Physical Crosslinking Research Articles

Characterization methods to predict extrusion performance in thermoplastic polyurethane batches

Thermoplastic polyurethanes (TPUs) are a class of urethane elastomers which flow at elevated temperatures, enabling a diverse set of processing techniques including industrial-scale extrusion and injection molding. Due to variations in the relative content of hard and soft segments within the polymer chains, as well as block lengths and chemistries, this material exhibits a wide range of viscoelastic properties depending on the synthetic process and thermal history. Numerous manufacturers produce their own proprietary brands of TPU, thus creating a diverse market for a product whose processability varies depending on the supplier. Lot dependent undesirable characteristics may be observed during melt extrusion, including degradation at process-relevant temperatures, increases in viscosity over time, and buildup of solid-like particulates during extrusion. This manuscript implements a combination of chemorheological, spectroscopic, solubility, light scattering, and calorimetric techniques to understand the formation of this solid particulate phase during extrusion. The presence of endothermic transitions, large degrees of branching, rapidly changing viscoelastic properties, and poor dissolution capabilities were correlated with the worst performing lots of TPU in terms of extrudability. These findings suggest that solidification is caused by physical crosslinking through hard phase aggregation, which is attributed to differences in polymer branching architecture, high chain mobility, and strain under extrusion conditions. The strong association between polymer branching and solidification during extrusion highlights the capability for these characterization techniques to rapidly screen for extrusion-related performance of TPUs prior to processing.

Chitinous Bioplastic Enabled by Noncovalent Assembly.

Natural polymeric-based bioplastics usually lack good mechanical or processing performance. It is still challenging to achieve simultaneous improvement for these two usual trade-off features. Here, we demonstrate a full noncovalent mediated self-assembly design for simultaneously improving the chitinous bioplastic processing and mechanical properties via plane hot-pressing. Tannic acid (TA) is chosen as the noncovalent mediator to (i) increase the noncovalent cross-link intensity for obtaining the tough noncovalent network and (ii) afford the dynamic noncovalent cross-links to enable the mobility of chitin molecular chains for benefiting chitinous bioplastic nanostructure rearrangement during the shaping procedure. The multiple noncovalent mediated network (chitin-TA and chitin-chitin cross-links) and the pressure-induced orientation nanofibers structure endow the chitinous bioplastics with robust mechanical properties. The relatively weak chitin-TA noncovalent interactions serve as water mediation switches to enhance the molecular mobility for endowing the chitin/TA bioplastic with hydroplastic processing properties, rendering them readily programmable into versatile 2D/3D shapes. Moreover, the fully natural resourced chitinous bioplastic exhibits superior weld, solvent resistance, and biodegradability, enabling the potential for diverse applications. The full physical cross-linking mechanism highlights an effective design concept for balancing the trade-off of the mechanical properties and processability for the polymeric materials.

Multifunctional chitosan-based lanthanide luminescent hydrogel with stretchability, adhesion, self-healing, color tunability and antibacterial ability

Lanthanide luminescent hydrogels have broad application prospects in various fields. However, most of lanthanide hydrogels possess relatively simple functions, which is not conducive to practical applications. Therefore, it is becoming increasingly urgent to develop multifunctional hydrogels. Herein, a multifunctional chitosan-based lanthanide luminescent hydrogel with ultra-stretchability, multi-adhesion, excellent self-healing, emission color tunability, and good antibacterial ability was prepared by a simple one-step free radical polymerization. In this work, our designed lanthanide complexes [Ln(4-VDPA)3] contain three reaction sites, which can be copolymerized with N-[tris(hydroxymethyl) methyl] acrylamide (THMA), acrylamide (AM), and diacryloyl poly(ethylene glycol) (DPEG) to form the first chemical crosslinking network, while hydroxypropyltrimethyl ammonium chloride chitosan (HACC) interacts with the hydroxyl and amino groups derived from the chemical crosslinking network through hydrogen bonds to form the second physical crosslinking network. The structure of the double network as well as the dynamic hydrogen bond and lanthanide coordination endow the hydrogel with excellent stretchability, adhesion and self-healing properties. Moreover, the introduction of lanthanide complexes and chitosan makes the hydrogel exhibit outstanding luminescence and antibacterial performances. This research not only realizes the simple synthesis of multifunctional luminescent hydrogels, but also provides a new idea for the fabrication of biomass-based hydrogels as intelligent and sustainable materials.

