Effect of temperature and cross-linking density on rheology of chemical cross-linked guar gum at the gel point

Cell wall polysaccharides from macauba pulp (Acrocomia aculeata L.): Fractionation and characterization of their chemical and rheological properties

Macauba fruit pulp (Acrocomia aculeata) is an emerging oil source. After de-oiling, the macauba pulp meal (MPM) offers a dietary fiber content of 40-50 %, which mainly comprises cell wall polysaccharides (CWP). The present work aimed to assess the potential of MPM as an innovative source of sustainable food polysaccharides. To this end, the macauba CWP were fractionated into water-soluble galactoglucomannans (21.7 %), calcium- and ester-bound pectins (3.4 %), loosely-bound xyloglucans (27.6 %), strongly-bound xylans (6.5 %), and a cellulose-rich fraction (39.3 %). The galactoglucomannans produced shear-thinning aqueous dispersions with an increase in consistency index from 3.03·10-2 to 3.58·101 Pa·sn by increasing the concentration from 1.0 to 5.0 %. The galactoglucomannans dispersions showed semi-dilute behavior, evidenced by relaxation times ranging from 1.24·10-2 to 1.17 s for concentrations from 2.5 to 10.0 %. Macauba pectins and xyloglucans showed weak gel behavior, with an increase in yield stress from 3.20·10-1 to 1.04·102 Pa and from 7.01·10-2 to 1.35·102 Pa for dispersions at 2.5 to 10.0 %, respectively. 2.5 to 5 times higher concentration of macauba polysaccharides is needed to obtain rheological behavior similar to guar and xanthan gum. The thickening and gelling properties of macauba CWP highlight their potential as thickeners and stabilizers for the food industry.

Drug delivery using reduction-responsive hydrogel based on carboxyethyl-succinoglycan with highly improved rheological, antibacterial, and antioxidant properties

The development of exopolysaccharide-based polymers is gaining increasing attention in various industrial biotechnology fields for materials such as thickeners, texture modifiers, anti-freeze agents, antioxidants, and antibacterial agents. High-viscosity carboxyethyl-succinoglycan (CE-SG) was directly synthesized from succinoglycan (SG) isolated from Sinorhizobium meliloti Rm 1021, and its structural, rheological, and physiological properties were investigated. The viscosity of CE-SG gradually increased in proportion to the degree of carboxyethylation substitution. In particular, when the molar ratio of SG and 3-chloropropionic acid was 1:100, the viscosity was significantly improved by 21.18 times at a shear rate of 10 s-1. Increased carboxyethylation of SG also improved the thermal stability of CE-SG. Furthermore, the CE-SG solution showed 90.18 and 91.78 % antibacterial effects against Escherichia coli and Staphylococcus aureus and effective antioxidant activity against DPPH and hydroxyl radicals. In particular, CE-SG hydrogels coordinated with Fe3+ ions, which improved both viscosity and rheological properties, while also exhibiting reduction-responsive drug release through 1,4-dithiothreitol. The results of this study suggest that SG derivatives, such as CE-SG, can be used as functional biomaterials in various fields such as food, cosmetics, and pharmaceutical industries.

Emerging horizons and prospects of polysaccharide-constructed gels in the realm of wound healing

Polysaccharides, with the abundant availability, biodegradability, and inherent safety, offer a vast array of promising applications. Leveraging the remarkable attributes of polysaccharides, biomimetic and multifunctional hydrogels have emerged as a compelling avenue for efficacious wound dressing. The gels emulate the innate extracellular biomatrix as well as foster cellular proliferation. The distinctive structural compositions and profusion of functional groups within polysaccharides confer excellent physical/chemical traits as well as distinct restorative involvements. Gels crafted from polysaccharide matrixes serve as a robust defense against bacterial threats, effectively shielding wounds from harm. This comprehensive review delves into wound physiology, accentuating the significance of numerous polysaccharide-based gels in the wound healing context. The discourse encompasses an exploration of polysaccharide hydrogels tailored for diverse wound types, along with an examination of various therapeutic agents encapsulated within hydrogels to facilitate wound repair, incorporating recent patent developments. Within the scope of this manuscript, the perspective of these captivating gels for promoting optimal healing of wounds is vividly depicted. Nevertheless, the pursuit of knowledge remains ongoing, as further research is warranted to bioengineer progressive polysaccharide gels imbued with adaptable features. Such endeavors hold the promise of unlocking substantial potential within the realm of wound healing, propelling us toward multifaceted and sophisticated solutions.

