of cut pattern shape,
size, and combinations, providing design guidelines for plastic film substrates across diverse applications.
Furthermore, the review discusses strategies for using intrinsically stretchable elastomer materials,
particularly approaches to spatially pattern moduli to minimize unwanted deformations in pristine
elastomers. This section also discusses techniques such as inducing network alignment or crosslink
patterning in homogeneous elastomers through external stimuli, along with utilizing compensatory effects
in heterogeneous structures to achieve multi-dimensional control over both local and global deformations.

In free-form display applications, electrodes, driving components, and light-emitting elements are layered
onto strain-engineered stretchable substrates, where the choice of substrate material and strain-engineering
strategy should be carefully tailored to factors such as the type of light-emitting element, processing
temperature, target resolution, and deformation behaviors. For example, while structured plastic substrates
have limited effective areas for device formation, they offer greater heat resistance and mechanical stability
than elastomers, ensuring compatibility with existing display manufacturing processes. Due to these
properties, plastic substrates can be quickly commercialized in low-resolution applications such as simple
signal displays or automotive screens. Conversely, elastomers provide intrinsic stretchability without
additional structures, offering a large effective area, making them suitable for high-resolution displays.
However, their low thermal stability restricts processing temperatures, necessitating further research to
develop materials with enhanced thermal stability or reduced processing temperatures .
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To successfully develop displays that support various form factors, ensuring compatibility between the
strain-engineered stretchable substrates proposed in this review and key display components is essential.
Additionally, for commercialization, hardware or software solutions are required to compensate for
[153]
resolution loss and enable seamless content transitions due to form-factor changes . Ideally, for high-
resolution, multi-dimensional displays, most display components, including the substrate, should possess
inherent stretchability. Free-form display technology is currently considered to be between the introductory
and growth stages, with intensive research underway on materials, manufacturing processes, and software-
based image compensation to develop optimized protocols for specific applications. However, challenges
remain regarding resolution, deformation characteristics, and mechanical reliability, necessitating ongoing
research and innovation to address these issues. The strain-engineering design strategies proposed in this
review are expected to help overcome some of these limitations, supporting the reliable operation of free-
form displays across various deformation conditions. This advancement could play a crucial role in
expanding the application potential of free-form displays from static shape transformations to real-time
dynamic deformations.

DECLARATIONS
Authors’ contributions
Conceptualization and supervision: Choi JC, Chung S
Prepared the figures and wrote the article: Lee DW, Park DH, Choi JC

Availability of data and materials
Not applicable.