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Page 2 of 43 Wang et al. Soft Sci 2024;4:41 https://dx.doi.org/10.20517/ss.2024.53

the research and development of micro-cylindrical electronic devices, promoting technological advancements and
innovation in emerging applications.

Keywords: Micro-cylindrical electronics, fibric electronic systems, conformal manufacturing, wearable devices,
surgical robotics, implantable medicine

INTRODUCTION
Micro-cylindrical and fibric electronic devices have garnered significant attention and application across
various fields in recent years due to their unique geometric structures and superior mechanical properties.
As shown in Table 1, fibric-based devices exhibit distinct advantages over traditional film-based flexible
electronics. These advantages include superior flexibility, breathability, and lightweight characteristics,
making them well-suited for applications requiring extended wear and adaptability to complex surfaces. In
[1]
addition, micro-cylindrical and fibric devices possess ultra-high curvature and high aspect ratios ,
enhancing space utilization and enabling the integration of complex, fiber-based electronic systems within
confined spaces. These devices typically exhibit exceptional flexibility and lightweight characteristics,
allowing them to maintain stable performance across diverse conditions. In particular, fibric and micro-
cylindrical materials are pivotal to the performance of micro-cylindrical and fibric electronic devices,
directly influencing their functionality and application range. These substrates encompass a diverse array of
types - including rigid, flexible, stretchable, and natural fibric materials - each suited to distinct structural
designs and application demands. Rigid substrates, for instance, provide stable support ideal for applications
such as sensors on the tips of surgical instruments . In contrast, flexible and stretchable substrates, prized
[2]
for their deformability and stretchability, are well-suited for wearable and implantable medical devices .
[3,4]
Natural fibers, known for their biocompatibility, degradability, and eco-friendly nature, further expand the
range of applications in sustainable and bio-integrated electronics . Beyond mechanical resilience, these
[5]
substrates must also meet the requirements of biocompatibility, electrical conductivity, and durability to
ensure stable and reliable device performance in practical settings.

The unique geometrical features of micro-cylindrical substrates, characterized by their high curvature,
aspect ratio, and flexibility, significantly influence the fabrication process of electronic devices.
Conventional electrospinning techniques are effective for producing disordered fiber networks, often
[6,7]
employed in the fabrication of thin-film sensors . However, they lack the capability to directly create
patterned, functional structures on each individual micro-cylindrical or fibric surface. Conformal
fabrication on micro-cylindrical surfaces requires not only addressing the mechanical adaptability of
materials but also overcoming challenges such as high-precision patterning and multilayer integration on
[8,9]
high curvature geometries . Based on these distinct characteristics, the manufacturing processes for
micro-cylindrical electronics can be categorized into three main types, including additive, subtractive, and
equivalent manners. Additive manufacturing builds complex three-dimensional structures onto micro-
cylindrical substrates by sequentially stacking materials, utilizing techniques such as chemical coating and
[10]
[14]
[13]
[12]
[11]
electroplating , inkjet printing , aerosol jet printing , and electrohydrodynamic (EHD) printing . The
key strength of additive manufacturing lies in its material compatibility and design flexibility, making it
highly suitable for customized production [15,16] . However, limitations remain in terms of precision and
material stability, which require further optimization. Subtractive manufacturing, in contrast, achieves the
desired structures through the removal of material, utilizing methods such as laser processing , rotational
[17]
[18]
exposure lithography , and various etching techniques. Rotational lithography, for instance, allows for the
generation of high-resolution patterns on curved surfaces by adopting high-precision masks. While
subtractive manufacturing offers superior precision and repeatability, it tends to be more expensive and less
efficient for complex designs. It is primarily employed in the fabrication of high-precision implantable
medical devices and high-performance microsensors . The equivalent manufacturing process is
[19]
[20]