Effects of post-processing methods on chitosan-genipin hydrogel properties

Comparative Analysis of Electron Microscopy Techniques for Hydrogel Microarchitecture Characterization: SEM, Cryo-SEM, ESEM, and TEM

Hydrogels have emerged as a versatile class of materials with broad applications in biomedical engineering, drug delivery, and tissue engineering. Understanding their intricate structures and morphologies is crucial for tailoring their properties to meet specific biomedical needs. It has been clearly established that the composition and microarchitecture of the materials play a critical role in essential cellular mechanisms such as mechanosensing, adhesion, and remodeling. This question is essential in tissue engineering, where precisely characterizing the microarchitecture of the materials used to model the cell microenvironment is a critical step to ensure the reproducibility and relevance of reconstructed tissues. In this study, we present a comprehensive comparison of four advanced electron microscopy techniques, namely, scanning electron microscopy, cryo-scanning electron microscopy, environmental scanning electron microscopy, and transmission electron microscopy, to observe the hydrogel microarchitecture, including a comparison of the sample preparation methods for each technique. Each technique's specific advantages and limitations are discussed in detail, highlighting their unique capabilities in characterizing the hydrogel structures. We illustrate this study with two semisynthetic hydrogels, such as gelatin methacrylate and hyaluronic acid methacrylate. Moreover, we delve into the critical sample preparation steps necessary for each method, emphasizing the need to preserve the hydrogel's native state while obtaining high-resolution images. This comparative analysis aims to select the most suitable electron microscopy technique for their hydrogel studies, fostering deeper insights into the design and development of advanced biomaterials for tissue engineering applications.

Hydrogel Biocomposite of Alginate and Mucilage of Opuntia ficus-indica Cactus in the Adsorption of Methylene Blue in Aqueous Solution

This work analyzes the production of a hydrogel composed of mucilage from the cactus Opuntia ficus-indica (OFI) and sodium alginate. In obtaining the new material, green synthesis was used, free of chemical compounds, and applied in the treatment of textile effluent for the adsorption of methylene blue (MB). The hydrogel was characterized by FT-IR, XRD, SEM, and zeta potential. The swelling study showed a maximum value of 262% at pH 6.0. Adsorption studies revealed a maximum adsorptive capacity of 7.21 mg g-1 in 400 min at 298 K. Furthermore, the experimental data showed better fit to the pseudo-second order and Langmuir models for kinetic and isothermal studies, respectively. The adsorptive process showed spontaneous and exothermic behavior as well as a chemisorptive nature. It is noteworthy that in the studies conducted at a higher concentration of the contaminant, the maximum adsorption was 760 mg g-1. The reuse of the hydrogel was effective for five cycles, maintaining the adsorption of approximately 50% MB removal. Therefore, the biodegradable hydrogel is a material that contributes to the environment, is low cost, with simple synthesis, and is a promising new material for large-scale applications, considering its sustainable character and high efficiency in the adsorption of MB in aqueous solution.

The influence of molecular weight on the anticorrosion properties of chitosan coatings

The effort to replace toxic compounds with natural alternatives led to intensive investigations on the use of polysaccharides as coatings for corrosion protection. Biological macromolecules, such as chitosan, demonstrate great potential for the development of sustainable anticorrosion coatings. However, the role played by important properties, such as molecular weight, on the performance of the coatings, remains unclear. In this paper, the influence of molecular weight on the anticorrosion properties of chitosan coatings is investigated using AA2024-T3 aluminum alloy as substrate. Chitosan of three different molecular weights were used for the preparation of coatings and free-standing films, and their properties (morphology, swelling degree, and water contact angle) were evaluated. The corrosion performance of the coated samples was investigated by an atmospheric corrosion essay and by electrochemical impedance spectroscopy, in NaCl 3.5 % solution. The results show that the low-molecular-weight chitosan coatings present the lowest swelling degree (603 %), highest water contact angle (86.4°), lowest porosity, and superior performance in both corrosion tests, reaching impedances close to 105Ωcm2 even after seven days of exposure to corrosive solution.

