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Page 2 of 13 Zhao et al. Soft Sci. 2025, 5, 10 https://dx.doi.org/10.20517/ss.2024.61

INTRODUCTION
Torticollis, also known as wry neck, is characterized by a sudden injury or overuse of neck muscles or
[1]
structures, resulting in neck pain and functional limitation . Diagnosis of torticollis is currently centered on
clinical evaluation, and computer vision and image recognition techniques have been applied to analyze
[2]
postures and movements recorded by surveillance cameras or other imaging devices . By identifying
abnormal motion patterns in the head and neck area, indicators of torticollis can be detected. Additionally,
specific wearable devices are capable of recording changes in head and neck positioning, aiding in the
recognition of abnormal neck movements and possible torticollis cases while asleep . As a key component
[3]
of wearable devices, flexible sensors can react to external stimuli and have become a prominent research
[4]
topic because of their distinctive performance benefits , including low cost, lightweight design, and
excellent biocompatibility . These sensors hold significant application potential in areas such as electronic
[5-7]
skin [8-10] , human-machine interaction [11-14] , and personal healthcare monitoring [15-19] . Furthermore, flexible
sensors can more readily achieve close contact with human skin, thereby aiding in the reduction of
environmental noise and enhancing the precision of physiological information detection.

Flexible strain sensors are typically made of conductive sensing materials and elastic substrates [20,21] . In
contrast to traditional conductive materials, nano-scale conductive materials with superior electrical and
mechanical properties are garnering increasing attention [22,23] . Two-dimensional (2D) graphene, noted for its
exceptional properties, has been a catalyst for transformation across various industries [24,25] . Graphene,
producible on a mass scale through chemical vapor deposition (CVD), serves as a cost-effective conductive
material for sensors [4,26] . Graphene-based flexible strain sensors are known for their ultra-high sensitivity,
[27]
attributed to the crack propagation mechanism ; however, they typically exhibit suboptimal tensile
[28]
properties . Incorporating high-aspect-ratio carbon nanotubes (CNTs) can enhance the sensing range, yet
CNTs-based strain sensors often demonstrate low sensitivity, as the conductive network remains stable even
[29]
at elevated strain levels . Thus, integrating graphene with CNTs effectively balances the fundamental
sensing performance of strain sensors.

Fabrics, with their softness, stretchability, and porosity derived from high-aspect-ratio fibers, are among the
most common and adaptable materials. The interlaced fiber structure endows fabrics with flexibility,
breathability, and comfort. Incorporating sensing units into fabrics used in daily personal items can readily
fulfill the fundamental requirements of wearable technology without causing significant discomfort to the
human body [7,30,31] . Consequently, fabrics are gaining significant attention as promising substrate materials
[32]
for wearable healthcare sensor devices . Given the inherent properties of fabrics (e.g., roughness, porosity,
and hygroscopicity), developing flexible fabric-based electronic devices presents numerous challenges.
Reports indicate that researchers commonly employ the following strategies to address the manufacturing
challenges of fabric-based electronic products. Initially, conductive fibers can be integrated into the fabric in
a manner that ensures sensing capabilities and wearability without compromising its performance and
aesthetics [33,34] . However, the porous, rough, and hygroscopic nature of fabrics can lead to uneven
distribution of sprayed conductive films, potentially diminishing electrical performance . Moreover, the
[35]
conductive film is susceptible to damage due to fiber movement throughout the stretching process.
[36]
Additionally, the low adhesion between the conductive material and the fabric necessitates a passivation
layer to avoid delamination or peeling of the film on the fabric.

At present, the adoption of flexible wearable strain sensors remains limited. Thus, while ensuring the
sensor’s high performance, advancing a scalable, cost-effective manufacturing process is essential for
fostering its commercialization. The printing process has become a trusted solution for manufacturing a
range of flexible devices, citing its high efficiency, cost-effectiveness, and versatility in patterning [37-39] .