Fermentation-Inspired Gelatin Hydrogels with a Controllable Supermacroporous Structure and High Ductility for Wearable Flexible Sensors

Abstract

Supermacroporous hydrogels have attracted wide concern due to their comfort and breathability in wearable health-monitoring applications. Size controllable supermacroporous structure and excellent mechanical properties are the most important for its application. However, they are normally fabricated by the cryogelation method, which is difficult to control pore size and maintain flexibility. Here, yeast fermentation-inspired gelatin hydrogels with a controllable supermacroporous structure and excellent mechanical properties were fabricated for the first time. The pore size can be controlled by adjusting the content of glucose and yeast, the ratio of glucose to yeast, fermentation time, and gelatin content during fermentation. The hydrogels demonstrated a controllable pore size range from 100 to 400 μm and rapid swelling characteristics. The mechanical properties were maintained by soaking ammonium sulfate solution for 12 h, showing maximum tensile and compressive strains over 300 and 99%, respectively. This novel approach can be easily applied to the preparation of supermacroporous and high ductility hydrogels under mild conditions. Furthermore, conductive hydrogels combined supermacroporous structures with conductive polyaniline and reduced oxidized graphene, and silver nanowires were prepared as wearable flexible sensors. The obtained sensors maintain well-distributed porosity, breathability, and mechanical flexibility, also showing excellent conductivity of 2.4 S m–1. Finally, the sensors were successfully applied to detect physiological signals and human–computer interaction.

Recent Progress of Biomaterials-Based Epidermal Electronics for Healthcare Monitoring and Human–Machine Interaction

“…In addition to the robotic control, the control on personal devices is also a common application direction that brings convenience to daily life [ 151 , 152 , 153 ]. Inspired by fermentation, Cheng et al proposed a gelatin-based hydrogel which has the controllable supermacroporous structure [ 135 ]. Figure 7 a shows the detailed fabrication process of the hydrogel.…”

“…( f ) HMI realized by GRPAY sensor. ( g ) Photographs illustrating playing Tetris game controlled by signals of 4 different gestures acquired from GRPAY sensor [ 135 ].…”

Recent Development of Self-Powered Tactile Sensors Based on Ionic Hydrogels

“…Polyelectrolytes are polymers containing ionic moieties in their repeating units [ 32 ], and they can be crosslinked chemically or physically to produce polyelectrolyte hydrogels. Polysaccharide-based polymers (alginate [ 33 ], chitosan [ 34 ], carrageenan [ 35 ]), polypeptide/protein-based polymers (gelatin [ 36 ], collagen [ 37 ]), and synthetic polymers (polyacrylic acid [ 38 ], poly(sulfobetaine) [ 39 ], carboxymethyl cellulose [ 40 ]) can be used to create polyelectrolyte hydrogels. Ionic liquids (ILs) are molten salts with melting temperatures under 100 °C that are made up of organic cations and organic or inorganic anions.…”

A Polysaccharide-Based pH-Sensitive Hybrid Hydrogel as a Sustained Release Matrix for Antimicrobial Drugs

“…The swelling study was processed at pH 1.2 and 7.4 at 37 ± 0.5 °C with all hydrogelators to observe the pH sensitivity. The equilibrium swelling ratio (ESR) and the swelling ratio per unit time (SRT) 51 were determined. Moreover, pH 1.2 and 7.4 were chosen to observe the swelling behavior of the hydrogel in the simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 7.4) and make a relationship with the drug release behavior.…”