Mechanical, microstructural, and rheological characterization of gelatin-dialdehyde starch hydrogels constructed by dual dynamic crosslinking

Hydrogel formed in situ through Schiff base reaction between gallic acid-grafted soybean protein isolate and oxidized dextran: Interactions, physicochemical properties, and digestive characteristics

Herein, we developed multifunctional hydrogels formed between soybean protein (SPI)-gallic acid conjugate and oxidized dextran (ODex) via a Schiff base reaction. The effects of ODex on the morphology, structure, and functional properties of the hydrogels were elucidated. The results showed that the crosslinking modes in the hydrogels include hydrogen bonding, Schiff bases, Michael addition, and π-π stacking. The synergistic crosslinking of gallic acid and ODex conferred the hydrogels with an appropriate equilibrium swelling ratio, dense morphology, excellent mechanical properties, high thermal stability, and water-holding properties. When the addition of ODex was 0.8 (w/w), the hydrogel had a higher crosslinking degree (76.31 %), smaller average pore diameter (0.322 μm), and higher zero shear viscosity (748.5 mPa. s). In addition, in vitro digestion tests showed that hydrogel degradation was delayed upon increasing the degree of crosslinking, which improved the hydrogel's capacity to adsorb bile salts and control the release of curcumin. This study provides a theoretical basis for the design of high-quality protein hydrogels and other multifunctional materials suitable for various applications.

Crosslinking of gelatin Schiff base hydrogels with different structural dialdehyde polysaccharides as novel crosslinkers: Characterization and performance comparison

Few studies have been conducted on the relationship between the crosslinking ability of dialdehyde polysaccharides (DPs) with different structures and the structure and properties of hydrogels. Herein, the effects of dialdehyde sodium alginate (DSA), dialdehyde guar gum (DGG), and dialdehyde dextran (DDE) as crosslinking agents for gelatin (GE)-based hydrogels were comparatively studied. First, the structure and aldehyde content of DPs were evaluated. Subsequently, the structure, crosslinking degree, and physicochemical properties of GE/DP hydrogels were characterized. Compared with pure GE hydrogels, GE/DP hydrogels had higher thermal stability and mechanical properties. Moreover, the aldehyde content of DPs was ordered as follows: DSA < DGG < DDE. The higher crosslinking degree of the hydrogels formed by DPs with a higher aldehyde content resulted in smaller hydrogel pores, higher mechanical strength, and a lower equilibrium swelling rate. These observations provide a theoretical basis for selecting crosslinking candidates for hydrogel-specific applications.

Cross-Linking Agents in Three-Component Materials Dedicated to Biomedical Applications: A Review

In biomaterials research, using one or two components to prepare materials is common. However, there is a growing interest in developing materials composed of three components, as these can offer enhanced physicochemical properties compared to those consisting of one or two components. The introduction of a third component can significantly improve the mechanical strength, biocompatibility, and functionality of the resulting materials. Cross-linking is often employed to further enhance these properties, with chemical cross-linking agents being the most widely used method. This article provides an overview of the chemical agents utilized in the cross-linking of three-component biomaterials. The literature review focused on cases where the material was composed of three components and a chemical substance was employed as the cross-linking agent. The most commonly used cross-linking agents identified in the literature include glyoxal, glutaraldehyde, dialdehyde starch, dialdehyde chitosan, and the EDC/NHS mixture. Additionally, the review briefly discusses materials cross-linked with the MES/EDC mixture, caffeic acid, tannic acid, and genipin. Through a critical analysis of current research, this work aims to guide the development of more effective and safer biopolymeric materials tailored for biomedical applications, highlighting potential areas for further investigation and optimization.

Natural blackcurrant extract contained gelatin hydrogel with photothermal and antioxidant properties for infected burn wound healing

Burns represent a prevalent global health concern and are particularly susceptible to bacterial infections. Severe infections may lead to serious complications, posing a life-threatening risk. Near-infrared (NIR)-assisted photothermal antibacterial combined with antioxidant hydrogel has shown significant potential in the healing of infected wounds. However, existing photothermal agents are typically metal-based, complicated to synthesize, or pose biosafety hazards. In this study, we utilized plant-derived blackcurrant extract (B) as a natural source for both photothermal and antioxidant properties. By incorporating B into a G-O hydrogel crosslinked through Schiff base reaction between gelatin (G) and oxidized pullulan (O), the resulting G-O-B hydrogel exhibited good injectability and biocompatibility along with robust photothermal and antioxidant activities. Upon NIR irradiation, the controlled temperature (around 45-50 °C) generated by the G-O-B hydrogel resulted in rapid (10 min) and efficient killing of Staphylococcus aureus (99 %), Escherichia coli (98 %), and Pseudomonas aeruginosa (82 %). Furthermore, the G-O-B0.5 hydrogel containing 0.5 % blackcurrant extract promoted collagen deposition, angiogenesis, and accelerated burn wound closure conclusively, demonstrating that this well-designed and extract-contained hydrogel dressing holds immense potential for enhancing the healing process of bacterial-infected burn wounds.

