Salinity Gradient Energy from Expansion and Contraction of Poly(allylamine hydrochloride) Hydrogels

Unraveling Flow Effect on Capacitive Energy Extraction from Salinity Gradients

The harvesting of salinity gradient energy through a capacitive double-layer expansion (CDLE) technique is directly associated with ion adsorption and desorption in electrodes. Herein, we show that energy extraction can be modulated by regulating ion adsorption/desorption through water flow. The flow effects on the output energy, capacitance, and energy density under practical conditions are systematically investigated from a theoretical perspective, upon which the optimal operating condition is identified for energy extraction. We demonstrate that the net charge accumulation displays a negative correlation with the water flow velocity and so does the surface charge density, and this causes a nontrivial variation in the magnitude of output energy when water flows are introduced. When high water flows are introduced in both the charging and discharging processes, the energy extraction can be significantly reduced by 47.69-49.32%. However, when a high flow is solely exerted in the discharging process, the energy extraction can be enhanced by 12.94-14.49% even at low operation voltages. This study not only offers a comprehensive understanding of the microscopic mechanisms of surface-engineered energy extraction with water flows but also provides a novel direction for energy extraction enhancement.

A humidity/thermal dual response 3D-fabric with porous poly(N-isopropyl acrylamide) hydrogel towards efficient atmospheric water harvesting

Atmospheric water harvesting is a promising approach for obtaining freshwater resources, but achieving high levels of light absorption, hygroscopic capacity, and desorption efficiency simultaneously remains a challenge. In this study, we developed an innovative atmospheric water harvester that incorporates a poly(N-isopropylacrylamide) hydrogel and a polydopamine/polypyrrole-modified 3D raised-fabric. The interlacing structure and polydopamine/polypyrrole synergistically enhance the harvester's photothermal conversion capability, while the hydrogel-modified raised-fabric with its increased pore structure and high specific surface area ensures effective contact between the internal adsorbent and external moisture, thereby improving moisture capture and storage capacity. Our results indicate that the hydrogel-modified 3D raised-fabric has excellent photothermal conversion performance, as evidenced by its rapid temperature rise to 75.9 °C under 1 sun light intensity, which effectively promotes water evaporation and harvesting. Furthermore, the 3D raised-fabric exhibits exceptional water absorption (3.1 g g-1, RH 90%) and water desorption (1.75 kg m-2h-1, 1 sun) properties. Overall, the 3D raised-fabric with its integrated photothermal, hygroscopic, and hydrophobic properties can effectively collect water under low humidity conditions, making it a promising solution for water scarcity issues.

pH and Thrombin Concentration Are Decisive in Synthesizing Stiff, Stable, and Open-Porous Fibrin-Collagen Hydrogel Blends without Chemical Cross-Linker

Fibrin-collagen hydrogel blends exhibit high potential for tissue engineering applications. However, it is still unclear whether the underlying cross-linking mechanisms are of chemical or physical nature. It is here hypothesized that chemical cross-linkers play a negligible role and that instead pH and thrombin concentration are decisive for synthetizing blends with high stiffness and hydrolytic stability. Different fibrin-collagen formulations (pure and with additional transglutaminase) are used and the blends' compaction rate, hydrolytic stability, compressive strength, and hydrogel microstructure are investigated. The effect of thrombin concentration on gel compaction is examined and the importance of pH control during synthesis observed. It is revealed that transglutaminase impairs gel stability and it is deduced that fibrin-collagen blends mainly cross-link by mechanical interactions due to physical fibril entanglement as opposed to covalent bonds from chemical cross-linking. High thrombin concentrations and basic pH during synthesis reduce gel compaction and enhance stiffness and long-term stability. Scanning electron microscopy reveals a highly interpenetrating fibrous network with unique, interconnected open-porous microstructures. Endothelial cells proliferate on the blends and form a confluent monolayer. This study reveals the underlying cross-linking mechanisms and presents enhanced fibrin-collagen blends with high stiffness, hydrolytic stability, and large, interconnected pores; findings that offer high potential for advanced tissue engineering applications.

Bioinspired ketoprofen-incorporated polyvinylpyrrolidone/polyallylamine/ polydopamine hydrophilic pressure-sensitive adhesives patches with improved adhesive performance for transdermal drug delivery

Inspired by the natural mussel adhesive mechanism, three different materials-polydopamine (PDA), polyvinylpyrrolidone (PVP), and polyallylamine (PAM)-were used to make innovative pressure-sensitive adhesives (PSAs) for transdermal delivery of ketoprofen. PDA was synthesized under alkaline conditions using a self-polymerization reaction and was exploited as a cross-linking agent due to its biocompatibility. The adhesive performance, physicochemical properties, drug content, and drug permeation through the skin were examined. Moreover, in vivo skin irritation and skin adhesion performance were investigated. PVP/PAM/PDA PSAs showed a significantly higher adhesion to human skin compared with commercial patches owing to the interaction between the catechol groups presented on the patches and the skin. In addition, the patches were stable for six months. Consequently, the PVP/PAM/PDA patches exhibited outstanding tissue adhesiveness, enabling universal tissue adherence while causing no skin tissue irritation or inflammatory reaction.

