Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Technology Roadmap for Flexible Sensors.

Catastrophically mechanical failure of soft self-healing materials is unavoidable due to their inherently poor resistance to crack propagation. Here, with a model system, i.e., soft self-healing polyurea, we present a biomimetic strategy of surpassing trade-off between soft self-healing and high fracture toughness, enabling the conversion of soft and weak into soft yet tough self-healing material. Such an achievement is inspired by vascular smooth muscles, where core-shell structured Galinstan micro-droplets are introduced through molecularly interfacial metal-coordinated assembly, resulting in an increased crack-resistant strain and fracture toughness of 12.2 and 34.9 times without sacrificing softness. The obtained fracture toughness is up to 111.16 ± 8.76 kJ/m2, even higher than that of Al and Zn alloys. Moreover, the resultant composite delivers fast self-healing kinetics (1 min) upon local near-infrared irradiation, and possesses ultra-high dielectric constants (~14.57), thus being able to be fabricated into sensitive and self-healing capacitive strain-sensors tolerant towards cracks potentially evolved in service. 

/pdf/vascular-smooth-muscle-inspired-architecture-enables-soft-1nfetqnn.pdf

Vascular smooth muscle-inspired architecture enables soft yet tough self-healing materials for durable capacitive strain-sensor

Reducing the swelling of tissue‐adhesive hydrogels is crucial for maintaining stable tissue adhesion and inhibiting tissue inflammation. However, reported strategies for reducing swelling always result in a simultaneous decrease in the tissue adhesive strength of the hydrogel. Furthermore, once the covalent bonds break in the currently reported hydrogels, they cannot be rebuilt, and the hydrogel loses its tissue adhesive ability. In this work, a nonswelling hydrogel (named as “PAACP”) possessing regenerable high tissue adhesion is synthesized by copolymerizing and crosslinking poly(vinyl butyral) with acrylic acid, gelatin, and chitosan‐grafted N‐acetyl‐l‐cysteine. The tissue adhesive strength of the obtained PAACP reaches 211.4 kPa, which is approximately ten times higher than that of the reported nonswelling hydrogels, and the hydrogel can be reused for multiple cycles. The as‐prepared hydrogel shows great potential in soft bioelectronics, as muscle fatigue is successfully monitored via the electrode array and strain sensor integrated on PAACP substrates. The success of these bioelectronics offers potential applicability in the long‐term diagnosis of muscle‐related health conditions and prosthetic manipulations.

A Nonswelling Hydrogel with Regenerable High Wet Tissue Adhesion for Bioelectronics

Unlike conventional rigid machines, soft robots generally have unique operation styles that rely heavily on soft matter engineering and smart material systems. Owing to the superior merits of both metals and fluids, liquid metal smart materials are increasingly being innovatively used as soft actuators and sensors to construct soft robots. To promote further development and prosperity in this field, this review organizes and summarizes the typical progress in liquid metal smart materials, with a special focus on their robotic response behaviors. In particular, the article emphasizes the concept of smart composite systems consisting of liquid metals and synergistic substances (e.g., solutions, particles, and polymers). The response behaviors of liquid metal smart materials under the actions of external factors (electricity, magnetism, ultrasound, light, heat, etc.) are examined and the smart properties occurring during these responses, such as motion, transformation, self-organization, adaptive healing, and autonomous sensing, are identified. Furthermore, soft actuators, control systems, and robots based on liquid metal smart materials are summarized and elaborated upon. Finally, the potential directions worth pursuing and challenges are outlined. It is expected that this review will stimulate further investigations into liquid metal smart materials with the aim of building a new generation of soft robots. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/aisy.202200375

