Wildfire prevention through prophylactic treatment of high-risk landscapes using viscoelastic retardant fluids

Water-Enhancing Gels Exhibiting Heat-Activated Formation of Silica Aerogels for Protection of Critical Infrastructure During Catastrophic Wildfire

A promising strategy to address the pressing challenges with wildfire, particularly in the wildland-urban interface (WUI), involves developing new approaches for preventing and controlling wildfire within wildlands. Among sprayable fire-retardant materials, water-enhancing gels have emerged as exceptionally effective for protecting civil infrastructure. They possess favorable wetting and viscoelastic properties that reduce the likelihood of ignition, maintaining strong adherence to a wide array of surfaces after application. Although current water-enhancing hydrogels effectively maintain surface wetness by creating a barricade, they rapidly desiccate and lose efficacy under high heat and wind typical of wildfire conditions. To address this limitation, unique biomimetic hydrogel materials from sustainable cellulosic polymers crosslinked by colloidal silica particles are developed that exhibit ideal viscoelastic properties and facile manufacturing. Under heat activation, the hydrogel transitions into a highly porous and thermally insulative silica aerogel coating in situ, providing a robust protective layer against ignition of substrates, even when the hydrogel fire suppressant becomes completely desiccated. By confirming the mechanical properties, substrate adherence, and enhanced substrate protection against fire, these heat-activatable biomimetic hydrogels emerge as promising candidates for next-generation water-enhancing fire suppressants. These advancements have the potential to dramatically improve the ability to protect homes and critical infrastructure during wildfire.

Modular and Photoreversible Polymer-Nanoparticle Hydrogels via Host-Guest Interactions

Polymer-nanoparticle (PNP) hydrogels are a class of nanocomposite materials showing potential as injectable platforms for biomedical applications. Their design is limited by incomplete knowledge of how the binding motif impacts the viscoelastic properties of the material and is generally constrained to non-responsive supramolecular interactions. Expanding the scope of available interactions and advancing the understanding of how defined interactions influence network formation would accelerate PNP hydrogel design. To address this gap in the design of PNP hydrogels, the study designs and investigates a tunable platform based on beta-cyclodextrin (βCD) host-guest cross-links between functionalized polymers and nanoparticles. A host-functionalized polymer (βCD hyaluronic acid) and guest harboring block co-polymer (poly(ethylene glycol)-b-poly(lactic acid)) NPs are synthesized. The presence and accessibility for binding of the host and guest moieties are characterized via isothermal titration calorimetry. PNP hydrogels with varying concentrations of functionalized polymer and NPs reveal a limited window of concentrations for gelation. It is hypothesized that network formation is governed by the capacity of polymer chains to effectively bridge NPs, which is related to the host-guest ratios present in the system. Further, photo-responsive guests are incorporated to engineer photoreversible gelation of PNP hydrogels via exposure to specific wavelengths of light.

Biomimetic Non-ergodic Aging by Dynamic-to-covalent Transitions in Physical Hydrogels

Hydrogels are soft materials engineered to suit a multitude of applications that exploit their tunable mechanochemical properties. Dynamic hydrogels employing noncovalent, physically cross-linked networks dominated by either enthalpic or entropic interactions enable unique rheological and stimuli-responsive characteristics. In contrast to enthalpy-driven interactions that soften with increasing temperature, entropic interactions result in largely temperature-independent mechanical properties. By engineering interfacial polymer-particle interactions, we can induce a dynamic-to-covalent transition in entropic hydrogels that leads to biomimetic non-ergodic aging in the microstructure without altering the network mesh size. This transition is tuned by varying temperature and formulation conditions such as pH, which allows for multivalent tunability in properties. These hydrogels can thus be designed to exhibit either temperature-independent metastable dynamic cross-linking or time-dependent stiffening based on formulation and storage conditions, all while maintaining structural features critical for controlling mass transport, akin to many biological tissues. Such robust materials with versatile and adaptable properties can be utilized in applications such as wildfire suppression, surgical adhesives, and depot-forming injectable drug delivery systems.

Self-healing, flame-retardant, and antimicrobial chitosan-based dynamic covalent hydrogels

This study reports the fabrication of chitosan-based hydrogels with potential to be applied as a flame-retardant coating on skin or other surfaces. These hydrogels possess remarkable antimicrobial properties that are highly desirable for the protection of epidermises. Hydrogels in this study were prepared via the cross-linking reaction of chitosan with a vanillin-based cross linker containing flame-retarding moieties through Schiff's base reaction. The synthesized hydrogels possess imine linkages enabling them to self-heal at room temperature. Self-healing abilities offered these hydrogels the ability to protect the skin for a longer time. One flame retarding mechanism of these hydrogels was by retaining the water in their polymeric network; thus, the role of bound and unbound water molecules was studied using DSC and Raman spectroscopy. The hydrogels synthesized in this study retained their flame-retarding properties even after drying due to the charring process that inhibited the pyrolysis process. Therefore, these chitosan-based hydrogels are able to prolong the protection time against fire.

