Self-Healing, Stretchable, Biocompatible, and Conductive Alginate Hydrogels through Dynamic Covalent Bonds for Implantable Electronics

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.

Novel Self-Healing Metallocopolymers with Pendent 4-Phenyl-2,2′:6′,2″-terpyridine Ligand: Kinetic Studies and Mechanical Properties

“…It is known that traditional synthetic polymer hydrogels usually have weak mechanical strength, low impact strength, and low recoverability [ 48 , 49 ]. This is largely due to their unified grid structure, which leads to internal structural heterogeneity, due to the irregular distribution of cross-linking sites and the absence of effective energy dissipation mechanisms.…”

Conductive Polymeric-Based Electroactive Scaffolds for Tissue Engineering Applications: Current Progress and Challenges from Biomaterials and Manufacturing Perspectives

“…A monolith structure consists of CP mixed with other polymers made into a singular structure, with CP-hydrogel composite being one such example [ 34 , 175 ]. Comparatively, this architecture has relatively low conductivity and unreliable mechanical stability, although the introduction of cations into the scaffold has been demonstrated to increase the conductivity of this approach [ 176 ]. Another approach is by creating a laminate structure, consisting of two or more layers of different materials bonded together into a single-layered architecture.…”

“…Citing comparable stiffness to muscle tissues and its naturally hydrated properties, hydrogels have emerged as an attractive candidate alongside CPs for muscle tissue engineering [ 186 ]. As discussed previously, hydrogels can be used to create a monolithic architecture [ 176 ], or to act as a passive layer in laminate architectures [ 60 , 182 , 187 ]. A recent study by Ting et al shows that PPy-DBS grown on on poly(N-isopropylarcylamide) (PNIPAM) hydrogel exhibits more than two times the actuation of bare PPy-DBS [ 187 ].…”

Recent advances in recording and modulation technologies for next-generation neural interfaces

“…More recently, hydrogel-based neural interfaces have drawn extensive interest owing to their intrinsic softness and chemical compatibility to biological tissue ( Choi et al., 2021 ; Huang et al., 2018 ; Liu et al., 2019 ; Yuk et al., 2019 ). They can be utilized for some applications including soft coating agents and adaptive interfaces that can facilitate the implantation by dynamically shifting their moduli upon swelling.…”