Adaptive Ion-Gel: Stimuli-Responsive,and Self-Healing Ion Gels

Ion gels are an emerging class of polymer gels in which a three-dimensional polymer network swells with an ionic liquid. Ion gels have drawn considerable attention in various fields such as energy and biotechnology owing to their excellent properties including nonvolatility, nonflammability, high ionic conductivity, and high thermal and electrochemical stability. Since the first report on ion gels (published ∼30 years ago), diverse functional ion gels exhibiting impressive physicochemical properties have been reported. In this review, recent developments in functional ion gels that can modulate their physical properties in response to environmental conditions are outlined. Stimuli-responsive ion gels that can adaptively undergo phase transitions in response to thermal and light stimuli are initially discussed, followed by an evaluation of diverse self-healing ion gels that can spontaneously mend mechanical damage through judiciously designed ion-gel networks.     

Triterpenoid‐Based Self‐Healing Supramolecular Polymer Hydrogels Formed by Host–Guest Interactions

Pentacyclic triterpenoids, a class of naturally bioactive products having multiple functional groups, unique chiral centers, rigid skeletons, and good biocompatibility, are ideal building blocks for fabricating versatile supramolecular structures. In this research, the natural pentacyclic triterpenoid glycyrrhetinic acid (GA) was used as a guest molecule for β‐cyclodextrin (β‐CD) to form a GA/β‐CD (1:1) inclusion complex. By means of GA and β‐CD pendant groups in N,N′‐dimethylacrylamide copolymers, a supramolecular polymer hydrogel can be physically cross‐linked by host–guest interactions between GA and β‐CD moieties. Moreover, self‐healing of this hydrogel was observed and confirmed by step‐strain rheological measurements, whereby the maximum storage modulus occurred at a [GA]/[β‐CD] molar ratio of 1:1. Additionally, these polymers displayed outstanding biocompatibility. The introduction of a natural pentacyclic triterpenoid into a hydrogel system not only provides a biocompatible guest–host complementary GA/β‐CD pair, but also makes this hydrogel an attractive candidate for tissue engineering.     

The Design of Rapid Self-Healing Alginate Hydrogel with Dendritic Crosslinking Network

Self-healing alginate hydrogels play important roles in the biological field due to their biocompatibility and ability to recover after cracking. One of the primary targets for researchers in this field is to increase the self-healing speed. Sodium alginate was oxidized, generating aldehyde groups on the chains, which were then crosslinked by poly(amino) amine (PAMAM) via Schiff base reaction. The dendritic structure was introduced to the alginate hydrogel in this work, which was supposed to promote intermolecular interactions and accelerate the self-healing process. Results showed that the hydrogel (ADA-PAMAM) formed a gel within 2.5 min with stable rheological properties. Within 25 min, the hydrogel recovered under room temperature. Furthermore, the aldehyde degree of alginate dialdehyde with a different oxidation degree was characterized through gel permeation chromatograph aligned with multi-angle laser light scattering and ultraviolet (UV) absorption. The chemical structure of the hydrogel was characterized through Fourier transform infrared spectroscopy and UV-vis spectra. The SEM and laser scanning confocal microscope (CLSM) presented the antibiotic ability of ADA-PAMAM against both S. aureus and E. coli when incubated with 10⁻⁷ CFU microorganism under room temperature for 2 h. This work presented a strategy to promote the self-healing of hydrogel through forming a dendritic dynamic crosslinking network.     

PH-Responsive and Self-Healing Hydrogels Fabricated with Guar Gum and Reactive Microgels

Hydrogels (MR gels) with pH-responsive and self-healing properties were prepared via guar gum solutions and reactive microgel. The reactive microgel was characterized through scanning electron microscope (SEM), laser particle-size analysis measurements, and FTIR. Compared with general hydrogels cross-linked by borax (B gels), the MR gels exhibit superior properties on the aspects of viscosity, viscoelasticies, and temperature resistance. Furthermore, the viscosities of MR gels increase with the rising pH value, and it can dynamically reconstruct after being destructed by external force. In addition, the microstructure of the MR gel was characterized by SEM, which confirms that the reactive microgel indeed as cross-linker and each microgel can cross-link several chains as if the chains were grafting from the microgels. These features show that the addition of reactive microgels can enhance the strength of MR gels significantly and indicate that the MR gels have a great potential application in hydraulic fracturing, especially in high-temperature oil fields.     