Toward Plant Cyborgs: Hydrogels Incorporated onto Plant Tissues Enable Programmable Shape Control

Engineered living materials (ELMs) that incorporate living organisms and synthetic materials enable advanced functional properties. Here, we seek to create plant cyborgs by combining plants or plant tissues with stimuli-responsive polymeric materials. Plant tissues with integrated shape control may find applications in regenerative medicine, and the shape control of living plants enables another dimension of adaptability and response to environmental threats, which can be applied to next-generation precision farming. In this work, we develop chemistry to integrate stimuli-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels with decellularized plant tissues assisted by 3D printing. We demonstrate programmable shape morphing in response to thermal cues and ultraviolet (UV) light. Specifically, by taking advantage of the extrusion-based 3D printing method, we deposit nanocomposite PNIPAM precursors onto silane-treated decellularized leaf surface with prescribed shapes and spatial control. When subjected to external stimuli, the strain mismatch generated between the swellable nanocomposite PNIPAM and nonswellable decellularized leaf enables folding and bending to occur. This strategy to integrate the plant tissues with stimuli-responsive hydrogels allows the control of leaf morphology, opening avenues for plant-based biosensors and soft actuators to enhance food security; such materials also may find applications in biomedicine as tissue-engineering scaffolds.

Milk Protein-Based Nanohydrogels: Current Status and Applications

Milk proteins are excellent biomaterials for the modification and formulation of food structures as they have good nutritional value; are biodegradable and biocompatible; are regarded as safe for human consumption; possess valuable physical, chemical, and biological functionalities. Hydrogels are three-dimensional, cross-linked networks of polymers capable of absorbing large amounts of water and biological fluids without dissolving and have attained great attraction from researchers due to their small size and high efficiency. Gelation is the primary technique used to synthesize milk protein nanohydrogels, whereas the denaturation, aggregation, and gelation of proteins are of specific significance toward assembling novel nanostructures such as nanohydrogels with various possible applications. These are synthesized by either chemical cross-linking achieved through covalent bonds or physical cross-linking via noncovalent bonds. Milk-protein-based gelling systems can play a variety of functions such as in food nutrition and health, food engineering and processing, and food safety. Therefore, this review highlights the method to prepare milk protein nanohydrogel and its diverse applications in the food industry.

Hydrogels: Properties and Applications in Biomedicine

Hydrogels are crosslinked polymer chains with three-dimensional (3D) network structures, which can absorb relatively large amounts of fluid. Because of the high water content, soft structure, and porosity of hydrogels, they closely resemble living tissues. Research in recent years shows that hydrogels have been applied in various fields, such as agriculture, biomaterials, the food industry, drug delivery, tissue engineering, and regenerative medicine. Along with the underlying technology improvements of hydrogel development, hydrogels can be expected to be applied in more fields. Although not all hydrogels have good biodegradability and biocompatibility, such as synthetic hydrogels (polyvinyl alcohol, polyacrylamide, polyethylene glycol hydrogels, etc.), their biodegradability and biocompatibility can be adjusted by modification of their functional group or incorporation of natural polymers. Hence, scientists are still interested in the biomedical applications of hydrogels due to their creative adjustability for different uses. In this review, we first introduce the basic information of hydrogels, such as structure, classification, and synthesis. Then, we further describe the recent applications of hydrogels in 3D cell cultures, drug delivery, wound dressing, and tissue engineering.

Supramolecular Reinforcement of Polymer-Nanoparticle Hydrogels for Modular Materials Design

Moldable hydrogels are increasingly used as injectable or extrudable materials in biomedical and industrial applications owing to their ability to flow under applied stress (shear-thin) and reform a stable network (self-heal). Nanoscale components can be added to dynamic polymer networks to modify their mechanical properties and broaden the scope of applications. Viscoelastic polymer-nanoparticle (PNP) hydrogels comprise a versatile and tunable class of dynamic nanocomposite materials that form via reversible interactions between polymer chains and nanoparticles. However, PNP hydrogel formation is restricted to specific interactions between select polymers and nanoparticles, resulting in a limited range of mechanical properties and constraining their utility. Here, a facile strategy to reinforce PNP hydrogels through the simple addition of α-cyclodextrin (αCD) to the formulation is introduced. The formation of polypseudorotoxanes between αCD and the hydrogel components resulted in a drastic enhancement of the mechanical properties. Furthermore, supramolecular reinforcement of CD-PNP hydrogels enabled decoupling of the mechanical properties and material functionality. This allows for modular exchange of structural components from a library of functional polymers and nanoparticles. αCD supramolecular binding motifs are leveraged to form CD-PNP hydrogels with biopolymers for high-fidelity 3D (bio)printing and drug delivery as well as with inorganic NPs to engineer magnetic or conductive materials.

