Advanced applications of chitosan-based hydrogels: From biosensors to intelligent food packaging system

Tough polyacrylic acid hydrogels with stable swelling and active functionalities enabled by quaternized cellulose nanofibrils and iron ions for absorbent pad interlayers

Hydrogels are highly sought-after absorbent materials for absorbent pads; however, it is still challenging to achieve a satisfactory balance between mechanical performance, water absorption capacity, and active functionalities. In this work, we presented double-network hydrogels synthesized through acrylic acid (AA) polymerization in the presence of quaternized cellulose nanofibrils (QCNF) and Fe3+. Spectroscopic and microscopic analyses revealed that the combined QCNF and Fe3+ facilitated the formation of double-network hydrogels with combined chemical and physical crosslinking. The synergistic effect of QCNF and Fe3+ resulted in impressive mechanical properties, including tensile strength of 1.98 MPa, fracture elongation of 838.8 %, toughness of 7.47 MJ m-3, and elastic modulus of 0.35 MPa. In comparison to the single-network PAA hydrogel, the PAA/QCNF/Fe3+ (PQFe) hydrogels showed higher and relatively stable swelling ratios under varying pH levels and saline conditions. The PQFe hydrogels exhibited notable antioxidant activity, as evidenced by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, and demonstrated effective antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). These hydrogels show promising potential as an absorbent interlayer in absorbent pads for active food packaging.

Antimicrobial starch-based cryogels and hydrogels for dual-active food packaging applications

The present study reports on the valorisation of starch waste biomass to produce dual-active cryogels and hydrogels able to adsorb water and deliver antimicrobial substances for fresh food packaging applications. Starch hydrogels were prepared by oxidation with sodium metaperiodate in water and mild conditions, while cryogels were obtained by freeze-drying process. To explore the role of starch composition on the final properties of materials, two starches differing in amylose/amylopectin ratio, were evaluated. The prepared materials were microstructurally and morphologically characterized by FTIR and NMR spectroscopy (1D, 2D, and DOSY experiments), and SEM microscopy. To provide the materials with active properties, they were loaded with antimicrobial molecules by absorption, or by crosslinking via Schiff-base reaction. All materials demonstrated high water absorption capacity and ability to deliver volatile molecules, including diacetyl and complex mixtures like mint essential oil. The release profiles of the adsorbed molecules were determined through quantitative NMR spectroscopy over time. The antibacterial activity was successfully demonstrated against Gram-positive bacterial strains for unloaded cryogels and hydrogels, and after loading with diacetyl and essential oil. The developed materials can be regarded as part of active pads for food packaging applications capable to control moisture inside the package and inhibit microbial contamination.

A comprehensive review of chitosan-based functional materials: From history to specific applications

Chitosan (CTS), a natural biopolymer derived from chitin, has garnered significant attention owing to its potential chemical, biological, and physical properties, such as biocompatibility, bioactivity, and biosafety. This comprehensive review traces the historical development of CTS-based materials and delves into their specific applications across various fields. The study highlights the evolution of CTS from its initial discovery to its current state, emphasizing key milestones and technological advancements that have expanded its utility. Despite the extensive research, the synthesis and functionalization of CTS to achieve desired properties for targeted applications remain a challenge. This review addresses current problems such as the scalability of production, consistency in quality, and the environmental impact of extraction and modification processes. Additionally, it explores the novel applications of CTS-based materials in biomedicine, agriculture, environmental protection, and food industry, showcasing innovative solutions and future potentials. By providing a detailed analysis of the current state of CTS research and identifying gaps in knowledge, this review offers a valuable resource for researchers and industry professionals. The novelty of this work lies in its holistic approach, combining historical context with a forward-looking perspective on emerging trends and potential breakthroughs in the field of CTS-based functional materials. Therefore, this review will be helpful for readers by summarizing recent advances and discussing prospects in CTS-based functional materials.

Systematic evaluations and integration of Assam indigenous Joha rice starch in intelligent packaging films for monitoring food freshness using beetroot extract

It is becoming increasingly important to have starch sources with different physicochemical properties to meet the needs of new applications in food, packaging, bioplastic, and pharmaceutical industries. The first part of this study dealt with the isolation of starch from culturally, geographically, nutritionally esteemed, and high-yielding Assam Joha rice. Fine and uniform particle size (6.3 ± 0.09 μm), high amylose content (28 ± 1.03 %), swelling behavior, viscoelastic rheological behavior, moderate gelatinization temperature (66 ± 1.7 °C), thermostable nature, type A crystallographic pattern with high (45 ± 3.3 %) crystallinity, and suitable microbial quality make the Joha rice derived starch physico-chemically and functionally suitable for potential applications in diverse domains. The latter part of the study focuses on one of the applications of derived starch as a suitable matrix for intelligent packaging films with the incorporation of betanin-enriched beetroot extract (BRE) as a bio-based pH sensor. The addition of 1.0 % w/v BRE to the starch film (starch-BRE III) significantly increased its functionality by reducing UV-visible light transmittance and water vapor permeability, along with enhancing flexibility and hydrophobicity due to intermolecular bonding between BRE and the starch film matrix. Moreover, starch-BRE films with different BRE concentrations were successfully used to monitor the real-time freshness of white meat (chicken and fish) and Indian cottage cheese samples. Overall, the results indicated that starch-BRE III has great potential as an intelligent packaging material for monitoring food freshness.

Gelatin-chitosan interactions in edible films and coatings doped with plant extracts for biopreservation of fresh tuna fish products: A review

The preservation of tuna fish products, which are extremely perishable seafood items, is a substantial challenge due to their instantaneous spoilage caused by microbial development and oxidative degradation. The current review explores the potential of employing chitosan-gelatin-based edible films and coatings, which are enriched with plant extracts, as a sustainable method to prolong the shelf life of tuna fish products. The article provides a comprehensive overview of the physicochemical properties of chitosan and gelatin, emphasizing the molecular interactions that underpin the formation and functionality of these biopolymer-based films and coatings. The synergistic effects of combining chitosan and gelatin are explored, particularly in terms of improving the mechanical strength, barrier properties, and bioactivity of the films. Furthermore, the application of botanical extracts, which include high levels of antioxidants and antibacterial compounds, is being investigated in terms of their capacity to augment the protective characteristics of the films. The study also emphasizes current advancements in utilizing these composite films and coatings for tuna fish products, with a specific focus on their effectiveness in preventing microbiological spoilage, decreasing lipid oxidation, and maintaining sensory qualities throughout storage. Moreover, the current investigation explores the molecular interactions associated with chitosan-gelatin packaging systems enriched with plant extracts, offering valuable insights for improving the design of edible films and coatings and suggesting future research directions to enhance their effectiveness in seafood preservation. Ultimately, the review underscores the potential of chitosan-gelatin-based films and coatings as a promising, eco-friendly alternative to conventional packaging methods, contributing to the sustainability of the seafood industry.

