Double Network Structures Research Articles

Controllable structure, super adhesion, multifunctional, conductive pressure-sensitive adhesive for electronic skin: Enhancing cohesion by cellulose-derived covalent crosslinking

Ensuring firm adhesion to the skin is essential for improving the detection of temperature and movement signals in electronic skin (E-skin). Self-adhesive eutectogel, an ideal material for E-skin, could act as an innovative pressure-sensitive adhesives (PSAs) that can be easily applied through simple pressing without requiring heating or irradiation. Herein, we synthesized a cellulose-derived polymer crosslinking agent (MCCAC) to create a eutectogel-based conductive PSA (CPSA). The MCCAC formed strong covalent bonds with polymer chains, significantly enhancing the cohesion of the CPSAs. As a result, the CPSAs exhibited high tensile lap-shear strength (99.5 kPa) among self-adhesive eutectogels. Unlike the construction of double-network structures, this method included a straightforward chemical reaction and a cohesion-enhancing strategy, and could adjust crosslinking density by changing the MCCAC content. The preparation process was simple, and the products were controllable. More importantly, this cohesion-enhancing strategy did not compromise the fluidity of polymer chains, which ensured that CPSAs maintain effective interfacial adhesion to adhere on skin, offering exceptional capabilities for capturing body temperature signals (−3.66 %/℃) as well as applications in motion detection and information transmission. This work resolved the cohesion and interfacial adhesion imbalances observed in previous self-adhesive eutectogels and provided a promising approach for designing the novel cellulose-reinforced CPSA for E-skins.

Fabrication of strong and elastic HIPPEs gel by rigid-flexible double network structure as a novel adipose tissue substitutes

Fat mimics are one of the most common substitutes for animal fats in processed foods. However, basing on high internal phase Pickering emulsion (HIPPEs) gel imitate adipose tissue to achieve the desired strength and elastic, while the formation and stabilization mechanism are barely understood. Here, we proposed a strategy to fabricate rigid-flexible double network using κ-carrageenan (CA) and bacterial cellulose (BC), in oder to improve the mechanical performance of HIPPEs gel. The effects of different ratios of CA/BC (2:1, 4:1, 8:1) and K+ addition on the properties of HIPPEs-CA/BC gels were investigated. Results showed that HIPPEs-CA/BC 8:1 & K+ exhibited better rheological, textural, oil holding capacity and organoleptic properties. Thermal softening behavior of HIPPEs-CA/BC 8:1 & K+ was similar to the pork adipose tissue. The microstructure of gel demonstrated that HIPPEs-CA/BC 8:1 & K+ was featured with honeycomb-like pore and network walls, which in turn comprise interpenetrated double network structures. Meanwhile, it showed an ultrahigh stress, high Young's modulus and good cyclic compress behavior. Additionally, the hydrogen bonds and K+-cross-linked were proved to play crucial roles in facilitating the formation of a stable and elastic CA/BC matrix. This study establishes structure-performance mechanisms in strongly and elastically structured HIPPEs gels, providing an advanced strategy for developing HIPPEs gel with promising applications in adipose tissue substitutes.

Core-Shell Double Gyroids Directed by Selective Solvation for ABC Triblock Terpolymers.

The formation of ABC triblock terpolymers through solution casting is still challenging. In this study, core-shell double gyroid network structures are fabricated via solution casting using poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) (F)-b-[poly(4-vinylpyridine) (P4VP) (P)]-b-[polystyrene (PS) (S)] (FPS) triblock terpolymers in N,N-dimethylformamide (DMF). Upon heat treatment, the polymer tends to form a sphere-in-lamellar structure at the F/S interface. Given the solubility properties of each component in DMF, it is anticipated that the effective volume fraction of F relative to P would increase in concentrated solutions and the effective volume fraction of S would decrease. The microphase-separated structure derived from the DMF solution consistently results in the formation of a network structure composed of a core-shell double gyroid, with F as the matrix, P as the shell, and S as the core, and their periodic lengths gradually increase to 110.8, 131.8, and 162.7nm as increase molecular weights of PS blocks to 13.8, 20.7, and 28.8kg mol-1. Based on the solubility properties of the polymer components highlighted in this study, the solvent selection strategy is broadly applicable to ABC triblock terpolymers featuring various polymer components, offering a more efficient avenue for fabricating core-shell double gyroid structures.

