Layer‐by‐Layer Assembly for Surface Tethering of Thin‐Hydrogel Films: Design Strategies and Applications

Manipulation and engineering of the surfaces has a key role in improving the materials properties. Anchoring of thin hydrogels on the materials surface is one of the recently developed methods to achieve surfaces with high potential applications. Layer‐by‐layer (LBL) has been used widely as a strong strategy for immobilization of thin hydrogel films on the surface of various organic/inorganic substrates. Electrostatic LBL and covalent LBL are two main strategies used in this regard. In electrostatic LBL, negatively and positively hydrophilic polymers are sequentially assembled to create a multilayer hydrogel which subsequent covalent crosslinking of multilayers improved the stability of the inserted layers. On the other hand, covalent LBL requires hydrophilic polymers bearing reactive telechelic groups. These reactive polymers are prepared by various polymerization techniques or by post‐functionalization of biopolymers. The principles of hydrogel anchoring have described along with representative examples. Besides, the potential applications of the modified surfaces in specific cases have been addressed and overviewed.     

UV光引发表面接枝两性离子水凝胶层的制备及抗细菌黏附性能

采用聚合和交联的SiO₂有机/无机杂化溶胶作为基材, 通过与两性离子单体层之间的过渡层, 在紫外光作用下引发杂化溶胶和两性离子单体溶液中的双键反应, 使生成的杂化层在基材和表面的两性离子聚合物之间形成辅助性黏接作用, 从而在基材表面构筑两性离子水凝胶层. 通过傅里叶红外光谱(FTIR)、 原子力显微镜(AFM)和接触角测试等方法对所制备的两性离子水凝胶层和杂化层的表面进行了表征. 以空白玻璃片为对照样品, 以金黄色葡萄球菌和大肠杆菌为试验菌, 研究了用两性离子凝胶层修饰的玻璃表面的抗细菌黏附性能. 结果表明, 在SiO₂杂化过渡层中引入线型-Si-(CH₂)₂-O-链段可有效提高杂化过渡层对基材的附着力, 并改善其柔韧性. 与对照样品相比, 用两性离子凝胶层修饰的玻璃表面具有优异的抗菌黏附性能.     

Design Strategies of Conductive Hydrogel for Biomedical Applications

Conductive hydrogel, with electroconductive properties and high water content in a three-dimensional structure is prepared by incorporating conductive polymers, conductive nanoparticles, or other conductive elements, into hydrogel systems through various strategies. Conductive hydrogel has recently attracted extensive attention in the biomedical field. Using different conductivity strategies, conductive hydrogel can have adjustable physical and biochemical properties that suit different biomedical needs. The conductive hydrogel can serve as a scaffold with high swelling and stimulus responsiveness to support cell growth in vitro and to facilitate wound healing, drug delivery and tissue regeneration in vivo. Conductive hydrogel can also be used to detect biomolecules in the form of biosensors. In this review, we summarize the current design strategies of conductive hydrogel developed for applications in the biomedical field as well as the perspective approach for integration with biofabrication technologies.     

Monolayers of a solvent-free polymer brush: Part 2. Crosslinking and transfer to form suspended films

Hydrophobic polymers with low glass transition temperature (polyisoprenes) and a single head group (sulfonate) bearing photoreactive side groups (anthracene) have been synthesised and characterised as insoluble monolayers on a water surface. The isotherms are similar to those of the parent polymers without anthracene side groups and the films can be transferred to solid substrates via the Langmuir-Blodgett technique with a transfer ratio of 0.85. The films on solid substrates as well as on the water surface can be crosslinked via irradiation with ultraviolet light. Films crosslinked on the water surface can be transferred to copper grids. The films span the openings of the grids and damaged parts of the suspended films have round borders. Irradiation of the monolayers through a mask followed by solvent treatment gives rise to laterally structured monolayers.     

Photovoltaic properties of the polymer solar cells comprising crosslinked maleimide polymers and fullerene‐derivative PCBM

A series of crosslinkable maleimide conjugated polymers with different vinyl group contents as side‐chain crosslinking sites have been synthesized by the Suzuki coupling reaction. Polymer solar cells (PSCs) were fabricated based on an interpenetrating network of the crosslinkable maleimide polymers as the electron donor, and a fullerene derivative, (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), as the electron acceptor. The crosslinkable maleimide polymers underwent crosslinking reaction at the side‐chain vinyl groups upon the thermal treatment with or without the addition of initiator, azobisisobutyronitrile (AIBN). Better photovoltaic (PV) performances were obtained for the PSCs based on the polymer crosslinking without using initiator, whereas poorer PV performances were observed for the PSCs based on the polymer crosslinking with the AIBN initiator. In addition, higher operational stability was observed for the crosslinked polymer based solar cell as compared to the solar cell based on the un‐crosslinked polymer. The photo‐physical and PV properties of the cross‐linked maleimide polymers/PCBM based PSCs are discussed in detail as the morphology and crosslinking density of the polymers are taken into account. Copyright © 2010 John Wiley & Sons, Ltd.     