Fluorescent carbon dots in situ polymerized biodegradable semi-interpenetrating tough hydrogel films with antioxidant and antibacterial activity for applications in food industry

A flexible, antioxidant, biodegradable, and UV-resistant polymeric nanocomposite hydrogel with heteroatom-doped carbon dots (CDs) has been fabricated using a simple one-step in situ free radical gelation process. The hydrogel formation and their physico-mehcanical characteristics have been assessed by rheology, uniaxial tensile and compression testing. The water uptake behaviour of the hydrogels is controlled by the CDs by manipulating their internal morphology and porosity. The porous nature of the hydrogels has been found from their scanning electron microscopic images which are also supported by their anomalous diffusion-based transport mechanism. The rheological signatures of the hydrogels show delayed network rupturing due to the secondary physical crosslinking alleviated by CDs. Moreover, CDs are directly influencing the permeabilites (oxygen and moisture) by lowering the values compared to their neat hydrogel films which are essential for a packing material. The biodegradability of the hydrogel films showed gradual weight loss (<75 %) within 3 weeks. The hydrogel films also have been qualified to be acted as antibacterial and antioxidant material. The shelf-life and non-leaching of CDs from gel matrices are also performed which shows its excellent capability to be used as a potential antibacterial, biodegradable, antioxidant alternative packaging material in food sectors.

Lactoferrin-Chitosan Composite Hydrogels Induced by Microbial Transglutaminase: Potential Delivery Systems for Thermosensitive Bioactive Substances

In this work, lactoferrin (LF)-chitosan (CS) composite hydrogels with good loading capacity of thermosensitive bioactive substances were successfully obtained by microbial transglutaminase (MTG)-induced cross-linking. We evaluated the rheological, textural, and microstructural characteristics of the composite hydrogels under different conditions. The results demonstrated that the concentrations of LF and CS as well as the amount of MTG could regulate the textural properties, rheological properties, and water holding capability. The results of FTIR and fluorescence spectroscopy indicated that the main interactions within the composite gel were hydrogen and isopeptide bonds. Additionally, in vitro digestion simulation results verified that riboflavin kept stable in stomach due to the protection of LF-CS composite hydrogels and was released in small intestine. These results suggested that thermosensitive bioactive substance could be encapsulated and delivered by the LF-CS composite hydrogel, which could be applied in lots of potential applications in functional food as a new material.

Emerging trends in CDs@hydrogels composites: from materials to applications

Carbon dots (CDs) are nanoscale carbon materials with unique optical properties and biocompatibility. Their applications are limited by their tendency to aggregate or oxidize in aqueous environments. Turning weakness to strengths, CDs can be incorporated with hydrogels, which are three-dimensional networks of crosslinked polymers that can retain large amounts of water. Hydrogels can provide a stable and tunable matrix for CDs, enhancing their fluorescence, stability, and functionality. CDs@hydrogels, known for their ease of synthesis, strong binding capabilities, and rich surface functional groups, have emerged as promising composite materials. In this review, recent advances in the synthesis and characterization of CDs@hydrogels, composite materials composed of CDs and various types of natural or synthetic hydrogels, are summarized. The potential applications of CDs@hydrogels in fluorescence sensing, adsorption, drug delivery, antibacterial activity, flexible electronics, and energy storage are also highlighted. The current challenges and future prospects of CDs@hydrogels systems for the novel functional materials are discussed.

A novel injectable thermo/photo dual-crosslinking hydrogel based on modified chitosan for fast sealing open globe injury

Open globe injuries (OGIs) demand immediate attention to prevent further complications and improve vision prognosis. Herein, we developed a thermo/photo dual-crosslinking injectable hydrogel, HBC_m_Arg, for rapidly sealing OGIs in emergency ophthalmic cases. HBC_m_Arg was prepared with arginine and methacrylic anhydride modified hydroxybutyl chitosan (HBC). HBC_m_Arg was initially in liquid form at 25 °C, enabling easy injection at the injury site. After reaching the ocular surface temperature, it underwent reversible heat-induced gelation to achieve in situ transformation. Further, HBC_m_Arg was capable of rapid photocrosslinking under UV light, forming a dual network structure to bolster mechanical strength, thereby facilitating effective OGI closure. Biocompatibility assessments, including in vitro studies with three ocular cell types and in vivo experiments on rabbit eyes, confirmed the safety profile of HBC_m_Arg. Ex vivo and in vivo burst pressure tests demonstrated the hydrogel's ability to promptly restore intraocular pressure and withstand elevated pressures, underscoring its potential for OGI stabilization. Additionally, the suitable degradation of HBC_m_Arg within ocular tissues, coupled with its stability in ex vivo assessments, presented a delicate balance between stability and biodegradability. In conclusion, HBC_m_Arg holds promise for improving emergency ophthalmic care by providing a rapid, effective, and safe way to seal OGIs in critical situations.

Antimicrobial polysaccharide hydrogels embedded with methyl-β-cyclodextrin/thyme oil inclusion complexes for exceptional mechanical performance and chilled chicken breast preservation

While hydrogels have potential for food packaging, limited research on hydrogels with excellent mechanical performance and antibacterial activity for preserving chicken breasts. Herein, we created antibacterial hydrogels by embedding methyl-β-cyclodextrin/thyme oil inclusion complexes (MCD/TO-ICs) into a polyvinyl alcohol matrix containing dendrobium polysaccharides and guar gum in varying ratios using freeze-thaw cycling method. The resulting hydrogels exhibited a more compact structure than those without MCD/TO-ICs, enhancing thermal stability and increasing glass transition temperature due to additional intermolecular interactions between polymer chains that inhibited chain movement. XRD analysis showed no significant changes in crystalline phase, enabling formation of a 3D network through abundant hydrogen bonding. Moreover, the hydrogel demonstrated exceptional durability, with a toughness of 350 ± 25 kJ/m3 and adequate tearing resistance of 340 ± 30 J/m2, capable of lifting 3 kg weight, 1200 times greater than the hydrogel itself. Additionally, the hydrogels displayed excellent antimicrobial activity and antioxidant properties. Importantly, the hydrogels effectively maintained TVB-N levels and microbial counts within acceptable ranges, preserving sensory properties and extending the shelf life of chilled chicken breasts by four days. This study highlights the potential of MCD/TO-IC-incorporated polysaccharide hydrogels as safe and effective active packaging solutions for preserving chilled chicken in food industry.