Analysis of the Mullins effect in buckling instability of double-network hydrogel beams under swelling equilibrium

Due to their outstanding physical and mechanical properties, double-network (DN) hydrogels have gained a most attention among various synthetic tough hydrogels. The Mullins effect and buckling instability are two frequent phenomena that may occur simultaneously in slender DN hydrogel structures as high load-bearing candidates. The swelling/deswelling degree of the DN hydrogel affects the coupling phenomena. It is essential to understanding the interplay between these behaviors. In this work, a physically based damage constitutive model for a DN polymer under water-diffusion equilibrium and cyclic loadings is developed. This theory of coupled swelling and load-induced deformations show good capability in capturing the Mullins effect of swollen DN hydrogels and the corresponding swelling ratio. The model parameters are determined by fitting experimental data of a freely swollen DN hydrogel under cyclic compression. Based on the constitutive model and determined parameters, the buckling instability of DN hydrogel beams is studied via the analytical formula of incremental modulus. The stability diagrams of the DN hydrogel beams under virgin loading and reloading are presented. The influences of stress softening, strain stiffening and chemical potential on buckling conditions for compressive stress and slenderness ratio are thoroughly analyzed. It demonstrates that the stress softening is dramatically against the stability of the beam, but the strain-stiffening effect would conversely help widen the stable range. Besides, it is found that a DN gel beam immersed in a sufficient low chemical potential environment has better buckling stability. These theoretical results are valuable in the preparation and structural design of DN hydrogels for repeated use purpose.

Development of a radical polymerization algorithm for molecular dynamics simulations of antifreezing hydrogels with double-network structures

The development and understanding of antifreezing hydrogels are crucial both in principle and practice for the design and delivery of new materials. The current antifreezing mechanisms in hydrogels are almost exclusively derived from their incorporation of antifreezing additives, rather than from the inherent properties of the polymers themselves. Moreover, developing a computational model for the independent yet interconnected double-network (DN) structures in hydrogels has proven to be an exceptionally difficult task. Here, we develop a multiscale simulation platform, integrating ‘random walk reactive polymerization’ (RWRP) with molecular dynamics (MD) simulations, to computationally construct a physically-chemically linked PVA/PHEAA DN hydrogels from monomers that mimic a radical polymerization and to investigate water structures, dynamics, and interactions confined in PVA/PHEAA hydrogels with various water contents and temperatures, aiming to uncover antifreezing mechanism at atomic levels. Collective simulation results indicate that the antifreezing property of PVA/PHEAA hydrogels arises from a combination of intrinsic, strong water-binding networks and crosslinkers and tightly crosslinked and interpenetrating double-network structures, both of which enhance polymer-water interactions for competitively inhibiting ice nucleation and growth. These computational findings provide atomic-level insights into the interplay between polymers and water molecules in hydrogels, which may determine their resistance to freezing.

Preparation of ambient-dried multifunctional cellulose aerogel by freeze-linking technique

Ambient drying is currently the cheapest and most efficient way to prepare aerogels, but it is invisible for the preparation of cellulose aerogels. In this paper, we describe a method of preparing cellulose aerogels that can be dried under atmospheric pressure by freeze-linking technique. The amino silane coupling agent forms an amino-rich polymer layer on the bacterial cellulose surface during the freezing process. And, the cross-linked network constructed by Schiff base reaction can strengthen the fiber skeleton in the process of solvent exchange. Due to the double cross-linked network structures, the cellulose ethanol gel can be dried directly under atmospheric pressure at 60 °C and the volume shrinkage can be as low as 3.3 %±1.4 %. In the process of solvent exchange, the loss of some polysiloxane causes defects in the aerogel, which not only reduces its thermal conductivity but also increases its specific surface area. And the water resistance, thermal performance, and dye adsorption performance of the aerogel are also significantly improved. This study provides a low-cost and high-efficiency solution for the manufacture of cellulose aerogels and promotes their wide applications.