Gelation and yielding behavior of polymer–nanoparticle hydrogels

Polymer–nanoparticle hydrogels are a unique class of self‐assembled, shear‐thinning, yield‐stress fluids that have demonstrated potential utility in many impactful applications. Here, we present a thorough analysis of the gelation and yielding behavior of these materials with respect to the polymer and nanoparticle component stoichiometry. Through comprehensive rheological and diffusion studies, we reveal insights into the structural dynamics of the polymer nanoparticle network that identify that stoichiometry plays a key role in gelation and yielding, ultimately enabling the development of hydrogel formulations with unique shear‐thinning and yield‐stress behaviors. Access to these materials opens new doors for interesting applications in a variety of fields including tissue engineering, drug delivery, and controlled solution viscosity.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Prolonged Codelivery of Hemagglutinin and a TLR7/8 Agonist in a Supramolecular Polymer-Nanoparticle Hydrogel Enhances Potency and Breadth of Influenza Vaccination

The sustained release of vaccine cargo has been shown to improve humoral immune responses to challenging pathogens such as influenza. Extended codelivery of antigen and adjuvant prolongs germinal center reactions, thus improving antibody affinity maturation and the ability to neutralize the target pathogen. Here, we develop an injectable, physically cross-linked polymer-nanoparticle (PNP) hydrogel system to prolong the local codelivery of hemagglutinin and a toll-like receptor 7/8 agonist (TLR7/8a) adjuvant. By tethering the TLR7/8a to a NP motif within the hydrogels (TLR7/8a-NP), the dynamic mesh of the PNP hydrogels enables codiffusion of the adjuvant and protein antigen (hemagglutinin), therefore enabling sustained codelivery of these two physicochemically distinct molecules. We show that subcutaneous delivery of PNP hydrogels carrying hemagglutinin and TLR7/8a-NP in mice improves the magnitude and duration of antibody titers in response to a single injection vaccination compared to clinically used adjuvants. Furthermore, the PNP gel-based slow delivery of influenza vaccines led to increased breadth of antibody responses against future influenza variants, including a future pandemic variant, compared to clinical adjuvants. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

Modulation of injectable hydrogel properties for slow co-delivery of influenza subunit vaccine components enhance the potency of humoral immunity

Vaccines are critical for combating infectious diseases across the globe. Influenza, for example, kills roughly 500,000 people annually worldwide, despite annual vaccination campaigns. Efficacious vaccines must elicit a robust and durable antibody response, and poor efficacy often arises from inappropriate temporal control over antigen and adjuvant presentation to the immune system. In this work, we sought to exploit the immune system's natural response to extended pathogen exposure during infection by designing an easily administered slow-delivery influenza vaccine platform. We utilized an injectable and self-healing polymer-nanoparticle (PNP) hydrogel platform to prolong the co-delivery of vaccine components to the immune system. We demonstrated that these hydrogels exhibit unique dynamic physical characteristics whereby physicochemically distinct influenza hemagglutinin antigen and a toll-like receptor 7/8 agonist adjuvant could be co-delivered over prolonged timeframes that were tunable through simple alteration of the gel formulation. We show a relationship between hydrogel physical properties and the resulting immune response to immunization. When administered in mice, hydrogel-based vaccines demonstrated enhancements in the magnitude and duration of humoral immune responses compared to alum, a widely used clinical adjuvant system. We found stiffer hydrogel formulations exhibited slower release and resulted in the greatest improvements to the antibody response while also enabling significant adjuvant dose sparing. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

Self-Assembled, Dilution-Responsive Hydrogels for Enhanced Thermal Stability of Insulin Biopharmaceuticals

Biotherapeutics currently dominate the landscape of new drugs because of their exceptional potency and selectivity. Yet, the intricate molecular structures that give rise to these beneficial qualities also render them unstable in formulation. Hydrogels have shown potential as stabilizing excipients for biotherapeutic drugs, providing protection against harsh thermal conditions experienced during distribution and storage. In this work, we report the utilization of a cellulose-based supramolecular hydrogel formed from polymer–nanoparticle (PNP) interactions to encapsulate and stabilize insulin, an important biotherapeutic used widely to treat diabetes. Encapsulation of insulin in these hydrogels prevents insulin aggregation and maintains insulin bioactivity through stressed aging conditions of elevated temperature and continuous agitation for over 28 days. Further, insulin can be easily recovered by dilution of these hydrogels for administration at the point of care. This supramolecular hydrogel system shows promise as a stabilizing excipient to reduce the cold chain dependence of insulin and other biotherapeutics.

Self-Powered and Green Ionic-Type Thermoelectric Paper Chips for Early Fire Alarming

Early fire alarming is of vital importance to lower the damages led by forest fires. Thus far, methods to monitor the forest fires at their early stage are mainly focused on artificial ground patrol, unmanned aerial vehicle cruise monitoring, observation by watchtower, or satellite inspection, whereas these methods are practically encountered with the problems of untimely feedback before the forest fires are out of control. This work proposes a particular kind of self-powered, low-cost, and green thermoelectric paper chips based on the principle of self-assembly and disassembly of ionic liquids on the surface of gold electrodes. By adjustment of the species of ionic liquids, both "n- and p-type" thermoelectric behaviors have been exploited that correspond to the opposite open-circuit voltages. Owing to the fluidic nature of ionic liquids, those "n- and p-type" thermoelectric units can be readily connected in series on one paper chip, leading to remarkable voltage signals in the presence of the temperature difference of 35 K. Followed by signal acquisition and transmission, such a thermoelectric paper chip successfully affords immediate electrical alarming at the early stage of an afire circumstance.