Fabrication of composite hydrogels by sonication-assisted assembly of okara cellulose nanofibers and chitosan: structure and properties

BACKGROUND

Okara cellulose is a highly abundant, green, sustainable, and biodegradable polymer with many potential industrial applications. In this study, we fabricated composite hydrogels with okara cellulose nanofibers (CNFs) and chitosan (CH) by hydrating, sonicating, and heating them at 100 °C for 30 min, and then induced their assembly by cooling. The effects of okara CNF (with and without 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) oxidation) and CH concentration on the structure and properties of the hydrogels was examined, including their microstructure, surface properties, rheological properties, and thermal stability.

RESULTS

Our results indicate that there was an electrostatic attraction between the anionic okara CNF and cationic CH, which facilitated hydrogel formation. The surface, textural, rheological, and thermal stability properties were better for the composite hydrogels than for the single CH ones, as well as for the CNF that had undergone TEMPO oxidation. For the TC-CH hydrogels, the contact angle was 39.5°, the interfacial tension was 69.1 mN m-1 , and the surface tension was 1.44 mN m-1 .

CONCLUSION

In this study, the novel hydrogels developed may be useful as a soft material in a range of applications in foods, supplements, health care products, cosmetics, and drugs. © 2023 Society of Chemical Industry.

Strong, tough, high-release, and antibacterial nanocellulose hydrogel for refrigerated chicken preservation

Enormous amounts of food resources are annually wasted because of microbial contamination, highlighting the critical role of effective food packaging in preventing such losses. However, traditional food packaging faces several limitations, such as low mechanical strength, poor fatigue resistance, and low water retention. In this study, we aimed to prepare nanocellulose hydrogels with enhanced stretchability, fatigue resistance, high water retention, and antibacterial properties using soy hull nanocellulose (SHNC), polyvinyl alcohol (PVA), sodium alginate (SA), and tannic acid (TA) as raw materials. These hydrogels were applied in food packaging to extend the shelf life of refrigerated chicken. The structure and properties (e.g., mechanical, antibacterial, and barrier properties) of these hydrogels were characterized using different techniques. Fourier-transform infrared spectroscopy revealed the presence of hydrogen and ester bonds in the hydrogels, whereas scanning electron microscopy revealed the three-dimensional network structure of the hydrogels. Mechanical testing demonstrated that the SHNC/PVA/SA/TA-2 hydrogel exhibited excellent tensile properties (elongation = 160 %), viscoelasticity (storage modulus of 1000 Pa), and mechanical strength (compressive strength = 10 kPa; tensile strength = 0.35 MPa). Moreover, under weak acidic and alkaline conditions, the ester bonds of the hydrogel broke down with an increase in pH, improving its swelling and release properties. The SHNC/PVA/SA/TA-2 hydrogel displayed an equilibrium swelling ratio exceeding 300 %, with a release rate of >80 % for the bioactive substance TA. Notably, antibacterial testing showed that the SHNC/PVA/SA/TA-2 hydrogel effectively deactivated Staphylococcus aureus and Escherichia coli, prolonging the shelf life of refrigerated chicken to 10 d. Therefore, the SHNC/PVA/SA/TA hydrogels can be used in food packaging to extend the shelf life of refrigerated meat products. Their cost-effectiveness and simple preparation make them suitable for various applications in the food industry.

Chitosan-based hydrogels: From preparation to applications, a review

Chitosan, derived from the deacetylation of chitin, is an abundant natural biopolymer on earth. Chitosan and its derivatives have become promising biological materials because of their unique molecular structure and excellent biological activities. The reactive functional groups of chitosan such as the amino and hydroxyl groups play a crucial role in facilitating the synthesis of three-dimensional hydrogel. Chitosan-based hydrogels have been widely used in medical, pharmaceutical, and environmental fields for years. Nowadays, chitosan-based hydrogels have been found in a wide range of applications in the food industry such as food sensors, dye adsorbents and nutrient carriers. In this review, recently developed methods for the preparation of chitosan-based hydrogels were given, and the biological activities of chitosan-based hydrogels were systematically introduced. Additionally, the recent progress in food sensors, packaging, dye adsorbents, and nutrient carriers was discussed. Finally, the challenges and prospects for the future development of chitosan-based hydrogels were discussed.

Visual Gustation via Regulable Elastic Photonic Crystals

The unique structural sensitivity of photonic crystals (PCs) endows them with stretchable or elastic tunability for light propagation and spontaneous emission modulation. Hydrogel PCs have been demonstrated to have biocompatibility and flexibility for potential human health detection and environmental security monitoring. However, current elastic PCs still possess a fixed elastic modulus and uncontrollable structural colors based on a tunable elastic modulus, posing considerable challenges for in situ detection, particularly in wearable or portable sensing devices. In this work, we introduced a novel chemo-mechanical transduction mechanism embedded within a photonic crystal nanomatrix, leading to the creation of structural colors and giving rise to a visual gustation sensing experience. By utilizing the captivating structural colors generated by the hydrogel PC, we employ abundant optical information to identify various analytes. The finite element analysis proved the electric field distribution in the PC matrix during stretch operations. The elastic-optical behaviors with various chemical cosolvents, including cations, anions, saccharides, or organic acids, were investigated. The mechanism of the Hofmeister effect regulating the elasticity of hydrogels was demonstrated with the network nanostructure of the hydrogels. The hydrogel PC matrix demonstrates remarkable capability in efficiently distinguishing a wide range of cations, anions, saccharides, and organic acids across various concentrations, mixtures, and even real food samples, such as tastes and soups. Through comprehensive research, a precise relationship between the structural colors and the elastic modulus of hydrogel PCs has been established, contributing to the biomatching elastic-optics platform for wearable devices, a dynamic environment, and clinical or health monitoring auxiliary.

Nanomicrosphere sustained-release urokinase systems with antioxidant properties for deep vein thrombosis therapy

Deep vein thrombosis (DVT) is a venous return disorder caused by abnormal clotting of blood in deep veins. After thrombosis, most of the thrombus will spread to the deep vein trunk throughout the limb. If DVT is not treated in time, most of them will develop into thrombosis sequelae and even threaten life. Intravenous thrombolytic drugs are the most promising strategy for treating DVT, but current drugs used for thrombolysis suffer from short half-lives and narrow therapeutic indexes. To effectively manage DVT, it is necessary to develop a novel multifunctional drug-loading system to effectively prolong the treatment time and improve the therapeutic efficacy. In this study, a urokinase-loaded protocatechuic aldehyde-modified chitosan microsphere drug-loading platform was constructed for the treatment of DVT. This microsphere adsorbed urokinase well through electrostatic interaction, and the introduction of bovine serum albumin conferred stability to the microspheres. Therefore, the microsphere drug delivery system could achieve slow drug release to effectively dissolve blood fibrin. In addition, chitosan grafted with protocatechuic aldehyde imparted excellent antioxidant activity to the system to reduce free radicals in the blood vessels. Effective management of oxidative stress could avoid abnormal platelet activation and new thrombus formation. The experimental results showed that this microsphere had good biocompatibility, anti-inflammatory properties, and considerable thrombolytic activity. In conclusion, this study provided a new direction and developed a novel multi-functional nano microsphere drug delivery platform for the treatment of DVT.