Sustainable ultra-strong polyesteramide elastomers with rapid degradation and high resilience

Degradable polymers typically require prolonged exposure to harsh conditions for degradation, but this extended duration and severe treatment often result in incomplete breakdown, leading to the formation of harmful microplastics that pose significant environmental pollution risks. In this work, degradable alternating polyamide hard segments and soft crystallizable segments were combined by amide groups to design thermoplastic bio-based polyesteramide elastomers (PEAEs) with customizable properties and rapid degradability. The hard segment of the polymer features an alternating arrangement of amide and ester bonds. This arrangement facilitates the formation of small molecule monomers when the ester bond is broken, preventing microplastic contamination that may arise from incomplete degradation of the hard segment. Additionally, the inclusion of side groups in the soft segment disrupts the crystallization, enhancing its susceptibility to solvent penetration and thereby accelerating the degradation rate. After step-cyclic tensile tests, additional physical cross-linking points were formed in PEAEs to enhance their mechanical strength and elasticity. Furthermore, PEAEs demonstrated outstanding processing capabilities, including compounding, extrusion, pelletization, and spinning. This innovative approach introduces fresh design concepts for the industrial application of bio-based degradable polymers, playing a pivotal role in advancing resource conservation and environmental protection.

Imidazolium‐based ionic thermoplastic polyurethane with low surface energy and antibacterial activities

AbstractA series of novel thermoplastic polyurethane elastomers with both low surface energy and antibacterial activity were synthesized in this paper. Firstly, four imidazole salt diols with different alkyl chain lengths at the N‐position of imidazolium cation ([CnIm+][Cl−]) were prepared. Then, imidazolium‐based ionic thermoplastic polyurethane elastomers (Si‐ITPUs) were formulated by incorporating polydimethylsiloxane and polytetramethylene glycol as a mixed soft segment, 1,4‐butanediol and [CnIm+][Cl−] as a chain extender, and 4,4′‐dicyclohexylmethane diisocyanate. The structure, thermal stability, mechanical properties, physical crosslinking density, and the anti‐graffiti properties of Si‐ITPUs were evaluated. The surface energy and water absorption were evaluated through static contact angle and water resistance tests, respectively. Furthermore, the antibacterial activities against both Staphylococcus.aureus and Escherichia coli were characterized by the plate colony counting method. The results demonstrated that Si‐ITPUs possessed surface energy of approximately 23 mN/m, which conferred excellent anti‐graffiti and self‐cleaning performance. Furthermore, the increase of the alkyl chain length of substitutions resulted in a decrease in the tensile strength but an increase in the elongation at break. Si‐ITPU‐C4 exhibited optimized antibacterial activities with an antibacterial rate of more than 99.9% against both S. aureus and E. coli. This novel polyurethane is anticipated to find applications in the medical device industry and food processing sector.

Injectable and In Situ Formed Dual-Network Hydrogel Reinforced by Mesoporous Silica Nanoparticles and Loaded with BMP-4 for the Closure and Repair of Skull Defects.

Bone defects are a common and challenging orthopedic problem with poor self-healing ability and long treatment cycles. The difficult-to-heal bone defects cause a significant burden of medical expenses on patients. Currently, biomaterials with mechanical stability, long-lasting action, and osteogenic activity are considered as a suitable way to effectively heal bone defects. Here, an injectable double network (DN) hydrogel prepared using physical and chemical cross-linking methods is designed. The first rigid network is constructed using methylpropenylated hyaluronic acid (HAMA), while the addition of chitosan oligosaccharide (COS) forms a second flexible network by physical cross-linking. The mesoporous silica nanoparticles (MSN) loaded with bone morphogenetic protein-4 (BMP-4) were embedded into DN hydrogel, which not only enhanced the mechanical stability of the hydrogel, but also slowly released BMP-4 to achieve long-term skull repair. The designed composite hydrogel showed an excellent compression property and deformation resistance. In vitro studies confirmed that the HAMA/COS/MSN@BMP-4 hydrogel had good biocompatibility and showed great potential in supporting proliferation and osteogenic differentiation of mouse embryo osteoblast precursor (MC3T3-E1) cells. Furthermore, in vivo studies confirmed that the DN hydrogel successfully filled and closed irregular skull defect wounds, effectively promoted bone regeneration, and significantly promoted bone repair compared with the control group. In addition, HAMA/COS/MSN@BMP-4 hydrogel precursor solution can quickly form hydrogel in situ at the wound by ultraviolet light, which can be applied to the closure and repair of wounds of different shapes, which provides the new way for the treatment of bone defects.

