Bioinspired 3D Printable, Self-Healable, and Stretchable Hydrogels with Multiple Conductivities for Skin-like Wearable Strain Sensors

Abstract

Bioinspired hydrogels have promising prospects in applications such as wearable devices, human health monitoring equipment, and soft robots due to their multifunctional sensing properties resembling natural skin. However, the preparation of intelligent hydrogels that provide feedback on multiple electronic signals simultaneously, such as human skin receptors, when stimulated by external contact pressure remains a substantial challenge. In this study, we designed a bioinspired hydrogel with multiple conductive capabilities by incorporating carbon nanotubes into a chelate of calcium ions with polyacrylic acid and sodium alginate. The bioinspired hydrogel consolidates self-healing ability, stretchability, 3D printability, and multiple conductivities. It can be fabricated as an integrated strain sensor with simultaneous piezoresistive and piezocapacitive performances, exhibiting sensitive (gauge factor of 6.29 in resistance mode and 1.25 kPa–1 in capacitance mode) responses to subtle pressure changes in the human body, such as finger flexion, knee flexion, and respiration. Furthermore, the bioinspired strain sensor sensitively and discriminatively recognizes the signatures written on it. Hence, we expect our ideas to provide inspiration for studies exploring the use of advanced hydrogels in multifunctional skin-like smart wearable devices.

Recent advances in wearable sensors and portable electronics for sleep monitoring

“…Pulse wave image: reproduced with permission, from ref ( Yokota et al., 2016 ), Copyright 2016, American Association for the Advancement of Science. Respiration image: reproduced with permission, from ref ( Wei et al., 2021 ), Copyright 2021, American Chemistry Society. Movement image: reproduced with permission, from ref ( Kwon et al., 2020 ), Copyright 2020, Springer Nature.…”

Smart Hydrogels Meet Carbon Nanomaterials for New Frontiers in Medicine

“…Alternatively, glutaraldehyde proved to be an effective cross-linker for PVA and CNTs thus yielding a tough yet highly elastic and conductive hydrogel ( Figure 7 ) whose applicability was demonstrated in wearable devices to detect finger motion, to monitor the pulse, and to record electromyograms [ 149 ]. Also, calcium divalent cations are effective cross-linkers, as shown on a PVA-alginate-CNT hydrogel whose piezoresistive and piezocapacitive performance allowed sensitive responses to subtle pressure changes in the human body, such as finger or knee flexion, and respiration, and was thus envisaged as integrated strain sensor for skin-like wearable electronics [ 161 ].…”

Bioengineered Biomimetic and Bioinspired Noninvasive Drug Delivery Systems

“…For example, Wei et al embedded carbon nanotubes into an alginate and polyacrylic acid hydrogel resulting in a hydrogel with multiple conductive capabilities. [73] For additional information about bioinspired flexible electronics. [74,75] Biomimetic human skin models are very important for transdermal DDS research.…”