Recent advances on the preparation conditions, structural characteristics, physicochemical properties, functional properties and potential applications of dialdehyde starch: A review

Starch, a natural storage polysaccharide of plant kingdom, has many industrial applications. However, native starch has some inherent shortages, which can be overcome by structural modification. Dialdehyde starch, one kind of oxidized starch produced by periodate oxidation, has good physical properties and bioactivities with wide applications in different fields. Dialdehyde starch is typically achieved by oxidizing native starch slurry through periodate oxidation under controlled reaction conditions. Several factors including the source of starch, the type of oxidant, the molar ratio of oxidant to starch, reaction temperature, reaction time and solution pH value can influence the synthesis of dialdehyde starch. Dialdehyde starch shows different spectroscopic/chromatographic characters and physicochemical properties from native starch. Moreover, dialdehyde starch exhibits good antioxidant activity, antimicrobial activity and cross-linking property. Based on these functional properties, dialdehyde starch has shown application potentials in food packaging, thermoplastic production, enzyme immobilization, heavy metal ion adsorption, drug delivery, wood adhesion and leather tanning. In this review, the preparation conditions, structural characteristics, physicochemical properties, functional properties and potential applications of dialdehyde starch are summarized for the first time. The future research and development prospects of dialdehyde starch are also discussed.

Oxidized dextran improves the stability and effectively controls the release of curcumin loaded in soybean protein nanocomplexes

Dextran dialdehyde (ODex) was added to a nanocomplex of soy protein isolate (SPI)-curcumin (Cur) to improve its stability and achieve controlled release of Cur. The SPI-to-ODex mass ratio was optimized to achieve excellent properties and stability. Interactions between various components were confirmed by spectroscopic analysis, and the effect of ODex on the stability and bioactivity of SPI-Cur colloids was discussed. ODex was found to be crosslinked with SPI via the Schiff base reaction, which increased the ζ-potential and improved the surface hydrophobicity of nanocomplexes. At a SPI-to-ODex mass ratio of 20:1, the nanocomplex had a smaller particle size (199.2 nm), higher ζ-potential (-45.48 mV), and higher encapsulation efficiency (96.25%). Furthermore, adding ODex changed the network structure and effectively improved the thermal and storage stability of Cur as well as its antioxidant properties. Moreover, controlled release of Cur was observed during simulated digestion in the gastrointestinal environment.

A dual encapsulation strategy to generate anion-responsive luminescent lanthanide hydrogels

We report a new method to generate ion-responsive luminescent hydrogels, involving encapsulation of a luminescent lanthanide probe within crosslinked amphiphilic polymer particles and subsequent entrapment within a hydrogel. The resulting hydrogels are capable of reversible bicarbonate sensing, exhibit no leaching, and can be tuned for a range of sensing applications.

Dual cross-linked starch hydrogel for eugenol encapsulation and the formation of hydrogen bonds on textural hydrogel

Physical and chemical cross-linked hydrogels combining N, N'-Methylenebisacrylamide (MBA)-grafted starch (MBAS) and sorbitol were successfully prepared and encapsulated with eugenol in this work. The dense porous structure with diameter of 10-15 μm and strong skeleton after restructuring inside the hydrogel was confirmed by SEM. The band shifts between 3258 cm^-1 and 3264 cm^-1 clarified the presence of a large number of hydrogen bonds in physical and chemical cross-linked hydrogels. The robust structure of the hydrogel was confirmed by mechanical and thermal property measurements. Molecular docking techniques were used to help understand the bridging pattern between three raw materials and to assess the advantageous conformation, which demonstrate sorbitol is beneficial to improve the characteristics of textural hydrogel by the formation of hydrogen bonds, creating a denser network, structural recombination and new intermolecular hydrogen bonds between starch and sorbitol afforded considerably junction zones. Compared to ordinary starch-based hydrogels, eugenol-loaded starch-sorbitol hydrogels (ESSG) exhibited a more attractive internal structure, swelling properties, viscoelasticity. Moreover, the ESSG showed excellent antimicrobial activity for typical undesired microorganisms in foods.

Controlled release of curcumin from gelatin hydrogels by the molecular-weight modulation of an oxidized dextran cross-linker

Controlled drug delivery could minimize side effects while maintaining a high local dose. Herein, a hydrogel carrier was prepared by forming dynamic imine bonds between gelatin and oxidized dextran (ODex) of different molecular weights (Mw = 10, 70, and 150 kDa). The morphology, thermal stability, rheology, mechanical properties, and swelling properties of the hydrogels and the controlled release of curcumin were characterized. When dextran with a higher Mw was used, the ODex contained more aldehyde groups, which led to a higher degree of cross-linking, considerably shorter gel time, decreased hydrogel porosity, and well-controlled release of curcumin. In addition, the cross-linked hydrogels exhibited not only high thermal stability but also excellent mechanical properties. However, because the matrix was hydrophilic, the swelling properties of the hydrogels were not significantly affected by the Mw of ODex. These observations suggest an approach for designing nutrient delivery carriers with improved controlled release.