Designing Antifreezing Hydrogels with Enhanced Mechanical Properties Using a Simple Crosslinker

Antifreezing hydrogels are essential for materials design and practical applications, but their development and understanding have been challenging due to their high-water content. Current antifreezing hydrogels typically rely on organic solvents or the addition of antifreezing agents. In this study, we present a novel crosslinking strategy to fabricate antifreezing hydrogels without the need for additional antifreezing agents. We introduce a new crosslinker, PEGn-EGINA, which combines highly hydrophilic EGINA with polyethylene glycol (PEG) of varying molecular weights. Utilizing PEGn-EGINA as the crosslinker, we synthesize Agar/Polyacrylamide (Agar/PAAm) double-network hydrogels, alongside conventional MBAA-crosslinked hydrogels for comparison. The resulting PEGn-EGINA-crosslinked hydrogels exhibit inherent antifreezing properties and retain their mechanical integrity even at subzero temperatures for extended periods. Molecular dynamics (MD) simulations further reveal that the antifreezing behavior observed in the PEGn-EGINA-crosslinked hydrogels can be attributed to their highly hydrophilic and tightly crosslinked double-network structures. These structures enable strong bindings between water and the hydrogel network, thus effectively preventing the formation of ice crystals within the hydrogels. Notably, PEGn-EGINA-crosslinked hydrogels not only demonstrate superior mechanical performance compared to MBAA-crosslinked hydrogels, but also maintain their mechanical properties even in frozen conditions, making them suitable for a wide range of applications. This study presents a simple yet effective design concept for highlighting the role of novel crosslinker in enhancing antifreezing and mechanical properties, showcasing their potential for various applications that require both antifreezing capabilities and robust mechanical performance.

A novel, robust mechanical strength, and naturally degradable double crosslinking starch-based bioplastics for practical applications

The increasing number of petroleum-based plastics has caused severe environmental pollution, which has attracted great research interest in the development of low-cost, renewable, and degradable starch-based bioplastics. However, developing starch-based bioplastics with robust mechanical strength, excellent water resistance, and thermal resistance remains a great challenge. In this study, we presented a simple and efficient method for preparing high-performance novel starch-based bioplastics with chemical and physical double crosslinking network structures filled with 2,2,6,6-tetramethylpiperidine 1-oxy-oxidized cellulose nanofibers and zinc oxide nanoparticles. Compared with pure starch-based bioplastics, the tensile strength of the novel robust strength starch-based bioplastics increased by 431.2 %. The novel starch-based bioplastics exhibited excellent mechanical properties (tensile strength up to 24.54 MPa), water resistance, thermal resistance, and biodegradability. In addition, the novel starch-based bioplastics could be reused, crushed, dissolved, and re-poured after use. After recycling, the novel starch-based bioplastics could be discarded in the soil to achieve complete degradation within six weeks. Owing to these characteristics, the novel starch-based bioplastics are good alternatives used to replace traditional petroleum-based plastics and have great development prospects.

