Abstract
Implantable electronics have recently been attracting attention because of the promising advances in personalized healthcare. They can be used to diagnose and treat chronic diseases by monitoring and applying bioelectrical signals to various organs. However, there are challenges regarding the rigidity and hardness of typical electronic devices that can trigger inflammatory reactions in tissues. In an effort to improve the physicochemical properties of conventional implantable electronics, soft hydrogel-based platforms have emerged as components of implantable electronics. It is important that they meet functional criteria, such as stretchability, biocompatibility, and self-healing. Herein, plant-inspired conductive alginate hydrogels composed of “boronic acid modified alginate” and “oligomerized epigallocatechin gallate,” which are extracted from plant compounds, are proposed. The conductive hydrogels show great stretchability up to 500% and self-healing properties because of the boronic acid-cis-diol dynamic covalent bonds. In addition, as a simple strategy to increase the electrical conductivity of the hydrogels, ionically crosslinked shells with cations (e.g., sodium) were generated on the hydrogel under physiological salt conditions. This decreased the resistance of the conductive hydrogel down to 900 ohm without trading off the original properties of stretchability and self-healing. The hydrogels were used for “electrophysiological bridging” to transfer electromyographic signals in an ex vivo muscle defect model, showing a great bridging effect comparable to that of a muscle-to-muscle contact model. The use of plant-inspired ionically conductive hydrogels is a promising strategy for designing implantable and self-healable bioelectronics.
Highlights
In recent years, implantable electronics (IEs) have been developed and improved, especially in the medical field, because of their ability to improve personalized healthcare
The conjugation of boronic acid onto alginate might enhance the shelf-life of unmodified alginate due to the increase in relative molecular weight and inter-crosslinking density, and oligomerized epigallocatechin-gallate” (OEGCG) can inhibit the growth of microorganism [39,40,41]
After soaking in the NaCl solution, the Alg-boronic acid (BA)/OEGCG hydrogel hardened from the surface, and the width of the hardened surface varied depending on the concentration of NaCl solution and soaking time (Figure 2aii)
Summary
Implantable electronics (IEs) have been developed and improved, especially in the medical field, because of their ability to improve personalized healthcare. They include biosensors, bioconductors, electrostimulated drug delivery systems, and tissue engineering for the diagnosis and treatment of chronic diseases [1]. As mechanical rigidity causes acute and chronic inflammation, soft and flexible properties matching those of biological tissues are required. To develop soft IE applications, conductive hydrogels have attracted attention as a candidate substrate for IEs because hydrogels can retain abundant water molecules similar to tissues, and the moist environment can offer a consecutive ionic conductivity [7]. It is challenging to fabricate soft and flexible conductive hydrogels with multiple desirable properties
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