Preparation and characterization of mussel-inspired hydrogels based on methacrylated catechol-chitosan and dopamine methacrylamide

A novel mussel-inspired adhesive hydrogel with enhanced adhesion based on methacrylated catechol-chitosan (MCCS) and dopamine methacrylate (DMA) was prepared via photopolymerization. The structure and morphology of the MCCS/DMA adhesive hydrogel were investigated by using FTIR, NMR, XRD, TG, and SEM. The rheological and texture properties, swelling and degradation characteristics, as well as the adhesion mechanism of the hydrogels were also examined. These results revealed that the MCCS/DMA hydrogels have a dense double cross-linking network structure with porous internal microstructures, and exhibited controllable swelling and degradation properties, good thermostability, and stable rheological characteristics. Furthermore, the adhesive mechanism of MCCS/DMA hydrogel has been confirmed by the FTIR and 2D correlation FTIR spectroscopy. Additionally, the results of in vitro cytotoxicity assessment indicated that the resulting hydrogels have good cytocompatibility. Overall, the MCCS/DMA adhesive hydrogel may have potential applications in medical bioadhesives.

Are Natural Compounds a Promising Alternative to Synthetic Cross-Linking Agents in the Preparation of Hydrogels?

The main aim of this review is to assess the potential use of natural cross-linking agents, such as genipin, citric acid, tannic acid, epigallocatechin gallate, and vanillin in preparing chemically cross-linked hydrogels for the biomedical, pharmaceutical, and cosmetic industries. Chemical cross-linking is one of the most important methods that is commonly used to form mechanically strong hydrogels based on biopolymers, such as alginates, chitosan, hyaluronic acid, collagen, gelatin, and fibroin. Moreover, the properties of natural cross-linking agents and their advantages and disadvantages are compared relative to their commonly known synthetic cross-linking counterparts. Nowadays, advanced technologies can facilitate the acquisition of high-purity biomaterials from unreacted components with no additional purification steps. However, while planning and designing a chemical process, energy and water consumption should be limited in order to reduce the risks associated with global warming. However, many synthetic cross-linking agents, such as N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, poly (ethylene glycol) diacrylates, epichlorohydrin, and glutaraldehyde, are harmful to both humans and the environment. One solution to this problem could be the use of bio-cross-linking agents obtained from natural resources, which would eliminate their toxic effects and ensure the safety for humans and the environment.

A study on the material properties of novel PEGDA/gelatin hybrid hydrogels polymerized by electron beam irradiation

Gelatin-based hydrogels are highly desirable biomaterials for use in wound dressing, drug delivery, and extracellular matrix components due to their biocompatibility and biodegradability. However, insufficient and uncontrollable mechanical properties and degradation are the major obstacles to their application in medical materials. Herein, we present a simple but efficient strategy for a novel hydrogel by incorporating the synthetic hydrogel monomer polyethylene glycol diacrylate (PEGDA, offering high mechanical stability) into a biological hydrogel compound (gelatin) to provide stable mechanical properties and biocompatibility at the resulting hybrid hydrogel. In the present work, PEGDA/gelatin hybrid hydrogels were prepared by electron irradiation as a reagent-free crosslinking technology and without using chemical crosslinkers, which carry the risk of releasing toxic byproducts into the material. The viscoelasticity, swelling behavior, thermal stability, and molecular structure of synthesized hybrid hydrogels of different compound ratios and irradiation doses were investigated. Compared with the pure gelatin hydrogel, 21/9 wt./wt. % PEGDA/gelatin hydrogels at 6 kGy exhibited approximately up to 1078% higher storage modulus than a pure gelatin hydrogel, and furthermore, it turned out that the mechanical stability increased with increasing irradiation dose. The chemical structure of the hybrid hydrogels was analyzed by Fourier-transform infrared (FTIR) spectroscopy, and it was confirmed that both compounds, PEGDA and gelatin, were equally present. Scanning electron microscopy images of the samples showed fracture patterns that confirmed the findings of viscoelasticity increasing with gelatin concentration. Infrared microspectroscopy images showed that gelatin and PEGDA polymer fractions were homogeneously mixed and a uniform hybrid material was obtained after electron beam synthesis. In short, this study demonstrates that both the presence of PEGDA improved the material properties of PEGDA/gelatin hybrid hydrogels and the resulting properties are fine-tuned by varying the irradiation dose and PEGDA/gelatin concentration.

The Effect of Crosslinking Degree of Hydrogels on Hydrogel Adhesion

The development of adhesive hydrogel materials has brought numerous advances to biomedical engineering. Hydrogel adhesion has drawn much attention in research and applications. In this paper, the study of hydrogel adhesion is no longer limited to the surface of hydrogels. Here, the effect of the internal crosslinking degree of hydrogels prepared by different methods on hydrogel adhesion was explored to find the generality. The results show that with the increase in crosslinking degree, the hydrogel adhesion decreased significantly due to the limitation of segment mobility. Moreover, two simple strategies to improve hydrogel adhesion generated by hydrogen bonding were proposed. One was to keep the functional groups used for hydrogel adhesion and the other was to enhance the flexibility of polymer chains that make up hydrogels. We hope this study can provide another approach for improving the hydrogel adhesion generated by hydrogen bonding.