Hydrogels Composed of Organic Amphiphiles and α‐Cyclodextrin: Supramolecular Networks of Their Pseudorotaxanes in Aqueous Media

Mixtures of N‐alkyl pyridinium compounds [py‐N‐(CH₂)_nOC₆H₃‐3,5‐(OMe)₂]⁺(X^?) ( 1b Cl: n=10, X=Cl; 1c Br: n=12, X=Br) and α‐cyclodextrin (α‐CD) form supramolecular hydrogels in aqueous media. The concentrations of the two components influences the sol–gel transition temperature, which ranges from 7 to 67 °C. Washing the hydrogel with acetone or evaporation of water left the xerogel, and ¹³C CP/MAS NMR measurements, powder X‐ray diffraction (XRD), and scanning electron microscopy (SEM) revealed that the xerogel of 1b Cl (or 1c Br) and α‐CD was composed of pseudorotaxanes with high crystallinity. ¹³C{¹H} and ¹H NMR spectra of the gel revealed the detailed composition of the components. The gel from 1b Cl and α‐CD contains the corresponding [2]‐ and [3]pseudorotaxanes, [ 1b? (α‐CD)]Br and [ 1b? (α‐CD)₂]Br, while that from 1c Br and α‐CD consists mainly of [3]pseudorotaxane [ 1c? (α‐CD)₂]Br. 2D ROESY ¹H NMR measurements suggested intermolecular contact of 3,5‐dimethoxyphenyl and pyridyl end groups of the axle component. The presence of the [3]pseudorotaxane is indispensable for gel formation. Thus, intermolecular interaction between the end groups of the axle component and that between α‐CDs of the [3]pseudorotaxane contribute to formation of the network. The supramolecular gels were transformed into sols by adding denaturing agents such as urea, C₆H₃‐1,3,5‐(OH)₃, and [py‐N‐nBu]⁺(Cl^?).     

Self-Healing Polymer Composites: Prospects,Challenges, and Applications

Self-healing polymer composites possess the inherent ability to heal the damage event autonomically or non-autonomically with external intervention. These advanced materials can be commercialized if the challenges and limitations of different self-healing mechanisms are well known and considered. These include capsule-based healing systems, vascular healing systems, and intrinsic healing systems. To date, most of the reviews have studied and reported on different self-healing mechanisms including their response to impact, fatigue, and corrosion tests. This review focuses mostly on extrinsic and intrinsic self-healing polymer composites which have been reported during the past five years by comparing their healing efficiency, advantages, and challenges in the prospect of their future development as well as their possible applications across various industries such as aerospace, automobile, coating, electronics, energy, etc.     

自修复有机硅材料的制备策略

近年来,通过仿生生命体自我修复损伤这一现象而研制的自修复材料,可有效延长材料的使用寿命、提高材料的使用安全性、降低资源浪费,具有巨大的发展潜力。其中,自修复有机硅材料因兼具自我修复的功能和有机硅材料的优异性能,已成为当下的研究热点。由于外界刺激条件如紫外光、温度等是材料实现损伤自我修复的外在驱动力,在很大程度上影响着材料的修复效能,且不同的刺激条件具有不同的优缺点和应用领域。因此,本文将基于自修复过程中外界刺激因素的不同,对自修复有机硅材料尤其是近五年来的最新研究成果进行综述,从外援型和本征型自修复有机硅材料两方面入手,以本征型自修复有机硅材料为重点,并对自修复有机硅材料今后的发展进行了分析展望。     

自修复高分子材料

高分子材料制造和使用过程中,经常由于内部的微裂纹和局部损伤,而导致性能下降,影响使用寿命。自修复高分子材料模仿生物体损伤愈合的原理,自行发现裂纹并通过一定机理自行愈合,是一种有着广泛应用需求的高分子智能材料,包括含修复剂型和不含修复剂型两类。它的特点在于自动化、精准化。本文旨在结合近年来最新的研究成果,介绍并归纳多种典型的自修复体系,总结各种优化手段,并针对已发展的自修复材料存在的局限性,对其研究前景进行合理的展望。     

A Rapidly and Highly Self-Healing Poly(Sulfobetaine Methacrylate) Hydrogel with Stretching Properties,Adhesive Properties,and Biocompatibility

This study focuses on the preparation of stretchable zwitterionic poly(sulfobetaine methacrylate) (PSBMA) hydrogels. To address the weak mechanical properties of chemically crosslinked PSBMA hydrogels, a physical crosslinking method utilizing hydrophobic interactions to crosslink hydrogels to approach tough properties is developed. Here, sodium dodecyl sulfate (SDS)-based micelle is used as a physical crosslinker to prepare physically crosslinked PSBMA (PSBMA_phy) hydrogels, and ethylene glycol dimethylacrylate (EGDMA) is used to prepare a control group of chemically crosslinked PSBMA (PSBMA_chem) hydrogels. The mechanical properties of the two hydrogels are compared, and PSBMA_phy hydrogels exhibit greater flexibility than the PSBMA_chem hydrogels. When the PSBMA_phy hydrogels are subjected to external forces, the micelles act as dynamic crosslinking sites, allowing the stress to disperse and prevent the hydrogel from breaking. In addition, the PSBMA_phy hydrogels have nearly 100% self-healing properties within 2.5 min. The PSBMA_phy hydrogels exhibit usable adhesive properties to porcine skin and subcutis. MTT and hemolysis tests show that the PSBMA_phy hydrogels have excellent biocompatibility and hemocompatibility. This study proposes that the multifunctional PSBMA_phy hydrogels with micelles will be potential to carry drugs for use in drug delivery systems in the future.     

