Abstract
Electroresponsive hydrogels possess a conducting material component and respond to electric stimulation through reversible absorption and expulsion of water. The high level of hydration, soft elastomeric compliance, biocompatibility, and enhanced electrochemical properties render these hydrogels suitable for implantation in the brain to enhance the transmission of neural electric signals and ion transport. This review provides an overview of critical electroresponsive hydrogel properties for augmenting electric stimulation in the brain. A background on electric stimulation in the brain through electroresponsive hydrogels is provided. Common conducting materials and general techniques to integrate them into hydrogels are briefly discussed. This review focuses on and summarizes advances in electric stimulation of electroconductive hydrogels for therapeutic applications in the brain, such as for controlling delivery of drugs, directing neural stem cell differentiation and neurogenesis, improving neural biosensor capabilities, and enhancing neural electrode-tissue interfaces. The key challenges in each of these applications are discussed and recommendations for future research are also provided.
Highlights
Neurons in the brain communicate by transmitting electric signals,[1, 2] which is important for their functional expression, differentiation, and survival.[3]
Since hydrogels undergo reversible changes in volume in response to electric stimuli, these platforms are advantageous as neural tissue engineering substrates.[23, 24]
This finding was further corroborated by a follow up study in which the researchers determined that in situ co-deposition/polymerization of PEDOT/Multiwalled carbon nanotubes (MWCNT) composites under galvanostatic modes improved the electrochemical stabilities compared to potentiostatic modes when microelectrodes were subjected to continuous, high charge density electric fields.[135]
Summary
Neurons in the brain communicate by transmitting electric signals,[1, 2] which is important for their functional expression, differentiation, and survival.[3]. Since hydrogels undergo reversible changes in volume in response to electric stimuli, these platforms are advantageous as neural tissue engineering substrates.[23, 24] Electroresponsive hydrogel implants in the brain have the potential to enable numerous therapeutic applications with tunable electric stimulation schemes to control the release of payloads, promote neural cell growth and differentiation, and serve as a biocompatible and conductive interface for enhancing signal transmission in neural biosensors and electrodes in vivo. A summary of the electroconductive materials used for each key study, as well as the specific electric stimulation parameters, hydrogel electric properties, cell culture or animal model used, and hydrogel biocompatibility are provided This synthesized information will aid future researchers in identifying and standardizing the optimal electric field parameters and hydrogel materials for specific electric stimulation outcomes in the brain. The challenges in each application, as well as recommendations for future research, are discussed
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