Dynamic Nanohybrid-Polysaccharide Hydrogels for Soft Wearable Strain Sensing

Abstract

Electroconductive hydrogels with stimuli-free self-healing and self-recovery (SELF) properties and high mechanical strength for wearable strain sensors is an area of intensive research activity at the moment. Most electroconductive hydrogels, however, consist of static bonds for mechanical strength and dynamic bonds for SELF performance, presenting a challenge to improve both properties into one single hydrogel. An alternative strategy to successfully incorporate both properties into one system is via the use of stiff or rigid, yet dynamic nano-materials. In this work, a nano-hybrid modifier derived from nano-chitin coated with ferric ions and tannic acid (TA/Fe@ChNFs) is blended into a starch/polyvinyl alcohol/polyacrylic acid (St/PVA/PAA) hydrogel. It is hypothesized that the TA/Fe@ChNFs nanohybrid imparts both mechanical strength and stimuli-free SELF properties to the hydrogel via dynamic catecholato-metal coordination bonds. Additionally, the catechol groups of TA provide mussel-inspired adhesion properties to the hydrogel. Due to its electroconductivity, toughness, stimuli-free SELF properties, and self-adhesiveness, a prototype soft wearable strain sensor is created using this hydrogel and subsequently tested.

Tannic acid: a versatile polyphenol for design of biomedical hydrogels

“…Both inter-and intramolecular hydrogen bonds between PVA chains, TA chains, and hydrogen bonds between TA and PVA were probably disrupted by NaCl, leading to densifying the hydrogel and, as a result, more entanglements of PVA and TA chain. 199 Moreover, biopolymers such as chitosan, 200 carboxymethyl chitosan, 201 collagen, 202 alginate, 134 SF, 203 bovine serum albumin (BSA), 204 cellulose derivatives 205 and as well as inorganic compounds such as Fe 3+ , 206 cuprous oxide, 207 carbon nanotubes (CNTs), 208 silver NPs, 209 can be incorporated to the PVA–TA hydrogel to improve the biological activity and gel formation ability of PVA–TA hydrogels.…”

Review of Materials and Fabrication Methods for Flexible Nano and Micro-Scale Physical and Chemical Property Sensors

“…Wearables have gained much attention in the last decade [11,48,[98][99][100][101][102][103][104]. These are electronic devices that are attached to the human body, a typical example being smart watches that had an estimated global market share of over 20 billion USD in 2019, 59 billion USD in 2021 and is predicted to rise to 96 billion USD by 2027 [8,9,103,104].…”

“…Wearables are improving the way of life by readily providing us with useful information including meteorological data (e.g., humidity and temperature), navigation (e.g., GPS), fitness/exercise (e.g., number of steps per day) and health monitoring (e.g., heart rate, sugar levels and body temperature). A significant amount of wearable research is centred on the relevant material science which includes the mechanical and electrical properties of the sensors [11,12,98,99,101]. Some of the commonly studied characteristics in wearables are summarised in Table 4.…”

“…Privacy issues, performance risks and social risks are other noted areas for future investigation [102]. Furthermore, regarding the materials research needs, nanomaterials have gained much attention due to the advanced physicochemical properties and the need to miniaturise wearables [11,41,48,98,99]. Three-dimensional printing is currently and will continue to play an important role in the development of wearables (and sensors in general) due to its ability to customise devices easily, achieve designs not possible via other techniques, reduce or avoid assembly operations, as well as the use of multi-material composites with advanced electrical/mechanical properties [56,59,102].…”

Starch-g-Acrylic Acid/Magnetic Nanochitin Self-Healing Ferrogels as Flexible Soft Strain Sensors

“…Inspired by this unique feature, in this research, we designed and developed a self-healing hydrogel constructed of magnetic nanochitin that can self-heal faster than human skin and might be used as a soft, flexible, self-healing strain sensor. As soft, wet, 3D crosslinked, hydrophilic polymers with unique properties, hydrogels have demonstrated their versatility in many research and industry fields, including medical applications [ 9 , 10 ], sensors [ 8 , 11 , 12 ], and water treatment [ 13 ]. However, the delicate and brittle nature of hydrogels makes their potential applications in wearable devices problematic.…”