Properties of Water Bound in Hydrogels

Collagen hydrogels with similar polymer content but different microstructure - A comparative analysis of mechanical response

Understanding the mechanical properties of collagen hydrogels is essential for successful applications in tissue engineering and 3D cell culture. This study compares the mechanical behavior of two collagen hydrogel sheets with similar collagen content but different microstructures. One of the differences is that one gel is isotropic while the other has collagen fibers oriented towards the sheet's plane. Experiments were performed at macro- (uniaxial tension in the sheet plane) and micro-length scale (AFM-based indentation perpendicular to the plane), and a discrete network model was developed to rationalize the observed differences. The experiments showed an order of magnitude difference in the uniaxial stiffness of the two gels. The softer gel exhibited near-incompressible behavior, while the stiffer gel showed a highly contractile response, with Poisson's ratios around 8. Conversely, the apparent modulus from nano-indentation showed an opposite trend, with higher local stiffness for the gel that was softer in uniaxial tests. The computational model represents the material using a network of bi-linear connectors for the fibrous component and a compressible neo-Hookean material for the surrounding water-rich matrix, assumed to form due to interactions between collagen and water. Under the constraint of equal collagen content, model parameters were tuned to reproduce the observed response of both materials, considering the observed differences in fiber diameter. Importantly, the computations indicate that the difference in collagen orientation cannot explain the observed differences between the mechanical responses of the gels. Successful scaling between the two gels depends on the assumption that, due to their crimped initial state individual fibers primarily experience bending rather than tension when the material is stretched. Moreover, high tensile stretch of the fibers is shown to elicit large lateral contraction. Overall, the results demonstrate the wide range of mechanical properties displayed by hydrogels with similar collagen content, which can be rationalized using discrete models representative of their microstructure.

A review on recent progress in polysaccharide/protein hydrogels in winter sports: Classification, synthesis routes, and application

In today's world, emerging materials play prominent roles in competitive sport applications. Among them, hydrogels gained increasing attention in winter sports applications owing to their unique advantages, such as flexibility, conductivity, and adhesion. However, traditional hydrogels prepared by synthetic routes from petroleum materials lose performance at freezing temperatures below zero degrees, limiting their direct use in winter sports. The emergence of natural polymer materials has brought new opportunities for winter sports. Polysaccharide or protein (polysaccharides/proteins) hydrogels obtained from biomass resources are renewable and abundant, especially when taking into consideration the depletion of resources and environmental pollution in contemporary society. The development and utilization of polysaccharide/protein hydrogels may contribute to solving the resource shortage problem. In this paper, the latest research dealing with natural polymer hydrogels for winter sports applications is reviewed. In the first section, recent research trends of hydrogel classification and crosslinking methods are summarized. The performance advantages and specific applications of polysaccharide/protein hydrogels in winter sports are then discussed, with the application scope covering index monitoring, event violation detection, protective equipment, rehabilitation, and venues. Finally, the practical challenges faced by polysaccharide/protein hydrogels in winter sports are prospected along with the innovation and optimization design routes, such as the introduction of natural crosslinking agents and bionic structures. These insights aim to provide a reference for the development of advanced materials for winter sports applications.

Insights into Dendrite Regulation by Polymer Hydrogels for Aqueous Batteries

Aqueous batteries, renowned for their high capacity, safety, and low cost, have emerged as promising candidates for next-generation, sustainable energy storage. However, their large-scale application is hindered by challenges, such as dendrite formation and side reactions at the anode. Hydrogel electrolytes, which integrate the advantages of liquid and solid phases, exhibit superior ionic conductivity and interfacial compatibility, giving them potential to suppress dendrite evolution. This Perspective first briefly introduces the fundamentals underlying dendrite formation and the unique features of hydrogels. It then identifies the key role of water and polymer networks in inhibiting dendrite formation, highlighting their regulation of water activity, ion transport, and electrode kinetics. By elucidating the principles of hydrogels in dendrite suppression, this work aims to provide valuable insights to advance the implementation of aqueous batteries incorporating polymer hydrogels.

Crosslinking substrate regulates frictional properties of tissue-engineered cartilage and chondrocyte response to loading

Hydrogels are frequently used in regenerative medicine due to their hydrated, tissue-compatible nature, and tuneable mechanics. While many strategies enable bulk mechanical modulation, little attention is given to tuning surface tribology, and its impact on cellular behavior under mechanical stimuli. Here, we demonstrate that photocrosslinking hydrogels on hydrophobic substrates leads to significant, long-lasting reductions in surface friction, ideal for cartilage tissue regeneration. Gelatin methacryloyl and hyaluronic acid methacrylate hydrogels photocrosslinked on polytetrafluoroethylene possess more hydrated, lubricious surfaces, with lower friction coefficients and crosslinking densities than those crosslinked on glass. This facilitated self-lubrication via water exudation, limiting shear during biaxial stimulation. When subject to intermittent biaxial loading mimicking joint movement, low-friction chondrocyte-laden neo-tissues formed superior hyaline cartilage, confirming the benefits of reduced friction on tissue development. Finally, in situ photocrosslinking enabled precise hydrogel formation in a full-thickness cartilage defect, highlighting the clinical potential and emphasizing the importance of crosslinking substrate in regenerative medicine.

Novel Buccal Xanthan Gum-Hyaluronic Acid Eutectogels with Dual Anti-Inflammatory and Antimicrobial Properties

Buccal drug delivery systems often struggle with poor drug solubility, limited adhesion, and rapid clearance, leading to suboptimal therapeutic outcomes. To address these limitations, we developed a novel hybrid eutectogel composed of xanthan gum (XTG), hyaluronic acid (HA), and a Natural Deep Eutectic Solvent (NADES) system (choline chloride, sorbitol, and glycerol in 2:1:1 mole ratio), incorporating 2.5% ibuprofen (IBU) as a model drug. The formulation was optimized using a face-centered central composite design to enhance the rheological, textural, and drug release properties. The optimized eutectogels exhibited shear-thinning behavior (flow behavior index, n = 0.26 ± 0.01), high mucoadhesion (adhesiveness: 2.297 ± 0.142 N·s), and sustained drug release over 24 h, governed by Higuchi kinetics (release rate: 237.34 ± 13.61 μg/cm2/min1/2). The ex vivo residence time increased substantially with NADES incorporation, reaching up to 176.7 ± 23.1 min. An in vivo anti-inflammatory evaluation showed that the eutectogel reduced λ-carrageenan-induced paw edema within 1 h and that its efficacy was sustained in the kaolin model up to 24 h (p < 0.05), achieving comparable efficacy to a commercial 5% IBU gel, despite a lower drug concentration. Additionally, the eutectogel presented a minimum inhibitory concentration for Gram-positive bacteria of 25 mg/mL, and through direct contact, it reduced microbial viability by up to 100%. Its efficacy against Bacillus cereus, Enterococcus faecium, and Klebsiella pneumoniae, combined with its significant anti-inflammatory properties, positions the NADES-based eutectogel as a promising multifunctional platform for buccal drug delivery, particularly for inflammatory conditions complicated by bacterial infections.

Tamarind seed gum-based hydrogel for the targeted delivery of imidazobenzothiazole sulfonamide derivative as an anticancer agent

The current investigation intended to assess the controlled delivery of 7-sulfonamide-2-(4-methylphenyl) imidazo[2,1-b] [1, 3] benzothiazole an anticancer agent (ACA) by tamarind seed gum-based hydrogel; for its potential activity against hepatocellular carcinoma. The FTIR spectra, SEM, 13C NMR, PXRD, and TGA analyses evidenced the successful loading of ACA into the hydrogel system. The rheological testing conveyed the increase in the elastic nature of ACA-loaded hydrogel helping in an effective release. In-vitro delivery of ACA from the hydrogel matrix was maximum at pH 5.5 with controlled and prolonged release of 98.93 ± 1 % over 1680 min. The ACA-release kinetics was well-fitted to the Hill equation model (R2 = 0.9925), leading to a non-Fickian diffusion process (n = 0.5217). The tamarind seed gum-based hydrogel as a potential matrix for the oral administration of the ACA at hepatocellular carcinoma was envisaged and acute oral toxicity assessment on the Drosophila Melanogaster model indicated a high safety profile in-vivo. The ACA-loaded TG-g-poly (AMPS) system showed an enhanced anticancer activity with an IC50 value of 37.27 μg/mL than the ACA (IC50 = 44.75 μg/mL). Studies on the ACA-loaded hydrogel's ability to induce apoptosis in hepatocellular carcinoma cells further supported its anticancer effectiveness in-vitro.

