Hydrogel-polyurethane interpenetrating network material as an advanced draw agent for forward osmosis process

Recent advances in hydrogel microneedle-based biofluid extraction and detection in food and agriculture

Microneedle (MN) technology has been extensively studied for its advantages of minimal invasiveness and user-friendliness. Notably, hydrogel microneedles (HMNs) have garnered considerable attention for biofluid extraction due to its high swelling properties and biocompatibility. This review provides a comprehensive overview of definition, materials, and fabrication methods associated with HMNs. The extraction mechanisms and optimization strategies for enhancing extraction efficiency are summarized. Moreover, particular emphasis is placed on HMN-based biofluid extraction and detection in the domains of food and agriculture, encompassing the detection of small molecules, nucleic acids, and other relevant analytes. Finally, current challenges and possible solutions associated with HMN-based biofluid extraction are discussed.

Advances in Membrane Separation for Biomaterial Dewatering

Biomaterials often contain large quantities of water (50-98%), and with the current transition to a more biobased economy, drying these materials will become increasingly important. Contrary to the standard, thermodynamically inefficient chemical and thermal drying methods, dewatering by membrane separation will provide a sustainable and efficient alternative. However, biomaterials can easily foul membrane surfaces, which is detrimental to the performance of current membrane separations. Improving the antifouling properties of such membranes is a key challenge. Other recent research has been dedicated to enhancing the permeate flux and selectivity. In this review, we present a comprehensive overview of the design requirements for and recent advances in dewatering of biomaterials using membranes. These recent developments offer a viable solution to the challenges of fouling and suboptimal performances. We focus on two emerging development strategies, which are the use of electric-field-assisted dewatering and surface functionalizations, in particular with hydrogels. Our overview concludes with a critical mention of the remaining challenges and possible research directions within these subfields.

Polymeric hydrogels-based materials for wastewater treatment

Low-cost and reliable wastewater treatment is a relevant issue worldwide to reduce the concentration of environmental pollutants. Industrial effluents containing dyes, heavy metals, and other inorganic and organic compounds can pollute water resources; therefore, novel technologies are required to mitigate and control their release into the environment. Adsorption is one of the simplest methods for treating contaminated water in which a wide spectrum of adsorbents can be used to remove emerging compounds. Hydrogels are interesting materials with high adsorption capacities that can be synthesized via green routes. These adsorbents are promising for large-scale industrial wastewater treatment applications; however, gaps still exist in achieving sustainable commercial implementation. This review focuses on the discussion and analysis of preparation, characterization, and adsorption properties of hydrogels for water purification. The advantages of these polymeric materials for water treatment were analyzed, including their performance in the removal of different organic and inorganic contaminants. Recent advances in the functionalization of hydrogels and the synthesis of novel composites have also been described. The adsorption capacities of hydrogel-based adsorbents are higher than 500 mg/g for different organic and inorganic pollutants, and can reach values of up to >2000 mg/g for organic compounds, significantly outperforming other materials reported for water cleaning. The main interactions involved in the adsorption of water pollutants using hydrogel-based adsorbents were described and explained to allow the interpretation of their removal mechanisms. The current challenges in the implementation of hydrogels for water purification in real-life operations are also highlighted. This review provides an updated picture of hydrogels as interesting materials to address water depollution worldwide.

Calcium alginate gels-functionalized polyurethane foam decorated with silver nanoparticles as an antibacterial agent for point-of-use water disinfection

This paper reports the preparation of calcium alginate gels-functionalized PUF decorated with AgNPs (CA/PUF@Ag) by in situ reduction of Ag⁺ ions to form AgNPs with weakly reducing glycerol in CA/PUF composite. The water-adsorbing capacity, chemical structure, crystalline nature, elemental composition and morphologies of the composite were characterized. The Ag release behavior of CA/PUF@Ag was investigated. The inhibition zone test, time-dependent co-culture assay, test tube test, and antibacterial filtration experiment with Escherichia coli as an indicator of bacterial contamination were conducted to explore the antimicrobial efficacy. Results indicated that the CA/PUF@Ag prepared at 0.25 % w/v of SA could absorb more water with a higher swelling ratio of 8.0 g/g than that of PUF@Ag (6.0 g/g), which was subsequently squeezed by minimal pressure stimuli. The CA/PUF@Ag had a larger initial AgNPs loading amount (8.48 mg/g), lower Ag release concentration (44.35 μg/L) and lower Ag release rate (0.27 %) after 14 days tests than those of PUF@Ag (7.93 mg/g, 80.87 μg/L and 0.60 % respectively). The CA/PUF@Ag was highly reusable because bacterial cells in the squeezed water recovered from the composite were completely inactivated over five cycles of operation, and exhibited good antibacterial efficacy as an antibacterial filter in a flow test.