Antibacterial Broad-Spectrum Dendritic/Gellan Gum Hybrid Hydrogels with Rapid Shape-Forming and Self-Healing for Wound Healing Application

Treating wound infections is a difficult task ever since pathogenic bacteria started to develop resistance to common antibiotics. The present study develops hybrid hydrogels based on the formation of a polyelectrolyte complex between the anionic charges of dopamine-functionalized Gellan Gum (GG-DA) and the cationic moieties of the TMP-G2-alanine dendrimer. The hydrogels thus obtained can be doubly crosslinked with CaCl₂, obtaining solid hydrogels. Or, by oxidizing dopamine to GG-DA, possibly causing further interactions such as Schiff Base and Michael addition to take place, hydrogels called injectables can be obtained. The latter have shear-thinning and self-healing properties (efficiency up to 100%). Human dermal fibroblasts (HDF), human epidermal keratinocytes (HaCaT), and mouse monocyte cells (RAW 264.7), after incubation with hydrogels, in most cases show cell viability up to 100%. Hydrogels exhibit adhesive behavior on various substrates, including porcine skin. At the same time, the dendrimer serves to crosslink the hydrogels and endows them with excellent broad-spectrum microbial eradication activity within four hours, evaluated using Staphylococcus aureus 2569 and Escherichia coli 178. Using the same GG-DA/TMP-G2-alanine ratios hybrid hydrogels with tunable properties and potential for wound dressing applications can be produced.     

A Shear-Thinning,Self-Healing,Dual-Cross Linked Hydrogel Based on Gelatin/Vanillin/Fe3+/AGP-AgNPs: Synthesis,Antibacterial, and Wound-Healing Assessment

A shear-thinning and self-healing hydrogel based on a gelatin biopolymer is synthesized using vanillin and Fe³⁺ as dual crosslinking agents. Rheological studies indicate the formation of a strong gel found to be injectable and exhibit rapid self-healing (within 10 min). The hydrogels also exhibited a high degree of swelling, suggesting potential as wound dressings since the absorption of large amounts of wound exudate, and optimum moisture levels, lead to accelerated wound healing. Andrographolide, an anti-inflammatory natural product is used to fabricate silver nanoparticles, which are characterized and composited with the fabricated hydrogels to imbue them with anti-microbial activity. The nanoparticle/hydrogel composites exhibit activity against Escherichia coli, Staphylococcus aureus, and Burkholderia pseudomallei, the pathogen that causes melioidosis, a serious but neglected disease affecting southeast Asia and northern Australia. Finally, the nanoparticle/hydrogel composites are shown to enhance wound closure in animal models compared to the hydrogel alone, confirming that these hydrogel composites hold great potential in the biomedical field.     

Self-Healing Molecular Biology for Microbial Concrete: A Review

The most extensively utilized material in construction is concrete, decreasing life of structure pointing toward loses in structural health. The crack is the major problem faced in the concrete construction. This causes the corrosion in the steel reinforcement. The structure gets deteriorated with the developing cracks; therefore need the proper attention toward this problem. The present work consists of the different self-healing techniques used by the researchers to inhibit the crack and prevent further deterioration in the structure. The self-healing mechanism proves advantageous in use of natural fibers to inhibit the corrosion process, to increase compressive strength, and to decrease water absorption is present in this study. The maximum strength increased and the width of crack get healed with the help of these techniques is also mentioned in the study.     

黏土基纳米复合水凝胶

介绍了一种以黏土为交联剂的新型纳米复合水凝胶, 重点阐述了水凝胶的结构特点, 制备方法及其特有的力学性能, 自修复性能, 透明度和溶胀性。     

Dynameric Collagen Self-Healing Membranes with High Mechanical Strength for Effective Cell Growth Applications