Controlling the drug delivery efficiency of chitosan-based systems through silver nanoparticles and oxygen plasma

Today, curcumin's therapeutic properties are used in drug delivery systems. In this work, chitosan (CS) /Montmorillonite (MMT) hydrogels were synthesized to improve the performance of curcumin molecules. According to the results, drug release characteristics of CS/MMT/curcumin highly depend on the pH of the environment and properties of Ag nanoparticles. Moreover, curcumin and Ag nanoparticles were placed under the influence of oxygen plasma. Our results indicate that oxygen plasma, as a simple, clean, and environment-friendly method, can be used as an effective method for controlling the efficiency of drug release and antibacterial characteristics of curcumin molecules in hydrogels. In this case, by increasing the exposure time of the samples under the influence of oxygen plasma, their antibacterial properties and drug release efficiency are significantly enhanced.

Phytochemical screening of an essential oil-loaded PVA/GA hydrogel membrane for potential wound healing application

The global concern over microbial resistance, particularly the emergence of antibiotic resistance, underscores the imperative for novel antimicrobial strategies. Plant essential oils and biopolymers offer promising alternatives to conventional drugs for bacterial and fungal infections. The objective was to achieve optimized antibacterial activity and to identify the phytochemical component of the essential oil. The essential oils passed the screening confirmed by Gas chromatography-mass spectrometry (GC-MS) analysis. The synthesized hydrogel was prepared by freeze drying polyvinyl alcohol (PVA)/gum Arabic (GA) with the addition of a crosslinker. The Essential oils compounds' antimicrobial effectiveness was confirmed using Fourier-transform infrared spectroscopy (FTIR) analysis upon their integration into the hydrogel membrane. Furthermore, scanning electron microscope (SEM) analysis was performed to investigate the morphological structure of the hydrogel membranes, and the results indicated that the material was successfully loaded. The antibacterial efficacy was evaluated against two gram positive and gram-negative bacteria strain. The best results of the antibacterial study for the synthesized hydrogels were obtained with the addition of 0.2 mL of Schinus Molle Essential Oil (SMEO) to the polyvinyl alcohol (PVA)/gum Arabic (GA) hydrogels of Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis), which were 10.2±0.2 mm and 9.3 ± 0.3 mm, respectively, while those of 0.4 mL were 8.2 ±0.2 mm and 8.2±0.3mm, respectively. Additionally, with 0.2 mL of Schinus Molle Essential Oil (SMEOs), the moisture retention capacity (MRC) and water vapor transmission rate (WVTR) were 93.12 % and 32.73 g/m2h, respectively. The results of this research study suggested that the phytochemical component of the essential oil and the synthesized hydrogel membrane exhibit greater antibacterial activity and physical features, making it suitable for potential use in wound healing and various biomedical applications.

Terahertz time-domain transmission spectroscopy of water and hydrogel thin films: Extraction of optical parameters and application to agarose gel characterization

Terahertz time-domain spectroscopy (THz-TDS) is an emerging optical technique that has potential applications in the characterization of (bio)materials. However, the complicated extraction of optical parameters from multi-layered and optically thin samples is a barrier towards its acceptance by applied scientists. Therefore, the aim of this work is to provide a straightforward approach for the extraction of the THz absorption coefficient and index of refraction profiles of aqueous thin films in a window-sample-window configuration, which is ubiquitous in many laboratories (i.e., sample in a cuvette). A numerical approach-based methodology that accounts for multiple layers, Fabry-Pérot effect, and sample thickness is elaborated which involves an optical interference model based on a tri-layer structure and a simple thickness estimation technique. This method was validated on water samples where a good agreement was found with the THz optical parameters of water reported in the literature, while the use of a commercial software resulted in erroneous optical parameters estimates when used without due regard to its limitations. A case study was then performed to demonstrate the ability of the proposed method to characterize agarose hydrogels with varying degree of sulfation. It was demonstrated that THz-TDS can provide insight into the hydration state of the agarose hydrogels, including the relative number of the hydrogen bonds between the hydroxyl moieties of water and the polysaccharide network which is perturbed by the presence of sulfate. The trend in the index of refraction profiles suggested microstructural differences between the agarose hydrogels, which were confirmed by visualizing the agarose network morphology using cryo-SEM imaging.

Highly sensitive and structure stable polyvinyl alcohol hydrogel sensor with tailored free water fraction and multiple networks by reinforcement of conductive nanocellulose

The wearable composite hydrogel sensors with high stretchability have attracted much attention in recent years, while the traditional hydrogels have weak molecular (chain) interaction and contain a lot of free water, leading to poor mechanical properties, unstable environmental tolerance and sensing ability. Herein, a novel ice crystal extrusion-crosslinking strategy is used to obtain polyvinyl alcohol (PVA) hydrogel with conductive nanocellulose-poly (3,4-ethylenedioxythiophene) (CNC-PEDOT) as skeleton network, sodium alginate (SA) and Ca2+ as tough segment of multi-bonding network. This strategy synergistically enhanced the interaction of hydrogen bonds and calcium (Ca2+) ion chelation within the hydrogel, building highly sensitive and stable multiple tough-elastic networks. Therefore, the optimal hydrogel sensor (PVA/SA-CP45) shows good structural stability, robust mechanical performance, excellent compress (Sensitivity = 68.7), stretching sensitivity (Gauge factor = 4.16), ultra-wide application range (-105-60 °C), fast response/relaxation time and outstanding dynamic durability with 6000 stretching-releasing cycles. Especially, it can give good sensing performance for omnidirectional monitoring of human motion and weak signals. Moreover, it was also designed into multifunctional sensing systems for gait guidance of model training and real-time monitoring ammonia gas for food preservation and public environmental safety, demonstrating great potential in flexible sensors devices for health monitoring.

Hydration effect and molecular geometry conformation as critical factors affecting the longevity stability of G4-structure-based supramolecular hydrogels

Nucleoside-derived supramolecular hydrogels based on G4-structures have been extensively developed in the biomedical sector and recognized for superior excellent biocompatibility and biodegradability. However, limited longevity and stability present a significant challenge. Chemical modifications in the molecular structure have been shown to enhance the longevity stability of G4-structure-based supramolecular hydrogels, but the precise way in which the molecular structure impacts the stability of the G4-structures and consequently affects the properties of the hydrogel remains to be elucidated. This issue represents a notable challenge in the field, which restricts their further applications to some extent. In this study, single crystals of Gd, αGd and αGd* were cultivated and compared with G. Notably, before this study, the single crystal structures of all natural nucleosides, with the exception of Gd, had been determined. The investigation into the molecular structure and supramolecular self-assembly properties of four guanosine analogs at the atomic scale revealed that the formation of G-quartets is critical for their ability to form hydrogels. The stability of the sugar ring geometry conformation (an intrinsic factor) and the disorder and strength of the hydration effect (extrinsic factors) are vital for maintaining the stability of the G4-structures. The rapid cooling changes the molecular geometry conformation, and the organic solvent changes the hydration effect, which can improve the longevity stability of G4-structure-based supramolecular hydrogels instead of chemical modifications. Consequently, the lifespan of the hydrogels was extended from 2 h to over one week. This advancement is expected to offer significant insights for future research in designing and developing G4-structure-based supramolecular hydrogels.

Zwitterionic cellulose nanofibers-based hydrogels with high toughness, ionic conductivity, and healable capability in cryogenic environments

Extreme environmental conditions often lead to irreversible structural failure and functional degradation in hydrogels, limiting their service life and applicability. Achieving high toughness, self-healing, and ionic conductivity in cryogenic environments is vital to broaden their applications. Herein, we present a novel approach to simultaneously enhance the toughness, self-healing, and ionic conductivity of hydrogels, via inducing non-freezable water within the zwitterionic cellulose-based hydrogel skeleton. This approach enables resulting hydrogel to achieve an exceptional toughness of 10.8 MJ m-3, rapid self-healing capability (98.9 % in 30 min), and high ionic conductivity (2.9 S m-1), even when subjected to -40 °C, superior to the state-of-the-art hydrogels. Mechanism analyses reveal that a significant amount of non-freezable water with robust electrostatic interactions is formed within zwitterionic cellulose nanofibers-modified polyurethane molecular networks, imparting superior freezing tolerance and versatility to the hydrogel. Importantly, this strategy harnesses the non-freezable water molecular state of the zwitterionic cellulose nanofibers network, eliminating the need for additional antifreeze and organic solvents. Furthermore, the dynamic Zn coordination within these supramolecular molecule chains enhances interfacial interactions, thereby promoting rapid subzero self-healing and exceptional mechanical strength. Demonstrating its potential, this hydrogel can be used in smart laminated materials, such as aircraft windshields.