Physically cross-linked chitosan gel with tunable mechanics and biodegradability for tissue engineering scaffold

Chitosan, a cationic polysaccharide, exhibits promising potential for tissue engineering applications. However, the poor mechanical properties and rapid biodegradation have been the major limitations for its applications. In this work, an effective strategy was proposed to optimize the mechanical performance and degradation rate of chitosan gel scaffolds by regulating the water content. Physical chitosan hydrogel (HG, with 93.57 % water) was prepared by temperature-controlled cross-linking, followed by dehydration to obtain xerogel (XG, with 2.84 % water) and rehydration to produce wet gel (WG, with 56.06 % water). During this process, changes of water content significantly influenced the water existence state, hydrogen bonding, and the chain entanglements of chitosan in the gel network. The mechanical compression results showed that the chitosan gel scaffolds exhibited tunable compressive strength (0.3128-139 MPa) and compressive modulus (0.2408-1094 MPa). XG could support weights exceeding 65,000 times its own mass while maintaining structural stability. Furthermore, in vitro and in vivo experiments demonstrated that XG and WG exhibited better biocompatibility and resistance to biodegradation compared with HG. Overall, this work contributes to the design and optimization of chitosan scaffolds without additional chemical crosslinkers, which has potential in tissue engineering and further clinical translation.

An antibacterial nanoclay- and chitosan-based quad composite with controlled drug release for infected skin wound healing

Microbial infections of surgical sites and other wounds represent a major impediment for patients. Multifunctional low-cost dressings promoting tissue reparation while preventing infections are of great interest to medical professionals. Here, clay-based laponite nanodiscs (LAP) were loaded with the antibacterial drug kanamycin (KANA) before being embedded into a poly(lactic-co-glycolic acid) (PLGA) membrane and coated with the biopolymer chitosan (CS). Results indicated that these biocompatible materials combined the excellent capacity of LAP for controlled drug release with the mechanical robustness of PLGA and the antibacterial properties of CS as well as its hydrophilicity to form a composite highly suitable as an infection-preventing wound dressing. In vitro, PLGA/LAP/KANA/CS released drugs in a sustainable manner over 30 d, completely inhibited the growth of infectious bacteria, prompted the adhesion fibroblasts, and accelerated their proliferation 1.3 times. In vivo, the composite enabled the fast healing of infected full-thickness skin wounds with a 96.19 % contraction after 14 d. During the healing process, PLGA/LAP/KANA/CS stimulated re-epithelization, reduced inflammation, and promoted both angiogenesis and the formation of dense collagen fibers with an excellent final collagen volume ratio of 89.27 %. Thus, multifunctional PLGA/LAP/KANA/CS made of low-cost components demonstrated its potential for the treatment of infected skin wounds.

An aquatic biomimetic butterfly soft robot driven by deformable photo-responsive hydrogel

Taking inspiration from the locomotor behaviors of a butterfly, we have developed an underwater soft robot that imitates its movements. This biomimetic robot is constructed using a deformable photo-responsive material that exhibits high biological compatibility and impressive deformation capabilities in response to external stimuli. First, we investigate composite materials consisting of poly-N-isopropylacrylamide (PNIPAM) and multi-walled carbon nanotubes (MWCNTs). Then, using photocuring printing technology, we successfully fabricate a biomimetic butterfly soft robot utilizing these composite materials. The robot is driven by visible light, enabling it to achieve periodic wing movement and fly upward at an average speed of 3.63 mm s-1. In addition, the robot achieves additional functionalities such as flying over obstacles and carrying small objects during the ascending flight. These outcomes have a significant impact on the advancement of flexible biomimetic robots and offer valuable insights for the research of biomimetic robots driven by visible light.

Sustainable polysaccharide and protein hydrogel-based packaging materials for food products: A review

Sustainable food packaging is a necessary element to ensure the success of a food system, the accomplishment of which is weighed in terms of quality retention and ensured products safety. Irrespective of the raised environmental concerns regarding petroleum-based packaging materials, a sustainable analysis and a lab to land assessment should be a priority to eliminate similar fates of new material. Functionalized bio-based hydrogels are one of the smartest packaging inventions that are expected to revolutionize the food packaging industry. Although in this review, the focus relies on recent developments in the sustainable bio-based hydrogel packaging materials, natural biopolymers such as proteins and polysaccharides from which hydrogels could be obtained, the challenges encountered in hydrogel-based packaging materials and the future prospects of hydrogel-based food packaging materials are also discussed. Moreover, the need for 'Life Cycle Assessment' (LCA), stress on certifications and a sustainable waste management system is also suggested which can bring both food and packaging into the same recycling bins.

Polysaccharides, proteins, and synthetic polymers based multimodal hydrogels for various biomedical applications: A review

Nature-derived or biologically encouraged hydrogels have attracted considerable interest in numerous biomedical applications owing to their multidimensional utility and effectiveness. The internal architecture of a hydrogel network, the chemistry of the raw materials involved, interaction across the interface of counter ions, and the ability to mimic the extracellular matrix (ECM) govern the clinical efficacy of the designed hydrogels. This review focuses on the mechanistic viewpoint of different biologically driven/inspired biomacromolecules that encourages the architectural development of hydrogel networks. In addition, the advantage of hydrogels by mimicking the ECM and the significance of the raw material selection as an indicator of bioinertness is deeply elaborated in the review. Furthermore, the article reviews and describes the application of polysaccharides, proteins, and synthetic polymer-based multimodal hydrogels inspired by or derived from nature in different biomedical areas. The review discusses the challenges and opportunities in biomaterials along with future prospects in terms of their applications in biodevices or functional components for human health issues. This review provides information on the strategy and inspiration from nature that can be used to develop a link between multimodal hydrogels as the main frame and its utility in biomedical applications as the primary target.