The fabrication of biocompatible adaptive materials with high stiffness and self-healing properties for medical applications is a challenging endeavor. Collagen is a major extracellular matrix component acting as a substrate for cell adhesion and migration. Dynamers are constitutional polymers whose monomeric components are linked through reversible bonds, able to modify their constitution through reversible exchange of their components. In the current work, we demonstrate that the rational combination of collagen and dynameric networks connected with reversible covalent imine bonds is a very important and previously unreported strategy to provide biocompatible membranes with self-healing ability and excellent mechanical strength. The key challenge in the construction of such membranes is the required adaptive interaction between collagen chains and the dynamic cross-linkers, preventing the formation of defects. For example, by varying structure and molecular lengths of the dynamers, the tensile strength of the dynameric membranes reach over 80 MPa, more than 400 % higher than that observed for the reference collagen membrane, and the highest value for break strain found, was 19 %. The self-healing properties were observed when reconnecting two membrane pieces or even from crushed status of the membranes. Moreover, both MTT assay and confocal laser scanning microscopy method demonstrated the good biocompatibility of the collagen membranes, leaving more than 90 % viability for NIH 3T3 cells after 24 h co-culture.     

基于超分子聚合物的自修复材料

材料的自修复功能对于材料应用具有重要的意义,如键组装/解组装常数、键的方向和链的弛豫时间等因素会影响自修复效率。根据提供修复功能的物质构成形式,可以分为外援型自修复材料和本征型自修复材料,其中本征型自修复材料是当前的热点方向,在本征型自修复材料中,超分子自修复材料以其独特的可逆性组装,以及在快速、可逆、多重响应方面的优势而成为研究重点。本文重点阐述了基于不同结合效应的超分子自修复聚合物的研究进展,并对今后的研究方向作了展望,认为材料的耐环境性能能否达标是未来能否获得应用的关键因素之一。     

Construction of Chemical‐Responsive Supramolecular Hydrogels from Guest‐Modified Cyclodextrins

A methodology for preparing supramolecular hydrogels from guest‐modified cyclodextrins (CDs) based on the host–guest and hydrogen‐bonding interactions of CDs is presented. Four types of modified CDs were synthesized to understand better the gelation mechanism. The 2D ROESY NMR spectrum of β‐CD‐AmTNB (Am=amino, TNB=trinitrobenzene) reveals that the TNB group was included in the β‐CD cavity. Pulsed field gradient NMR (PFG NMR) spectroscopy and AFM show that β‐CD‐AmTNB formed a supramolecular polymer in aqueous solution through head‐to‐tail stacking. Although β‐CD‐AmTNB did not produce a hydrogel due to insufficient growth of supramolecular polymers, β‐CD‐CiAmTNB (Ci=cinnamoyl) formed supramolecular fibrils through host–guest interactions. Hydrogen bonds between the cross‐linked fibrils resulted in the hydrogel, which displayed excellent chemical‐responsive properties. Gel‐to‐sol transitions occurred by adding 1‐adamantane carboxylic acid (AdCA) or urea. ¹H NMR and induced circular dichroism (ICD) spectra reveal that AdCA released the guest parts from the CD cavity and that urea acts as a denaturing agent to break the hydrogen bonds between CDs. The hydrogel was also destroyed by adding β‐CD, which acts as the competitive host to reduce the fibrils. Furthermore, the gel changed to a sol by adding methyl orange (MO) as a guest compound, but the gel reappeared upon addition of α‐CD, which is a stronger host for MO.     

Noncovalent Hydrogel Beads as Microcarriers for Cell Culture

Hydrogel beads as microcarriers could have many applications in biotechnology. However, bead formation by noncovalent cross‐linking to achieve high cell compatibility by avoiding chemical reactions remains challenging because of rapid gelation rates and/or low stability. Here we report the preparation of homogeneous, tunable, and robust hydrogel beads from peptide–polyethylene glycol conjugates and oligosaccharides under mild, cell‐compatible conditions using a noncovalent crosslinking mechanism. Large proteins can be released from beads easily. Further noncovalent modification allows for bead labeling and functionalization with various compounds. High survival rates of embedded cells were achieved under standard cell culture conditions and after freezing the beads, demonstrating its suitability for encapsulating and conserving cells. Hydrogel beads as functional system have been realized by generating protein‐producing microcarriers with embedded eGFP‐secreting insect cells.     

生物医用类环糊精/聚合物(准)聚轮烷

环糊精及其衍生物具有“内疏水、外亲水”的特殊分子结构,可与许多客体分子包结形成包合物。利用环糊精与聚合物的包结作用构建稳定、结构可控并具有广泛应用前景的生物医用材料是材料及医学界研究的焦点之一。本文介绍了环糊精基(准)聚轮烷的概念及其组装驱动力,同时围绕由环糊精和聚合物组装形成的(准)聚轮烷在生物医用方面的研究包括药物载体(如超分子凝胶、超分子胶束、超分子纳米囊泡、药物键合(准)聚轮烷、刺激响应型(准)聚轮烷等)、基因载体、多重识别与靶向、形状记忆材料及其它相关领域工作进展作一概述。