A Review of Whey Protein-Based Bioactive Delivery Systems: Design, Fabrication, and Application

The efficacy of many edible bioactive agents is limited by their low water dispersibility and chemical instability in foods, as well as by their poor bioaccessibility, low absorption, and metabolism within the human gastrointestinal tract. Whey proteins are amphiphilic molecules that can be used to construct a variety of edible carrier systems that can improve the performance of bioactive ingredients. These carrier systems are being used by the food and biomedical industries to encapsulate, protect, and deliver a variety of bioactive agents. In this article, we begin by providing an overview of the molecular and functional characteristics of whey proteins, and then discuss their interactions with various kinds of bioactive agents. The ability of whey proteins to be used as building blocks to assemble different kinds of carrier systems is then discussed, including nanoparticles, hydrogels, oleogels, bigels, nanofibers, nanotubes, and nanoemulsions. Moreover, applications of these carrier systems are highlighted. Different kinds of whey protein-based carriers can be used to encapsulate, protect, and deliver bioactive agents. Each kind of carrier has its own characteristics, which make them suitable for different application needs in foods and other products. Previous studies suggest that whey protein-based carriers are particularly suitable for protecting chemically labile bioactive agents and for prolonging their release profiles. In the future, it is likely that the applications of whey protein-based carriers in the food and pharmaceutical fields will expand.

An investigation of water status in gelatin methacrylate hydrogels by means of water relaxometry and differential scanning calorimetry

The relationship between molecular structure and water dynamics is a fundamental yet often neglected subject in the field of hydrogels for drug delivery, bioprinting, as well as biomaterial science and tissue engineering & regenerative medicine (TE&RM). Water is a fundamental constituent of hydrogel systems and engages via hydrogen bonding with the macromolecular network. The methods and techniques to measure and reveal the phenomena and dynamics of water within hydrogels are still limited. In this work, differential scanning calorimetry (DSC) was used as a quantitative method to analyze freezable (including free and freezable bound) and non-freezable bound water within gelatin methacrylate (GelMA) hydrogels. Nuclear magnetic resonance (NMR) is a complementary method for the study of water behavior and can be used to measure the spin-relaxation of water hydrogen nuclei, which is related to water dynamics. In this research, nuclear magnetic resonance relaxometry was employed to investigate the molecular state of water in GelMA hydrogels using spin-lattice (T1) and spin-spin (T2) spin-relaxation time constants. The data displays a trend of increasing bound water content with increasing GelMA concentration. In addition, T2 values were further applied to calculate microviscosity and translational diffusion coefficients. Water relaxation under various chemical environments, including different media, temperatures, gelatin sources, as well as crosslinking effects, were also examined. These comprehensive physical data sets offer fundamental insight into biomolecule transport within the GelMA hydrogel system, which ultimately are important for drug delivery, bioprinting, as well as biomaterial science and TE&RM communities.

Entangled Mesh Hydrogels with Macroporous Topologies via Cryogelation for Rapid Atmospheric Water Harvesting

Sorption-based atmospheric water harvesting (SAWH) is a promising technology to alleviate freshwater scarcity. Recently, hygroscopic salt-hydrogel composites (HSHCs) have emerged as attractive candidates with their high water uptake, versatile designability, and scale-up fabrication. However, achieving high-performance SAWH applications for HSHCs has been challenging because of their sluggish kinetics, attributed to their limited mass transport properties. Herein, a universal network engineering of hydrogels using a cryogelation method is presented, significantly improving the SAWH kinetics of HSHCs. As a result of the entangled mesh confinements formed during cryogelation, a stable macroporous topology is attained and maintained within the obtained entangled-mesh hydrogels (EMHs), leading to significantly enhanced mass transport properties compared to conventional dense hydrogels (CDHs). With it, corresponding hygroscopic EMHs (HEMHs) simultaneously exhibit faster moisture sorption and solar-driven water desorption. Consequently, a rapid-cycling HEMHs-based harvester delivers a practical freshwater production of 2.85 Lwater kgsorbents -1 day-1 via continuous eight sorption/desorption cycles, outperforming other state-of-the-art hydrogel-based sorbents. Significantly, the generalizability of this strategy is validated by extending it to other hydrogels used in HSHCs. Overall, this work offers a new approach to efficiently address long-standing challenges of sluggish kinetics in current HSHCs, promoting them toward the next-generation SAWH applications.

3D Printed Hydrogel Sensor for Rapid Colorimetric Detection of Salivary pH

Salivary pH is one of the crucial biomarkers used for non-invasive diagnosis of intraoral diseases, as well as general health conditions. However, standard pH sensors are usually too bulky, expensive, and impractical for routine use outside laboratory settings. Herein, a miniature hydrogel sensor, which enables quick and simple colorimetric detection of pH level, is shown. The sensor structure was manufactured from non-toxic hydrogel ink and patterned in the form of a matrix with 5 mm × 5 mm × 1 mm individual sensing pads using a 3D printing technique (bioplotting). The authors' ink composition, which contains sodium alginate, polyvinylpyrrolidone, and bromothymol blue indicator, enables repeatable and stable color response to different pH levels. The developed analysis software with an easy-to-use graphical user interface extracts the R(ed), G(reen), and B(lue) components of the color image of the hydrogel pads, and evaluates the pH value in a second. A calibration curve used for the analysis was obtained in a pH range of 3.5 to 9.0 using a laboratory pH meter as a reference. Validation of the sensor was performed on samples of artificial saliva for medical use and its mixtures with beverages of different pH values (lemon juice, coffee, black and green tea, bottled and tap water), and correct responses to acidic and alkaline solutions were observed. The matrix of square sensing pads used in this study provided multiple parallel responses for parametric tests, but the applied 3D printing method and ink composition enable easy adjustment of the shape of the sensing layer to other desired patterns and sizes. Additional mechanical tests of the hydrogel layers confirmed the relatively high quality and durability of the sensor structure. The solution presented here, comprising 3D printed hydrogel sensor pads, simple colorimetric detection, and graphical software for signal processing, opens the way to development of miniature and biocompatible diagnostic devices in the form of flexible, wearable, or intraoral sensors for prospective application in personalized medicine and point-of-care diagnosis.

Recent advances in hydrogels applications for tissue engineering and clinical trials

Hydrogels are biomolecules made of artificial and natural polymers. Their quasi-three-dimensional structure has created unique features. They are very hydrophilic, and in addition to the high inflation rate, they also have excellent water maintenance capacity, biodegradability, biocompatibility, and strong mechanical properties. These properties are used in many tissue engineering applications. All these features have made these scaffolds widely used as attractive structures in the world of tissue engineering and regeneration medicine. In addition to research, scaffolds entered the field of medicine and are expected to play a significant role in the repair of many tissues in the future. This study aims to review the various polymers involved in hydrogel fabrication and their application in the repair of diverse tissues and clinical trials.

Comparative Analysis of Irrigation Techniques for Cleaning Efficiency in Isthmus Structures

INTRODUCTION

This study aimed to evaluate the removal of a biofilm-mimicking hydrogel from isthmus structures in a simulated complex root canal system consisting of 2 curved root canals by Laser-activated irrigation (LAI, AdvErl Evo, Morita) and mechanical activation techniques.

METHODS

A 3D-printed root canal model with 2 parallel root canals (60°-curvature, radius 5 mm, dimension 25/.06) with a total length of 20 mm connected via isthmuses (2.5 × 0.4 × 0.2 mm) at 5 mm and 8 mm from the apical endpoint and with lateral canals (diameter 0.2 mm) in all directions at 2, 5, and 8 mm from the apex was filled with a colored biofilm-mimicking hydrogel. Irrigation protocols under continuous irrigation with distilled water (3 × 20s per root canal; 3 ml/20s; n = 20) included conventional needle irrigation (=NI); manual agitation (=MA, gutta-percha point 25/.06); EndoActivator (=SAI-EA, 25/.04); EDDY (=SAI-E, 25/.04); ultrasonically-activated irrigation (=UAI) and LAI (Er:YAG-laser; P400FL tip at canal entrance; 25pps, 50 mJ, 300μs). Removal of the hydrogel was determined as a percentage via standardized photos through a microscope. Statistical analysis was performed using Kruskal-Wallis and Conover tests (P = .05).