The Electrical and Mechanical Characteristics of Conductive PVA/PEDOT:PSS Hydrogel Foams for Soft Strain Sensors

Conductive hydrogels are of interest for highly flexible sensor elements. We compare conductive hydrogels and hydrogel foams in view of strain-sensing applications. Polyvinyl alcool (PVA) and poly(3,4-ethylenedioxythiophene (PEDOT:PSS) are used for the formulation of conductive hydrogels. For hydrogel foaming, we have investigated the influence of dodecylbenzenesulfonate (DBSA) as foaming agent, as well as the influence of air incorporation at various mixing speeds. We showed that DBSA acting as a surfactant, already at a concentration of 1.12wt%, efficiently stabilizes air bubbles, allowing for the formulation of conductive PVA and PVA/PEDOT:PSS hydrogel foams with low density (<400 kg/m3) and high water uptake capacity (swelling ratio > 1500%). The resulting Young moduli depend on the air-bubble incorporation from mixing, and are affected by freeze-drying/rehydration. Using dielectric broadband spectroscopy under mechanical load, we demonstrate that PVA/PEDOT:PSS hydrogel foams exhibit a significant decrease in conductivity under mechanical compression, compared to dense hydrogels. The frequency-dependent conductivity of the hydrogels exhibits two plateaus, one in the low frequency range, and one in the high frequency range. We find that the conductivity of the PVA/PEDOT:PSS hydrogels decreases linearly as a function of pressure in each of the frequency regions, which makes the hydrogel foams highly interesting in view of compressive strain-sensing applications.

A facile alternative strategy of upcycling mixed plastic waste into vitrimers

Chemical depolymerization has been identified as a promising approach towards recycling of plastic waste. However, complete depolymerization may be energy intensive with complications in purification. In this work, we have demonstrated upcycling of mixed plastic waste comprising a mixture of polyester, polyamide, and polyurethane through a reprocessable vitrimer of the depolymerized oligomers. Using poly(ethylene terephthalate) (PET) as a model polymer, we first demonstrated partial controlled depolymerization, using glycerol as a cleaving agent, to obtain branched PET oligomers. Recovered PET (RPET) oligomer was then used as a feedstock to produce a crosslinked yet reprocessable vitrimer (vRPET) despite having a wide molecular weight distribution using a solventless melt processing approach. Crosslinking and dynamic interactions were observed through rheology and dynamic mechanical analysis (DMA). Tensile mechanical studies showed no noticeable decrease in mechanical strength over multiple repeated melt processing cycles. Consequently, we have clearly demonstrated the applicability of the above method to upcycle mixed plastic wastes into vitrimers and reprocessable composites. This work also afforded insights into a potentially viable alternative route for utilization of depolymerized plastic/mixed plastic waste into crosslinked vitrimer resins manifesting excellent mechanical strength, while remaining reprocessable/ recyclable for cyclical lifetime use.

Preparation of benzenesulfonyl hydrazone modified guar gum and its adsorption properties for dyes and phytotoxicity assays

Herein, a novel environmentally friendly benzenesulfonyl hydrazone modified guar gum (DGH) that carries excellent adsorption performance towards dyes was facilely prepared through oxidation and condensation. The structure, morphology, and physics-chemical of DGH were fully characterized by multiple analysis techniques. The as-prepared adsorbent yielded highly efficient separating performance towards multiple anionic and cation dyes, including CR, MG, and ST with the maximum adsorption capacity of 1065.3839 ± 10.5695, 1256.4467 ± 2.9425, and 1043.8140 ± 0.9789 mg/g at 298.15 K, respectively. The adsorption process well fitted the Langmuir isotherm models and the pseudo-second-order kinetic models. The adsorption thermodynamics revealed that the adsorption of dyes onto DGH was spontaneous and endothermic. The adsorption mechanism indicated that the hydrogen bonding and electrostatic interaction participated in the fast and efficient removal of dyes. Furthermore, the removal efficiency of DGH still remained above 90 % after six adsorption-desorption cycles, and the presence of Na⁺, Ca²⁺, and Mg²⁺ have weakly impacted the removal efficiency of DGH. The phytotoxicity assay was conducted via the germination of mung bean seeds, which confirmed the adsorbent can effectivity decreased the toxicity of dyes. Overall, the modified gum-based multifunctional material has good promising applications for wastewater treatment.