Functionalised Sodium-Carboxymethylcellulose-Collagen Bioactive Bilayer as an Acellular Skin Substitute for Future Use in Diabetic Wound Management: The Evaluation of Physicochemical, Cell Viability, and Antibacterial Effects

The wound healing mechanism is dynamic and well-orchestrated; yet, it is a complicated process. The hallmark of wound healing is to promote wound regeneration in less time without invading skin pathogens at the injury site. This study developed a sodium-carboxymethylcellulose (Na-CMC) bilayer scaffold that was later integrated with silver nanoparticles/graphene quantum dot nanoparticles (AgNPs/GQDs) as an acellular skin substitute for future use in diabetic wounds. The bilayer scaffold was prepared by layering the Na-CMC gauze onto the ovine tendon collagen type 1 (OTC-1). The bilayer scaffold was post-crosslinked with 0.1% (w/v) genipin (GNP) as a natural crosslinking agent. The physical and chemical characteristics of the bilayer scaffold were evaluated. The results demonstrate that crosslinked (CL) groups exhibited a high-water absorption capacity (>1000%) and an ideal water vapour evaporation rate (2000 g/m2 h) with a lower biodegradation rate and good hydrophilicity, compression, resilience, and porosity than the non-crosslinked (NC) groups. The minimum inhibitory concentration (MIC) of AgNPs/GQDs presented some bactericidal effects against Gram-positive and Gram-negative bacteria. The cytotoxicity tests on bilayer scaffolds demonstrated good cell viability for human epidermal keratinocytes (HEKs) and human dermal fibroblasts (HDFs). Therefore, the Na-CMC bilayer scaffold could be a potential candidate for future diabetic wound care.

Effect of Crosslinking Agents on Chitosan Hydrogel Carriers for Drug Loading and Release for Targeted Drug Delivery

Numerous studies report on chitosan hydrogels in different forms, such as films, porous structures, nanoparticles, and microspheres, for biomedical applications; however, this study concentrates on their modifications with different crosslinking agents and observes their effects on drug loading and releasing capacities. Linear chitosan, along with chitosans crosslinked with two major crosslinkers, i.e., genipin and disulfide, are used to formulate three different hydrogel systems. The crosslinking process is heavily impacted by temperature and pH conditions. Three different drugs, i.e., thymoquinone, gefitinib, and erlotinib, are loaded to the hydrogels in de-ionized water solutions and released in phosphate-buffered solutions; thus, a total of nine combinations are studied and analyzed for their drug loading and releasing capabilities with ultraviolet-visible (UV-Vis) spectroscopy. This study finds that thymoquinone shows the lowest loading efficacy compared to the two other drugs in all three systems. Gefitinib shows stable loading and releasing regardless of crosslinking system, and the genipin-crosslinked system shows stable loading and releasing with all three drug molecules. These experimental results agree well with the findings of our previously published results conducted with molecular dynamics simulations.

Characterization and Optimization of Injectable In Situ Crosslinked Chitosan-Genipin Hydrogels

In recent years, there has been an increased interest in injectable, in situ crosslinking hydrogels due to their minimally invasive application and ability to conform to their environment. Current in situ crosslinking chitosan hydrogels are either mechanically robust with poor biocompatibility and limited biodegradation due to toxic crosslinking agents or the hydrogels are mechanically weak and undergo biodegradation too rapidly due to insufficient crosslinking. Herein, the authors developed and characterized a thermally-driven, injectable chitosan-genipin hydrogel capable of in situ crosslinking at 37 °C that is mechanically robust, biodegradable, and maintain high biocompatibility. The natural crosslinker genipin is utilized as a thermally-driven, non-toxic crosslinking agent. The chitosan-genipin hydrogel's crosslinking kinetics, injectability, viscoelasticity, swelling and pH response, and biocompatibility against human keratinocyte cells are characterized. The developed chitosan-genipin hydrogels are successfully crosslinked at 37 °C, demonstrating temperature sensitivity. The hydrogels maintained a high percentage of swelling over several weeks before degrading in biologically relevant environments, demonstrating mechanical stability while remaining biodegradable. Long-term cell viability studies demonstrated that chitosan-genipin hydrogels have excellent biocompatibility over 7 days, including during the hydrogel crosslinking phase. Overall, these findings support the development of an injectable, in situ crosslinking chitosan-genipin hydrogel for minimally invasive biomedical applications.