Flexible and recoverable ion-conductive hydrogels with cross-linked triple network for highly sensitive wearable Motion-monitoring sensors

The practical applications of hydrogel-based sensors are limited by their low mechanical strength, insufficient sensitivity and machining difficulties caused by electrically conductive fillers. It is of great practical importance for facile preparation of hydrogel sensor combined with excellent mechanical properties and conductive sensitivity. In this work, a series of ion-conductive hybrid hydrogels based on in-situ polymerized polyacrylamide with double and triple network structures have been fabricated via both chemical and physical cross-linking. The triple network structured hydrogels achieve the tensile strength of 2.105 MPa and compression strength of 57.56 MPa, which are much higher than those of hydrogels with double network due to the established energy dissipation gradient. The reversible non-covalent cross-linking in the network also leads a relatively fast recovery in tensile cycle tests and double compression tests, enabling the excellent stability of strain sensing in the durability test. The hydrogels show the tensile resistance sensitivity factor of 0.9352 at 0–120% strain and a high pressure sensitivity factor of 5.134 kPa−1 with the pressure ranged from 0 to 6 kPa. The hydrogels are also assembled as flexible sensors for human motion monitoring, and the signals of motions can be distinguished by different resistance variation values and certain curve shape, showing the potential of applications on flexible device and human-machine interface.

Printing Double-Network Tough Hydrogels Using Temperature-Controlled Projection Stereolithography (TOPS).

We report a new method to shape double-network (DN) hydrogels into customized 3D structures that exhibit superior mechanical properties in both tension and compression. A one-pot prepolymer formulation containing photo-cross-linkable acrylamide and thermoreversible sol-gel κ-carrageenan with a suitable cross-linker and photoinitiators/absorbers is optimized. A new TOPS system is utilized to photopolymerize the primary acrylamide network into a 3D structure above the sol-gel transition of κ-carrageenan (80 °C), while cooling down generates the secondary physical κ-carrageenan network to realize tough DN hydrogel structures. 3D structures, printed with high lateral (37 μm) and vertical (180 μm) resolutions and superior 3D design freedoms (internal voids), exhibit ultimate stress and strain of 200 kPa and 2400%, respectively, under tension and simultaneously exhibit a high compression stress of 15 MPa with a strain of 95%, both with high recovery rates. The roles of swelling, necking, self-healing, cyclic loading, dehydration, and rehydration on the mechanical properties of printed structures are also investigated. To demonstrate the potential of this technology to make mechanically reconfigurable flexible devices, we print an axicon lens and show that a Bessel beam can be dynamically tuned via user-defined tensile stretching of the device. This technique can be broadly applied to other hydrogels to make novel smart multifunctional devices for a range of applications.

Temperature-Induced Nanostructure Transition for Supramolecular Gelation in Water.

Thermogel is an injectable biomaterial that functions at body temperatures due to the ease of the sol-to-gel transition. However, most conventional physically cross-linked thermogels generally have relatively low stiffness, which limits various biomedical applications, particularly for stem-cell-based studies. While chemical cross-linking through double-network (DN) structures can increase the stiffness of the hydrogel, they generally lack injectable and thermoresponsive properties due to strong covalent bonds between molecules. To address this challenge, we have developed a temperature-induced nanostructure transition (TINT) system for preparing physical DN supramolecular hydrogels. These hydrogels possess injectable, thermoreversible characteristics and relatively high storage modulus (G'), which increases ∼14-fold from 20 to 37 °C (body temperature). Our bottom-up strategy is based on the co-assembly of aromatic peptide (Ben-FF) and poly(ethylene glycol) (PEG) to form a thermogel at 37 °C through a nanofiber dissociation pathway that differs from the well-known micelle aggregation or polymer shrinkage mechanisms. Peptide molecules form helical packing and weak, noncovalent interactions with PEG, resulting in co-assembled metastable nanofibers. Thermal perturbation initiates lateral dissociation of nanofibers into extensively cross-linked DN nanostructures and subsequent hydrogelation (ΔG = -13.32 kJ/mol). The TINT hydrogel is nontoxic to human mesenchymal stem cells and supports enhanced cell adhesion, suggesting the potential of this strategy in the applications of tissue engineering and regenerative medicine.