Design, synthesis, and application of thermally responsive draw solutes for sustainable forward osmosis desalination: A review

Forward osmosis (FO) is an emerging sustainable desalination technology; however, it is not a stand-alone process and requires an additional step to recover the water or regenerate the draw solute (DS), making it energy extensive. Therefore, incorporating inexpensive energy sources for DS regeneration is a viable solution to compete with reverse osmosis desalination technology. Hence, selecting suitable DS and its regeneration became a crucial research focus in FO desalination. Among various DSs reported, thermally responsive DSs (TRDS) provide an opportunity to integrate low-grade energy sources for DS regeneration. Utilizing such inexpensive energy will reduce fossil fuel energy demand, lower the cost of desalination, and minimize the carbon footprint. Hence, this review explores the TRDS for FO-based desalination with its design, synthesis, and applications. The manuscript has discussed the classification and selection criteria for the DSs, and how traditional and new-generation TRDSs are designed and synthesized from cationic and anionic moieties of ionic liquids, hydrogels, and other chemicals. The manuscript has also given importance to design criteria such as osmotic strength, viscosity, toxicity, and thermal stability for TRDSs. Furthermore, a detailed discussion on the FO performance, energy, and economic aspects of TRDSs has been reviewed, along with a discussion on the possible low-grade energy sources for the recovery of TRDS. Finally, the challenges and future directions for TRDSs have been discussed to drive FO toward sustainable desalination technology.

Thermo-responsive nonionic amphiphilic copolymers as draw solutes in forward osmosis process for high-salinity water reclamation

Recently, thermo-responsive nonionic amphiphilic copolymers have shown a great potential as forward osmosis (FO) draw solutes for high-salinity water desalination and zero-liquid discharge (ZLD). However, the relationship between the copolymer structural properties and key characteristics as draw solutes, as well as copolymer's chemical stability after regeneration have not been much studied. In this work, we systematically investigated poly (ethylene oxide)-block-poly (propylene oxide)-block-poly (ethylene oxide) (PEO-PPO-PEO) copolymers as draw solute. The results showed that the PEO segments significantly influenced the viscosity, osmotic pressure and lowest phase separation temperature of the copolymer aqueous solutions. Among four commercial copolymers studied, Pluronic® L35 with moderate molecular weight (Mn 1,900 Da), 50% PEO, and relatively high hydrophilic-lipophilic balance (HLB) showed the best draw solution (DS) performance. It also showed great stability in physiochemical properties and draw capacity after more than ten cycles of regeneration. On the other hand, despite the fact that membrane fouling was observed due to the use of copolymer DS, the FO flux (∼1.2 L m^‒2 h^‒1, as similar with the virgin membrane) was not affected when high-salinity feedwater such as seawater RO brine was applied. Overall, our study has provided a more comprehensive understanding on the characteristics of nonionic amphiphilic copolymer DS and showcased the promise of copolymer-driven FO process in high-salinity water desalination and ZLD.

Improving the Hydrophilicity of Flexible Polyurethane Foams with Sodium Acrylate Polymer

Hydrophilic, flexible polyurethane (FPU) foams made from Hypol prepolymers are capable of retaining large amounts of water and saline solutions. The addition of different catalysts and surfactant agents to Hypol JM 5008 prepolymer was assayed to obtain a foam with good structural stability and elasticity. The combination of three catalysts, stannous octoate and two amine-based ones (Tegoamin 33 and Tegoamin BDE), and the surfactant Niax silicone L-620LV allowed to synthesize a foam with a homogeneous cell size distribution, exhibiting the highest saline absorption capacity (2.4 g/gram of foam) and almost complete shape recovery, with up to a 20% of remaining deformation. Then, superabsorbent sodium acrylate polymer (PNaA) was added to the FPU foam up to 8 pph. The urine absorption capacity of the foam was increased about 24.8% by incorporating 6 pph of PNaA, absorbing 17.46 g of saline solution per foam gram, without any negative impact on the rest of the foam properties. All these properties make the synthesized foams suitable for corporal fluids absorption applications in which elasticity and low-density are required.