RESULTS

Laser-activated irrigation (LAI) was associated with the greatest removal of hydrogel from the entire root canal system (P < .05), followed by SAI-E. No significant differences were reported for the coronal isthmus between LAI, SAI-E, NI, and MA (P > .05), but inferior results for SAI-EA and UAI (P < .05). In the apical isthmus, all techniques outperformed UAI (P < .05), with LAI, SAI-E, and NI showing the best results (P < .05).

CONCLUSIONS

Laser-activated irrigation (LAI) was superior to other irrigation techniques in the entire root canal system. SAI-E and NI performed comparable to LAI in the isthmuses.

Exploring the Model of Cefazolin Released from Jellyfish Gelatin-Based Hydrogels as Affected by Glutaraldehyde

Due to its excellent biocompatibility and ease of biodegradation, jellyfish gelatin has gained attention as a hydrogel. However, hydrogel produced from jellyfish gelatin has not yet been sufficiently characterized. Therefore, this research aims to produce a jellyfish gelatin-based hydrogel. The gelatin produced from desalted jellyfish by-products varied with the part of the specimen and extraction time. Hydrogels with gelatin: glutaraldehyde ratios of 10:0.25, 10:0.50, and 10:1.00 (v/v) were characterized, and their cefazolin release ability was determined. The optimal conditions for gelatin extraction and chosen for the development of jellyfish hydrogels (JGel) included the use of the umbrella part of desalted jellyfish by-products extracted for 24 h (WU24), which yielded the highest gel strength (460.02 g), viscosity (24.45 cP), gelling temperature (12.70 °C), and melting temperature (22.48 °C). The quantities of collagen alpha-1(XXVIII) chain A, collagen alpha-1(XXI) chain, and collagen alpha-2(IX) chain in WU24 may influence its gel properties. Increasing the glutaraldehyde content in JGel increased the gel fraction by decreasing the space between the protein chains and gel swelling, as glutaraldehyde binds with lateral amino acid residues and produces a stronger network. At 8 h, more than 80% of the cefazolin in JGel (10:0.25) was released, which was higher than that released from bovine hydrogel (52.81%) and fish hydrogel (54.04%). This research is the first report focused on the production of JGel using glutaraldehyde as a cross-linking agent.

Influence of pulse energy, tip design and insertion depth during Er:YAG-activated irrigation on cleaning efficacy in simulated severely curved complex root canal systems in vitro

AIM

To investigate the influence of pulse energy, tip geometry and tip position in simulated 3D-printed root canals with multiple side canals at different levels in all directions on the cleaning performance of laser-activated irrigation (LAI) compared to sonic activation (EDDY) and conventional needle irrigation (NI).

METHODOLOGY

3D-printed root canal models (25/.06, length 20 mm, curvature 60°, radius 5 mm) with side canals (diameter 0.2 mm) at 2, 5 and 8 mm from the apex were filled with coloured biofilm-mimicking hydrogel. LAI (Morita AdvErL Evo, Kyoto, Japan) was performed with six settings (n = 20; pulse-energy, pulses per second [PPS], tip position): LAI1 (50 mJ, 25 PPS, P400FL, canal entrance [CE]), LAI2 (same as LAI1, but insertion depth 9 mm before the apical endpoint [AE] [corresponding to 1 mm above the first lateral canals]), LAI3 (80 mJ, 25 PPS, P400FL, 9 mm before AE), LAI4 (same as LAI 3, but at CE) for 3 × 20 s each, LAI5 (50 mJ, 25 PPS, P400FL 2 × 20 s, CE & R200T (30 mJ, 25 PPS, 1 × 20 s, 9 mm before AE), LAI6 (30 mJ, 25 PPS, R200T, 9 mm before AE, 3 × 20 s). A continuous irrigation (3 mL/20 s) using distilled water accompanied the irrigation cycles. NI and EDDY (3 × 20 s each; 3 mL/20 s irrigation, insertion AE minus 1 mm, amplitude 4 mm) served as control groups. Biofilm-mimicking hydrogel removal (ImageJ, NIH) was assessed for the entire system, the central canal and the lateral canals using standardized photographs with a microscope (Expert DN, Müller-Optronic) and statistically analysed was performed using Kruskal-Wallis and Dunn tests (p = .05). Irrigant extrusion beyond the foramina was also recorded.

RESULTS

LAI2 (99.08%; interquartile range [IQR]: 96.85-100.00) and LAI3 (97.50%; 96.24-100.00) achieved the significantly best and LAI6 (80.08%; 73.41-84.69) the significantly worst removal of hydrogel from the entire root canal system amongst all LAI configurations (p < .05). There were no significant differences between LAI6, EDDY (72.89%; 67.49-76.22) and manual irrigation (54.39%; 51.01-56.94) (p > .05). R200T laser tip caused significantly more often irrigant extrusion than all other techniques (p < .05).

CONCLUSION

Tip design, energy settings, and the positioning of the laser tip below the canal entrance caused an improvement in cleaning performance of the LAI. However, the small R200T tip created significantly more procedural errors (irrigant extrusion) due to higher concentrated energy.

Cleaning Efficiency of Different Irrigation Techniques in Simulated Severely Curved Complex Root Canal Systems

INTRODUCTION

To compare the biofilm-mimicking hydrogel removal efficiency of laser-activated irrigation (LAI) with five other irrigation techniques in simulated curved root canals with lateral canals.

METHODS

Three-dimensional-printed root canal models (60°-curvature, radius 5 mm; dimension 25/.06) with a total length of 20 mm and lateral canals in all directions at 2, 5, and 8 mm (diameter 0.2 mm) from the apex were filled with a colored biofilm-mimicking hydrogel. The following protocols (each 3 × 20 seconds continuous irrigation with distilled water 3 ml/20 seconds; n = 20) were carried out: conventional needle irrigation; manual agitation ([MA], gutta-percha point 25/.06); EndoActivator (=sonically-activated irrigation EndoActivator, 25/.04); EDDY (=sonically-activated irrigation EDDY [SAI-E]; 25/.04); ultrasonically-activated irrigation and LAI (Erbium-doped Yttrium Aluminum Garnet laser; P400FL tip at canal entrance; 25 pps, 50 mJ, 300 μs). Standardized photos were taken with a microscope and the removal of the hydrogel was determined as a percentage for the entire system, the main canal and the lateral canals. Statistical analysis was performed using analysis of variance and Scheffé test (P = .05).

RESULTS

LAI (89.3% ± 5.9%) showed the greatest hydrogel removal followed by SAI-E (65.5% ± 3.3%) and ultrasonically-activated irrigation (59.1% ± 4.7%), with significant differences between these groups (P < .05). Needle irrigation, MA, and sonically-activated irrigation EndoActivator performed equally (P > .05) and obtained the significantly lowest values (P < .05). LAI and SAI-E showed the significantly best hydrogel removal from the main canal (P < .05). At all three levels, LAI removed significantly more hydrogel from the lateral canals than all other techniques (P < .05).

CONCLUSIONS

LAI was superior to other techniques in both the entire system and the lateral canals in removing the hydrogel. SAI-E achieved comparable results in the main canal.

Dual-drug (Curcumin/Ciprofloxacin) loading and release from chitosan-based hydrogels embedded with magnetic Montmorillonite/Hyaluronic acid for enhancing wound healing

Montmorillonite (MMt) is extensively applied as an efficient drug-carrier in designing drug delivery systems (DDS) due to its high specific surface area to load drugs. Modification of MMt via iron (Fe) blending can thus be a desirable method to improve its biocompatibility. Herein, magnetic nano-carriers involving the magnetic MMt (mMMt) core surrounded by chitosan (Chito) as a biopolymer and hyaluronic acid (HA) were prepared. To coat the mMMt fabricated through the coprecipitation of the Fe3+/Fe2+ ions in the presence of MMt, the acquired mMMt as the core was then treated with the Chito/HA solution to induce the cross-linked Chito/HA as the shell (namely, the Chito/HA-mMMt). The transmission electron microscopy (TEM) results accordingly revealed the existence of the mMMt inside the Chito/HA solution. Curcumin (CUR) and ciprofloxacin (CIP) were further employed as two model drugs. The CUR and CIP release from the Chito/HA-mMMt subsequently occurred in a sustained manner and pH-dependently. Additionally, an upsurge in the CUR and CIP release by applying an external magnetic field was observed. Thus, the prepared Chito/HA-mMMt hydrogels promise an outstanding potential performance in terms of expanding novel pH-dependent DDS with a sustained release behavior. The scratch assay of the given hydrogels also confirms their applications for wound healing.