Effect of purple red rice bran anthocyanins on pasting, rheological and gelling properties of rice starch

Purple red rice bran (PRRBA), a by-product of the rice polishing process, is frequently thrown away, resulting in a waste of resources. This study investigated the effects of PRRBA on the pasting, rheological property, chemical structure, microstructure, and water migration of rice starch. The results demonstrated that the peak viscosity (PV), final viscosity (FV), and activation energy (retrogradation energy) of rice starch were all decreased by a dose of PRRBA. Furthermore, the gel strength and hardness of rice starch were positively correlated with the addition of PRRBA. Rice starchs particle size distribution can be improved by PRRBA, which may be a result of the non-covalent bonds that exist between PRRBA and rice starch. The addition of PRRBA resulted in a decrease in the spin relaxation time (T2) of rice starch, from 259.7 to 143.6 ms. This can be attributed to that PRRBA improved the water-holding capacity of rice starch. These results could contribute to the development of high-value-added products of PRRBA and facilitate the application of anthocyanins in starch-based foods.

A comprehensive review of chitosan applications in paper science and technologies

Using environmentally friendly biomaterials in different aspects of human life has been considered extensively. In this respect, different biomaterials have been identified and different applications have been found for them. Currently, chitosan, the well-known derivative of the second most abundant polysaccharide in the nature (i.e., chitin), has been receiving a lot of attention. This unique biomaterial can be defined as a renewable, high cationic charge density, antibacterial, biodegradable, biocompatible, non-toxic biomaterial with high compatibility with cellulose structure, where it can be used in different applications. This review takes a deep and comprehensive look at chitosan and its derivative applications in different aspects of papermaking.

State-of-the-Art Insights and Potential Applications of Cellulose-Based Hydrogels in Food Packaging: Advances towards Sustainable Trends

Leveraging sustainable packaging resources in the circular economy framework has gained significant attention in recent years as a means of minimizing waste and mitigating the negative environmental impact of packaging materials. In line with this progression, bio-based hydrogels are being explored for their potential application in a variety of fields including food packaging. Hydrogels are three-dimensional, hydrophilic networks composed of a variety of polymeric materials linked by chemical (covalent bonds) or physical (non-covalent interactions) cross-linking. The unique hydrophilic nature of hydrogels provides a promising solution for food packaging systems, specifically in regulating moisture levels and serving as carriers for bioactive substances, which can greatly affect the shelf life of food products. In essence, the synthesis of cellulose-based hydrogels (CBHs) from cellulose and its derivatives has resulted in hydrogels with several appealing features such as flexibility, water absorption, swelling capacity, biocompatibility, biodegradability, stimuli sensitivity, and cost-effectiveness. Therefore, this review provides an overview of the most recent trends and applications of CBHs in the food packaging sector including CBH sources, processing methods, and crosslinking methods for developing hydrogels through physical, chemical, and polymerization. Finally, the recent advancements in CBHs, which are being utilized as hydrogel films, coatings, and indicators for food packaging applications, are discussed in detail. These developments have great potential in creating sustainable packaging systems.

Nanoporous hydrogel absorbent based on salep: Swelling behavior and methyl orange adsorption capacity

This study used the gas-blowing method to develop a nanoporous hydrogel using poly (3-sulfopropyl acrylate-co-acrylic acid-co-acrylamide) grafted onto salep. The synthesis of the nanoporous hydrogel was optimized by various parameters for maximum swelling capacity. The nanoporous hydrogel was characterized using FT-IR, TGA, XRD, TEM, and SEM analyses. Images from SEM showed numerous pores and channels in the hydrogel with an average size of about 80 nm, forming a honeycomb-like shape. The change in surface charge was investigated by zeta potential and revealed that the surface charge of the hydrogel ranged from 20 mV at acidic conditions to -25 mV at basic conditions. The swelling behavior of optimum superabsorbent hydrogel was determined under different environmental conditions, such as different pH values, ionic strengths of the environment, and solvents. In addition, the swelling kinetics and the absorbance under loading of the hydrogel sample in different environments were investigated. Moreover, Methyl Orange (MO) dye was removed from aqueous solutions using the nanoporous hydrogel as an adsorbent. The adsorption behavior of the hydrogel was examined under various conditions, and the adsorption capacity of the hydrogel was found tobe 400 mg g^-1. The maximum water uptake was obtained under the following conditions: Salep weight = 0.01 g, AA = 60 μL, MBA = 300 μL, APS = 60 μL, TEMED = 90 μL, AAm = 600 μL, and SPAK = 90 μL. Lastly, the adsorption kinetics was studied by employing pseudo-first-order, pseudo-second-order, and intra-particle diffusion models.

Fabrication of Poly(ε-caprolactone)-embedded Lignin-Chitosan Nanocomposite Porous Scaffolds from Pickering Emulsions

Poly(ε-caprolactone) (PCL)-incorporated lignin-chitosan biomass-based nanocomposite porous scaffolds have been effectively prepared by templating oil-in-water Pickering high internal phase emulsions (HIPEs). PCL is dissolved in oil and chitosan and lignin nanoparticles originate in water. The continuous phase of the emulsions is gelled by cross-linking of chitosan with genipin and then freeze-dried to obtain porous scaffolds. The resulting scaffolds display interconnected and tunable pore structures. An increase in PCL content increases the mechanical strength and greatly reduces the water absorption capacity of the scaffolds. Scaffolds loaded with the anti-bacterial drug enrofloxacin show a slow drug release profile, adjustable release rate, and favorable long-term anti-bacterial activity. Moreover, Pickering emulsion templates with suitable viscosity are used as 3D printing inks to construct porous scaffolds with personalized geometry. The results imply that the simplicity and versatility of the technique of combining freeze-drying with Pickering HIPE templates is a promising approach to fabricate hydrophobic biopolymer-incorporated biomass-based nanocomposite porous scaffolds for biomedical applications.

Recent trends of 3D printing based on starch-hydrocolloid in food, biomedicine and environment

People are exploring the potential application of 3D printing in food, biomedicine and environment, but it is urgent to find suitable bio-ink. Bio-ink compounded with starch and hydrocolloid can not only improve the rheology, structure and printability of starch-based edible bio-ink, but also endow it with other functional characteristics, so that it can be applied to food, biomedicine and even the environment, and meet the strategic needs of national health, green and sustainable development. In this paper, hydrocolloids are reviewed as potential means to regulate the physicochemical properties of starch, which endows it with good printability and presents excellent printing products. The specific applications of the bio-ink in the fields of food, biomedicine and environment in hypoglycemic, lipid-lowering, swallowable food, delivery, intelligent materials, and bio-sensor are also discussed. Then, the challenges and future development trends of realizing large-scale application are prospected. Proper physicochemical properties of starch-hydrocolloid are positively correlated with printability. The presentation of excellent printability has realized the application in different fields, not only satisfies most people, but also create benefits for some specific people. This review is expected to provide some theoretical guidance for the further development of 3D printing technology and its large-scale application.