Thermal associated pressure-retarded osmosis processes for energy production: A review

Climate change is an existential threat to global environments and human life. To achieve global mean temperature rise of below 1.5 °C, increasing utilization of renewable energy and minimizing CO₂ emission from fossil fuel industries have been emphasized by the United Nations. Pressure-retarded osmosis (PRO) has displayed its technical feasibility in capturing renewable energy from the salinity gradient of two streams through a semipermeable membrane. Towards achieving economic feasible PRO, process optimization, waste stream/heat utilization, and hybrid PRO processes have been attempted by theoretically modelling and experimental examination. Among these efforts, the thermal associated PRO processes have received great attention due to their improved power generation. In this paper, we aim to provide a comprehensive review on thermal associated PRO processes, focusing on the role of thermal behaviour in both stand-alone PRO and hybrid PRO processes (e.g. PRO-membrane distillation, PRO-thermosiphon, PRO-solar pond). Meanwhile, thermal associated draw solution development has been highlighted. Finally, a combination of PRO with high temperature/high pressure geothermal waste gas as draw solution is proposed and its technical and economic feasibility is discussed, especially under Icelandic scenario.

Synthesis of a super-absorbent nanocomposite hydrogel based on vinyl hybrid silica nanospheres and its properties

Superabsorbent polymers as soft materials that can absorb water have aroused great interest in the fields of agriculture and forestry. Water absorption and water retention performance of a hydrogel are important indicators to evaluate its practical application. However, few reports show that hydrogels have both excellent water absorption and water retention properties. To date, superabsorbent hydrogels with a swelling capacity of more than 3000 g g⁻¹ have rarely been reported. In this work, a novel superabsorbent poly(acrylic acid) (PAA)-based nanocomposite hydrogel (NC gel) was prepared via free radical polymerization of acrylic acid by using vinyl hybrid silica nanospheres (VSNPs) as the cross-linking agent. The PAA NC hydrogel achieved a great swelling ratio of more than 5000 times in deionized water at 323 K, and the swollen hydrogel could hold 60% moisture when it was exposed to the air at 303 K for 42 h. Moreover, the hydrogel also obtained a good swelling ratio of 136 g g⁻¹ in NaCl solution. The PAA NC hydrogel showed excellent repetitive swelling ability. The influences of variable factors (acrylic acid, initiator and sodium hydroxide) on the swelling ratio of the NC hydrogel were researched. It can be speculated that the PAA NC hydrogel has potential application in agriculture and forestry areas due to its excellent water absorption and water retention properties.

Superabsorbent polymers as soft materials that can absorb water have aroused great interest in the fields of agriculture and forestry.

Recent Developments and Future Challenges of Hydrogels as Draw Solutes in Forward Osmosis Process

Forward osmosis (FO) has been recently regarded as a promising water treatment technology due to its lower energy consumption and lower membrane fouling propensity compared to the reverse osmosis (RO). The absence of suitable draw solute constraints the wide-range application of the FO. Hydrogels are three-dimensional hydrophilic polymer networks that can absorb a huge amount of water. Particularly, stimuli-responsive polymer hydrogels can undergo a reversible volume change or solution-gel phase transition in response to external environmental stimuli, including temperature, light, pressure, solvent composition, and pH. These intrinsic properties indicate the lowest regeneration cost of draw solutes compared to the thermal method and other membrane processes. This review aims to introduce the research progress on hydrogels as draw solutes, clarify the existing problems and point out the further research direction.

