This review focuses on deepening the structural understanding of crack-based strain sensors (CBSS) on stretchable and flexible polymeric substrates and promoting sensor performance optimization. CBSS are cutting-edge devices that purposely incorporate cracks into their functional elements, thereby achieving high sensitivity, wide working ranges, and rapid response times. To optimize the performance of CBSS, systematic research on the structural characteristics of cracks is essential. This review comprehensively analyzes the key factors determining CBSS performance such as the crack mechanism, geometrical factors, and functional structures and proposes optimization strategies grounded in these insights. In addition, we explore the potential of numerical analysis and machine learning to offer novel perspectives for sensor optimization. Following this, we introduce various applications of CBSS. Finally, we discuss the current challenges and future prospects in CBSS research, providing a roadmap for next-generation technologies.

Biology is characterized by smooth, elastic, and nonplanar surfaces; as a consequence, soft electronics that enable interfacing with nonplanar surfaces allow applications that could not be achieved with the rigid and integrated circuits that exist today. Here, we review the latest examples of technologies and methods that can replace elasticity through a structural approach; these approaches can modify mechanical properties, thereby improving performance, while maintaining the existing material integrity. Furthermore, an overview of the recent progress in wave/wrinkle, stretchable interconnect, origami/kirigami, crack, nano/micro, and textile structures is provided. Finally, potential applications and expected developments in soft electronics are discussed.

The patterning of electrospun fibers is a key technology applicable to various fields. This study reports a novel focused patterning method for electrospun nanofibers that uses a cylindrical dielectric guide. The finite elements method (FEM) was used to analyze the electric field focusing phenomenon and ground its explanation in established theory. The horizontal and vertical electric field strengths in the simulation are shown to be key factors in determining the spatial distribution of nanofibers. The experimental results demonstrate a relationship between the size of the cylindrical dielectric guide and that of the electrospun area accumulated in the collector. By concentrating the electric field, we were able to fabricate a pattern of less than 6 mm. The demonstration of continuous line and square patterning shows that the electrospun area can be well controlled. This novel patterning method can be used in a variety of applications, such as sensors, biomedical devices, batteries, and composites.

A versatile coatable strain (CS) sensor was developed using a wet process, achieving a high sensitivity (GF ≈ 100). It overcame traditional polymer limitations, enabling real-time growth measurements on complex biological and non-planar surfaces.

Objective measurement of tremors is important for assessing the severity and preventing misdiagnosis of Parkinson's disease (PD). To address this demand, this study presents a multichannel, wireless, patch‐type tremor monitoring system that integrates a high‐repeatable fibrous crack‐based strain (FCBS) sensor with a flexible wireless communication circuit. The FCBS sensor, incorporating crack structures, random fiber orientation, junction melting, and polymer penetration within a 3D conductive fiber network, achieves high sensitivity (gauge factor up to 476.89), a fast response time (≈ 6.64 ms), a wide working range (>200% strain), low Young's modulus (≈45 kPa), and excellent repeatability (>100 000 cycles). In addition, this study demonstrates the first clinical application of a flexible strain sensor‐based tremor monitoring system in patients with PD and ET for simultaneous multilocation tremor measurement. Through clinical trials, our system measured tremor indicators (peak amplitude and fundamental frequency), and tremor indicators obtained from multilocation showed improved correlation and statistical significance with tremor scoring in UPDRS III under specific conditions. These results demonstrate the applicability and potential of the flexible strain sensor‐based system as a wearable platform for quantitative and objective tremor measurement.