Self-healing and freezing-tolerant strain sensor based on a multipurpose organohydrogel with information recording and erasing function

Smart hydrogels with various stimuli-responsiveness have shown tremendous prospects in the areas of electronic skins, artificial medical organization and soft robotics. Herein, a multifunctional organohydrgel is prepared by introducing polyvinylpyrrolidone (PVP), acrylic acid (AA) and acrylamide (AAm) into water/dimethyl sulfoxide (H2O/DMSO) binary solvent system. The introduced PVP and chemical cross-linked P(AA-co-AAm) chains based double network structures and the amount of reversible hydrogen bonds between polymer chains endow the as-prepared organohydrogel with excellent mechanical property (1554 % strain) and self-healing capability. Meanwhile, the organohydrogel exhibits extraordinary low-temperature tolerance (−40 ℃) and long-term anti-drying property (83 % moisture retention after 7 days) due to the strong interactions between water and DMSO. Furthermore, the flexible strain sensor based on the organohydrogel displays a wide strain sensing range (0–500 %) and repeatable response capability, which can precisely monitor varying degrees of stretching deformations and a series of intricate human movements. Owing to the remarkable freezing resistance and self-healing property, the original and healed organohydrogel sensors still exhibit stable sensing behaviors in freezing environment of −40 ℃. Noticeably, the obtained organohydrogel can also be served as a special paper to realize the information recording and erasing function at subzero temperatures. These outstanding performances indicate the organohydrogels may be employed as durable and freezing-tolerant smart materials applied in future flexible electronics, soft robots and information platform.

Cover Image, Volume 61, Issue 1

Journal of Polymer ScienceVolume 61, Issue 1 p. i-i COVER IMAGEFree Access Cover Image, Volume 61, Issue 1 First published: 01 January 2023 https://doi.org/10.1002/pol.20220714AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract The cover image, submitted by Jinping Zhou and co-workers for the article on page 7, shows representative polysaccharides (e.g., cellulose, chitin, and chitosan), a class of renewable natural materials with biocompatible and biodegradable properties. Utilized as building blocks for double-network structures through physical and/or chemical crosslinking and benefiting fromthe peculiar physicochemical properties and unique network structures, these are promising materials for biomedical and energy storage and conversion fields. (DOI: 10.1002/pol.20220510) Volume61, Issue11 January 2023Pages i-i RelatedInformation

FDM-3D printing LLDPE/BN@GNPs composites with double network structures for high-efficiency thermal conductivity and electromagnetic interference shielding

Towards the high-frequency and miniaturization of modern electronic devices, the multi-functional materials with high-efficiency thermal management and electromagnetic interference shielding performance are urgently demanded. The contributions in materials are mostly focused on a single function, and difficult to meet the requirement of the precision device with complicated structures. Herein, linear low-density polyethylene (LLDPE)/boron nitride (BN)@graphene nanoplatelets (GNPs) composite parts with double network structures were designed and realized by combining ball-milling strategy and fused deposition modeling (FDM) 3D printing technology. The FDM-3D printed parts could exhibit a thermal conductivity of 3.11 W/(m·K) along the printing direction at 3.51 vol% GNPs loading, achieving an improvement of ∼2.88 and ∼8.33 times over that of flat printing parts and pure LLDPE, respectively. The long-range aligned network along the printing direction is formed due to the shear extrusion effect during FDM-3D printing. Also, FDM-3D printing is applied to print heat sinks with excellent thermal conductive property in vertical direction. Furthermore, the ball milling process could enable the GNPs to form thermal and electrical conductivity pathways in LLDPE/BN composites. The printed parts accordingly exhibit good electromagnetic shielding performance (27.8 dB) and electrical conductivity (12.5 S/m). This study not only enriches the strategy for preparation of multifunctional FDM 3D printed parts, but also paves the way for further applications in advanced thermal management and protection against electromagnetic irradiation.

