Recent Progress in Natural Biopolymers Conductive Hydrogels for Flexible Wearable Sensors and Energy Devices: Materials, Structures, and Performance

Abstract

Natural biopolymer-based conductive hydrogels, which combine inherent renewable, nontoxic features, biocompatibility and biodegradability of biopolymers, and excellent flexibility and conductivity of conductive hydrogels, exhibit great potential in applications of wearable and stretchable sensing devices. Compared to traditional flexible substrates deriving from petro-materials-derived polymers, conductive hydrogels consisting of continuous cross-linked polymer networks and a large amount of water exhibit more fantastic combination of stretchability and conductivity because their polymer networks endow the hydrogels with mechanical flexibility and the water offers them a consecutive ionic transport property. Different from petro-materials-derived polymers, biopolymers that are extracted from bioresource with intrinsic biocompatibility and biodegradability are commonly considered as appropriate candidates for constructing wearable devices. For example, biopolymers such as cellulose, chitosan, and silk fibroin are usually chosen as promising candidates to construct conductive hydrogels, endowing the hydrogels with enhanced mechanical properties and remarkable biocompatibility. This review summarizes the recent progress of natural biopolymer-based conductive hydrogels that are utilized for electrical sensing devices with a series of typical biopolymers including cellulose, chitosan, silk fibroin, and gelatin. The chemical structures and physicochemical properties of the four typical biopolymers are demonstrated, and their applications in diverse conductive hydrogel sensors are discussed in detail. Finally, the remaining challenges and expectations are discussed.

Self‐Healing Hydrogels as Flexible Sensor for Human Motion Monitoring

“…The reason might that under the higher stress, the hydrogels network was collapsed and changed to solution state. [19] As the stress recovered to 1 Pa, G' and G'' immediately returned to almost the original values in seconds, indicating the reconstruction of the inner structure of the hydrogels. The self-healing behavior was fully invertible and repeated during the cyclic test, which further confirm the outstanding and rapid self-healing performance of DF-PEG/CS hydrogels.…”

Recent Application of Cellulose Gel in Flexible Sensing-A Review

“…Many electronic devices used in medical treatment have been developed into flexible wearable. [68,[107][108][109][110][111][112][113][114][115] Although cellulose hydrogel has made great progress in the electronic field of wearable devices, the differences between humans and metal or semiconductor devices cannot meet the diverse needs of biological applications. For example, metals and semiconductors are inherently poorly flexible and cannot be stretched.…”

“…It can be used to monitor various human movements, including vocalization, swallowing process, finger movement and limb movement, and provide real-time feedback, so how to ensure that the electrons are evenly spread in flexible materials, and can work in different environments like human skin. [68,[107][108][109][110][111] Responsiveness is our key development direction in the future. However, the gel still cannot work normally in the cold winter and other non-mild environments.…”

Towards conductive hydrogels in e-skins: a review on rational design and recent developments

“…64,65 Among all the copolymerization strategies, direct copolymerization and graing are two widely utilized approaches to fabricate conductive hydrogels through copolymerization, realizing multifunctional features of hydrogels, such as conductivity, stretchability, stability, self-healing property, and biocompatibility. 34,35,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81] However, the majority of hydrogels are restricted by the poor mechanical strength, 82 leading to insufficient stability and efficiency for practical utilization. To tackle the limitations on structural robustness, incorporation of high-strength llers and constructing crosslinked structures are designed during fabrication.…”