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

emerging fields. To this end, this paper first reviews a range of commonly used materials for micro-
cylindrical electronic devices, focusing on key properties such as suitability, conductivity, biocompatibility,
and durability. Following this, a comprehensive overview of fabrication methods is provided, including
conformal additive, subtractive, and equivalent manufacturing approaches. The respective advantages and
limitations of each process will be adequately evaluated. Building on this analysis, the paper will further
explore the typical applications of micro-cylindrical electronic devices across various fields, including
wearable electronics, environmental monitoring, surgical robotics, implantable bioelectronics, and
interventional magnetic resonance imaging (MRI) [Figure 1]. Additionally, this paper will examine the key
technological bottlenecks that currently hinder the broader adoption of these devices, such as insufficient
manufacturing precision, poor material compatibility, and high production costs. Proposed solutions to
these challenges will be discussed, with the aim of advancing the practical application of micro-cylindrical
electronics. In all, this paper seeks to provide a systematic overview of the fabrication processes and
application scenarios for micro-cylindrical surface electronics, offering insights into their technical
characteristics, applicable fields, and development trends. It is hoped that this work will serve as a valuable
theoretical foundation and reference for future innovations in the field.

MATERIAL
In micro-cylindrical or fibric electronics and microsensors, the choice of substrate material is critical to
device performance, comfort, and biocompatibility. Each type of substrate, whether rigid, flexible,
stretchable, or natural fiber, offers distinct advantages in mechanical properties, electrical characteristics,
and specific application scenarios. Rigid substrates are optimal for maintaining geometric stability, making
them ideal for applications such as surgical instruments where precision and strength are paramount.
Flexible substrates provide high mechanical tolerance and enhanced biocompatibility, addressing the need
for durability and adaptability in wearable devices. With recent technological advancements, stretchable
materials have further broadened the applications of flexible substrates, enabling smart sensors, soft
robotics, and other devices in environments involving large deformations. In addition, natural fiber
materials, due to their excellent biocompatibility and environmental sustainability, are increasingly selected
for functional designs and eco-friendly electronics. While each substrate type shows significant potential in
its respective domain, optimizing stability, performance, and long-term reliability remains essential for
advancing future applications.

Rigid micro-cylindrical/fibric materials
Rigid micro-cylindrical substrates, such as stainless-steel pins, tungsten pins, and polyimide (PI) rods, are
widely used as foundational materials for constructing micro-sensors, high-density electrodes, and other
electronic devices, particularly in applications requiring precise localization. With stable mechanical
properties, these substrates offer highly controllable geometries and structural strength, making them ideal
for accurate signal acquisition and transmission in complex environments. This stability supports delicate
operations such as deep tissue dissection and electrical monitoring [46-48] . For instance, in tissue biopsies,
multimodal sensor arrays integrated onto the surface of a rigid micro-cylindrical needle can simultaneously
measure parameters such as tissue conductivity, pH, and glucose concentration . Rigid substrates are also
[2]
[50]
commonly used in neural interfaces and minimally invasive surgical tools . These materials typically
[49]
exhibit good chemical stability and durability, maintaining their mechanical and electrical properties even
after extended use or repeated sterilizations.

Compared to flexible or stretchable substrates, rigid materials are more suitable for applications demanding
a wider temperature tolerance and greater penetration into biological tissues . However, rigid micro-
[32]
cylindrical substrates face limitations in biological applications, including reduced compatibility and