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Abstract Polymeric hydrogels, known for their excellent mechanical properties and pre-cross-linking flowability, provide a promising solution for recycling waste propellants, ensuring safety and maintaining explosive performance. This study developed a double cross-linked network energetic hydrogel that effectively combines mechanical strength with explosive capabilities. Using a Ford 4 Cup, temperature data logger, universal testing machine, and detonation performance tests, we examined the impacts of kinematic viscosity, cross-linking time, compressive strength, and explosive properties. The optimal kinematic viscosity for stabilizing hollow glass microspheres (GM) was found to be 129.7 mm2/s. Cross-linking time was negatively correlated with initiator, catalyst levels, and reaction temperature, but positively correlated with retarder content. Compressive strength increased with acrylamide (AM) content and showed an initial rise before decreasing with N,N′-methylenebisacrylamide (MBAA) content and reaction temperature. The maximum compressive strength was achieved with 5% MBAA (of AM mass fraction) at 40 °C. Detonation velocity and steel plate damage decreased with increasing AM content and initially increased then decreased with GM content. A balance of mechanical and explosive properties was achieved with 6% AM and 4% GM, resulting in a detonation velocity of 4536 m/s. This hydrogel shows significant potential for waste munitions management.

Traditional electromagnetic shielding materials are difficult to realize practical applications due to excessive fillers, poor mechanical properties, and difficulty in preservation, etc. Hydrogel is a biomaterial with good biocompatibility and sustainability, which not only can overcome the aforementioned issues, but its biomimetic hierarchical porous structure also enables multifunctional applications. In this paper, a honeycomb-like unidirectional porous wall structured hydrogel is prepared by a simple freeze-thaw cycle and salting out method. Polyvinyl alcohol (PVA) and chitosan (CS) form a double cross-linked network (DN) enhanced by MXene, resulting in excellent mechanical and flexibility. Due to the synergistic effects of MXene, water, Fe 3 O 4 , abundant interfaces and micrometer porous wall structure, the electromagnetic shielding performance is enhanced. EMI SE increases by 30.7 dB as the MXene concentration increases from 0 to 1.5 wt%, and EMI SE increases from 7.9 to 66.7 dB as the water content increases from 0 to 76 %. Besides this, we encapsulate the hydrogel into a simple sensor, the signal response is rapid, the response /recovery time is 50/100 ms respectively, and it exhibits good sensitivity (0.0187 kPa−1). Different signals are generated based on variations in pressure, which holds significant importance for the development of wearable flexible sensors and information encoding. [Display omitted] • The double network hydrogels can achieve reversible conversion with aerogels. • The optimal EMI SE and EMI SE/d of hydrogel are 66.7 dB and 69.7 dB/mm respectively. • The response /recovery time of the sensor is 50/100 ms respectively. • The hydrogels based on different signals can encode and encrypt various information. [ABSTRACT FROM AUTHOR]

Hydrogels, promising biological materials, need to have both strong mechanical properties and also inherent self-healing properties. In this work a double cross-linked network (DN) hydrogel was designed and prepared by combining a Diels-Alder click reaction and coordination effects. This DN hydrogel had good thermodynamic properties, anti-EDTA performance and self-healing properties. In addition, the mechanical properties, swelling properties and surface morphology of DN hydrogels can be controlled by adjusting the ratio of Fe 3 + -catechol. The adjustment of pH value can change the color, crosslinking mode and mechanical properties of the DN hydrogel. This smart hydrogel created from DA click chemistry and coordination effects has significance for guiding the design of new hydrogels with good mechanical properties, self-healing properties and controlled cross-link density. [ABSTRACT FROM AUTHOR]

Vascularization is essential for the regeneration of three-dimensional (3D) bioprinting organs. As a general method to produce microfluidic channels in 3D printing constructs, coaxial extrusion has attracted great attention. However, the biocompatible bioinks are very limited for coaxial extrusion to fabricate microchannels with regular structure and enough mechanical properties. Herein, a hybrid bioink composed of alginate (Alg) and silk fibroin (SF) was proposed for 3D bioprinting of microchannel networks based on coaxial extrusion. The rheological properties of the bioink demonstrated that the hybrid Alg/SF bioink exhibited improved viscosity and shear thinning behavior compared with either pure Alg or SF bioink and had similar storage and loss modulus in a wide range of shear frequency, indicating a sound printability. Using a coaxial extrusion system with calcium ions and Pluronic F127 flowing through the core nozzle as cross-linkers, the Alg/SF bioink could be extruded and deposited to form a 3D scaffold with interconnected microchannels. The regular structure and smooth pore wall of microchannels inside the scaffold were demonstrated by optical coherence tomography. Micropores left by the rinse of F127 were observed by scanning electron microscope, constituting a hierarchical structure together with the microchannels and printed macropores. Fourier transform infrared spectroscopy analysis proved the complete rinse of F127 and the formation of β-sheet SF structure. Thus, Alg/SF could form a double cross-linked network, which was much stronger than the pure Alg network. Moreover, cells in the Alg/SF scaffold showed higher viability and proliferation rate than in the Alg scaffold. Therefore, Alg/SF is a promising bioink for coaxial extrusion-based 3D bioprinting, with the printed microchannel network beneficial for complex tissue and organ regeneration., Competing Interests: No competing financial interests exist., (Copyright 2020, Mary Ann Liebert, Inc., publishers.)

A novel biocompatible polysaccharide-based hydrogel with double cross-linked network (DN) was designed and developed by combining dynamic imine bond and Diels-Alder (DA) click reaction. Our results showed that the dynamic covalent imine bond led to the hydrogel's self-healing property, while the DA reaction gave the superior thermodynamic property and acid resistance to the hydrogel. At the same time, the double cross-linked structure improved the mechanical properties of hydrogels. Moreover, the DN hydrogel had good biocompatibility, as confirmed by three-dimensional cell encapsulation. On the basis of these excellent properties, the present prepared hydrogel holds great potential in the field of biomaterials.