On the gelation of humins: from transient to covalent networks

Humins are a by-product of many acid-catalyzed biorefinery processes converting polysaccharides into platform chemicals. The valorization of humin residue to increase the profit of biorefinery operations and reduce waste is a field that is growing interest as the production of humins continues to increase. This includes their valorization in materials science. For successful processing of humin-based materials, this study aims to understand the thermal polymerization mechanisms of humins from a rheological perspective. Thermal crosslinking of raw humins leads to an increase in their molecular weight, which in turn leads to the formation of a gel. Humin's gels structure combines physical (thermally reversible) and chemical (thermally irreversible) crosslinks, and temperature plays an essential role in the crosslink density and the gel properties. High temperatures delay the formation of a gel due to the scission of physicochemical interactions, drastically decreasing their viscosity, whereas upon cooling a stronger gel is formed combining the recovered physicochemical bonds and the newly created chemical crosslinks. Thus, a transition from a supramolecular network to a covalently crosslinked network is observed, and properties such as the elasticity or reprocessability of humin gels are influenced by the stage of polymerization.

Novel Photo- and Thermo-Responsive Nanocomposite Hydrogels Based on Functionalized rGO and Modified SIS/Chitosan Polymers for Localized Treatment of Malignant Cutaneous Melanoma

Melanoma is an aggressive type of skin cancer that accounts for over 75% of skin cancer deaths despite comprising less than 5% of all skin cancers. Despite promising improvements in surgical approaches for melanoma resection, the survival of undetectable microtumor residues has remained a concern. As a result, hyperthermia- and drug-based therapies have grown as attractive techniques to target and treat cancer. In this work, we aim to develop a stimuli-responsive hydrogel based on chitosan methacrylate (ChiMA), porcine small intestine submucosa methacrylate (SISMA), and doxorubicin-functionalized reduced graphene oxide (rGO-DOX) that eliminates microtumor residues from surgically resected melanoma through the coupled effect of NIR light-induced photothermal therapy and heat-induced doxorubicin release. Furthermore, we developed an in silico model to optimize heat and mass transport and evaluate the proposed chemo/photothermal therapy in vitro over melanoma cell cultures.

Direct Ink Writing: A 3D Printing Technology for Diverse Materials

Additive manufacturing (AM) has gained significant attention due to its ability to drive technological development as a sustainable, flexible, and customizable manufacturing scheme. Among the various AM techniques, direct ink writing (DIW) has emerged as the most versatile 3D printing technique for the broadest range of materials. DIW allows printing of practically any material, as long as the precursor ink can be engineered to demonstrate appropriate rheological behavior. This technique acts as a unique pathway to introduce design freedom, multifunctionality, and stability simultaneously into its printed structures. Here, a comprehensive review of DIW of complex 3D structures from various materials, including polymers, ceramics, glass, cement, graphene, metals, and their combinations through multimaterial printing is presented. The review begins with an overview of the fundamentals of ink rheology, followed by an in-depth discussion of the various methods to tailor the ink for DIW of different classes of materials. Then, the diverse applications of DIW ranging from electronics to food to biomedical industries are discussed. Finally, the current challenges and limitations of this technique are highlighted, followed by its prospects as a guideline toward possible futuristic innovations.