Construction of porous and hydrophilic polypropylene-based membrane with microphase separation in amorphous region

Polypropylene (PP) membrane with low porosity and poor hydrophilicity limits the performance of lithium-ion batteries. In mechanism, the function of amorphous structure of precursor film on microporous structure of PP membrane is yet unknown. In this work, the porous and hydrophilic PP/reduced hydroxyl-modified polypropylene (PPrOH) membrane was fabricated by blending esterified-PPOH firstly and then hydrolyzing to introduce the hydrogen bond in amorphous region and avoid phase separation. The results showed that the hydrogen bond was successfully introduced into the amorphous region of PP/PPrOH film and led to an increase of physical crosslinking points. Therefore, a large region of microphase separation emerged in the PP/PPrOH membrane after cold stretching, which resulted in a 45.6 % increase of porosity at maximum compared to the PP membrane. Besides, the hydrophilicity of PP/PPrOH membrane was improved with the blend content exceeding 10 wt%. Eventually, the lithium-ion conductivity of PP/PPrOH-10 membrane enhanced by 37.5 % over the base PP membrane. This work provides a novel perspective for preparing hydrophilic PP membrane with high porosity.

Preparation of KHA/SA/MMT composites and their adsorption properties for Rhodamine B.

Two natural adsorbent materials, potassium humate (KHA) and montmorillonite (MMT), were successfully prepared by embedding them in sodium alginate (SA) gel spheres through physical cross-linking with CaCl2. And CaCO3 was used as a porogenic agent to prepare the porous composites, KHA/SA/MMT. The materials were characterized by using XRD, TGA, SEM, and N2 adsorption/desorption equipment. The results showed that MMT and KHA were successfully embedded in the SA gel; the introduction of MMT increased the thermal stability of the composites and the embedding of MMT, and the porogenic effect of CaCO3 increased the specific surface area of the composites substantially, which provided favorable conditions for adsorption and treatment of pollutants. In addition, a one-way exploratory experiment yielded a higher removal rate of Rhodamine B (RhB) at D = 0.6 g/L, pH = 5, C0 = 100 mg/L, and t = 360 min. The adsorption kinetics and adsorption isotherm conformed to the secondary kinetic model and Langmuir model, respectively, and the maximum adsorption of RhB by KHA/SA/MMT could reach up to 884.96 mg/g at 303 K. The adsorption mechanism for RhB was shown by FT-IR and XPS analyses to be possibly bound by non-covalent bonding forces. After seven consecutive adsorption-desorption cycles, the adsorption of RhB by KHA/SA/MMT still reached 80.75%. Therefore, the prepared gel spheres have the advantages of easy regeneration and efficient reuse and great potential for application in purifying RhB from wastewater.

Exploring the potential applications of amphiphilic carbon dots based nanocomposite hydrogel in liquid chromatographic separations