Effect of chemical structure on properties of polyurethanes: Temperature responsiveness and biocompatibility

Polyurethanes are known as one of the most biocompatible and inherently blood-compatible materials and have a wide range of applications in the medical field due to their controllable structure and properties. Durability, elasticity, elastomeric structure, fatigue resistance, versatility, and easy acceptance by the biological media after the application makes these polymers preferable in medical area. In this study, polyurethane films were prepared using poly(propylene-ethylene glycol) and either toluene-2,4-diisocyanate or 4,4′-methylenediphenyl diisocyanate without adding any other ingredients such as solvent, catalyst, or chain extender to prevent negative effects of leachable molecules. Mechanical tests were performed at room temperature while swelling tests were conducted in water and phosphate-buffered saline at 4°C, 25°C, and 37°C. Temperature responsiveness was observed for the samples synthesized using toluene-2,4-diisocyanate and poly(propylene-ethylene glycol). These samples had more than 100% swelling at 4°C and about 4% swelling at 25°C and 37°C. Cytocompatibility tests were performed by culturing the samples and their extracts with mouse fibroblast cells (L929). Viability of human umbilical vein endothelial cells was studied to examine the compatibility of the films for blood contacting devices. Both toluene-2,4-diisocyanate and 4,4-methylenediphenyl diisocyanate–based polyurethane films showed no cytotoxic effect and good biocompatibility. Oxygen plasma treatment enhanced hydrophilicity of the films. After plasma treatment, human umbilical vein endothelial cell attachment on toluene-2,4-diisocyanate–based polyurethane films improved and 4,4-methylenediphenyl diisocyanate–based polyurethane films maintained their high cell affinity. Polyurethanes presenting temperature responsiveness, high biocompatibility, and high affinity for human umbilical vein endothelial cells were synthesized in medical purity and in a reaction media involving only diisocyanate and diol components without addition of any solvent, chain extender, or catalyst. Polyurethanes with these properties and as produced in this study are reported for the first time in the literature.

Effect of the Sodium Polyacrylate on the Magnetite Nanoparticles Produced by Green Chemistry Routes: Applicability in Forward Osmosis

Aqueous dispersions of magnetic nanocomposites have been proposed as draw electrolytes in forward osmosis. One possible approach for the production of nanocomposites based on magnetite nanoparticles and sodium polyacrylate is the synthesis of the magnetic iron oxide by coprecipitation or oxidative precipitation in the presence of an excess of the polymer. In this work, we explored the effect of the polymer proportion on the nanomaterials produced by these procedures. The materials obtained were compared with those obtained by the coating of magnetite nanocrystals produced beforehand with the same polymer. The samples were characterized by chemical analysis, photon correlation spectroscopy, thermogravimetry, X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and magnetometry. The general trend observed is that the polymers heavily modify the texture of the magnetic material during the synthesis, with a drastic reduction of the particle size and magnetic response. The polycrystalline texture that is generated permits the incorporation of the polymer both on the external surface and in the intergranular space. The aqueous dispersions of the nanocomposites were highly stable, with a hydrodynamic size that was roughly independent of the polymer/magnetite ratio. Such dispersions show an osmotic pressure that is proportional to the concentration of the polymer. Interestingly, the proportionality constant was similar to that of the free polymer only in the case of the samples prepared by oxidative precipitation, being lower in the case of the samples prepared by coprecipitation. Finally, the possibilities of using these materials as draw electrolytes in forward osmosis will be briefly discussed.

Mechanical characterization and modeling of sponge-reinforced hydrogel composites under compression

Load-bearing applications of hydrogels call for materials with excellent mechanical properties. Despite the considerable progress in developing tough hydrogels, there is still a requirement to prepare high-performance hydrogels using simple strategies. In this paper, a sponge-reinforced hydrogel composite is synthesized by combining poly(acrylamide) (PAAm) hydrogel and polyurethane (PU) sponge. Uniaxial compressive testing of the hydrogel composites reveals that both the compressive modulus and the strength of the hydrogel composites are much higher than those of the PAAm hydrogel or sponge. In order to predict the compressive modulus of the hydrogel composite, we develop a theoretical model that is validated by experiments and numerical simulations. The present work may guide the design and manufacture of hydrogel-based composite materials, especially for biomaterial scaffolds and soft transducers.

Zwitterionic polymers showing upper critical solution temperature behavior as draw solutes for forward osmosis

We investigated the suitability of homopolymer with UCST characteristics as draw solutes for the FO process for the first time.