Electrochemical Wearable Biosensors and Bioelectronic Devices Based on Hydrogels: Mechanical Properties and Electrochemical Behavior

Hydrogel-based wearable electrochemical biosensors (HWEBs) are emerging biomedical devices that have recently received immense interest. The exceptional properties of HWEBs include excellent biocompatibility with hydrophilic nature, high porosity, tailorable permeability, the capability of reliable and accurate detection of disease biomarkers, suitable device-human interface, facile adjustability, and stimuli responsive to the nanofiller materials. Although the biomimetic three-dimensional hydrogels can immobilize bioreceptors, such as enzymes and aptamers, without any loss in their activities. However, most HWEBs suffer from low mechanical strength and electrical conductivity. Many studies have been performed on emerging electroactive nanofillers, including biomacromolecules, carbon-based materials, and inorganic and organic nanomaterials, to tackle these issues. Non-conductive hydrogels and even conductive hydrogels may be modified by nanofillers, as well as redox species. All these modifications have led to the design and development of efficient nanocomposites as electrochemical biosensors. In this review, both conductive-based and non-conductive-based hydrogels derived from natural and synthetic polymers are systematically reviewed. The main synthesis methods and characterization techniques are addressed. The mechanical properties and electrochemical behavior of HWEBs are discussed in detail. Finally, the prospects and potential applications of HWEBs in biosensing, healthcare monitoring, and clinical diagnostics are highlighted.

Evaluation of Poly(vinyl alcohol)-Xanthan Gum Hydrogels Loaded with Neomycin Sulfate as Systems for Drug Delivery

In recent years, multidrug-resistant bacteria have developed the ability to resist multiple antibiotics, limiting the available options for effective treatment. Raising awareness and providing education on the appropriate use of antibiotics, as well as improving infection control measures in healthcare facilities, are crucial steps to address the healthcare crisis. Further, innovative approaches must be adopted to develop novel drug delivery systems using polymeric matrices as carriers and support to efficiently combat such multidrug-resistant bacteria and thus promote wound healing. In this context, the current work describes the use of two biocompatible and non-toxic polymers, poly(vinyl alcohol) (PVA) and xanthan gum (XG), to achieve hydrogel networks through cross-linking by oxalic acid following the freezing/thawing procedure. PVA/XG-80/20 hydrogels were loaded with different quantities of neomycin sulfate to create promising low-class topical antibacterial formulations with enhanced antimicrobial effects. The inclusion of neomycin sulfate in the hydrogels is intended to impart them with powerful antimicrobial properties, thereby facilitating the development of exceptionally efficient topical antibacterial formulations. Thus, incorporating higher quantities of neomycin sulfate in the PVA/XG-80/20-2 and PVA/XG-80/20-3 formulations yielded promising cycling characteristics. These formulations exhibited outstanding removal efficiency, exceeding 80% even after five cycles, indicating remarkable and consistent adsorption performance with repeated use. Furthermore, both PVA/XG-80/20-2 and PVA/XG-80/20-3 formulations outperformed the drug-free sample, PVA/XG-80/20, demonstrating a significant enhancement in maximum compressive stress.

3D bio-printed hydrogel inks promoting lung cancer cell growth in a lab-on-chip culturing platform

The results of a lab-on-chip (LOC) platform fabrication equipped with a hydrogel matrix is reported. A 3D printing technique was used to provide a hybrid, "sandwiched" type structure, including two microfluidic substrates of different origins. Special attention was paid to achieving uniformly bio-printed microfluidic hydrogel layers of a unique composition. Six different hydrogel inks were proposed containing sodium alginate, agar, chitosan, gelatin, methylcellulose, deionized water, or 0.9% NaCl, varying in proportions. All of them exhibited appropriate mechanical properties showing, e.g., the value of elasticity modulus as similar to that of biological tissues, such as skin. Utilizing our biocompatible, entirely 3D bio-printed structure, for the first time, a multi-drug-resistant lung cancer cell line (H69AR) was cultured on-chip. Biological validation of the device was performed qualitatively and quantitatively utilizing LIVE/DEAD assays and Presto blue staining. Although all bio-inks exhibited acceptable cell viability, the best results were obtained for the hydrogel composition including 3% sodium alginate + 7% gelatin + 90% NaCl (0.9%), reaching approximately 127.2% after 24 h and 105.4% after 48 h compared to the control group (100%). Further research in this area will focus on the microfluidic culture of the chosen cancer cell line (H69AR) and the development of novel drug delivery strategies towards appropriate in vivo models for chemotherapy and polychemotherapy treatment.

Cellulose-Based Ionic Conductor: An Emerging Material toward Sustainable Devices

Ionic conductors (ICs) find widespread applications across different fields, such as smart electronic, ionotronic, sensor, biomedical, and energy harvesting/storage devices, and largely determine the function and performance of these devices. In the pursuit of developing ICs required for better performing and sustainable devices, cellulose appears as an attractive and promising building block due to its high abundance, renewability, striking mechanical strength, and other functional features. In this review, we provide a comprehensive summary regarding ICs fabricated from cellulose and cellulose-derived materials in terms of fundamental structural features of cellulose, the materials design and fabrication techniques for engineering, main properties and characterization, and diverse applications. Next, the potential of cellulose-based ICs to relieve the increasing concern about electronic waste within the frame of circularity and environmental sustainability and the future directions to be explored for advancing this field are discussed. Overall, we hope this review can provide a comprehensive summary and unique perspectives on the design and application of advanced cellulose-based ICs and thereby encourage the utilization of cellulosic materials toward sustainable devices.

Application of Hydrogels in the Device of Ophthalmic Iontophoresis: Theory, Developments and Perspectives

The human eye is a consolidated organ with delicate structures and unique immune privileges. Ocular diseases are intractable due to the intrinsic biological barriers within the eyeball. Hydrogels are excellent drug-carrying substances with soft material and excellent properties. They have been extensively used to deliver drugs into ocular tissue via iontophoresis devices. Ophthalmic iontophoresis is an electrochemical technique using tiny electrical currents to deliver drugs into the eye non-invasively. The early infantile iontophoresis technique often required long applying time to achieve therapeutic dose in the posterior ocular segment. The potential limitations in the initial drug concentration and the maximum safe currents would also impede the efficiency and safety of iontophoresis. Moreover, the poor patient compliance always leads to mechanical damage to the cornea and sclera during application. Advantageously, the flexible drug-carrying hydrogel can be in direct contact with the eye during iontophoresis, thereby reducing mechanical damage to the ocular surface. Moreover, the water absorption and adjustable permeability of hydrogels can reduce the electrochemical (EC) reactions and enhance the efficiency of iontophoresis. In this review, we focus on recent developments of hydrogels iontophoresis in ophthalmologic practice. Refinements of the knowledge would provide an outlook for future application of hydrogels in treating ocular disease.

Rapid Prototyping of 3D-Printed AgNPs- and Nano-TiO2-Embedded Hydrogels as Novel Devices with Multiresponsive Antimicrobial Capability in Wound Healing

Two antimicrobial agents such as silver nanoparticles (AgNPs) and titanium dioxide (TiO₂) have been formulated with natural polysaccharides (chitosan or alginate) to develop innovative inks for the rapid, customizable, and extremely accurate manufacturing of 3D-printed scaffolds useful as dressings in the treatment of infected skin wounds. Suitable chemical-physical properties for the applicability of these innovative devices were demonstrated through the evaluation of water content (88-93%), mechanical strength (Young's modulus 0.23-0.6 MPa), elasticity, and morphology. The antimicrobial tests performed against Staphylococcus aureus and Pseudomonas aeruginosa demonstrated the antimicrobial activities against Gram+ and Gram- bacteria of AgNPs and TiO₂ agents embedded in the chitosan (CH) or alginate (ALG) macroporous 3D hydrogels (AgNPs MIC starting from 5 µg/mL). The biocompatibility of chitosan was widely demonstrated using cell viability tests and was higher than that observed for alginate. Constructs containing AgNPs at 10 µg/mL concentration level did not significantly alter cell viability as well as the presence of titanium dioxide; cytotoxicity towards human fibroblasts was observed starting with an AgNPs concentration of 100 µg/mL. In conclusions, the 3D-printed dressings developed here are cheap, highly defined, easy to manufacture and further apply in personalized antimicrobial medicine applications.