BackgroundDue to their excellent stability, low toxicity, flexible modification and adjustable functionality, carbon dots (CDs) have a promising application prospect in the field of chromatographic stationary phases. Hydrogels are new functional polymer materials with three-dimensional network structure that have excellent hydrophilicity, high porosity and unique mechanical properties, which are also good candidate materials for liquid chromatography. Nevertheless, a review of the literature reveals that CDs based nanocomposite hydrogels have not yet been reported as HPLC stationary phases. ResultsIn this work, amphiphilic CDs with multiple functional groups and polyacrylic acid hydrogel were grafted to the surface of silica gel by an in-situ polymerization method, and a CDs/polyacrylic acid nanocomposite hydrogel stationary phase (CDs/hydrogel@SiO2) was prepared. CDs act as the macroscopic cross-linking agents to form a cross-linked network with polyacrylic acid chains through physical cross-linking by hydrogen bonding and chemical cross-linking by amidation and esterification reactions, which not only improve the swelling property of the hydrogel but also increase its stability. Additionally, the introduction of CDs with multifunctional groups modulates the hydrophilic-hydrophobic balance of the hydrogel that also imparts good hydrophobicity to the composite hydrogel. Through the study of retention mechanism and influencing factors, it is certificate that the CDs/hydrogel@SiO2 has mixed-mode chromatographic performance. Furthermore, the CDs/hydrogel@SiO2 column shows great potential for the determination of organic contaminants in environmental water samples. SignificanceThis work confirms the potential application of CDs/hydrogel composite for the separation of various samples and provides the possibility of developing CDs based nanocomposite hydrogel in the field of liquid chromatography. Introducing CDs into hydrogel can open up a new way for nanocomposite hydrogels to be used in HPLC, which expands the advance of hydrogel and CDs in separation field.

A polypyrrole-dopamine/poly(vinyl alcohol) anisotropic hydrogel for strain sensor and bioelectrodes

Flexible hydrogel-based wearable sensors are of interest for monitoring human movement and electrophysiological signal detection. The high mechanical properties, high conductivity, and sensing sensitivity are the main performance parameters. Inspired by the structure of human muscles, ligaments, and other tissues, a polypyrrole-dopamine/poly(vinyl alcohol) (DA-PPy/PVA) hydrogel with a bionic anisotropic structure is prepared in this study using a directed freeze–thaw strategy. The introduction of DA-PPy nanoparticles can significantly improve the mechanics, adhesion, and conductivity due to the high water dispersibility. Moreover, they can act as physical cross-linking sites to further improve the mechanical properties. The anisotropic structure would influence many properties (mechanical, conductivity, resistance to crack extension, etc.) of DA-PPy/PVA hydrogel. In addition, the prepared DA-PPy/PVA hydrogel exhibits a wide range of strain responses, moreover, its relative resistance change (ΔR/R0) strain curve maintains a line linear within 400% strain. The oriented structure would influence the sensing sensitivity, the gauge factor of anisotropic DA-PPy/PVA in parallel direction is 3.00. In addition, the anisotropic DA-PPy/PVA can effectively motor the physiological electrical signals as a bioelectrode. For example, the acquired electrocardiogram (ECG) and electromyography (EMG) signals not only are clearer than those of the commercial electrodes but show a higher signal-to-noise ratio. It is conceivable that the bionic anisotropic DA-PPy/PVA hydrogels provide a feasible material to construct flexible wearable sensors for monitoring human movement and electrophysiological signals.

Fluorescent carbon dots in situ polymerized biodegradable semi-interpenetrating tough hydrogel films with antioxidant and antibacterial activity for applications in food industry

A flexible, antioxidant, biodegradable, and UV-resistant polymeric nanocomposite hydrogel with heteroatom-doped carbon dots (CDs) has been fabricated using a simple one-step in situ free radical gelation process. The hydrogel formation and their physico-mehcanical characteristics have been assessed by rheology, uniaxial tensile and compression testing. The water uptake behaviour of the hydrogels is controlled by the CDs by manipulating their internal morphology and porosity. The porous nature of the hydrogels has been found from their scanning electron microscopic images which are also supported by their anomalous diffusion-based transport mechanism. The rheological signatures of the hydrogels show delayed network rupturing due to the secondary physical crosslinking alleviated by CDs. Moreover, CDs are directly influencing the permeabilites (oxygen and moisture) by lowering the values compared to their neat hydrogel films which are essential for a packing material. The biodegradability of the hydrogel films showed gradual weight loss (<75 %) within 3 weeks. The hydrogel films also have been qualified to be acted as antibacterial and antioxidant material. The shelf-life and non-leaching of CDs from gel matrices are also performed which shows its excellent capability to be used as a potential antibacterial, biodegradable, antioxidant alternative packaging material in food sectors.

Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions.