The Synthesis of (Magnetic) Crosslinked Enzyme Aggregates With Laccase, Cellulase, β-Galactosidase and Transglutaminase

Immobilized enzymes have important aspects due to the fact that they possess higher stability, have the possibility to be easily removed from the reaction mixture, and are much easier to use when compared to free enzymes. In this research, the enzymes laccase, cellulase, β-galactosidase (β-gal), and transglutaminase (TGM) were immobilized by two different methods: crosslinked enzyme aggregates (CLEAs) and magnetic crosslinked enzyme aggregates (mCLEAs). The processes for CLEAs and mCLEAs preparation with different enzymes have been optimized, where the aim was to achieve the highest possible relative activity of the immobilized enzyme. The optimal conditions of the synthesis of CLEAs in mCLEAs are described, thus emphasizing the difference between the two types of immobilization based on different enzymes. This comparative study, which represents the synthesis of crosslinked enzyme aggregates using different enzymes, has not been performed so far. Moreover, the obtained activity of CLEAs and mCLEAs is presented, which is important for further use in different biocatalytic processes. Specifically, of a higher importance is the selection of enzymes involved in immobilization, as they belong to the three different most applicable enzymes (oxidoreductases, hydrolases, and transferases). The study confirmed that the resulting activity of the immobilized enzyme and the optimization of enzyme immobilization depended on the type of the enzyme. Moreover, the prepared CLEAs and mCLEAs were exposed to the supercritical carbon dioxide (scCO₂) at different pressures to determine the effect of scCO₂ on enzyme activity in immobilized form. Additionally, to demonstrate the reuse and stability of the immobilized enzyme, the stability and reusability tests of CLEAs and mCLEAs were performed. The catalytic performance of immobilized enzyme was tested, where the catalytic efficiency and long-term operational stability of mCLEAs were obviously superior to those of CLEAs. However, the higher activity observed for CLEAs compared to mCLEAs suggests a significant effect of magnetic nanoparticles in the stabilization of an enzyme crosslinked aggregate structure.

Preparation and Characterization of an Injectable and Photo-Responsive Chitosan Methacrylate/Graphene Oxide Hydrogel: Potential Applications in Bone Tissue Adhesion and Repair

As life expectancy continues to increase, the inevitable weakening and rupture of bone tissue have grown as concerns in the medical community, thus leading to the need for adhesive materials suitable for bone repair applications. However, current commercially available adhesives face certain drawbacks that prevent proper tissue repair, such as low biocompatibility, poor adhesion to wet surfaces, and the need for high polymerization temperatures. This work aims to develop an injectable and photo-responsive chitosan methacrylate/graphene oxide (ChiMA/GO) adhesive nanocomposite hydrogel of high biocompatibility that is easy to apply by simple extrusion and that offers the possibility for in situ polymer and physiological temperatures. The nanocomposite was thoroughly characterized spectroscopically, microscopically, rheologically, thermally, and through mechanical, textural, and biological assays to fully evaluate its correct synthesis and functionalization and its performance under physiological conditions that mimic those observed in vivo. In addition, a finite element analysis (FEA) simulation was used to evaluate its performance in femur fractures. Results suggest the material’s potential as a bioadhesive, as it can polymerize at room temperature, shows superior stability in physiological media, and is capable of withstanding loads from body weight and movement. Moreover, the material showed remarkable biocompatibility as evidenced by low hemolytic and intermediate platelet aggregation tendencies, and high cytocompatibility when in contact with osteoblasts. The comprehensive studies presented here strongly suggest that the developed hydrogels are promising alternatives to conventional bone adhesives that might be further tested in vivo in the near future.

Glyceraldehyde as an Efficient Chemical Crosslinker Agent for the Formation of Chitosan Hydrogels

The rheological changes that occur during the chemical gelation of semidilute solutions of chitosan in the presence of the low-toxicity agent glyceraldehyde (GCA) are presented and discussed in detail. The entanglement concentration for chitosan solutions was found to be approximately 0.2 wt.% and the rheological experiments were carried out on 1 wt.% chitosan solutions with various amounts of GCA at different temperatures (25 °C and 40 °C) and pH values (4.8 and 5.8). High crosslinker concentration, as well as elevated temperature and pH close to the pKa value (pH ≈ 6.3-7) of chitosan are three parameters that all accelerate the gelation process. These conditions also promote a faster solid-like response of the gel-network in the post-gel region after long curing times. The mesh size of the gel-network after a very long (18 h) curing time was found to contract with increasing level of crosslinker addition and elevated temperature. The gelation of chitosan in the presence of other chemical crosslinker agents (glutaraldehyde and genipin) is discussed and a comparison with GCA is made. Small angle neutron scattering (SANS) results reveal structural changes between chitosan solutions, incipient gels, and mature gels.