Structure-property relationships in high-performance thermoset-thermoplastic blends

Semi-crystalline and amorphous aromatic polymers have become well established as high-performance engineering polymers and composite matrices. Such polymers with functional groups introduced, may be used to toughen, and modify the processing properties of, a range of thermosetting resins, in addition to being copolymerisable, crosslinkable and/or chain-extendable. This paper describes structure/property relationships which have been established for functionalised polyaromatics and systems which utilise them.     

Amorphous Silk Fibroin Nanofiber Hydrogels with Enhanced Mechanical Properties

Silk fibroin (SF) hydrogels have been engineered as universal substrates for various tissue regenerations and drug delivery. Although different physical and chemical crosslinking strategies are developed to form SF hydrogels with suitable performances, a significant gap remains to match specific requirements of various tissues. Here, amorphous SF nanofibers with more tyrosine residues outside the surfaces are used to replace traditional SF. Under the same crosslinking conditions, the use of amorphous SF nanofibers results in tougher properties, four times higher stiffness than that from traditional SF solutions. Unlike previous SF hydrogels, the SF nanofiber hydrogels show high tunability in wide modulus range of 0.6–160 kPa under low SF concentrations (below 5 wt%), showing improved mechanical match with various soft tissues. Better stability and cytocompatibility are also achieved, further confirming the superiority of the hydrogels as the tissue substrates. Therefore, a feasible strategy is developed to optimize the performances of SF hydrogel via tuning the nano‐structural state in aqueous solutions, which will enrich SF‐based hydrogel family in future.     

Aligned/unaligned conducting polymer cryogels with three-dimensional macroporous architectures from ice-segregation-induced self-assembly of PEDOT-PSS

Porous conducting polymers are of great interest because of the huge potential to combine high surface areas in the dry state with physical properties relevant to organic electronics. Aligned or unaligned conducting polymer cryogels with 3D macroporous architectures have been prepared using the ice-segregation-induced self-assembly (ISISA) of different poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) freezing precursors as a dispersion or a formed hydrogel. The chemical composition and molecular structure of the resulting conducting polymer cryogels have been investigated by X-ray photoelectron spectroscopy and Raman spectroscopy, respectively. The morphologies of the PEDOT-PSS cryogels, together with their textural structures, have been revealed by scanning electron microscopy, mercury porosimetry, and nitrogen sorption tests. Processing PEDOT-PSS via ISISA endows the conducting polymers with novel properties, as demonstrated by a series of X-ray diffraction, differential scanning calorimetry, and electrical conductivity tests. These conducting polymer cryogels with aligned/unaligned macroporous architectures suggest the potential in the development of electronic components, tissue engineering, and next-generation catalytic and separation supports.     

A Charge‐Transfer‐Induced Self‐Healing Supramolecular Hydrogel

In this study, a dual‐component charge‐transfer (CT)‐induced supramolecular hydrogel was fabricated using pyrene‐tailored pyridinium (PYP) and 2,4,7‐trinitrofluorenone (TNF) as the electron donor and acceptor, respectively. Its thermal stability and mechanical property have been modulated effectively by altering the concentration or molar ratio of PYP and TNF. Moreover, this CT hydrogel exhibited a distinct injectable self‐healing property that could be utilized to create desired patterns on substrates. Such property holds potential for this CT hydrogel in fields like three‐dimensional printing and surface coating.     

Spherical phospholipid polymer hydrogels for cell encapsulation prepared with a flow-focusing microfluidic channel device

To prepare spherical polymer hydrogels, we used a flow-focusing microfluidic channel device for mixing aqueous solutions of two water-soluble polymers. Continuous encapsulation of cells in the hydrogels was also examined. The polymers were bioinspired 2-methacryloyloxyethyl phosphorylcholine polymer bearing phenyl boronic acid groups (PMBV) and poly(vinyl alcohol) (PVA), which spontaneously form a hydrogel in aqueous medium via specific molecular complexation upon mixing, even when they were in cell culture medium. The microfluidic device was prepared with polydimethylsiloxan, and the surface of the channel was treated with fluoroalkyl compound to prevent sticking of the polymers on the surface. The microfluidic channel process could control the diameter of the spherical hydrogels in the range of 30-90 μm and generated highly monodispersed diameter spherical hydrogels. We found that the polymer distribution in the hydrogel was influenced by the PVA concentration and that the hydrogel could be dissociated by the addition of d-sorbitol to the suspension. The single cells could be encapsulated and remain viable in the hydrogels. The localized distribution of polymers in the hydrogel may provide an environment for modulating cell function. It is concluded that the spontaneous hydrogel formation between PMBV and PVA in the flow-focusing microfluidic channel device is applicable for continuous preparation of a spherical hydrogel-encapsulating living cell.     