Nonprestretching double-network enabled by physical interaction-induced aggregation

The design of double-network (DN) improves the properties of matrix effectively, which has attracted wide attention. The recently reported construction of DN structure usually involves the prestretching process (swelling process). However, such complicated multistep swelling processes become more difficult in high molecular weight matrix, which are not suitable for constructing DN structure in the universal elastomers (for example, natural rubber and polyisoprene rubber). To expand the application fields of DN, this work designs the dense crosslinking domain and the sparse crosslinking domain to construct nonprestretching DN structure through physical interaction-induced aggregation. We find that physical interaction induced-aggregation form the dense crosslinking domain and the sparse crosslinking domain, which builds the two contrasting DN structures. Double-quantum nuclear magnetic resonance, dynamic mechanical analyzer, and mechanical property characterization demonstrate that the dense crosslinking domain as the brittle first network is preferentially ruptured upon deformation, leading to a large energy dissipation. This design concept represents a general approach to develop the nonprestretching DN structure, which expands the application fields of DN structure in the elastomer matrix.

Double-network strategy for a cost-effective soybean meal-based adhesive with required and stable water resistance for structural use

Although soybean meal (SM)-based adhesives, modified by polyamidoamine-epichlorohydrin (PAE) resin exhibit satisfactory characteristics to replace formaldehyde-based adhesives, their broad commercialization is still limited due to poor water resistance and high cost. This study employed a novel double-network strategy to effectively crosslink SM and fabricated an SM-based adhesive with required and stable water resistance using a co-crosslinker (PM) composed of PAE and melamine-urea-glyoxal (MUG) resins. Analyses including 1 H NMR, 13 C NMR, FTIR, TGA, and XPS revealed that the robust double-network structures were constructed from MUG-SM and PAE-SM networks, which were further reinforced by the co-crosslinking between PAE and MUG resins. Thus, up to 40% of the expensive PAE could be substituted by low-cost MUG resin, resulting in a novel SM/PM adhesive with the required water resistance for structural use at a 16% reduced cost. Furthermore, PM exhibited much better storage stability than PAE and MUG resins. The presented double-network strategy sufficiently promotes the cost-effective application of SM-based adhesives in wood composites and extends it from indoor to outdoor products. • PAE resin blended with MUG resin to produce a PM resin via co-crosslinking. • Double-network structure constructed from PM-soybean meal crosslinking. • Enhanced adhesion properties produced by a double-network structure revealed. • Storage stability of PM resin in 60 days traced and characterized. • SM/PM adhesive reduced cost by 16% with comparable water resistance.

Three-dimensional porous sodium alginate/gellan gum environmentally friendly aerogel: Preparation, characterization, adsorption, and kinetics studies

Three-dimensional porous sodium alginate/gellan gum aerogels (SAG aerogels) were prepared by the method of freeze-drying and ion cross-linking for the removal of methylene blue (MB) in wastewater. The physical morphology and chemical structure of the SAG aerogels were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results revealed that the addition of gellan gum (GG) formed interpenetrating double network structures by ion cross-linking and hydrogen bonding interaction with sodium alginate (SA), which improved the chemical resistance of SAG aerogels and the adsorption capacity of aerogel for MB at a mass ratio of 3:1. The pseudo-second-order kinetic model and Langmuir isothermal model could be used to describe the adsorption process of MB, and the maximum adsorption capacity of the SAG aerogel for MB was 1456.45 mg/g, at 313 K. The adsorption thermodynamic analysis results showed that the adsorption process of MB was spontaneous and exothermic. After 5 adsorption-desorption cycles, the adsorption capacity of SAG aerogel only decreased 1.44% compared with their initial adsorption capacity. The obtained results indicated that the SAG aerogels could be successful and effective used to remove the MB in wastewater.