Neat Chitosan Porous Materials: A Review of Preparation, Structure Characterization and Application

This review presents an overview of methods for preparing chitosan-derived porous materials and discusses their potential applications. This family of materials has garnered significant attention owing to their biocompatibility, nontoxicity, antibacterial properties, and biodegradability, which make them advantageous in a wide range of applications. Although individual porous chitosan-based materials have been widely discussed in the literature, a summary of all available methods for preparing materials based on pure chitosan, along with their structural characterization and potential applications, has not yet been presented. This review discusses five strategies for fabricating porous chitosan materials, i.e., cryogelation, freeze-drying, sol-gel, phase inversion, and extraction of a porogen agent. Each approach is described in detail with examples related to the preparation of chitosan materials. The influence of the fabrication method on the structure of the obtained material is also highlighted herein. Finally, we discuss the potential applications of the considered materials.

Adsorption of Cu2+, Cd2+ and Pb2+ in wastewater by modified chitosan hydrogel

Heavy metal pollution is extraordinary critical, so it is urgent to develop an effective adsorbent to dispose of such pollution. Modified chitosan was combined with polyacrylic acid to form N-carboxymethyl chitosan hydrogel (NCS-hydrogel) adsorbent. The morphology and structure of NCS-hydrogel were analyzed and identified by infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and other characterization methods. NCS-hydrogel adsorption was used to treat water pollution of Cu, Cd and Pb ions, and the influencing factors of adsorption performance were studied. The intrinsic mechanism of adsorption process was discussed by thermodynamic, kinetic and isotherm models. The results show that the adsorption process of metal ions by NCS-hydrogel meets the spontaneous monolayer chemisorption, and the adsorption process is accompanied by heat release.

Injectable and self-healing chitosan-based hydrogel with MOF-loaded α-lipoic acid promotes diabetic wound healing

The difficulty of wound healing in patients with diabetes mellitus remains a considerable challenge for clinical and scientific research. To address the problem of poor healing that affects chronic wounds in patients with diabetes, we developed an injectable self-healing hydrogel based on chitosan (CS), hyaluronic acid (HA), and kalium γ-cyclodextrin metal organic frameworks (K-γ-CD-MOFs) loaded α-lipoic acid (α-LA) with antibacterial activity and antioxidant performance. In vitro analysis showed that the hydrogel could promote cell proliferation and migration on the basis of Cell Counting Kit-8 (CCK-8) assay and Transwell experiments. Moreover, the addition of α-LA allowed the reversal of oxidative stress-induced cell damage. In vivo analyses were performed involving a full-thickness wound model in diabetic Sprague-Dawley (SD) rats. The hydrogel dressing significantly promoted the wound healing process with better granulation tissue formation and more collagen deposition because of its multifunctional traits, suggesting that it can be an excellent treatment for chronic full-thickness skin wound healing.

Polymer and Crosslinker Content Influences Performance of Encapsulated Live Biotherapeutic Products

INTRODUCTION

Live biotherapeutic products (LBPs), or therapeutic microbes, are an emerging therapeutic modality for prevention and treatment of gastrointestinal diseases. Since LBPs are living, they are uniquely sensitive to external stresses (e.g., oxygen, acid) encountered during manufacturing, storage, and delivery. Here, we systematically evaluate how polymer and crosslinker concentration affects the performance of an encapsulated LBP toward developing a comprehensive framework for the characterization and optimization of LBP delivery systems.

METHODS

We encapsulate a model LBP, Lactobacillus casei ATCC 393, in calcium chloride (CaCl2)-crosslinked alginate beads, and evaluate how alginate and CaCl2 concentrations influence LBP formulation performance, including: (i) encapsulation efficiency, (ii) shrinkage upon drying, (iii) survival upon lyophilization, (iv) acid resistance, (v) release, and (vi) metabolite secretion. Approaches from microbiology (e.g., colony forming unit enumeration), materials science (e.g., scanning electron microscopy), and pharmaceutical sciences (e.g., release assays) are employed.

RESULTS

LBP-encapsulating alginate beads were systematically evaluated as a function of alginate and CaCl2 concentrations. Specifically: (i) encapsulation efficiency of all formulations was >50%, (ii) all alginate beads shrunk (after lyophilization) and recovered (after rehydration) similarly, (iii) at 10% alginate concentration, lower CaCl2 concentration decreased survival upon lyophilization, (iv) 10% alginate improved acid resistance, (v) sustained release was enabled by increasing alginate and CaCl2 concentrations, and (vi) encapsulation did not impair secretion of l-lactate as compared to free LBP.

CONCLUSIONS

This research demonstrates that polymer content and crosslinking extent modulate the performance of polymer-based LBP delivery systems, motivating research into the optimization of material properties for LBP delivery systems.