High-Voltage and Stable Manganese Hexacyanoferrate/Zinc Batteries Using Gel Electrolytes

Because of the high safety and environmental friendliness, aqueous zinc-ion batteries have gained a lot of attention in recent years. Prussian blue and its analogues are regarded as a promising cathode material of zinc-ion batteries. Manganese hexacyanoferrate is appropriate among them due to its high operating voltage, large capacity, and cheap price. However, the poor cycling stability of manganese hexacyanoferrate, mainly caused by transition metal dissolution, side reaction, and phase transition, greatly restricts its practical application. In this work, gelatin is used to limit the content of free water in the electrolyte, thus reducing the dissolution effect of transition metal manganese. The introduction of gelatin improves the durability of the Zn anode as well. The optimized MnHCF/gel-0.3/Zn battery displays a high reversible capacity (120 mAh·g^-1 at 0.1 A·g^-1), an excellent rate performance (42.7 mAh·g^-1 at 2 A·g^-1), and a good capacity retention (65% at 0.5 A·g^-1 after 1000 cycles).

A Critical Review on Classified Excipient Sodium-Alginate-Based Hydrogels: Modification, Characterization, and Application in Soft Tissue Engineering

Alginates are polysaccharides that are produced naturally and can be isolated from brown sea algae and bacteria. Sodium alginate (SA) is utilized extensively in the field of biological soft tissue repair and regeneration owing to its low cost, high biological compatibility, and quick and moderate crosslinking. In addition to their high printability, SA hydrogels have found growing popularity in tissue engineering, particularly due to the advent of 3D bioprinting. There is a developing curiosity in tissue engineering with SA-based composite hydrogels and their potential for further improvement in terms of material modification, the molding process, and their application. This has resulted in numerous productive outcomes. The use of 3D scaffolds for growing cells and tissues in tissue engineering and 3D cell culture is an innovative technique for developing in vitro culture models that mimic the in vivo environment. Especially compared to in vivo models, in vitro models were more ethical and cost-effective, and they stimulate tissue growth. This article discusses the use of sodium alginate (SA) in tissue engineering, focusing on SA modification techniques and providing a comparative examination of the properties of several SA-based hydrogels. This review also covers hydrogel preparation techniques, and a catalogue of patents covering different hydrogel formulations is also discussed. Finally, SA-based hydrogel applications and future research areas concerning SA-based hydrogels in tissue engineering were examined.

Intrinsic Anti-Freezing and Unique Phosphorescence of Glassy Hydrogels with Ultrahigh Stiffness and Toughness at Low Temperatures

Most hydrogels become frozen at subzero temperatures, leading to degraded properties and limited applications. Cryoprotectants are massively employed to improve anti-freezing property of hydrogels; however, there are accompanied disadvantages, such as varied networks, reduced mechanical properties, and the risk of cryoprotectant leakage in aqueous conditions. Reported here is the glassy hydrogel having intrinsic anti-freezing capacity and excellent optical and mechanical properties at ultra-low temperatures. Supramolecular hydrogel of poly(acrylamide-co-methacrylic acid) with moderate water content (≈50 wt.%) and dense hydrogen-bond associations is in a glassy state at room temperature. Since hydrogen bonds become strengthened as the temperature decreases, this gel becomes stronger and stiffer, yet still ductile, with Young's modulus of 900 MPa, tensile strength of 30 MPa, and breaking strain of 35% at -45 °C. This gel retains high transparency even in liquid nitrogen. It also exhibits unique phosphorescence due to presence of carbonyl clusters, which is further enhanced at subzero temperatures. Further investigations elucidate that the intrinsic anti-freezing property is related to a fact that most water molecules are tightly bound and confined in the glassy matrix and become non-freezable. This correlation, as validated in several systems, provides a roadmap to develop intrinsic anti-freezing hydrogels for widespread applications at extreme conditions.

Monitoring of freezing patterns within 3D collagen-hydroxyapatite scaffolds using infrared thermography

The importance of cryopreservation in tissue engineering is unceasingly increasing. Preparation, cryopreservation, and storage of tissue-engineered constructs (TECs) at an on-site location offer a convenient way for their clinical application and commercialization. Partial freezing initiated at high sub-zero temperatures using ice-nucleating agents (INAs) has recently been applied in organ cryopreservation. It is anticipated that this freezing technique may be efficient for the preservation of both scaffold mechanical properties and cell viability of TECs. Infrared thermography is an instrumental method to monitor INAs-mediated freezing of various biological entities. In this paper, porous collagen-hydroxyapatite (HAP) scaffolds were fabricated and characterized as model TECs, whereas infrared thermography was proposed as a method for monitoring the crystallization-related events on their partial freezing down to -25 °C. Intra- and interscaffold latent heat transmission were descriptively evaluated. Nucleation, freezing points as well as the degree of supercooling and duration of crystallization were calculated based on inspection of respective thermographic curves. Special consideration was given to the cryoprotective agent (CPA) composition (Snomax®, crude leaf extract from Hippophae rhamnoides, dimethyl sulfoxide (Me₂SO) and recombinant type-III antifreeze protein (AFP)) and freezing conditions ('in air' or 'in bulk CPA'). For CPAs without ice nucleation activity, thermographic measurements demonstrated that the supercooling was significantly milder in the case of scaffolds present in a CPA solution compared to that without them. This parameter (ΔT, °C) altered with the following tendency: 10 Me₂SO (2.90 ± 0.54 ('in air') vs. 7.71 ± 0.43 ('in bulk CPA', P < 0.0001)) and recombinant type-III AFP, 0.5 mg/ml (2.65 ± 0.59 ('in air') vs. 7.68 ± 0.34 ('in bulk CPA', P < 0.0001)). At the same time, in CPA solutions with ice nucleation activity the least degree of supercooling and the longest crystallization duration (Δt, min) for scaffolds frozen 'in air' were documented for crude leaf homogenate (CLH) from Hippophae rhamnoides (1.57 ± 0.37 °C and 21.86 ± 2.93 min compared to Snomax, 5 μg/ml (2.14 ± 0.33 °C and 23.09 ± 0.05), respectively). The paper offers evidence that infrared thermography provides insightful information for monitoring partial freezing events in TECs when using different freezing containers, CPAs and conditions. This may further TEC-specific cryopreservation and optimization of CPA compositions with slow-nucleating properties.

Poly(vinyl alcohol)/sodium alginate/magnetite composites: magnetic force microscopy for tracking magnetic domains

Hydrogels of poly(vinyl alcohol) (PVA)/sodium alginate (SA), and magnetic nanoparticles (MNPs) were prepared by solvent casting in the absence and in the presence of magnets, in order to obtain MNPs distributed randomly (PVA/SA-rMNP) and magnetically oriented MNPs (PVA/SA-gMNP) in the polymer matrix. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques were used to evaluate the topography and to map the distribution of magnetic domains in the polymer matrix, respectively. The tip-surface distance (lift distance) of 50 nm during the MFM analyses facilitated the mapping of magnetic domains because the van der Waals forces were minimized. The magnetic signal stemming from clusters of MNPs were more easily identified than that from isolated MNPs. PVA and SA, PVA/SA, PVA/SA-rMNP, and PVA/SA-gMNP coatings with surface roughness (R_a) values of 3.8 nm, 28.7 nm, and 49.8 nm, respectively, were tested for the proliferation of mouse hippocampal HT-22 cells. While PVA/SA, PVA/SA-rMNP, and PVA/SA-gMNP coatings preserved cell viability >70% in comparison to the control (plastic plate) over 48 h, cell proliferation tended to decrease on surfaces with higher R_a values (PVA/SA-gMNP). These findings showed that the orientation of magnetic domains led to an increase of surface roughness, which decreased the viability of HT-22 cells. Thus, these results might be interesting for situations, where the control of cell proliferation is necessary.

Exploring the microstructure of hydrated collagen hydrogels under scanning electron microscopy

Collagen hydrogels are a rapidly expanding platform in bioengineering and soft materials engineering for novel applications focused on medical therapeutics, medical devices and biosensors. Observations linking microstructure to material properties and function enables rational design strategies to control this space. Visualisation of the microscale organisation of these soft hydrated materials presents unique technical challenges due to the relationship between hydration and the molecular organisation of a collagen gel. Scanning electron microscopy is a robust tool widely employed to visualise and explore materials on the microscale. However, investigation of collagen gel microstructure is difficult without imparting structural changes during preparation and/or observation. Electrons are poorly propagated within liquid-phase materials, limiting the ability of electron microscopy to interrogate hydrated gels. Sample preparation techniques to remove water induce artefactual changes in material microstructure particularly in complex materials such as collagen, highlighting a critical need to develop robust material handling protocols for the imaging of collagen hydrogels. Here a collagen hydrogel is fabricated, and the gel state explored under high-vacuum (10^-6  Pa) and low-vacuum (80-120 Pa) conditions, and in an environmental SEM chamber. Visualisation of collagen fibres is found to be dependent on the degree of sample hydration, with higher imaging chamber pressures and humidity resulting in decreased feature fidelity. Reduction of imaging chamber pressure is used to induce evaporation of gel water content, revealing collagen fibres of significantly larger diameter than observed in samples dehydrated prior to imaging. Rapid freezing and cryogenic handling of the gel material is found to retain a porous 3D structure following sublimation of the gel water content. Comparative analysis of collagen hydrogel materials demonstrates the care needed when preparing hydrogel samples for electron microscopy.