Evaluation of calcium alginate bead formation kinetics: An integrated analysis through light microscopy, rheology and microstructural SAXS

Ca(II)-alginate beads are being produced for a broad spectrum of biotechnological uses. Despite the simplicity of their manufacturing process, in these highly complex arrangements, the final properties of the material strongly depend on the supramolecular scaffolding. Here we present a cost-effective automatized Optical Video Microscopy approach for in situ evaluation of the kinetics of alginate bead formation. With simple mathematic modeling of the acquired data, we obtained key parameters that reveal valuable information on the system: the time course of gel-front migration correlates with the plateau of the storage module, and total volume shrinkage is highly related to the stabilization of shear strain and shear stress at the yield point. Our results provide feasible and reproducible tools, which allow for a better interpretation of bead formation kinetics and a rapid screening technique to use while designing gelling materials with specific properties for technological applications.

Diffusion of water and protein drug in 1,4-butanediol diglycidyl ether crosslinked galactomannan hydrogels and its correlation with the physicochemical properties

The aim of the present study was to obtain a better and safer galactomannan-based material for drug release applications. A novel epoxy-crosslinked galactomannan hydrogel (EGH) was prepared from guar gum using 1,4-butanediol diglycidyl ether as a crosslinking agent. The diffusion rate constant of water molecules in freeze-dried EGH positively correlated with water uptake/equilibrium swelling rate (WU/ESR), and the water molecules participated in Fickian diffusion. The ESR, WU/ESR, and bovine serum albumin (BSA) loading capacity of a customized EGH with a crosslinking density of 48.9% were 48.7 ± 0.15 g/g, 95.3%, and 56.4 mg/g, respectively. The release of BSA from freeze-dried EGH was affected by the WU/ESR and the pH; the release equilibrium time was ~40 h at pH 1.2, decreasing to ~24 h at pH 7.4. Furthermore, the cumulative release rate increased from 63.5% to 80.7% and the t₅₀ decreased from 59 to 41 min upon changing from the acidic to basic pH. The release process conformed to the Ritger-Peppas and Hixson-Crowell models, and represented Fickian diffusion and chain relaxation. The EGH showed no cytotoxicity toward HeLa cells. Together, these results demonstrate the properties of a novel galactomannan-based hydrogel that can potentially be employed as a vehicle for drug delivery.

Technologies and Formulation Design of Polysaccharide-Based Hydrogels for Drug Delivery

Polysaccharide-based hydrogel particles (PbHPs) are very promising carriers aiming to control and target the release of drugs with different physico-chemical properties. Such delivery systems can offer benefits through the proper encapsulation of many drugs (non-steroidal and steroidal anti-inflammatory drugs, antibiotics, etc) ensuring their proper release and targeting. This review discusses the different phases involved in the production of PbHPs in pharmaceutical technology, such as droplet formation (SOL phase), sol-gel transition of the droplets (GEL phase) and drying, as well as the different methods available for droplet production with a special focus on prilling technique. In addition, an overview of the various droplet gelation methods with particular emphasis on ionic cross-linking of several polysaccharides enabling the formation of particles with inner highly porous network or nanofibrillar structure is given. Moreover, a detailed survey of the different inner texture, in xerogels, cryogels or aerogels, each with specific arrangement and properties, which can be obtained with different drying methods, is presented. Various case studies are reported to highlight the most appropriate application of such systems in pharmaceutical field. We also describe the challenges to be faced for the breakthrough towards clinic studies and, finally, the market, focusing on the useful approach of safety-by-design (SbD).