Antioxidant Biomaterials in Cutaneous Wound Healing and Tissue Regeneration: A Critical Review

Natural-based biomaterials play an important role in developing new products for medical applications, primarily in cutaneous injuries. A large panel of biomaterials with antioxidant properties has revealed an advancement in supporting and expediting tissue regeneration. However, their low bioavailability in preventing cellular oxidative stress through the delivery system limits their therapeutic activity at the injury site. The integration of antioxidant compounds in the implanted biomaterial should be able to maintain their antioxidant activity while facilitating skin tissue recovery. This review summarises the recent literature that reported the role of natural antioxidant-incorporated biomaterials in promoting skin wound healing and tissue regeneration, which is supported by evidence from in vitro, in vivo, and clinical studies. Antioxidant-based therapies for wound healing have shown promising evidence in numerous animal studies, even though clinical studies remain very limited. We also described the underlying mechanism of reactive oxygen species (ROS) generation and provided a comprehensive review of ROS-scavenging biomaterials found in the literature in the last six years.

Recent progressions in biomedical and pharmaceutical applications of chitosan nanoparticles: A comprehensive review

Nowadays, the most common approaches in the prognosis, diagnosis, and treatment of diseases are along with undeniable limitations. Thus, the ever-increasing need for using biocompatible natural materials and novel practical modalities is required. Applying biomaterials, such as chitosan nanoparticles (CS NPs: FDA-approved long-chain polymer of N-acetyl-glucosamine and D-glucosamine for some pharmaceutical applications), can serve as an appropriate alternative to overcome these limitations. Recently, the biomedical applications of CS NPs have extensively been investigated. These NPs and their derivatives can not only prepare through different physical and chemical approaches but also modify with various molecules and bioactive materials. The potential properties of CS NPs, such as biocompatibility, biodegradability, serum stability, solubility, non-immunogenicity, anti-inflammatory properties, appropriate pharmacokinetics and pharmacodynamics, and so forth, have made them excellent candidates for biomedical applications. Therefore, CS NPs have efficiently applied for various biomedical applications, like regenerative medicine and tissue engineering, biosensors for the detection of microorganisms, and drug delivery systems (DDS) for the suppression of diseases. These NPs possess a high level of biosafety. In summary, CS NPs have the potential ability for biomedical and clinical applications, and it would be remarkably beneficial to develop new generations of CS-based material for the future of medicine.

Preparation and comparison of dialdehyde derivatives of polysaccharides as cross-linking agents

Dialdehyde-based cross-linking agents are widely used in the cross-linking of amino group-containing macromolecules. However, the most commonly used cross-linking agents, glutaraldehyde (GA) and genipin (GP), have safety issues. In this study, a series of dialdehyde derivatives of polysaccharides (DADPs) were prepared by oxidation of polysaccharides, and their biocompatibility and cross-linking properties were tested using chitosan as a model macromolecule. The DADPs showed outstanding cross-linking and gelation properties comparable to GA and GP. The DADPs and hydrogels cross-linked with the DADPs exhibited excellent cytocompatibility and hemocompatibility with different concentrations while significant cytotoxicity was observed in GA and GP. The experimental results showed that the cross-linking effect of DADPs increased along with their oxidation degree. The outstanding cross-linking effect of the DADPs show a potential for use in the cross-linking of biomacromolecules with amino groups and could be an adequate alternative to existing cross-linkers.

Application of chitosan nanoparticles in quality and preservation of postharvest fruits and vegetables: A review

Chitosan is an interesting alternative material for packaging development due to its biodegradability. However, its poor mechanical properties and low permeability limit its actual applications. Chitosan nanoparticles (CHNPs) have emerged as a suitable solution to overcome these intrinsic limitations. In this review, all studies regarding the use of CHNPs to extend the shelf life and improve the quality of postharvest products are covered. The characteristics of CHNPs and their combinations with essential oils and metals, along with their effects on postharvest products, are compared and discussed throughout the manuscript. CHNPs enhanced postharvest antioxidant capacity, extended shelf life, increased nutritional quality, and promoted tolerance to chilling stress. Additionally, the CHNPs reduced the incidence of postharvest phytopathogens. In most instances, smaller CHNPs (<150 nm) conferred higher benefits than larger ones (>150 nm). This was likely a result of the greater plant tissue penetrability and surface area of the smaller CHNPs. The CHNPs were either applied after preparing an emulsion or incorporated into a film, with the latter often exhibiting greater antioxidant and antimicrobial activities. CHNPs were used to encapsulate essential oils, which could be released over time and may enhance the antioxidant and antimicrobial properties of the CHNPs. Even though most applications were performed after harvest, preharvest application had longer lasting effects.

Past, present and future of biomedical applications of dextran-based hydrogels: A review

This review extensively surveys the biomedical applications of hydrogels containing dextran. Dextran has gained much attention as a biomaterial due to its distinctive properties such as biocompatibility, non-toxicity, water solubility and biodegradability. It has emerged as a critical constituent of hydrogels for biomedical applications including drug delivery devices, tissue engineering scaffolds and biosensor materials. The benefits, challenges and potential prospects of dextran-based hydrogels as biomaterials are highlighted in this review.

Preparation of a multifunctional non-stick tamarind polysaccharide-polyvinyl alcohol hydrogel immobilized with a quorum quenching enzyme for maintaining fish freshness

Hydrogels have become promising materials for food packaging due to their unique microstructure. However, hydrogel materials suitable for seafood preservation have rarely been reported. In this study, a tamarind polysaccharide-polyvinyl alcohol hydrogel with the ability to maintain seafood freshness was prepared and characterized. The hydrogel possesses quick self-healing, good tissue fitting, and freezing tolerance capability. Moreover, a peeling force of only 0.1 N between the hydrogel and the fillet tissue confirmed the non-stick properties. The FTIR characteristic peak at 1600 cm^-1 and 1450 cm^-1 proved the ester bond-based chemical cross-linking of the hydrogel. Release profiles at pH 6.0 to 8.0 verified the pH-responsive release of quorum-quenching (QQ) enzymes over 120 h, which enabled the hydrogel to achieve biofilm and protease inhibitory activities. In vivo spoilage tests showed that the shelf life of hydrogel-coated red snapper fillets was extended by >3 days. These results illustrate the potential of the prepared hydrogel as functional packaging for seafood preservation.