“One‐step” Preparation of Thiol‐Ene Clickable PEG‐Based Thermoresponsive Hyperbranched Copolymer for In Situ Crosslinking Hybrid Hydrogel

A well‐defined poly(ethylene glycol) based hyperbranched thermoresponsive copolymer with high content of acrylate vinyl groups was synthesized via a “one‐pot and one‐step” deactivation enhanced atom transfer radical polymerization approach, which provided an injectable and in situ crosslinkable system via Michael‐type thiol‐ene reaction with a thiol‐modified hyaluronan biopolymer. The hyperbranched structure, molecular weight, and percentage of vinyl content of the copolymer were characterized by gel permeation chromatography and ¹H NMR. The lower critical solution temperature of this copolymer is close to body temperature, which can result in a rapid thermal gelation at 37 °C. The scanning electron microscopy analysis of crosslinked hydrogel showed the network formation with porous structure, and 3D cell culture study demonstrated the good cell viability after the cells were embedded inside the hydrogel. This injectable and in situ crosslinking hybrid hydrogel system offers great promise as a new class of hybrid biomaterials for tissue engineering.     

A Two‐Step Method for Transferring Single‐Walled Carbon Nanotubes onto a Hydrogel Substrate

Carbon nanotube (CNT)‐hydrogel nanocomposites are beneficial for various biomedical applications, such as nerve regeneration, tissue engineering, sensing, or implant coatings. Still, there are impediments to developing nanocomposites, including attaining a homogeneous CNT‐polymer dispersion or patterning CNTs on hydrogels. While few approaches have been reported for patterning CNTs on polymeric substrates, these methods include high temperature, high vacuum or utilize a sacrificial layer and, hence, are incompatible with hydrogels as they lead to irreversible collapse in hydrogel structure. In this study, a novel two‐step method is designed to transfer CNTs onto hydrogels. First, dense CNTs are grown on quartz substrates. Subsequently, hydrogel solutions are deposited on the quartz‐grown CNTs. Upon gelation, the hydrogel with transferred CNTs is peeled from the quartz. Successful transfer is confirmed by scanning electron microscopy and indirectly by cell attachment. The efficient transfer is attributed to π‐interactions pregelation between the polymers in solution and the CNTs.

     

Impact of polymeric films and hydrogels: Physical characteristics on bacterial growth

Hydrogels find diverse applications in manipulating bacteria, and serving purposes like elevation, maintenance, and elimination. Several factors of hydrogel have been studied in the benefits of antibacterial activity. Factors such as hydrogel stiffness and roughness gain significance in surface coating, influencing bacterial behavior. However, the intricate interplay of hydrogel stiffness, roughness, polymer types, and bacterial species necessitates further exploration. The choice of polymer is dictated by the specific objectives, particularly in antibacterial scenarios where polymers with positive charge, hydrophilicity, and acidity prove effective. These properties induce robust electrostatic and hydrophobic/hydrophilic interactions, along with pH-induced cell membrane damage, collectively contributing to hindered bacterial adhesion and growth. Additionally, extracellular polymeric substances (EPS) emerge as pivotal influencers in bacterial adhesion and proliferation. EPS production alters bacterial surfaces, fostering connections between bacteria and facilitating biofilm formation. The hydrophobic nature of EPS further complicates bacterial interactions with surface materials, emphasizing the nuanced interplay of hydrophilic and hydrophobic forces in bacterial adhesion. Herein, this work article has reviewed the related study of each physical property related to antibacterial property on the surface of the hydrogel. Moreover, this work also illustrates applications of the antibacterial properties of hydrogel for medical and surface treatment, including wound healing, food packaging, and surface coating. Additionally, the bacteria growing on hydrogel for engineered living materials, have been updated in various applications.     

Siloxane/silane‐crosslinked systems from supercritical carbon dioxide: I. Fluorinated poly(ether/siloxane)s

A series of new, fluorinated, silicone‐containing polymers with crosslinkable units has been synthesized by hydrosilation in toluene and supercritical carbon dioxide (70°C, 3000 psi) using platinum‐divinyltetramethyldisiloxane (Pt‐DVTMS) as a catalyst. The polymers were characterized by FTIR, NMR, GPC, TGA, and DSC. The molecular weights of these polymers ranged from 9,900 to 41,000. Comparison of the properties between reactions in toluene versus supercritical carbon dioxide indicated that the green solvent is a suitable alternative for hydrosilation. The hydrolysis and thermal curing of the crosslinkable precursor polymers produced higher molecular weight polymers with thermal stabilities ranging from 347 to 417°C. Copyright © 2007 John Wiley & Sons, Ltd.     