The production of pH indicator Ca and Cu alginate ((1,4)- β -d-mannuronic acid and α -l-guluronic acid) cryogels containing anthocyanin obtained via red cabbage extraction for monitoring chicken fillet freshness

In recent days, intelligent food packaging has gained attention due to consumers' needs and monitoring of the freshness of food. Biopolymers are used to produce matrix parts and dye chemicals, because of their unique properties, such as biodegradability and biocompatibility. In this study, alginate molecules and anthocyanins were used to produce to monitor chicken fillet freshness via pH response characteristics. Anthocyanins' color and UV characteristics at different pHs were investigated. The obtained anthocyanin solution showed visible color response at different pH level. In the red cabbage extract, the anthocyanin concentration was as 0.65 ± 0.03 mg/g. Alginate and extracted anthocyanins from red cabbage were mixed at the solution phase, then metal alginate hydrogels were synthesized via crosslinking Ca²⁺ and Cu²⁺ with alginate molecules. Due to the porous structure of the cryogels, hydrogels were freeze dried at -80 °C for 24 h at vacuum atmosphere. The obtained cryogel indicated significant color changes from pH 4 to pH 10, and at a basic environment, the color change was observed with the naked eye. The porosity amounts and sizes of the produced cryogels were examined, the average pore amount of cryogels was found to be 85.46 ± 4.36 %, and the average pore size 97.98 ± 26.20 μm. Furthermore, it was seen that the color change was not directly related to the porosity, but the interaction of anthocyanin and metal alginate matrix effected color changes degree of cryogels. Due to the electronegativity of Cu²⁺ ions, and the use of a low amount of anthocyanin was found to be more suitable for color change. The color was changed to blue-purple while total volatile basic nitrogen content increased to 46.67 mg/100 g from 14.00 mg/100 g. As a result, prepared cryogels should be a better candidates for use as a freshness indicator and intelligent packaging.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Hydrogels with electrically conductive nanomaterials for biomedical applications

Hydrogels, soft 3D materials of cross-linked hydrophilic polymer chains with a high water content, have found numerous applications in biomedicine because of their similarity to native tissue, biocompatibility and tuneable properties. In general, hydrogels are poor conductors of electric current, due to the insulating nature of commonly-used hydrophilic polymer chains. A number of biomedical applications require or benefit from an increased electrical conductivity. These include hydrogels used as scaffolds for tissue engineering of electroactive cells, as strain-sensitive sensors and as platforms for controlled drug delivery. The incorporation of conductive nanomaterials in hydrogels results in nanocomposite materials which combine electrical conductivity with the soft nature, flexibility and high water content of hydrogels. Here, we review the state of the art of such materials, describing the theories of current conduction in nanocomposite hydrogels, outlining their limitations and highlighting methods for improving their electrical conductivity.

Anionic polysaccharides for stabilization and sustained release of antimicrobial peptides

Chemical and enzymatic in vivo degradation of antimicrobial peptides represents a major challenge for their therapeutic use to treat bacterial infections. In this work, anionic polysaccharides were investigated for their ability to increase the chemical stability and achieve sustained release of such peptides. The investigated formulations comprised a combination of antimicrobial peptides (vancomycin (VAN) and daptomycin (DAP)) and anionic polysaccharides (xanthan gum (XA), hyaluronic acid (HA), propylene glycol alginate (PGA) and alginic acid (ALG)). VAN dissolved in buffer of pH 7.4 and incubated at 37 °C showed first order degradation kinetics with a reaction rate constant k_obs of 5.5 × 10^-2 day^-1 corresponding with a half-life of 13.9 days. However, once VAN was present in a XA, HA or PGA-based hydrogel, k_obs decreased to (2.1-2.3) × 10^-2 day^-1 while k_obs was not affected in an alginate hydrogel and a dextran solution (5.4 × 10^-2 and 4.4 × 10^-2 day^-1). Under the same conditions, XA and PGA also effectively decreased k_obs for DAP (5.6 × 10^-2 day^-1), whereas ALG had no effect and HA even increased the degradation rate. These results demonstrate that the investigated polysaccharides (except ALG for both peptides and HA for DAP) slowed down the degradation of VAN and DAP. DSC analysis was used to investigate on polysaccharide ability to bind water molecules. Rheological analysis highlighted that the polysaccharides containing VAN displayed an increase in G' of their formulations, pointing that the peptides interaction act as crosslinker of the polymer chains. The obtained results suggest that the mechanism of stabilization of VAN and DAP against hydrolytic degradation is conferred by electrostatic interactions between the ionizable amine groups of the drugs and the anionic carboxylate groups of the polysaccharides. This, in turn, results in a close proximity of the drugs to the polysaccharide chain, where the water molecules have a lower mobility and, therefore, a lower thermodynamic activity.

Multi-responsive chitosan-based hydrogels for controlled release of vincristine

As medical research progresses, the derivation and development of biological materials such as hydrogels have steadily gained more interest. The biocompatibility and non-toxicity of chitosan make chitosan hydrogels potential carriers for drug delivery. This work aims to develop two multi-reactive, safe, and highly swellable bio-hydrogels consisting of chitosan-graft-glycerol (CS-g-gly) and carboxymethyl chitosan-graft-glycerol (CMCS-g-gly), for sustained and controlled drug release, improved bioavailability along with entrapment in nanocarriers, which reduces side effects of vincristine sulphate. CS-g-gly and CMCS-g-gly are successfully prepared and fully characterized using analytical techniques. Under various conditions, the prepared hydrogels exhibit a high swelling ratio. Vincristine-loaded CS-g-gly (VCR/CS-g-gly), and CMCS-g-gly (VCR/CMCS-g-gly) show high encapsulation efficiency between 72.28-89.97%, and 56.97-71.91%, respectively. VCR/CS-g-gly show a sustained release behavior, and the maximum release of VCR from hydrogels reached 82% after 120 h of incubation. MCF-7 (breast cancer cell line) and MCF-10 (normal breast cell line) are evaluated for cell viability and apoptosis induction. The in-vitro anti-tumor efficacy is investigated using flow cytometry. The tetrazolium-based MTT assay of hydrogels shows no evidence of significant cytotoxicity in MCF-7 and MCF-10 cells. According to these findings, these hydrogels can effectively deliver drugs to MCF-7 and other breast cancer cells.

Bimetallic NiPt nanoparticles-enhanced catalyst supported on alginate-based biohydrogels for sustainable hydrogen production

Alginate hydrogel beads were loaded with bimetallic NiPt nanoparticles by in situ reduction of the respective polymer matrix containing precursor metallic ions using a NaBH₄ aqueous solution. The alginate hydrogel beads loaded with NiPt nanoparticles were characterized by TEM, AAS, FT-IR, TGA, XPS, and oscillatory rheometry. The prepared hybrid hydrogels were proven to be effective as catalytic materials for the hydrolysis of ammonia borane (AB) for quantitative hydrogen generation using catalytic loadings of 0.1 mol%. In addition, the reaction mechanism of the hydrolytic reaction using NiPt loaded alginate hydrogel beads was determined by Langmuir-Hinshelwood model. The experimental results showed that the reaction mechanism consisted of an initial fast adsorption of reactants at the surface of the nanoparticles, followed by a rate-limiting surface reaction. The NiPt nanoalloys exhibited an enhanced behavior for hydrogen generation with a maximum TOF of 84.1 min^-1, almost 71 % higher compared to monometallic platinum atoms, and likely related to a synergistic interaction between both metals. Finally, the hydrogel matrix enabled the material to be easily recovered from the reaction medium and reused in further catalytic cycles without desorption of active nanoparticles from the material.