Trifunctional Microgel-Mediated Preparation and Toughening of Printable High-Performance Chitosan Hydrogels for Underwater Communications

Natural and biocompatible chitosan has demonstrated wide applications. However, rapidly fabricating high-performance chitosan hydrogels in one-step controllable processes is still a challenge for some advanced applications. Here, we report a trifunctional microgel-mediated photochemical (TMMP) strategy to achieve the fabrication of printable tough chitosan-based hydrogels (PTCHs) in seconds. Such microgels help the slow release of persulfate anions and their uniform dispersion in an aqueous solution of cationic chitosan. The released persulfates are available for preparing multiple networks of phenolic coupling of modified chitosan and radical polymerization of Pluronic F127 via orthogonal tris(bipyridine)ruthenium(II)-based photochemistry, respectively. Trifunctional microgels have reversible Ca2+-crosslinked networks that further improve the hydrogels' mechanical properties and toughness. The maximum stress and toughness increase by >20 folds compared to the chitosan and F127 hydrogels with single network structures. Moreover, these microgels enable the precursor to have a good shearing-thinning property and benefit the controllable preparation of PTCHs in a short time, as low as ∼4 s under visible light irradiation. It, therefore, is compatible with standard printing techniques to make complex structures. Strain sensors based on structured PTCHs have stable mechanical and responsive properties in the water, which are applied for real-time underwater communications (<0.4 s). It is anticipated that this one-step TMMP strategy opens new horizons for designing advanced chitosan hydrogels.

Polysaccharide-Based Multifunctional Hydrogel Bio-Adhesives for Wound Healing: A Review

Wound healing is a long-term and complex biological process that involves multiple hemostasis, inflammation, proliferation, and remodeling stages. In order to realize comprehensive and systematic wound management, appropriate wound treatment bio-adhesives are urgently needed. Hydrogel bio-adhesives have excellent properties and show unique and remarkable advantages in the field of wound management. This review begins with a detailed description of the design criteria and functionalities of ideal hydrogel bio-adhesives for wound healing. Then, recent advances in polysaccharide-based multifunctional hydrogel bio-adhesives, which involve chitosan, hyaluronic acid, alginate, cellulose, dextran, konjac glucomannan, chondroitin sulfate, and other polysaccharides, are comprehensively discussed. Finally, the current challenges and future research directions of polysaccharide-based hydrogel bio-adhesives for wound healing are proposed to stimulate further exploration by researchers.

High-Release, Residue-Free Polysaccharide Hydrogel for Refrigerated Food Preservation

Hundreds of millions of tons of food resources are wasted annually due to microbial contamination. Effective food packaging can prevent food contamination and wastage. However, traditional food packaging has the problem of low release of bioactive substances. This study aimed to prepare a pH-responsive polysaccharide hydrogel (GDPP) by double cross-linking of ester and hydrogen bonds that could result in a high release of bioactive substances and no residual peeling. The infrared results showed the existence of ester bonds in the hydrogel, and the scanning electron microscopy results showed the porous network structure of the hydrogel. The results of texture profile analysis and self-healing tests showed that GDPP-1 has good mechanical and self-healing properties. Moreover, the ester bond of the hydrogel broke in response to the pH in the environment, improving the swelling and release properties of the hydrogel. The equilibrium swelling ratio of GDPP-1 was greater than 1000%, and the release rate of bioactive substances was more than 80%. Notably, the results of peeling experiments showed that only 0.1 N external force was needed to separate the hydrogel from the salmon, and no residue was observed on the salmon surface. The final freshness test results showed that the hydrogel effectively prolonged the shelf life of refrigerated salmon for 3-6 days. These findings indicated that hydrogels could be used in food packaging to extend the shelf life of refrigerated food. Furthermore, their advantages of low cost and simple preparation can better meet the needs of food industry applications.

An electrochemical aptasensor based on AuNRs/AuNWs for sensitive detection of apolipoprotein A-1 (ApoA1) from human serum

For early detection and diagnosis of cancer, it is essential to develop an electrochemical biosensor that is quick, accurate, and sensitive. Here, we use gold nanorod (AuNR) and gold nanowire (AuNW) nanocomposites (AuNR/AuNW/CS) as electrode modifiers on a glassy carbon electrode (GCE) to construct a sensitive label-free electrochemical aptasensor to detect ApoA1. The thiolated ApoA1-specific aptamers were immobilized onto the modified electrode surface through self-assembled monolayers. Electrochemical techniques, such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV), were used to analyze the fabrication steps. The concentration of ApoA1 was measured with DPV on the aptasensor, with a linear range of 0.1 to 1000 pg mL^-1 and a detection limit of 0.04 pg mL^-1. When compared to results from ELISA tests (which have a detection limit of 80 pg mL^-1), the results achieved here were over 2000 times better. The aptasensor's performance was successfully evaluated using human serum spiked with ApoA1, suggesting that it has great potential for practical application. The electrochemical apatsensor additionally demonstrated outstanding selectivity responses and strong stability toward the target analyte.

Chitosan-Based Hydrogels for Bioelectronic Sensing: Recent Advances and Applications in Biomedicine and Food Safety

Due to the lack of efficient bioelectronic interfaces, the communication between biology and electronics has become a great challenge, especially in constructing bioelectronic sensing. As natural polysaccharide biomaterials, chitosan-based hydrogels exhibit the advantages of flexibility, biocompatibility, mechanical tunability, and stimuli sensitivity, and could serve as an excellent interface for bioelectronic sensors. Based on the fabrication approaches, interaction mechanisms, and bioelectronic communication modalities, this review divided chitosan-based hydrogels into four types, including electrode-based hydrogels, conductive materials conjugated hydrogels, ionically conductive hydrogels, and redox-based hydrogels. To introduce the enhanced performance of bioelectronic sensors, as a complementary alternative, the incorporation of nanoparticles and redox species in chitosan-based hydrogels was discussed. In addition, the multifunctional properties of chitosan-based composite hydrogels enable their applications in biomedicine (e.g., smart skin patches, wood healing, disease diagnosis) and food safety (e.g., electrochemical sensing, smart sensing, artificial bioelectronic tongue, fluorescence sensors, surface-enhanced Raman scattering). We believe that this review will shed light on the future development of chitosan-based biosensing hydrogels for micro-implantable devices and human-machine interactions, as well as potential applications in medicine, food, agriculture, and other fields.

Research on the Properties of Polysaccharides, Starch, Protein, Pectin, and Fibre in Food Processing

As food components, polysaccharides, starch, protein, pectin, and fibre are often used in the food industry due to their particular functional properties, as well as their efficient, safe, and green characteristics [...].