Ice Templating Soft Matter: Fundamental Principles and Fabrication Approaches to Tailor Pore Structure and Morphology and Their Biomedical Applications

Porous scaffolds are widely used in biomedical applications where pore size and morphology influence a range of biological processes, including mass transfer of solutes, cellular interactions and organization, immune responses, and tissue vascularization, as well as drug delivery from biomaterials. Ice templating, one of the most widely utilized techniques for the fabrication of porous materials, allows control over pore morphology by controlling ice formation in a suspension of solutes. By fine-tuning freezing and solute parameters, ice templating can be used to incorporate pores with tunable morphological features into a wide range of materials using a simple, accessible, and scalable process. While soft matter is widely ice templated for biomedical applications and includes commercial and clinical products, the principles underpinning its ice templating are not reviewed as well as their inorganic counterparts. This review describes and critically evaluates fundamental principles, fabrication and characterization approaches, and biomedical applications of ice templating in polymer-based biomaterials. It describes the utility of porous scaffolds in biomedical applications, highlighting biological mechanisms impacted by pore features, outlines the physical and thermodynamic mechanisms underpinning ice templating, describes common fabrication setups, critically evaluates complexities of ice templating specific to polymers, and discusses future directions in this field.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

A novel blue crab chitosan/protein composite hydrogel enriched with carotenoids endowed with distinguished wound healing capability: In vitro characterization and in vivo assessment

This work aimed to the development of chitosan and protein isolate composite hydrogels, for carotenoids-controlled delivery and wound healing. By increasing the concentration of the protein isolate, chitosan hydrogels were more elastic at a protein isolate concentration not exceeding 15% (w/w). Chitosan-protein isolate composite hydrogels revealed low cytotoxicity towards MG-63 osteosarcoma cells. Thanks to its appropriate structural, swelling and mechanical resistance properties, chitosan hydrogel (3%; w/v), reinforced with 15% (w/w) of protein isolate, was selected for the carotenoids in vitro release study. Release profiles, show delivery patterns, where carotenoids were more barely released at a pH 7.4 medium (p < .05), compared to more acidic microenvironments (pH 4.0 and pH 2.0). Thus, developed hydrogels could be applied as pH-sensitive intelligent carriers, for drugs-controlled release, with interesting antioxidant abilities. The in vivo healing potential of hydrogels in rats' models was further studied. Topical application of hydrogel-based patches allowed the acceleration of wound healing and the complete healing, for composite hydrogel enriched with carotenoids.

In Situ H2O Meter by Visualization in Hydrogels

The solvent content strongly affects the viscoelastic properties and network structure of hydrogels. Because of the gels' structural susceptibility and autofluorescence background, there is still no visual method to evaluate the water content in micropores. Herein, a colorimetric molecular probe (DHBYD) was synthesized for in situ visualization of water content in the micropores of hydrogels. The rapid and reversible colorimetric responses of DHBYD to solvents were obtained, which resulted a full linearity range (0 to 100%) for detecting water content in real time. Demonstrated by theoretical calculations, the sensing was attributed to changes in intramolecular charge transfer via deprotonation of phenol group. A cubic polynomial, on correlation of RGB values with water content, was established for real detection of water content in hydrogels. It reveals a new pathway for simple, in situ, and full-range evaluation of solvent content in micropores of hydrogels without any complicated procedures or expensive instruments. This would achieve fast and in situ monitoring of hydrogels to improve gel properties for better applications. It can be extended to evaluate the solvent content in other fields such as synthesis and industrial applications.

Processing and modification of hydrogel and its application in emerging contaminant adsorption and in catalyst immobilization: a review

Due to the wonderful property of hydrogels, they can provide a platform for a wide range of applications. Recently, there is a growing research interest in the development of potential hydrogel adsorbents in wastewater treatment due to their adsorption ability toward aqueous pollutants. It is important to prepare such a hydrogel that possesses appropriate robustness, adsorption capacity, and adsorption efficiency to meet the need of water treatment. In order to improve the property of hydrogels, much effort has been made by researchers to modify hydrogels, among which incorporating inorganic components into the polymeric networks is the most common method, which can reduce the product cost and simplify the preparation procedure. Not only can hydrogel be applied as adsorbent, but it also can be used as matrix for catalyst immobilization. In this review, the key advancement on the preparation and modification of hydrogels is discussed, with special emphasis on the introduction of inorganic materials into polymeric networks and consequential changes in the properties of mechanical strength, swelling, and adsorption. Besides, hydrogels used as adsorbents for removal of dyes and inorganic pollutants have been widely explored, but their use for adsorbing emerging contaminants from aqueous solution has not received much attention. Thus, this review is mainly focused on hydrogels' application in removing emerging contaminants by adsorption. Furthermore, hydrogels can be also applied in immobilizing catalysts, such as enzyme and photocatalyst, to remove pollutants completely and avoid secondary pollution, so their progress as catalyst matrix is overviewed.

