3D Porous Hydrogel/Conducting Polymer Heterogeneous Membranes with Electro‐/pH‐Modulated Ionic Rectification

Abstract

Heterogeneous membranes composed of asymmetric structures or compositions have enormous potential in sensors, molecular sieves, and energy devices due to their unique ion transport properties such as ionic current rectification and ion selectivity. So far, heterogeneous membranes with 1D nanopores have been extensively studied. However, asymmetric structures with 3D micro-/nanoscale pore networks have never been investigated. Here, a simple and versatile approach to low-costly fabricate hydrogel/conducting polymer asymmetric heterogeneous membranes with electro-/pH-responsive 3D micro-/nanoscale ion channels is introduced. Due to the asymmetric heterojunctions between positively charged nanoporous polypyrrole (PPy) and negatively charged microscale porous hydrogel poly (acrylamide-co-acrylic acid) (P(AAm-co-AA)), the membrane can rectify ion transmembrane transport in response to both electro- and pH-stimuli. Numerical simulations based on coupled Poisson and Nernst-Plank equations are carried out to explain the ionic rectification mechanisms for the membranes. The membranes are not dependent on elaborately fabricated 1D ion channel substrates and hence can be facilely prepared in a low-cost and large-area way. The hybridization of hydrogel and conducting polymer offers a novel strategy for constructing low-cost, large-area and multifunctional membranes, expanding the tunable ionic rectification properties into macroscopic membranes with micro-/nanoscale pores, which would stimulate practical applications of the membranes.

Janus Membranes: Creating Asymmetry for Energy Efficiency

“…When the applied electric field is reversed, it can lead to an accumulation of ions in the pores and results in higher ionic conductivity. This nonlinear ionic conductivity response eventually leads to the ionic rectification performance of ionic diodes (Figure c) …”

An injectable scaffold based on temperature‐responsive hydrogel and factor‐loaded nanoparticles for application in vascularization in tissue engineering

“…Co‐loading of nanoparticles with molecules of different charge, VEGF (negative charge), and SDF‐1 (positive charge) can improve the controllable and selective release of the whole delivery system. The development of environmental‐responsive hydrogels with response to temperature, pH, enzymes, and so forth allows for better targeting of tissue engineering scaffolds (Bao et al, ; Tang et al, ; Zhong et al, ). In particular, injectable hydrogel scaffolds may avoid surgical trauma and infection as much as possible, to further reduce the risk of surgery, and simultaneously improve in situ the precision of the gel at the focus of the lesion (Rose & Laura, ).…”

Conductive Hydrogels as Smart Materials for Flexible Electronic Devices

“…This synthetic strategy of preparing mechanical strong conductive hydrogels would be a useful approach for other systems. Otherwise, electrochemical polymerization also can be used to grow conducting polymers in a prefabricated hydrogel …”

“…Until now,v arious strategies have been developed to fabricate conductive hydrogel for flexible electronic devices,i ncluding co-networks,b lends and self-assembly. [50][51][52][53][54][55][56][57][58] These strategies provide ab road perspective on designing and fabricating nanocomposite conductive hydrogels. We further divide theses trategies into several approaches:( i) electro or chemicalp olymerization of ac onducting monomer in ap refabricatedh ydrogel, (ii)mixing the conductive materials/monomers and hydrophilicp olymers/monomers followed by simultaneous or step-wise cross-linking to produce conductive hydrogels, and (iii)self-assembling the modified electrical conductive materials.…”

“…Otherwise, electrochemical polymerization also can be used to grow conducting polymers in ap refabricated hydrogel. [50,63] However,t he resulting conductive hydrogels by these methods are consisting of not only conductive components, but also nonconductive components, which deteriorating the conductivity.I nr ecent researches, some moleculesw ere found that they could cross-link several conductive polymer chains by multi-groups, resulting in various CPHs free of insulating components. [52,64] Among them, phytic acid was first reported and used to form PANI hdyrogels.…”