Encapsulation and delivery of phage as a novel method for gut flora manipulation in situ: A review

Intestinal flora regulation is an effective method to intervene and treat diseases associated with microbiome imbalance. In addition to conventional probiotic supplement, phage delivery has recently exhibited great prospect in modifying gut flora composition and regulating certain gene expression of gut bacteria. However, the protein structure of phage is vulnerable to external factors during storage and delivery, which leads to the loss of infection ability and flora regulation function. Encapsulation strategy provides an effective solution for improving phage stability and precisely controlling delivery dosage. Different functional materials including enzyme-responsive and pH-responsive polymers have been used to construct encapsulation carriers to protect phages from harsh conditions and release them in the colon. Meanwhile, diverse carriers showed different characteristics in structure and function, which influenced their protective effect and delivery efficiency. This review systematically summarizes recent research progress on the phage encapsulation and delivery, with an emphasis on function properties of carrier systems in the protection effect and colon-targeted delivery. The present review may provide a theoretical reference for the encapsulation and delivery of phage as microbiota modulator, so as to expedite the development of functional material and delivery carrier, as well as the advances in practical application of intestinal flora regulation.

Eco-design and tunable structure-properties of chitosan-epoxy-glycerol-silicate biohybrids using integrated crosslinking

Tunable structure-properties were achieved for chitosan-epoxy-glycerol-silicate (CHTGP) biohybrids, eco-designed via integrated amine-epoxy and waterborne sol-gel crosslinking reactions. Medium molecular weight chitosan (CHT), with 83 % degree of deacetylation was prepared by microwave-assisted alkaline deacetylation of chitin. The amine group of chitosan was covalently bonded to the epoxide of 3-glycidoxypropyltrimethoxysilane (G) for further crosslinking with a sol-gel derived glycerol-silicate precursor (P) from 0.5 % to 5 %. The impact of crosslinking density on the structural morphology, thermal, mechanical, moisture-retention and antimicrobial properties of the biohybrids were characterized by FTIR, NMR, SEM, swelling and bacterial inhibition studies and contrasted with a corresponding series (CHTP) without epoxy silane. Water uptake was significantly reduced in all biohybrids with a 12 % window of variation between the two series. Properties observed in biohybrids with only epoxy-amine (CHTG) or sol-gel crosslinking reactions (CHTP), were reversed in the integrated biohybrids (CHTGP) to impart improved thermal and mechanical stability and antibacterial activity.

Synthesis of Gallic Acid-Loaded Chitosan-Grafted-2-Acrylamido-2-Methylpropane Sulfonic Acid Hydrogels for Oral Controlled Drug Delivery: In Vitro Biodegradation, Antioxidant, and Antibacterial Effects

In this study, chitosan (CS) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS)-based hydrogels were formulated by the free radical polymerization technique for the controlled release of gallic acid. Fourier transform infrared spectroscopy (FTIR) confirmed the successful preparation and loading of gallic acid within the hydrogel network. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) confirmed the increased thermal stability of the hydrogels following the crosslinking and polymerization of chitosan and AMPS. In X-ray diffraction analysis (XRD), the crystallinity of the raw materials decreased, indicating strong crosslinking of the reagents and the formation of a new polymeric network of hydrogels. Scanning electron microscopy (SEM) revealed that the hydrogel had a rough, dense, and porous surface, which is consistent with the highly polymerized composition of the hydrogel. After 48 h, the hydrogels exhibited higher swelling at pH 1.2 (swelling ratio of 19.93%) than at pH 7.4 (swelling ratio of 15.65%). The drug release was analyzed using ultraviolet-visible (UV-Vis) spectrophotometer and demonstrated that after 48 h, gallic acid release was maximum at pH 1.2 (85.27%) compared to pH 7.4 (75.19%). The percent porosity (78.36%) and drug loading increased with the increasing concentration of chitosan and AMPS, while a decrease was observed with the increasing concentration of ethylene glycol dimethyl methacrylate (EGDMA). Crosslinking of the hydrogels increased with concentrations of chitosan and EGDMA but decreased with AMPS. In vitro studies demonstrated that the developed hydrogels were biodegradable (8.6% degradation/week) and had antimicrobial (zone of inhibition of 21 and 16 mm against Gram-positive bacteria Escherichia coli and Staphylococcus aureus as well as 13 mm against Gram-negative bacteria Pseudomonas aeruginosa, respectively) and antioxidant (73% DPPH and 70% ABTS) properties. Therefore, the prepared hydrogels could be used as an effective controlled drug delivery system.

Newly designed acrylamide derivative-based pH-responsive hydrogel-urease bioconjugates: synthesis and catalytic urea hydrolysis

Jack bean urease, the first nickel metalloenzyme, and crystallized enzymes have historical significance due to their several applications in the biomedical and other fields. For the first time, cross-linker free pH-responsive hydrogel-urease bioconjugates have been reported. Without the use of divinyl benzene or divinyl acrylamide derivatives, urease was immobilized inside the hydrogel matrix and various grades of bioconjugates were synthesized. The hydrogel-urease bioconjugate exhibits excellent swelling-deswelling and pH-responsive characteristics without affecting the urease enzyme. The pH-responsive bioconjugates were characterized by FT-IR, powder XRD, SEM, TGA, and UV-vis spectroscopy. Urea hydrolysis and enzyme affinity have been investigated at pH 4, pH 7, and pH 11 using bioconjugates and free urease. At basic pH, BCs showed excellent enzyme activity. In summary, this technique is effective for stabilizing biomacromolecules at different pHs for a variety of real applications.

Graphene Oxide-alginate Hydrogel for Drawing Water through an Osmotic Membrane

We report the preparation and evaluation of graphene oxide (GO)-enhanced alginate hydrogels for drawing water across an osmotic desalination membrane. GO-incorporated calcium alginate hydrogels (GO-HG) and pure calcium alginate hydrogels (P-HG) were synthesized for this study. Environmental scanning electron microscopy, water contact angle, and water uptake tests showed both samples to be strongly hydrophilic. The synthesized hydrogels demonstrated the ability to successfully and continuously draw water through a selective osmotic membrane in experiments. This was driven by the surface energy gradient-induced negative pressure between the more hydrophilic hydrogel and less hydrophilic membrane surface. The GO-HG was found to draw 21.2% more water than the P-HG, owing to the flexible GO nanosheets, which can be easily incorporated into the hydrogel framework. The GO nanosheets not only offer more hydrophilic functional sites but also enhance the connectivity within the alginate hydrogel framework so as to enhance the water production performance. The average amount of water drawn through the membrane by the GO-HG and the P-HG is 23.4 ± 0.9 g and 19.3 ± 1.8 g, respectively. It was found that no external stimuli were needed as water flows through the hydrogel due to gravitational force. The GO-enhanced alginate hydrogel, combined with the osmotic membrane, is a promising surface energy gradient-driven functional material for water purification and desalination without applying external pressure.