3D Printing techniques are being explored to create gel-based membranes with intricate structures, customizable geometries, and multi-functional regions
[68,69][54][55]. Tayebi et al.
[63][49] highlighted the creation of scaffolds designed for the cultivation of full-thickness oral mucosa, representing a type of heterogeneous tissue. By exploring these dimensions, the paper provided insights into the nuanced production of biologically relevant models using 3D printing technology, which holds potential for advancing tissue engineering and regenerative medicine. Biological membranes, while seemingly two-dimensional, possess intricate structures extending into the third dimension. Three-dimensional printing, particularly through layer-by-layer assembly, emerged as a sophisticated technique for crafting models that embody this complexity. Nonetheless, printing certain hydrogels like gelatin can be challenging due to their unique rheological properties. The authors tackled these challenges by analyzing the complexities of 3D printing gelatin, proposing a reproducible method to surmount the associated experimental hurdles, and detailing the design specifications and fabrication process for 3D printed gelatin membranes.
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These modern synthesis methods underscore the versatility and adaptability of gel-based membrane technology. By leveraging these techniques, researchers can design membranes for specific applications with unprecedented precision, paving the way for innovations across diverse industrial domains.
The advancements in gel-based membrane technology have ushered in significant enhancements in mechanical strength, selectivity, and longevity. The density and nature of cross-linking have been optimized to provide higher mechanical robustness
[70][56]. For instance, dual cross-linking, involving both physical and chemical bonds, can significantly boost strength
[71][57]. The introduction of nanofillers like silica nanoparticles, carbon nanotubes, or graphene oxide can reinforce the gel matrix, leading to improved tensile strength and toughness
[72][58]. Creating hybrid structures by incorporating both organic and inorganic components can marry the flexibility of polymers with the rigidity of inorganic materials, leading to enhanced mechanical properties
[73][59]. Advanced synthesis methods allow for precise control over pore sizes, enabling high selectivity based on the size of molecules or ions. The introduction of specific functional groups or ligands can enhance selectivity based on chemical interactions, such as hydrogen bonding, electrostatic attractions, or even affinity-based separations
[74][60]. Incorporation of hydrophilic groups or zwitterionic components can provide antifouling properties, reducing membrane fouling and thereby extending its lifespan for applications. Chemical modifications or the inclusion of stabilizing agents can render the membranes more resistant to harsh conditions like extreme pH, high temperatures, or aggressive solvents
[75][61]. Some modern gel-based membranes are imbued with self-healing capabilities, where minor damage can be auto-repaired, thus prolonging their operational lifespan
[76,77][62][63]. The addition of protective coatings or layers can shield the membrane from mechanical abrasions, aggressive chemicals, or microbial attacks, thereby extending its durability
[78][64]. The development of efficient cleaning-in-place (CIP) and maintenance protocols has further bolstered the longevity of gel-based membranes in industrial applications
[79][65].
These enhancements in mechanical strength, selectivity, and longevity underline the commitment of researchers and industries to optimize gel-based membrane technology. Such improvements ensure that these membranes can meet the rigorous demands of contemporary applications while maintaining operational efficiency over extended periods. Incorporating nanoparticles or functional groups into membranes has provided an avenue to tailor membrane properties to specific needs
[80][66]. This customizable approach ensures that the resultant membranes are not only more efficient but also versatile in handling a wide range of applications. For example, by incorporating metal and metal oxide nanoparticles like silver (Ag), gold (Au), titanium dioxide (TiO
2), and zinc oxide (ZnO), they can impart antimicrobial properties, improve thermal stability, and enhance mechanical strength
[81,82,83][67][68][69]. Also, incorporating magnetic nanoparticles is useful in applications where remote actuation or controlled movement is required, like in drug delivery or targeted separations. Nanoparticles can add size-exclusion properties or even specific affinity interactions that can enhance the selectivity of membranes
[84][70]. Certain nanoparticles can improve the porosity and hydrophilicity of the membranes, leading to improved permeation rates
[85][71]. Incorporating groups like -OH, -COOH, or -NH
2 can also enhance the hydrophilicity of the membrane, reducing fouling and improving water flux. Zwitterionic Groups have both positive and negative charges, which can greatly reduce protein or microbial fouling due to their unique surface properties
[86][72].
Functional groups like epoxy, carboxyl, or amine can allow for further modifications, tethering of other molecules, or even specific interactions with target substances
[87][73].
The introduction of charged moieties (like sulfonic or quaternary ammonium groups) can enhance the ionic selectivity of the membrane, useful in processes like desalination or ion exchange
[88][74]. Functional groups that have a specific affinity for certain contaminants (e.g., chelating agents for heavy metal capture) can be introduced into membranes to provide selectivity based on chemical interactions
[89][75].
The integration of nanoparticles and functional groups into water treatment membranes has set a new benchmark for efficiency, selectivity, and sustainability. These advanced membranes not only ensure cleaner water but also promise more energy-efficient and eco-friendly water treatment solutions. Gel-based membranes, with their unique properties and adaptability, hold great potential in revolutionizing water treatment processes, providing both efficiency and sustainability
[90][76].