Liquid Metal Smart Materials toward Soft Robotics

The emergence of liquid metal (LM) emulsion as a soft multifunctional filler brings a new opportunity for fabricating hydrogel-based strain sensors with multifunctional properties. However, the extremely large surface tension and high density of LMs inhibit emulsification. Herein, we demonstrated a strategy for stabilizing LM emulsions using cationic cellulose nanofibers (CCNFs) to encapsulate LM droplets through strong electrostatic attraction with LM. By inducing acrylic acid (AA) polymerization in the presence of a CCNF-stabilized LM emulsion, a conductive hydrogel was prepared with the formation of reversible hydrogen bonds, ionic coordination, and electrostatic interactions among CCNFs, LM droplets, and poly(acrylic acid) (PAA). The hydrogel obtained, named the CCNF-LM-PAA hydrogel, shows good conductivity (1.54 S m−1), remarkable tensile strength and elongation at break, self-adhesiveness, and quick self-healing capability. As a strain-sensing material, the CCNF-LM-PAA hydrogel exhibits a very high sensing sensitivity (gauge factor = 16.2), a low strain detection limit (less than 1%), a short response/recovery time (107/91 ms), and good durability (300 cycles). These results enable the CCNF-LM-PAA hydrogel-based strain sensor to be an excellent wearable device for monitoring various human activities. Therefore, introducing additional electrostatic interactions by using CCNFs to stabilize LM emulsions provides a practical way to enhance the strain-sensing performance of LM emulsion-based hydrogels for assembling self-attached wearable devices. 

/pdf/highly-sensitive-and-self-healing-conductive-hydrogels-1614sxsr.pdf

Highly sensitive and self-healing conductive hydrogels fabricated from cationic cellulose nanofiber-dispersed liquid metal for strain sensors

The field of stretchable electronics mainly includes electronic products conformal with tissues, being integrated into skin or clothing. Since these products need to work during deformation, their requirements for materials focus on stretchability and conductivity. Liquid metals are excellent materials with these properties. However, liquid metals have extremely high surface tension at room temperature, which will spontaneously form a spherical shape and are difficult to form the shape required by stretchable devices, which is the biggest obstacle to their development in this emerging field. Therefore, the emphasis is placed on the principle of overcoming the high surface tension in this review, and various methods of using liquid metals to fabricate stretchable electronic devices based on these principles have been linked. Liquid metals show promise in the convenience of sensing, energy harvesting, etc. The existing challenges and opportunities are also discussed here. 

/pdf/from-liquid-metal-to-stretchable-electronics-overcoming-the-3riz8glo.pdf

From liquid metal to stretchable electronics: Overcoming the surface tension

Developing neural electrodes with high stretchability and stable conductivity is a promising method to explore applications of them in biological medicine and electronic skin. However, considering the poor mechanical stretchability of typical conductive materials, maintaining the connection of electrode conductive paths under high stretching is still a challenge. Herein, for the first time, a double-microcrack coupling strategy for highly stretchable neural electrodes is proposed. Compared with single-layer stretchable microcrack electrodes, the design utilizes the complement between two gold microcrack films to contribute more conductive paths. It shows that the resistance change (R/R0) of the electrode under 100% strain is about 5.6 times, which is much lower than other electrodes and exhibits a high stretchability of ≈200%. Simultaneously, this design is an encapsulation-free design which avoids the electrode performance degradation caused by encapsulation. Furthermore, it is found that the adhesion strength between metal electrode and substrate is critical to the stretchability and stability of electrodes, so polydimethylsiloxane0.9-isophorone diisocyanate elastomer (PDMS0.9-IPDI), whose adhesion to gold electrode is 4.5 times higher than that of the commercial polydimethylsiloxane (PDMS), is synthesized. Finally, the electrophysiological communication between different organisms by electrodes is successfully demonstrated. 

Double‐Microcrack Coupling Stretchable Neural Electrode for Electrophysiological Communication

The monitoring of plant physiology and ecology:from materials to flexible devices

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Zixu Yang

Author Tools

Chat about Author

Papers

From liquid metal to stretchable electronics: Overcoming the surface tension

Double‐Microcrack Coupling Stretchable Neural Electrode for Electrophysiological Communication

The monitoring of plant physiology and ecology:from materials to flexible devices