Enzymatic Crosslinked Silk Fibroin Hydrogel for Biodegradable Electronic Skin and Pulse Waveform Measurements

Abstract

The development of a portable, controllable, and environmentally friendly electronic skin (e-skin) is highly desirable; however, it presents a major challenge. Herein, a biocompatible, biodegradable, and easily usable hydrogel was designed and fabricated as e-skin to enable the transmission of information regarding the spatial pressure distribution. Silk fibroin (SF) was used as the hydrogel skeleton, which endowed the hydrogel with intelligent mechanical sensitivity. During its conditioning in weakly acidic media, the density of the enzymatic crosslink increased and a dense network was formed due to the formation of covalent/hydrogen bonds. Additionally, a conductive SF/polyvinyl alcohol (PVA) hybrid film was molded as a flexible electrode after graphite deposition. The above SF sensing unit based on SF hydrogels and SF/PVA hybrid films showed high strain sensitivity (4.78), fast responsiveness (<0.1 s), good cycling stability (≥10,000), excellent biocompatibility, and biodegradability. Importantly, a coplanar 8 × 8 pixel SF-based e-skin array was successfully fabricated and applied for 3D signal transmission of the object. The SF-based e-skin was capable of precisely tracking the changes in the pulse pressure, the movement of the finger joint, and the vibrations of the vocal cord. Therefore, the current findings provide a solid foundation for future studies exploring the next generation of electronic devices.

Microsphere-Structured Protein Hydrogel Dielectrics for Capacitive Wearable Sensors

“…The morphology and structure of the prepared materials were examined by scanning electron microscopy (SEM; Hitachi SU70, SU8010, Tokyo, Japan). The hydrogels were frozen at −20 °C for 12 h in a refrigerator and then dried in a vacuum freeze-dryer (Labconco Freeze-dryer 4.5 Plus 7386070) at −80 °C for 48 h. Prior to testing, the samples were coated with gold using an off-jet coater …”

“…The hydrogels were frozen at −20 °C for 12 h in a refrigerator and then dried in a vacuum freeze-dryer (Labconco Freeze-dryer 4.5 Plus 7386070) at −80 °C for 48 h. Prior to testing, the samples were coated with gold using an off-jet coater. 31 2.4.3. Mechanical Tests.…”

Body-attachable multifunctional electronic skins for bio-signal monitoring and therapeutic applications

“…The biodegradable properties of these materials are suited to monitor temporary phenomena such as wound healing, aftereffects, and side effects. Veeralingam et al reported a NiSe 2 -grown cellulose paper with silver paste for a low-cost and disposable sensing platform that can be applied to pH meters, breath analysis, and strain sensors [75] . The cellulose paper-based flexible substrate was dipped in a seed solution with selenium powder, sodium borohydride, and NiCl 2 in deionized (DI) water for about one hour.…”

Application of Silk-Fibroin-Based Hydrogels in Tissue Engineering

“…In motion tests on subjects' sweaty forearms, the DN hydrogel adhesive exhibited strong adhesion and was integrated into arrays of different epidermal sensors [199]. In addition, SF hydrogel and SF/PVA hybrid film can be combined to form electronic skin (e-skin) that functions as a capacitive pressure sensor [200]. Concerning the composition of this e-skin, one is the SF hydrogel cross-linked with acetate esterase, which is highly elastic and used as the pressure-sensitive layer and the dielectric layer of the sensor.…”

“…Then, the hydrogel is sandwiched between the two films and fixed with resin adhesive to form an SF sensing unit, which can be expanded to become an e-skin. The test results of the e-skin show that it has good stability, biocompatibility, and biodegradability and excellent sensitivity and can quickly respond to small changes in human joints, vocal cords, and pulses [200].…”