Chitosan-driven skin-attachable hydrogel sensors toward human motion and physiological signal monitoring.

Recently, flexible and wearable sensors assembled from conductive hydrogels have attracted widespread attention. However, it is still a great challenge to make hydrogels with sufficient mechanical properties, self-adhesiveness and strain sensitivity. Here, a strong, tough, and self-adhesive hydrogel is successfully fabricated by a one-pot method, which introducing chitosan and 2-acrylamido-2-methylpropane sulfonic acid into the polyacrylamide network. The hydrogels exhibited adhesion (the peel strength reaches 798 N/m), mechanical property (The breaking strength and strain can reach 111 kPa and 2839%) and electrical conductivity (conductivity up to 0.0848 S/cm), which are suitable for wearable epidermal sensors. Besides, the hydrogels also possessed transparency. Therefore, this work would provide a novel insight on the fabrication of multi-functional self-adhesive hydrogel sensors.

Tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution.

In general, chitosan should be dissolved in strong acidic media (such as acetic acid) before it could be applied as hydrogels. However, it was found that chitosan could also be dissolved in the ferric solution to form ferric-chitosan complex via coordination interaction. Subsequently, the ferric-chitosan complex was successfully introduced into the hydrogel system to obtain tough, adhesive and conductive chitosan-polyacrylamide double network (CS-PAAm DN) hydrogels. Surprisingly, CS-PAAm DN hydrogel could repeatedly adhere to various solid materials and biological tissues through physical interactions. The maximum peeling force was 256 N/m on the aluminum surface. Moreover, the hydrogel exhibited adequate mechanical performance (135 kPa, 2332%). And the introduction of ferric chloride could also endow the hydrogel with conductive performance. As a result, the strategy based on tough, adhesive and conductive polysaccharide hydrogels mediated by ferric solution would broaden the path to fabricate a new generation of soft materials for wide applications.