Microgels are commonly applied as solute carriers, where the size, density, and functionality of the microgels depend on solute binding. As representatives for ionic solutes with high affinity for the microgel, we study here the effect of superchaotropic Keggin polyoxometalates (POMs) PW12O403- (PW) and SiW12O404- (SiW) on the aqueous swelling and internal structure of nonionic poly(N-isopropylacrylamide) (pNiPAM) microgels by light scattering techniques and small-angle X-ray scattering. Due to their weak hydration, these POMs bind spontaneously to the microgels at millimolar concentrations. The microgels thus become charged and swell at low POM concentration, surprisingly without strongly increasing the volume phase transition temperature, and deswell at higher POM concentration. The swelling arises because of the osmotic pressure of dissociated counterions of the POMs, while the deswelling is due to POMs acting as physical cross-links in the microgels under screened electrostatics in NaCl or excess POM solution. This swelling/deswelling transition is sharper for PW than for SiW related to the lower charge density, weaker hydration, and stronger binding of PW. The POMs elicit qualitatively and quantitatively different swelling effects from ionic surfactants and classical salts. Moreover, the network softness and topology govern the swelling response upon POM binding. The softer the microgel, the stronger is the swelling response, while, inside the microgel, regions of high polymer density swell/contract more upon electric charging/cross-linking than regions with low polymer density. POM binding thus enables fine-tuning of microgel properties and highlights the role of network topology in microgel swelling. Because POMs decompose at an alkaline pH, these POM/microgel systems also exhibit pH-responsive swelling in addition to the typical temperature responsiveness of pNiPAM microgels.

Study on the Influence of Porous Gel on Coal Pyrolysis Performance Based on Experiments and Molecular Simulation

ABSTRACT Studying the kinetics of pyrolysis in pure coals and mixed coals (coals treated with porous gel) holds immense significance in effectively preventing and controlling the spontaneous combustion occurrences in coal. Firstly, porous gel materials were prepared based on physical mixing and chemical crosslinking reaction. Then, based on the thermogravimetric analysis method, the pyrolysis mechanism of porous gel in coal was studied using Flynn-Wall-Ozawa(FWO), Kissinger-Akahira-Sunose(KAS) and Coats Redfern models. Determine the mechanism of coal pyrolysis reaction using the Reaxx FF MD reaction mechanics model. Finally, the inhibition mechanism of porous gel on coal is analyzed through leading temperature rise experiment. The main reaction mechanisms of coal pyrolysis are the diffusion model in the low-conversion-rate range (D4), the R2 and R3 in the high-conversion-rate range, and the Avrami erofeev model (A2, A3). The molecular simulation results indicate that increasing the heating rate can accelerate the rate of coke cracking.

A hybrid reversible crosslinked polysiloxane elastomer with high toughness and recyclability

AbstractThe preparation of polysiloxane elastomers with outstanding mechanical properties, self‐healing capabilities, and high recyclability remains a formidable challenge despite their promising application prospects in flexible electronic devices. Herein, the polysiloxane elastomer is fortified with a hybrid reversible crosslinked network, incorporating Diels‐Alder (D‐A) and disulfide bonds for chemical crosslinking, as well as multiple hydrogen bonds for physical crosslinking, to effectively address this challenge. The presence of D‐A covalent bonds not only enhances the stability of the polymer network but also facilitates the reconstruction of dynamic disulfide and hydrogen bonds as sacrificial bonds for dissipating energy. This design further enhances the toughness of the obtained elastomer while simultaneously providing self‐healing capabilities and recyclability. Specially, relying on the hybrid reversible crosslinked network, the resulting polysiloxane elastomer PDMS3‐IPDI4‐SS‐F‐M demonstrates exceptional mechanical performance, boasting a toughness of 13.6 MJ/m3. Moreover, it exhibits commendable self‐healing ability with a self‐healing efficiency of 92% at 65°C for 24 h, as well as high thermal stability and recyclability without necessitating chemical treatment for polymer chain decomposition. The elastomer exhibits promising prospects for application in sustainable flexible support materials.

Powdered Cross-Linked Gelatin Methacryloyl as an Injectable Hydrogel for Adipose Tissue Engineering.

