Self-Healing Mechanism and Conductivity of the Hydrogel Flexible Sensors: A Review

Abstract

Sensors are devices that can capture changes in environmental parameters and convert them into electrical signals to output, which are widely used in all aspects of life. Flexible sensors, sensors made of flexible materials, not only overcome the limitations of the environment on detection devices but also expand the application of sensors in human health and biomedicine. Conductivity and flexibility are the most important parameters for flexible sensors, and hydrogels are currently considered to be an ideal matrix material due to their excellent flexibility and biocompatibility. In particular, compared with flexible sensors based on elastomers with a high modulus, the hydrogel sensor has better stretchability and can be tightly attached to the surface of objects. However, for hydrogel sensors, a poor mechanical lifetime is always an issue. To address this challenge, a self-healing hydrogel has been proposed. Currently, a large number of studies on the self-healing property have been performed, and numerous exciting results have been obtained, but there are few detailed reviews focusing on the self-healing mechanism and conductivity of hydrogel flexible sensors. This paper presents an overview of self-healing hydrogel flexible sensors, focusing on their self-healing mechanism and conductivity. Moreover, the advantages and disadvantages of different types of sensors have been summarized and discussed. Finally, the key issues and challenges for self-healing flexible sensors are also identified and discussed along with recommendations for the future.

Recent Advances in Mechanical Reinforcement of Zwitterionic Hydrogels

“…Structures with hydrophobic interaction, π–π stacking, dipole interaction, hydrogen bond interaction, and electrostatic interaction are the most common strengthening elements ( Figure 2 b1,b2) [ 61 , 62 , 63 ]. The introduction of strong noncovalent interaction units also gives hydrogels excellent self-healing capabilities [ 64 , 65 ]. In addition, replacing 0-dimensional covalently cross-linked dot and non-covalently cross-linked dot with multi-dimensional structures can deliver more value to hydrogel ( Figure 2 c1,c2) [ 66 ].…”

Modeling Tunable Fracture in Hydrogel Shell Structures for Biomedical Applications

“…In recent years, research into hydrogels has made significant breakthroughs (e.g., self-healing hydrogels [ 88 , 89 , 90 , 113 ], smart hydrogels [ 98 ], cellulose hydrogels [ 97 ], double chain hydrogels [ 114 ], supramolecular hydrogels [ 115 ], etc.). However, most of the research focuses on hydrogel functionality, as for flexible wearable sensors, drug delivery, and medical engineering.…”

Advances and Progress in Self-Healing Hydrogel and Its Application in Regenerative Medicine

“…However, despite their many favorable properties, the main drawback of hydrogels is their low strength, leading to mechanical damage, which greatly shortens the lifetime and limits the application [ 6 ]. Self-healing hydrogels [ 7 ], a new type of hydrogel that can be repaired by itself after external damage, have exhibited better fatigue resistance, reusability, hydrophilicity, and responsiveness to environmental stimuli. They show great advantages in regenerative medicine compared with traditional hydrogels [ 8 , 9 ].…”

“…In addition, since hydrogel inserts do not require surgical incisions, injectable self-healing hydrogels can deliver drugs to the body without causing obvious harm. Previously published reviews mainly introduced its mechanism and summarized the conductivity of self-healing hydrogel flexible sensors [ 7 , 14 ]. Other reviews focused on the single component, such as pectin-based or polypeptide-based self-healing hydrogels [ 15 , 16 ], unified compound mechanisms such as chitosan-based hydrogels [ 17 ], or cross-linking and supramolecular self-healing hydrogels [ 18 , 19 ], and discussed how they could be applied in a specific medical application [ 20 , 21 ].…”