Influence of Cross-Linking Conditions on Drying Kinetics of Alginate Hydrogel

Hydrogels are three-dimensional cross-linked polymeric networks capable of a large amount of fluid retention in their structure. Hydrogel outputs manufactured using additive manufacturing technologies are exposed to water loss, which may change their original shape and dimensions. Therefore, the possibility of retaining water is important in such a structure. In this manuscript, kinetic analysis of water evaporation from sodium alginate-based hydrogels exposed to different environmental conditions such as different temperatures (7 and 23 °C) and ambient humidity (45, 50 and 95%) has been carried out. The influence of the cross-linking method (different calcium chloride concentration-0.05, 0.1 and 0.5 M) of sodium alginate and cross-linking time on the water loss was also considered. Studies have shown that a decrease in the temperature and increase in the storage humidity can have a positive effect on the water retention in the structure. The storage conditions that led to the least weight and volume loss were T 7 °C and 95% humidity. These experiments may help in selecting the appropriate hydrogel preparation method for future applications, as well as their storage conditions for minimum water loss and, consequently, the least change in dimensions and shape.

Incorporation of PEG Diacrylates (PEGDA) Generates Hybrid Fmoc-FF Hydrogel Matrices

Generated by a hierarchical and multiscale self-assembling phenomenon, peptide-based hydrogels (HGs) are soft materials useful for a variety of applications. Short and ultra-short peptides are intriguing building blocks for hydrogel fabrication. These matrices can also be obtained by mixing low-molecular-weight peptides with other chemical entities (e.g., polymers, other peptides). The combination of two or more constituents opens the door to the development of hybrid systems with tunable mechanical properties and unexpected biofunctionalities or morphologies. For this scope, the formulation, the multiscale analysis, and the supramolecular characterization of novel hybrid peptide-polymer hydrogels are herein described. The proposed matrices contain the Fmoc-FF (N^α-fluorenylmethyloxycarbonyl diphenylalanine) hydrogelator at a concentration of 0.5 wt% (5.0 mg/mL) and a diacrylate α-/ω-substituted polyethylene-glycol derivative (PEGDA). Two PEGDA derivatives, PEGDA 1 and PEGDA2 (mean molecular weights of 575 and 250 Da, respectively), are mixed with Fmoc-FF at different ratios (Fmoc-FF/PEGDA at 1/1, 1/2, 1/5, 1/10 mol/mol). All the multicomponent hybrid peptide-polymer hydrogels are scrutinized with a large panel of analytical techniques (including proton relaxometry, FTIR, WAXS, rheometry, and scanning electronic microscopy). The matrices were found to be able to generate mechanical responses in the 2-8 kPa range, producing a panel of tunable materials with the same chemical composition. The release of a model drug (Naphthol Yellow S) is reported too. The tunable features, the different topologies, and the versatility of the proposed materials open the door to the development of tools for different applicative areas, including diagnostics, liquid biopsies and responsive materials. The incorporation of a diacrylate function also suggests the possible development of interpenetrating networks upon cross-linking reactions. All the collected data allow a mutual comparison between the different matrices, thus confirming the significance of the hybrid peptide/polymer-based methodology as a strategy for the design of innovative materials.

Additive manufacturing of micro-architected metals via hydrogel infusion

Metal additive manufacturing (AM) enables the production of high value and high performance components1 with applications from aerospace2 to biomedical3 fields. Layer-by-layer fabrication circumvents the geometric limitations of traditional metalworking techniques, allowing topologically optimized parts to be made rapidly and efficiently4,5. Existing AM techniques rely on thermally initiated melting or sintering for part shaping, a costly and material-limited process6-8. We report an AM technique that produces metals and alloys with microscale resolution via vat photopolymerization (VP). Three-dimensional-architected hydrogels are infused with metal precursors, then calcined and reduced to convert the hydrogel scaffolds into miniaturized metal replicas. This approach represents a paradigm shift in VP; the material is selected only after the structure is fabricated. Unlike existing VP strategies, which incorporate target materials or precursors into the photoresin during printing9-11, our method does not require reoptimization of resins and curing parameters for different materials, enabling quick iteration, compositional tuning and the ability to fabricate multimaterials. We demonstrate AM of metals with critical dimensions of approximately 40 µm that are challenging to fabricate by using conventional processes. Such hydrogel-derived metals have highly twinned microstructures and unusually high hardness, providing a pathway to create advanced metallic micromaterials.

Intrinsic-water desorption induced thermomechanical response of hydrogels

We report an interplay between the desorption of intrinsic water and relaxation of polymer chains resulting in an unusual thermomechanical response of a hydrogel, wherein the elastic modulus increases in a certain temperature range followed by a sharp decrease with a further increase in temperature. We establish that, in a hydrogel, the desorption of disparate water types having distinct binding energy affects the consolidation and relaxation behaviour of the matrix, which in turn affects the mechanical properties at different temperature ranges. Using temperature-dependent dielectric relaxation spectroscopy and nanoindentation techniques, the chain dynamics and mechanical properties are investigated.

Hydrogels Enable Future Smart Batteries

The growing trend of intelligent devices ranging from wearables and soft robots to artificial intelligence has set a high demand for smart batteries. Hydrogels provide opportunities for smart batteries to self-adjust their functions according to the operation conditions. Despite the progress in hydrogel-based smart batteries, a gap remains between the designable functions of diverse hydrogels and the expected performance of batteries. In this Perspective, we first briefly introduce the fundamentals of hydrogels, including formation, structure, and characteristics of the internal water and ions. Batteries that operate under unusual mechanical and temperature conditions enabled by hydrogels are highlighted. Challenges and opportunities for further development of hydrogels are outlined to propose future research in smart batteries toward all-climate power sources and intelligent wearables.

A Molecular Description of Hydrogel Forming Polymers for Cement-Based Printing Paste Applications

This research endeavors to link the physical and chemical characteristics of select polymer hydrogels to differences in printability when used as printing aids in cement-based printing pastes. A variety of experimental probes including differential scanning calorimetry (DSC), NMR-diffusion ordered spectroscopy (DOSY), quasi-elastic neutron scattering (QENS) using neutron backscattering spectroscopy, and X-ray powder diffraction (XRD), along with molecular dynamic simulations, were used. Conjectures based on objective measures of printability and physical and chemical-molecular characteristics of the polymer gels are emerging that should help target printing aid selection and design, and mix formulation. Molecular simulations were shown to link higher hydrogen bond probability and larger radius of gyration to higher viscosity gels. Furthermore, the higher viscosity gels also produced higher elastic properties, as measured by neutron backscattering spectroscopy.

Macroporous Cell-Laden Gelatin/Hyaluronic Acid/Chondroitin Sulfate Cryogels for Engineered Tissue Constructs

Cryogels are a unique macroporous material for tissue engineering. In this work, we study the effect of hyaluronic acid on the physicochemical properties of cryogel as well as on the proliferation of a 3D model of mesenchymal stem cells. The functional groups of the synthesized cryogels were identified using Fourier transform infrared spectroscopy. With an increase in the content of hyaluronic acid in the composition of the cryogel, an increase in porosity, gel content and swelling behavior was observed. As the hyaluronic acid content increased, the average pore size increased and more open pores were formed. Degradation studies have shown that all cryogels were resistant to PBS solution for 8 weeks. Cytotoxicity assays demonstrated no toxic effect on viability of rat adipose-derived mesenchymal stem cells (ADMSCs) cultured on cryogels. ADMSC spheroids were proliferated on scaffolds and showed the ability of the cryogels to orient cell differentiation into chondrogenic lineage even in the absence of inductive agents. Thus, our results demonstrate an effective resemblance to extracellular matrix structures specific to cartilage-like microenvironments by cryogels and their further perspective application as potential biomaterials.

Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates

The ubiquitous nature of atmospheric moisture makes it a significant water resource available at any geographical location. Atmospheric water harvesting (AWH) technology, which extracts moisture from the ambient air to generate clean water, is a promising strategy to realize decentralized water production. The high water uptake by salt-based sorbents makes them attractive for AWH, especially in arid environments. However, they often have relatively high desorption heat, rendering water release an energy-intensive process. A  LiCl-incorporating polyacrylamide hydrogel (PAM-LiCl) capable of effective moisture harvesting from arid environments is proposed. The interactions between the hydrophilic hydrogel network and the captured water generate more free and weakly bonded water, significantly lowering the desorption heat compared with conventional neat salt sorbents. Benefiting from the affinity for swelling of the polymer backbones, the developed PAM-LiCl achieves a high water uptake of ≈1.1 g g^-1 at 20% RH with fast sorption kinetics of ≈0.008 g g^-1  min^-1  and further demonstrates a daily water yield up to ≈7 g g^-1 at this condition. These findings provide a new pathway for the synthesis of materials with efficient water absorption/desorption properties, to reach energy-efficient water release for AWH in arid climates.