A defined heat pretreatment of gelatin enables control of hydrolytic stability, stiffness, and microstructural architecture of fibrin-gelatin hydrogel blends

Fibrin-gelatin hydrogel blends exhibit high potential for tissue engineering in vitro applications. However, the means to tailor these blends in order to control their properties, thus opening up a broad range of new target applications, have been insufficiently explored. We hypothesized that a controlled heat treatment of gelatin prior to blend synthesis enables control of hydrolytic swelling and shrinking, stiffness, and microstructural architecture of fibrin-gelatin based hydrogel blends while providing tremendous long-term stability. We investigated these hydrogel blends' compressive strength, in vitro degradation stability, and microstructure in order to test this hypothesis. In addition, we examined the gel's ability to support endothelial cell proliferation and stretching of encapsulated smooth muscle cells. This research showed that a controlled heat pretreatment of the gelatin component strongly influenced the stiffness, swelling, shrinking, and microstructural architecture of the final blends regardless of identical gelatin mass fractions. All blends offered high long-term hydrolytic stability. In conclusion, the results of this study open the possibility to use this technique in order to tune low-concentrated, open-porous fibrin-based hydrogels, even in long-term tissue engineering in vitro experiments.

Controlled Decomposable Hydrogel Triggered with a Specific Enzyme

In this study, superabsorbent polyelectrolyte hydrogels were synthesized by cross-linking a nondegradable poly (allylamine hydrochloride) (PAH) and a recombinant protein with a specific enzymatic cleavage site. The recombinant protein was produced by E. coli with the pET-32b(+) plasmid, which is featured with the thioredoxin (Trx) gene containing a thrombin recognition site and a T7/lac hybrid promoter for high expression of recombinant protein. The swelling test shows that the composite hydrogel still maintained a high swelling ratio to 900% when 15% recombinant protein was cross-linked with PAH. The degradation test shows that such a PAH composite hydrogel could be decomposed by the addition of specific enzyme thrombin, which might lead to new biomedical applications of hydrogels needed to be decomposable by specific time not determined by the time period.

Recovered Energy from Salinity Gradients Utilizing Various Poly(Acrylic Acid)-Based Hydrogels

Hydrogels can be utilized to extract energy from salinity gradients when river water mixes with seawater. Saline-sensitive hydrogels exhibit a reversible swelling/shrinking process when they are, alternately, exposed to fresh and saline water. We present a comparison of several poly(acrylic acid)-based hydrogels, including poly(acrylic acid) (PAA), poly(acrylic acid-co-vinylsulfonic acid) (PAA/PVSA), and poly(4-styrenessulfonic acid-co-maleic acid) interpenetrated in a poly(acrylic acid) network (PAA/PSSA-MA). The hydrogels were synthesized by free radical polymerization, copolymerization, and by semi-IPN (interpenetrating polymer network). The hydrogels were placed in a piston-like system to measure the recovered energy. Semi-IPN hydrogels exhibit a much higher recovered energy compared to the copolymer and PAA hydrogel. The recovered energy of 60 g swollen gel was up to 4 J for the PAA/PSSA-MA hydrogel. The obtained energy per gram dried gel was up to 13.3 J/g. The swelling volume of the hydrogels was maintained for 30 cycles without decline in recovered energy.

Poly(sodium acrylate) hydrogels: synthesis of various network architectures, local molecular dynamics, salt partitioning, desalination and simulation

Various poly(sodium acrylate) hydrogels with different architectures, such as single networks, interpenetrating double networks and surface crosslinked hydrogels, are synthesized with a systematic change in their degree of crosslinking. The influence of these 3D structures on the absorbency of aqueous NaCl solutions is investigated. The local polymer mobility in water is probed in the form of transverse (T2) 1H-relaxation at a low field, which allowed confirming the structural aspects of the studied network topologies. Salt partitioning between the gel and the surrounding solution phase in NaCl solutions with an initial salt concentration of c0 = 0.017-0.60 mol L-1 (≙1-35 g L-1) is investigated. The data are compared with an idealized mean-field Donnan model, which fit the experimental findings only under the assumption of a drastically reduced effective charge density of feff ≈ 25 mol% independent of the hydrogel used. The unequal salt distribution allows desalination of salt water by applying an external pressure to a swollen hydrogel to recover its water which has a lower salinity. The specific energy needed to desalinate 1 m3 was estimated to be 6-18 kW h m-3. This value decreases with a lower degree of swelling independent of the network topology. Besides the experiments, simulations based on a Poisson-Boltzmann mean-field model and MD simulations are performed to determine the degree of swelling and salt partitioning as a function of c0 for different hydrogels. Both simulations describe qualitatively the experimental data, where deviations can be ascribed to model simplifications and the imperfect structure of the hydrogels synthesized via free radical polymerization.