Stretchable Sponge-like Hydrogels with a Unique Colloidal Network Produced by Polymerization-Induced Microphase Separation

Superporous sponge prepared by secondary network compaction with enhanced permeability and mechanical properties for non-compressible hemostasis in pigs

Developing superporous hemostatic sponges with simultaneously enhanced permeability and mechanical properties remains challenging but highly desirable to achieve rapid hemostasis for non-compressible hemorrhage. Typical approaches to improve the permeability of hemostatic sponges by increasing porosity sacrifice mechanical properties and yield limited pore interconnectivity, thereby undermining the hemostatic efficacy and subsequent tissue regeneration. Herein, we propose a temperature-assisted secondary network compaction strategy following the phase separation-induced primary compaction to fabricate the superporous chitosan sponge with highly-interconnected porous structure, enhanced blood absorption rate and capacity, and fatigue resistance. The superporous chitosan sponge exhibits rapid shape recovery after absorbing blood and maintains sufficient pressure on wounds to build a robust physical barrier to greatly improve hemostatic efficiency. Furthermore, the superporous chitosan sponge outperforms commercial gauze, gelatin sponges, and chitosan powder by enhancing hemostatic efficiency, cell infiltration, vascular regeneration, and in-situ tissue regeneration in non-compressible organ injury models, respectively. We believe the proposed secondary network compaction strategy provides a simple yet effective method to fabricate superporous hemostatic sponges for diverse clinical applications.

Thermal-Rectified Gradient Porous Polymeric Film for Solar-Thermal Regulatory Cooling

Solar-thermal regulation concerning thermal insulation and solar modulation is pivotal for cooling textiles and smart buildings. Nevertheless, a contradiction arises in balancing the demand to prevent external heat infiltration with the efficient dissipation of excess heat from enclosed spaces. Here, a concentration-gradient polymerization strategy is presented for fabricating a gradient porous polymeric film comprising interconnected polymeric microspheres. This method involves establishing an electric field-driven gradient distribution of charged crosslinkers in the precursor solution, followed by subsequent polymerization and freeze-drying processes. The resulting porous film exhibits a significant porosity gradient along its thickness, leading to exceptional unidirectional thermal insulation capabilities with a thermal rectification factor of 21%. The gradient porous film, with its thermal rectification properties, effectively reconciles the conflicting demands of diverse thermal conductivity for cooling unheated and spontaneously heated enclosed spaces. Consequently, the gradient porous film demonstrates remarkable enhancements in solar-thermal management, achieving temperature reductions of 3.0 and 4.1 °C for unheated and spontaneously heated enclosed spaces, respectively, compared to uniform porous films. The developed gradient-structured porous film thus holds promise for the development of thermal-rectified materials tailored to regulate solar-thermal conditions within enclosed environments.

Phase-Separated Dielectric Gels Based on Christiansen Effect

Phase separation is a trivial phenomenon but a mature strategy in materials science. The flexible materials are provided toughness and strength by phase separation, yet there are few applications in optics and electronics industry. A novel phase-separated dielectric gel (PSDG) with a strong Christiansen effect is prepared via radical polymerization using hydroxyethyl methacrylate as a monomer, 4-cyano-4'-pentylbiphenyl and tributyl citrate as mixed solvents, and polyethylene glycol as a softener. The solvent ratios and ambient conditions can efficiently change the color of PSDG which makes it strongly selective for the wavelength of transmitted light. Besides, it has a high dielectric constant (10 at 1 kHz), sensitively responding to the electric field. The phase separation degree of PSDG varies with applied electric field, which will induce its transmittance alteration accordingly. The current field sensitive PSDG provides a novel idea for "smart windows". Additionally, varying the size and shape of the electrodes can precisely control the phase separation in PSDG and also enables the function of free writing on flexible materials. Therefore, the designed PSDG has great application potential for flexible touch and interesting interactions.

An impact resistant hydrogel enabled by bicontinuous phase structure and hierarchical energy dissipation

High performance hydrogels have essential applications in many fields such as tissue engineering and soft robot. Herein, we develop an impact resistant hydrogel composed of bicontinuous structures of polymer-hard phase and polymer-soft phase. This unique bicontinuous phase structure is formed by modulating various hydrogen bonding interactions. During loading, the polymer-hard phase is broken accompanied by the dissociation of hydrogen bonds to dissipate energy, while the polymer-soft phase distributes the load to avoid stress concentration, thus enabling the bicontinuous hydrogel to achieve excellent strength and toughness simultaneously. Furthermore, the fracture of hierarchical energy dissipation structures efficiently reduces impact strength and increases buffer time. Owing to the synergy of the bicontinuous phase structure and hierarchical energy dissipation, the resulting bicontinuous hydrogel remains intact even if it undergoes impact at a strain rate of ∼13 000 s^-1. Based on these findings, it is expected that the bicontinuous hydrogel has a potential application in the field of articular cartilage repair.

Regulable Mixed-Solvent-Induced Phase Separation in Hydrogels for Information Encryption

The rapid progress of information technology is accompanied by plenty of information embezzlement and forgery, but developing advanced encryption technologies to ensure information security remains challenging. Phase separation commonly leads to a dramatic change in the transmittance of hydrophilic polymer networks, which is a potential method for information security but is often neglected. Here, taking the polyacrylamide (PAAm) hydrogel system as a typical example, facilely adjustable information encryption and decryption via its regulable phase separation process in ethanol/water mixed solvent, are reported. By controlling the osmotic pressure of the external and internal environment, it is demonstrated that the diffusion coefficient during deswelling and reswelling, as well as the corresponding change of transmittance of the gel, can be well controlled. Relatively high osmotic pressure leads to rapid phase separation of the initial gel but slow phase remixing of the phase-separated gel, opening the opportunity of applying the gel as a reversible information encryption device. As proof-of-concept demonstrations, several stable and reversible information encryption and decryption systems by making use of the phase separation process of the gels are designed, which are expected to inspire the development of next-generation soft devices for information technology.

Hydrogen-Bonding Affords Sustainable Plastics with Ultrahigh Robustness and Water-Assisted Arbitrarily Shape Engineering

Herein, the supramolecular plastic-like hydrogel (SPH) is introduced as a platform to fabricate sustainable plastics with ultrahigh stiffness and strength as well as water-assisted arbitrarily shapeable capability. The transparent plastics are constructed from SPHs of cellulose ether/polycarboxylic acid complexes and demonstrate mechanical robustness with Young's modulus up to 3.4 GPa and tensile strength up to 124.0 MPa, superior or comparable to most common plastics. Meanwhile, the shape of the plastics can be reversibly engineered by air drying of the SPHs with diverse 2D/3D shapes and structures, which are generated conveniently via origami, kirigami, embossing, etc., in virtue of plastic deformation and shape memory effect of SPHs. On the basis of multi-dimensional infrared-spectral analysis, it is revealed that the dense acid-acid and acid-ether hydrogen (H)-bonding network in the plastic is responsible for the mechanical robustness while the evolution of water-polymer H-bonds into polymer-polymer H-bonds during air drying contributes to the shape fixing. This work provides a novel method of manufacturing sustainable plastics with simultaneous strong mechanical performance and convenient processibility from hydrogels with plastic-like mechanical behavior.