Intelligent Silk Fibroin Ionotronic Skin for Temperature Sensing

Abstract

The emergence of ionotronic materials has substantially extended the applications of artificial skins by allowing intimate interfaces between electronics and biological/bionic surfaces toward achieving improved sensing and communication with surrounding stimuli. However, ionotronic skins are intrinsically temperature dependent, since water molecules play crucial roles in regulating both mechanical and ionic conductivity of the materials. Hence, most of the ionotronic skins will fail at temperatures below 0 °C. In this study, a highly sensitive ionotronic skin that can be used in the entire natural environmental temperature range (−30–80 °C) is developed by using silk fibroin and Ca(II) ions as starting materials. In such a system, silk fibroin serves as both structural supports and ion capture agent to provide structural stability, mechanical flexibility, and interfacial adhesion ability, while Ca(II) ions work as ionic conductor, hygroscopic agent, and deicing salt to offer highly stable ionic conductivity at a temperature range from −30 to 80 °C. These synergetic merits, together with favorable advances of silk fibroin ionotronic skins in biocompatibility, transparency, and self‐healing, allow them to be used in multiple emerging fields, such as regenerative medicine, implantable electronics, and human–machine interface.

Ultra‐Conformable Ionic Skin with Multi‐Modal Sensing, Broad‐Spectrum Antimicrobial and Regenerative Capabilities for Smart and Expedited Wound Care

“…Elevated temperature at wound sites is a well‐established marker of infection and can be employed as an early indicator of chronic wounds. [ 77 ] Test in an ex vivo wound model demonstrated that the resistance of MiS was responsive to temperature with a relatively high sensitivity and responsiveness, [ 78,79 ] with the change in resistance strongly correlated to the change in temperature (Figure 6e and Figure S7: Supporting Information). This indicated that the MiS was capable of timely monitoring the wound temperature to allow identification of emerging inflammation or infection.…”

Mechanical Training‐Driven Structural Remodeling: A Rational Route for Outstanding Highly Hydrated Silk Materials

“…SF/CaCl 2 membranes (weight ratio of 3/1) were used as the starting material for HHSMs preparation, it can stretch by more than 7‐fold in length and is present in a highly hydrated state (water content of 54 ± 3%), since CaCl 2 has good hygroscopicity and a calcium ion could capture six water molecules from the surroundings through coordination interactions, thus plasticizing silk proteins membranes ( Figure a ). [ 21–24 ]…”

“…Nevertheless, the silk in this Silk/CaCl 2 membrane was amorphous and primarily stabilized by intermolecular hydrogen bonds and ion chelation. [ 21–24 ] Thus, the resultant materials appeared with a gum‐like soft state, where small forces induced large deformations. Therefore, β‐sheet crosslinks among the chains were required, akin to natural silk (Figure 1b).…”

“…Notably, the above‐specified parameters were adopted from the previous study on polymorphic regenerated silk fibers, wherein the parameters were carefully tuned to capture the mechanical properties of SMFs (e.g., density, modulus, strength, toughness) observed in experiments. [ 24 ]…”

Strategies for Fabricating Protein Films for Biomaterial Applications

“…[ 93 ] Additionally, silk fibroin films have also been used to fabrication of flexible and wearable electronic skins for monitoring human physiological responses. [ 94,95 ] Recently, wearable electronic devices have been developed using protein nanowire films for humidity sensing. [ 96 ] Composite materials of amyloid aggregates and graphene have exhibited shape memory and enzyme sensing properties.…”