Antibacterial Hybrid Hydrogels

Bacterial infectious diseases and bacterial‐infected environments have been threatening the health of human beings all over the world. In view of the increased bacteria resistance caused by overuse or improper use of antibiotics, antibacterial biomaterials are developed as the substitutes for antibiotics in some cases. Among them, antibacterial hydrogels are attracting more and more attention due to easy preparation process and diversity of structures by changing their chemical cross‐linkers via covalent bonds or noncovalent physical interactions, which can endow them with various specific functions such as high toughness and stretchability, injectability, self‐healing, tissue adhesiveness and rapid hemostasis, easy loading and controlled drug release, superior biocompatibility and antioxidation as well as good conductivity. In this review, the recent progress of antibacterial hydrogel including the fabrication methodologies, interior structures, performances, antibacterial mechanisms, and applications of various antibacterial hydrogels is summarized. According to the bacteria‐killing modes of hydrogels, several representative hydrogels such as silver nanoparticles‐based hydrogel, photoresponsive hydrogel including photothermal and photocatalytic, self‐bacteria‐killing hydrogel such as inherent antibacterial peptides and cationic polymers, and antibiotics‐loading hydrogel are focused on. Furthermore, current challenges of antibacterial hydrogels are discussed and future perspectives in this field are also proposed.     

Synthesis and properties of water-soluble gold colloids covalently derivatized with neutral polymer monolayers

Citrate-capped gold nanoparticles as well as planar gold surfaces can be efficiently grafted with a covalently attached polymer monolayer a few nanometers thick, by simple contact of the metal surface with dilute aqueous solutions of hydrophilic polymers that are end-capped with disulfide moieties, as shown by UV/vis absorption, dynamic light scattering, and surface plasmon resonance studies. The hydrophilic polymer-coated gold colloids can be freeze-dried and stored as powders that can be subsequently dissolved to yield stable aqueous dispersions, even at very large concentrations. They allow for applying filtrations, gel permeation chromatography, or centrifugation. They do not suffer from undesirable nonspecific adsorption of proteins while allowing the diffusion of small species within the hydrogel surface coating. In addition, specific properties of the original hydrophilic polymers are retained such as a lower critical solution temperature. The latter feature could be useful to enhance optical responses of functionalized gold surfaces toward interaction with various substrates.     

含苯乙炔基的可交联聚芳醚酮交替共聚物的合成与热性能

以耐高温高性能树脂-聚芳醚酮作为研究对象, 从改善材料的加工工艺性及提高材料的使用温度出发, 对含有苯乙炔基的交替共聚物进行了系统研究. 实验结果表明, 该系列聚合物固化前具有较好的溶解性, 固化过程中显示出较好的热稳定性, 固化后具有较高的玻璃化转变温度和优异的热稳定性与热氧稳定性, 且降低聚合物的分子量没有对固化物的热性能产生明显影响, 在高性能复合材料基体树脂方面具有潜在的应用价值.     

Modern Trends in Organic Light-Emitting Devices (OLEDs)

Synthesis of crosslinkable small and large organic molecules having OLED properties will be presented. Three strategies for the construction of multilayer devices will be described. In the first case small, well-defined OLED-molecules are functionalized with oxetanes as crosslinker. The second case deals with polymers having OLED active units in the main chain and pendant crosslinkers and finally it was shown that styrene polymers with pendant OLED functions and crosslinkers can be applied for the construction of such multilayer and multicolour devices.     

Structure property correlation in crosslinkable copolyimides

Three copolyimides containing crosslinkable alkyne groups either in the main chain backbone or as endgroups, have been synthesized and characterized in regard to their structure, molecular weight, solubility, film-forming properties, crystallinity, crosslinking behavior, and thermal stability. A good correlation between the structure of the polymers and their properties has been established.     

Modern Trends in Organic Light-Emitting Devices (OLEDs)

Summary. Synthesis of crosslinkable small and large organic molecules having OLED properties will be presented. Three strategies for the construction of multilayer devices will be described. In the first case small, well-defined OLED-molecules are functionalized with oxetanes as crosslinker. The second case deals with polymers having OLED active units in the main chain and pendant crosslinkers and finally it was shown that styrene polymers with pendant OLED functions and crosslinkers can be applied for the construction of such multilayer and multicolour devices.