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Page 6 of 43 Wang et al. Soft Sci 2024;4:41 https://dx.doi.org/10.20517/ss.2024.53

[55]
through repeated bending cycles . For instance, by depositing silver nanoparticles (AgNPs) onto the
surface of flexible fibers, high-sensitivity pressure sensors can achieve long-term durability exceeding 5,000
[56]
cycles . Additionally, flexible fibric structures are breathable and biocompatible, making them well-suited
for skin-contact applications such as wearable electronics and biosensors [57,58] . In the field of energy storage,
flexible fibric substrates also find a broad range of applications. By integrating poly(terephthaloyl
terephthalamide) (PPTA) fibers with carbon nanotubes (CNTs) or conductive polymers, flexible
supercapacitor electrodes with high mechanical strength and thermal resistance can be produced, ensuring
[59]
excellent electrochemical stability even under elevated temperatures . The porous nature and high specific
surface area of flexible micro-cylindrical substrates further enhance their performance in energy storage and
sensing applications. The rough fiber structure on these substrates can accommodate more active materials,
[3]
thereby improving the energy and power density of the device . With ongoing advancements in material
science and fabrication processes, flexible micro-cylindrical and fibric substrates are poised to play a crucial
role in the development of next-generation wearable devices and smart electronic products.

Stretchable micro-cylindrical and fibric substrate materials represent an advanced extension of flexible
materials, specifically designed to maintain stable performance under large deformations or extreme tensile
conditions. Unlike flexible materials, stretchable materials can endure substantial mechanical strains (even
[60]
over 100% elongation) . These materials are typically engineered using highly elastic polymers, which not
only provide significant elongation but also retain strong mechanical and electrical properties during
stretching [41,61] . For example, conductive polymer materials in stretchable sensors enable continuous
operation even in high-strain environments [62,63] . Additionally, hydrogels, with their unique elasticity,
stretchability, and excellent biocompatibility, demonstrate great potential for flexible sensors and
biomedical devices [4,64-66] . As a result, stretchable materials not only improve the comfort of wearable devices
but also expand their potential for use in high-strain environments, such as smart sensors and soft robotics.

Natural micro-cylindrical/fibric materials
Natural fibric materials offer excellent environmental sustainability and biodegradability, and their
structures can be adjusted both physically and chemically to meet the specific requirements of various
applications [67,68] . Among these, silk, a natural fiber, is particularly notable for its exceptional mechanical
strength, biocompatibility, and degradability. However, natural silk is inherently non-conductive,
necessitating the coating with other materials, such as CNTs, to enhance its functionality . Other natural
[68]
fibers, such as cotton, have also garnered significant attention in the field of flexible electronics. By
assembling gold nanoparticles (AuNPs) onto cotton fibers, their electrical conductivity can be substantially
enhanced, improving their electrical interaction with enzymes and enabling their use in biofuel cells .
[69]

Overall, natural fibric substrates are valued for their outstanding mechanical and chemical properties, as
well as their biocompatibility, making them an attractive choice for the development of functionalized
designs and environmentally friendly electronic materials [5,70] . However, the mechanical properties of
natural fibers are sensitive to variations in humidity and temperature, and they may experience degradation
over prolonged use, which could compromise their reliability and stability in long-term applications.
Despite these challenges, the limitations of natural fibers can be effectively mitigated through advanced
processing techniques and optimized composite structures. These advancements facilitate the widespread
[71]
adoption of natural fibers in flexible electronics, smart textiles, and biomedical applications .

FABRICATION
Driven by the multifunctionality and wide applications of micro-cylindrical electronic devices, substantial
research has been conducted on manufacturing technologies for these devices. There is increasing interest