The degree of compactness of the incipient High Methoxyl Pectin networks. A rheological insight at the sol-gel transition

Fractal analysis can be properly applied to complex structures, like physical and chemical networks formed by particles or polymers, when they exhibit self-similarity over an extended range of length scales and, hence, can be profitably used not only for their morphological characterization but also for individuating possible relationships between morphology and mechanisms of aggregation and crosslinking, as well as between morphology and physical properties. Several experimental methods are available to determine the fractal dimension of gel networks, including various scattering techniques and microscopies, permeability measurements and rheology. The present study regards the self-assembly kinetics of High Methoxyl Pectin (HMP) solutions with different pectin and sucrose concentrations investigated by rheological measurements to highlight the effects of pectin and sucrose concentrations on the gel point and to evaluate the degree of compactness of the incipient gel networks through an interpretation of the viscoelastic response at the sol-gel transition.

In situ fabrication of a composite hydrogel with tunable mechanical properties for cartilage tissue engineering

A composite hydrogel with tunable mechanical properties has been fabricated and characterized in this study.

Development of curcumin loaded sodium hyaluronate immobilized vesicles (hyalurosomes) and their potential on skin inflammation and wound restoring

In the present work new highly biocompatible nanovesicles were developed using polyanion sodium hyaluronate to form polymer immobilized vesicles, so called hyalurosomes. Curcumin, at high concentration was loaded into hyalurosomes and physico-chemical properties and in vitro/in vivo performances of the formulations were compared to those of liposomes having the same lipid and drug content. Vesicles were prepared by direct addition of dispersion containing the polysaccharide sodium hyaluronate and the polyphenol curcumin to a commercial mixture of soy phospholipids, thus avoiding the use of organic solvents. An extensive study was carried out on the physico-chemical features and properties of curcumin-loaded hyalurosomes and liposomes. Cryogenic transmission electron microscopy and small-angle X-ray scattering showed that vesicles were spherical, uni- or oligolamellar and small in size (112-220 nm). The in vitro percutaneous curcumin delivery studies on intact skin showed an improved ability of hyalurosomes to favour a fast drug deposition in the whole skin. Hyalurosomes as well as liposomes were biocompatible, protected in vitro human keratinocytes from oxidative stress damages and promoted tissue remodelling through cellular proliferation and migration. Moreover, in vivo tests underlined a good effectiveness of curcumin-loaded hyalurosomes to counteract 12-O-tetradecanoilphorbol (TPA)-produced inflammation and injuries, diminishing oedema formation, myeloperoxydase activity and providing an extensive skin reepithelization. Thanks to the one-step and environmentally-friendly preparation method, component biocompatibility and safety, good in vitro and in vivo performances, the hyalurosomes appear as promising nanocarriers for cosmetic and pharmaceutical applications.

Sonication-based improvement of the physicochemical properties of Guar Gum as a potential substrate for modified drug delivery systems

Guar Gum is a natural polysaccharide that, due to its physicochemical properties, is extensively investigated for biomedical applications as a matrix for modified drug delivery, but it is also used in the food industry as well as in cosmetics. A commercial sample of Guar Gum was sonicated for different periods of time, and the reduction in the average molecular weight was monitored by means of viscometric measurements. At the same time, the rheological behaviour was also followed, in terms of viscoelasticity range, flow curves, and mechanical spectra. Sonicated samples were used for the preparation of gels in the presence of borate ions. The effect of borax on the new samples was investigated by recording mechanical spectra, flow curves, and visible absorption spectra of complexes with Congo Red. The anisotropic elongation, observed in previous studies with tablets of Guar Gum and borax, was remarkably reduced when the sonicated samples were used for the preparation of the gels.

Properties of xyloglucan hydrogel as the biomedical sustained-release carriers

This study introduces an easy method of preparing xyloglucan hydrogel from xyloglucan, which is purified from tamarind seed gum. Xyloglucan hydrogel was prepared in 2 wt% solution by treating with β-galactosidase. Physical and chemical properties (molecular mass, size and viscosity) of xyloglucan hydrogel and xyloglucan solution were tested for a comparison. Experiments of drug release in vitro and in vivo were operated to investigate the potentialities of xyloglucan hydrogel as the biomedical sustained-release carriers for drug delivery system.