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

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.     

A Bioinspired Mineral Hydrogel as a Self‐Healable,Mechanically Adaptable Ionic Skin for Highly Sensitive Pressure Sensing

In the past two decades, artificial skin‐like materials have received increasing research interests for their broad applications in artificial intelligence, wearable devices, and soft robotics. However, profound challenges remain in terms of imitating human skin because of its unique combination of mechanical and sensory properties. In this work, a bioinspired mineral hydrogel is developed to fabricate a novel type of mechanically adaptable ionic skin sensor. Due to its unique viscoelastic properties, the hydrogel‐based capacitive sensor is compliant, self‐healable, and can sense subtle pressure changes, such as a gentle finger touch, human motion, or even small water droplets. It might not only show great potential in applications such as artificial intelligence, human/machine interactions, personal healthcare, and wearable devices, but also promote the development of next‐generation mechanically adaptable intelligent skin‐like devices.     

PAA-Na/PVA半互穿网络水凝胶的离子强度及pH敏感性

采用水溶液聚合法制备了聚丙烯酸钠(PAA-Na)/聚乙烯醇(PVA)半互穿网络水凝胶,研究了水凝胶在不同pH溶液、不同浓度NaCl与CaCl2溶液中的溶胀行为,结果表明,溶胀比随丙烯酸含量增大而增加,在碱性溶液中的溶胀度明显高于酸性溶液,溶胀平衡凝胶在酸性及碱性条件下均出现收缩,在pH=2和pH=12溶液中反复交换时,表现出可逆溶胀-退溶胀性能,具有较好的pH敏感性,凝胶在不同浓度NaCl与CaCl2溶液中溶胀性表明,溶液的离子强度及阳离子的电荷数对凝胶溶胀行为有较大影响。     

Self‐Assembly of Enzyme‐Like Nanofibrous G‐Molecular Hydrogel for Printed Flexible Electrochemical Sensors

Conducting hydrogels provide great potential for creating designer shape‐morphing architectures for biomedical applications owing to their unique solid–liquid interface and ease of processability. Here, a novel nanofibrous hydrogel with significant enzyme‐like activity that can be used as “ink” to print flexible electrochemical devices is developed. The nanofibrous hydrogel is self‐assembled from guanosine (G) and KB(OH)₄ with simultaneous incorporation of hemin into the G‐quartet scaffold, giving rise to significant enzyme‐like activity. The rapid switching between the sol and gel states responsive to shear stress enables free‐form fabrication of different patterns. Furthermore, the replication of the G‐quartet wires into a conductive matrix by in situ catalytic deposition of polyaniline on nanofibers is demonstrated, which can be directly printed into a flexible electrochemical electrode. By loading glucose oxidase into this novel hydrogel, a flexible glucose biosensor is developed. This study sheds new light on developing artificial enzymes with new functionalities and on fabrication of flexible bioelectronics.     

PVA/P(AA-AM)复合水凝胶的制备及性能

采用水溶液聚合方法合成了不同组成的丙烯酸-丙烯酰胺共聚物(P(AA-AM))。将聚乙烯醇(PVA)与所合成的P(AA-AM)共混,以戊二醛为交联剂,制备出了不同结构的PVA/P(AA-AM)复合水凝胶。采用扫描电镜观察了凝胶形貌,研究了复合水凝胶的结构与性能关系。结果表明,复合水凝胶溶胀性能与所用交联剂加量有关,复合水凝胶的溶胀度随着交联剂加量增加先增大后减小,在交联剂加量为0.5%时水凝胶溶胀度达到最大值。复合凝胶中的聚合物组成对溶胀度影响显著,随着P(AA-AM)含量提高,水凝胶的溶胀度逐渐增大。适当结构的复合水凝胶具有pH敏感性,敏感程度随着凝胶中P(AA-AM)含量的增加而增强。     

聚(丙烯酸-丙烯酰胺)高吸水树脂吸水保水性能研究

高吸水树脂具有良好的吸水性、保水性及耐盐性,受到广泛的关注及应用。研究了不同阴、阳离子强度、pH值及不同质地的土壤对聚(丙烯酸-丙烯酰胺)(PAA-AM)树脂的吸水保水性能的影响。结果表明,对于不同价态的阴、阳离子盐溶液,其对树脂吸液性能影响的大小顺序为三价>二价>一价;树脂在酸碱性环境中的最佳使用条件为pH值=6～8;在不同泥沙比的土壤中施加PAA-AM树脂,能显著改善土壤的蓄水保水能力及土壤团粒结构,其中施加PAA-AM树脂的沙土蓄水保水能力优于经同样处理的其它土壤,故PAA-AM树脂更适合施用于沙性土质土壤中。     

Recent Advances in Poly(N-isopropylacrylamide) Hydrogels and Derivatives as Promising Materials for Biomedical and Engineering Emerging Applications

Temperature-sensitive (thermosensitive) hydrogels, which are part of the family of stimulus-sensitive hydrogels, consist of water-filled polymer networks that display a temperature-dependent degree of swelling. Thermosensitive hydrogels, which can undergo phase transition or swell/de-swell as temperature changes, have great potential in various technological and biomedical purposes for a number of reasons: their temperature response is reversible, hydrogels are stable and easy to prepare, they can be biocompatible and also be suitably combined with other organic and inorganic materials, resulting in new materials with outstanding properties. Among thermosensitive hydrogels poly(N-isopropylacrylamide) (PNIPAAm) is the most extensively studied because it brings together the best properties of these materials. Consequently, in the past few years, a wide number of applications and new chemical processes to prepare PNIPAAm and their derivatives are being proposed. The objective of this review is to summarize the fundamentals of thermosensitive hydrogels and recent advances in preparation and both technological and biomedical applications of thermosensitive hydrogel, with a special focus on PNIPAAm and their derivatives. Special attention has been given to the discussion of challenges and future research perspectives based on new horizons not yet considered.     

Poly(ethylene oxide)-silica hybrids entrapping sensitive dyes for biomedical optical pH sensors: Molecular dynamics and optical response

Polymer-silica hybrid nanocomposites prepared by sol-gel process based on triethoxisilane-terminated poly(ethylene oxide) chains and tetraethoxysilane as silica precursor, doped with organic pH sensitive dyes, have been prepared and their suitability for use as sensors coupled with plastic optic fibers has been evaluated. Sensors were prepared by immobilizing a drop of the hybrid materials onto the tip of a multi-mode poly(methyl methacrylate) optical fiber. The performance of the optical sensor in terms of sensitivity and response time was tested in different experimental conditions, and was found to be markedly higher than analogous sensors present on the market. The very fast kinetic of the hybrid’s optical response was supported by studies performed at the molecular level by broadband dielectric relaxation spectroscopy (DRS), investigated over a wide range of frequency and temperature, showing that poly(ethylene oxide) chains maintain their dynamics even when covalently bonded to silica domains, which decrease the self-association interactions and promote motions of polymer chain segments. Due to the fast response kinetic observed, these pH optical sensors result suitable for the fast-detection of biomedical parameters, i.e. fast esophageous pH-metry.