The tissue engineering field is currently advancing towards minimally invasive procedures to reconstruct soft tissue defects. In this regard, injectable hydrogels are viewed as excellent scaffold candidates to support and promote the growth of encapsulated cells. Cross-linked gelatin methacryloyl (GelMA) gels have received substantial attention due to their extracellular matrix-mimicking properties. In particular, GelMA microgels were recently identified as interesting scaffold materials since the pores in between the microgel particles allow good cell movement and nutrient diffusion. The current work reports on a novel microgel preparation procedure in which a bulk GelMA hydrogel is ground into powder particles. These particles can be easily transformed into a microgel by swelling them in a suitable solvent. The rheological properties of the microgel are independent of the particle size and remain stable at body temperature, with only a minor reversible reduction in elastic modulus correlated to the unfolding of physical cross-links at elevated temperatures. Salts reduce the elastic modulus of the microgel network due to a deswelling of the particles, in addition to triple helix denaturation. The microgels are suited for clinical use, as proven by their excellent cytocompatibility. The latter is confirmed by the superior proliferation of encapsulated adipose tissue-derived stem cells in the microgel compared to the bulk hydrogel. Moreover, microgels made from the smallest particles are easily injected through a 20G needle, allowing a minimally invasive delivery. Hence, the current work reveals that powdered cross-linked GelMA is an excellent candidate to serve as an injectable hydrogel for adipose tissue engineering.

High mechanical properties nanocomposite hydrogel achieved based on montmorillonite and tailored microgel suspensions reinforcing polyacryamide networks

Hydrogels have attracted much attention because of their softness and water retention ability, but their poor mechanical properties have severely limited their application in various aspects. Herein, we reported a strategy to fabricate polyacrylamide/montmorillonite nanocomposite hydrogel by introducing montmorillonite via a facile and universal two-step method composed of microgel suspension system and in situ free radical polymerization. Compared with microgel, microgel suspension is simpler to prepare and better dispersed in hydrogels, which it could act as physical crosslinking points, interpenetrate with polyacrylamide networks embedded, and serve as sacrifical bonds to strengthen the hydrogels. Simultaneously, montmorillonite synergistically facilitated the formation of a robust and uniform polymer structure through the interaction of hydrogen bonds and polyacrylamide networks, resulting in significant improvements in mechanical properties. As a result, the satisfactory mechanical properties of the nanocomposite hydrogels are achieved at a relative high water content (80 wt%), including a superior compressive strength (95% deformation) of 37.96 MPa, tensile strength of 311.1 ± 8.2 kPa, elongation at break of 316.5 ± 21.1%, Young's modulus of 165.8 ± 7.5 kPa, and excellent toughness of 644.1 ± 21.8 kJ/m3, respectively. In addition, it was found that the hydrogel had excellent cycle compression stability through 10 cycles of loading and unloading at 80% strain. These new high-performance nanocomposite hydrogels are expected to be used in the fields of structural or load-bearing materials.

Dual-stimuli-responsive poly(vinyl alcohol) nanofibers for localized cancer treatment: Magnetic hyperthermia and drug release studies

Smart materials are a promising option for a more personalized cancer treatment approach. In particular, materials that can respond to an external stimulus may be manipulated to provide a tailored response when and where it is needed. This work confined thermoresponsive poly (N-isopropyl acrylamide) microgels and superparamagnetic iron oxide nanoparticles into poly (vinyl alcohol) nanofibrous membranes. Physical and chemical crosslinking methods were tested to obtain membranes stable in physiological environments for long-term applications, and their effect on the membranes' morphology, swelling, and mechanical properties was evaluated. The results demonstrated that thermal crosslinking for 10 min is enough to obtain a robust membrane for biomedical applications that retain their components' magnetic and thermal responses. The swelling degree decreases with the increase of crosslinking time and is even smaller for chemically crosslinked membranes. Similarly, a high crosslinking degree is associated with more brittle membranes than ductile membranes with thermal crosslinking. Drug delivery assays using doxorubicin as a model drug demonstrated that only membranes with a smaller crosslinking degree are suitable for drug delivery purposes, with about 10 % of doxorubicin released for 15 days. Additionally, magnetic hyperthermia assays showed that composite membranes can increase the surrounding temperature by 10 °C in only 10 min of applying an alternating magnetic field. This work demonstrates the potential of combining stimuli-responsive materials using a simple, low-cost, and easily scalable technique (electrospinning) to produce smart materials for biomedical applications.