3D-printed high-toughness double network hydrogels via digital light processing

Double-network hydrogels have attracted more and more attention in the field of hydrogels due to their high toughness and strength. Up to now, such hydrogels were processed only via model casting and extrusion-based three-dimensional (3D) printing, greatly restricting the freedom of design and manufacture. Herein, we provide a pre-hydrogel ink material composed of commercially available compounds, such as acrylamide and stearyl methacrylate, which can not only be suitable for vat photopolymerization, but also produces a hydrogel with double-network structures. Various hydrogel objects can be printed with a good CAD fidelity, verifying the good printability of the ink material. The printed hydrogels are based on an interpenetrated polymeric network consisting of covalent bond and hydrophobic association, enabling excellent toughness, puncture resistance, and self-recovering performance of the printed objects. The proposed approach may provide an effective way to design the ink of double-network hydrogels suitable for photocurable 3D printing, which may have great application prospects in the fields of customizing wearable sensors, robotics and biomedicine.

Supramolecular polymer/peptide hybrid hydrogels with tunable stiffness mediated by interchain acid-amide hydrogen bonds.

Hydrogels are a class of biomaterials used in the field of tissue engineering and drug delivery. Many tissue engineering applications depend on the material properties of hydrogel scaffolds, such as mechanical stiffness, pore size, and interconnectivity. In this work, we describe the synthesis of peptide/polymer hybrid double-network (DN) hydrogels composed of supramolecular and covalent polymers. The DN hydrogels were prepared by combining the self-assembled pentafluorobenzyl diphenylalanyl aspartic acid (PFB-FFD) tripeptide for the first network and the polymeric PNIPAM-PEGDA copolymer for the second network. During this process, self-assembled peptide nanostructures are cross-linked to the polyacrylamide group in the polymer network through non-covalent interactions. The PNIPAM-PEGDA:PFB-FFD hydrogel exhibited higher mechanical stiffness (G′ ∼2 kPa) than the PNIPAM-PEGDA copolymer. Moreover, PNIPAM-PEGDA:PFB-FFD hydrogel shows a decrease in pore size (∼1.2 μm) compared to the original copolymer (∼5.2 μm), with the structural framework of highly interconnected fibrous peptide network. The mechanical stiffness of hydrogels was systematically investigated by rheological analysis in response to various variables, including UV exposure time, concentration of peptides, and amino acid functionalization. Modulating the time of UV irradiation resulted in PNIPAM-PEGDA:PFB-FFD hydrogels with a four-fold increase in stiffness. The influence of amino acid side chains and terminal charge of peptides on the strength of DN hydrogels was also investigated using pentafluorobenzyl diphenylalanyl lysine (PFB-FFK). Interestingly, PFB-FFK, which has an amine group on the side chain, does not exhibit the DN structures. The mechanical properties and pore sizes of PNIPAM-PEGDA:PFB-FFK hydrogel were very similar to those of the PNIPAM-PEGDA copolymer due to poor cross-linking. The biocompatibility of the hydrogel materials was tested with the hMSC cell line using the MTT method, and the results indicate that the materials are non-toxic and potentially useful for biological applications.

Production, deformation and magnetorheological characteristics of the alginate/chitosan hydrogel magnetic microspheres

To improve dispersion stability and magnetorheological (MR) characteristics of carbonyl iron (CI) particles, we proposed novel hydrogel magnetic microspheres (MPs) dual-coated with alginate (AL) and chitosan (CTS) for the first time. The double-network structures formed by biological crosslinking and chelation reactions are capable to enhance its own structural stability and mechanical properties. The structural characterization, MR properties, and dispersion stability for different MPs were investigated. Additionally, the swelling behaviors were studied by swelling the dried MPs in the deionized water and sodium chloride solution, respectively. The results showed that the AL/CTS hydrogel core/shell MPs displayed the advantages of simple manufacturing, superior MR properties and deformability compared to pure micron-sized CI particles, indicating the improved dispersion stability of the MR fluids compared to that of the pure CI particles-based MR fluids. The introduction of double network structures with natural biopolymers will provide a new thought for the development of MR materials.