Using bacterial cellulose to bridge covalent and physical crosslinks in hydrogels for fabricating multimodal sensors

Network optimization is vital for the polysaccharide based hydrogels with multiple crosslinks. In this study, we developed a ‘two-step’ strategy to activate synergistic effect of chemical and physical crosslinks using a poly (vinyl alcohol) (PVA)/bacterial cellulose (BC) hydrogel as a template. The BC nanofibers, on the one hand, acted as nucleating agents, participating in the crystallization of PVA, and on the other hand, were also involved in the formation of boronic ester bond, anchored with the PVA chains via chemical bonding. Therefore, the existence of BC nanofibers, as ‘bridge’, linked the crystalline regions and amorphous parts of PVA together, associating the two characteristic crosslinks, which was conducive to load transfer. The mechanical properties of resultant hydrogels, including the tensile elongation and strength, as well as fracture toughness, were significantly improved. Moreover, the dually cross-linked hydrogels possessed ionic conductivity, which was sensitive to the tensile deformation and environmental temperature. This study clarifies a unique role of BC nanofibers in hydrogels, and proposes an effective approach to construct multiple networks in the nanocellulose reinforced PVA hydrogels.

Microstructure of the silk fibroin-based hydrogel scaffolds derived from the orb-web spider Trichonephila clavata

Due to the unique properties of the silk fibroin (SF) made from silkworm, SF-based hydrogels have recently received significant attention for various biomedical applications. However, research on the SF-based hydrogels isolated from spider silks has been rtricted due to the limited collection and preparation of naïve silk materials. Therefore, this study focused on the microstructural characteristics of hydrogel scaffolds derived from two types of woven silk glands: the major ampullate gland (MAG) and the tubuliform gland (TG), in the orb-web spider Trichonephila clavate. We compared these spider glands with those of the silk fibroin (SF) hydrogel scaffold extracted from the cocoon of the insect silkworm Bombyx mori. Our FESEM analysis revealed that the SF hydrogel has high porosity, translucency, and a loose upper structure, with attached SF fibers providing stability. The MAG hydrogel displayed even higher porosity, as well as elongated fibrous structures, and improved mechanical properties: while the TG hydrogel showed increased porosity, ridge-like or wall-like structures, and stable biocapacity formed by physical crosslinking. Due to their powerful and versatile microstructural characteristics, the MAG and TG hydrogels can become tailored substrates, very effective for tissue engineering and regenerative medicine applications.

Microstructure of ice with physical crosslinking structure and its mechanical properties under impact load

Ice is formed by the crystallization of water. Although ice appears to be less brittle under low strain rates during compression and shearing processes, it is still considered a brittle material, which poses significant challenges for its wide applications in industries. Therefore, the study of the mechanical properties of ice has always been a topic of great interest. This paper investigates the influence of single physical crosslinking structure (PCS) and dual PCS on the microstructure and dynamic mechanical properties of ice. Firstly, a solution with 0.2 wt% of sodium alginate (SA), a solution with 0.2 wt% of hydroxypropyl methyl cellulose (HPMC), and a mixture solution with 0.1 wt% of SA and 0.1 wt% of HPMC are prepared. The molecular chain connection methods in the prepared solutions are then analyzed. Subsequently, the microstructure of ice (Ice, SA-ice, HPMC-ice, SA&HPMC-ice) formed from different solutions is observed by a cryo-scanning electron microscope (Cryo-SEM). Finally, Hopkinson pressure bar (HPB) experiments are carried out to compare and analyze the time-strain rate and stress–strain relationships of different types of ice, thus elucidating the effect of microstructure on the strength of ice. Additionally, the variations in time-strain rate/strain energy and stress–strain curves of SA&HPMC-ice under different launch pressure are analyzed. This study provides valuable reference and guidance for enhancing the mechanical properties of ice and its engineering applications.