Construction of a Lignosulfonate-Lysine Hydrogel for the Adsorption of Heavy Metal Ions

Industrial wastewater has brought great disaster to water bodies and soils and seriously affected the growth of crops. It is necessary to prepare a stable, effective, and sustainable treatment agent to control water pollution to obtain clean water. The adsorption effect of a lignosulfonate-lysine hydrogel (CLS-Lys adsorbent) on heavy metal ions (Cu²⁺ and Co²⁺) in water is studied. In the synthesis experiment, a response surface method is used to optimize the content of sodium lignosulfonate, lysine, initiator, and cross-linker. The CLS-Lys adsorbent is characterized by Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, thermal analysis, and zeta potential analysis. The performance of the CLS-Lys adsorbent under different influencing factors is studied. The kinetic and isothermal models of the CLS-Lys adsorbent are established. The results show that the main adsorption model of the CLS-Lys adsorbent is chemical adsorption, accompanied by electrostatic adsorption. These two ions have a competitive adsorption relationship, and when the two ions are present at the same time, they inhibit each other. In addition, the CLS-Lys adsorbent has good adsorption and analytical regeneration performance. It is an economic and effective adsorbent and has a broad application prospect.

Resveratrol-loaded peptide-hydrogels inhibit scar formation in wound healing through suppressing inflammation

Scar formation seriously affects the repair of damaged skin especially in adults and the excessive inflammation has been considered as the reason. The self-assembled peptide-hydrogels are ideal biomaterials for skin wound healing due to their similar nanostructure to natural extracellular matrix, hydration environment and serving as drug delivery systems. In our study, resveratrol, a polyphenol compound with anti-inflammatory effect, is loaded into peptide-hydrogel (Fmoc-FFGGRGD) to form a wound dressing (Pep/RES). Resveratrol is slowly released from the hydrogel in situ, and the release amount is controlled by the loading amount. The in vitro cell experiments demonstrate that the Pep/RES has no cytotoxicity and can inhibit the production of pro-inflammatory cytokines of macrophages. The Pep/RES hydrogels are used as wound dressings in rat skin damage model. The results suggest that the Pep/RES dressing can accelerate wound healing rate, exhibit well-organized collagen deposition, reduce inflammation and eventually prevent scar formation. The Pep/RES hydrogels supply a potential product to develop new skin wound dressings for the therapy of skin damage.

Poly (ethylene glycol) hydrogel scaffolds with multiscale porosity for culture of human adipose-derived stem cells

Three-dimensional (3 D) hydrogel scaffolds are an attractive option for tissue regeneration applications because they allow for cell migration, fluid exchange, and can be synthesized to closely mimic the physical properties of the extracellular matrix environment. The material properties of hydrogels play a vital role in cellular migration and differentiation. In light of this, in-depth understanding of material properties is required before such scaffolds can be used to study their influence on cells. Herein, various blends and thicknesses of poly (ethylene glycol) dimethacrylate (PEGDMA) hydrogels were synthesized, flash frozen, and dried by lyophilization to create scaffolds with multiscale porosity. Environmental scanning electron microscopy (ESEM) images demonstrated that lyophilization induced microporous voids in the PEGDMA hydrogels while swelling studies show the hydrogels retain their innate swelling properties. Change in pore size was observed between drying methods, polymer blend, and thickness when imaged in the hydrated state. Human adipose-derived stem cells (hASCs) were seeded on lyophilized and non-lyophilized hydrogels to determine if the scaffolds would support cell attachment and proliferation of a clinically relevant cell type. Cell attachment and morphology of the hASCs were evaluated using fluorescence imaging. Qualitative observations in cell attachment and morphology of hASCs on the surface of the different hydrogel spatial configurations indicate these multiscale porosity hydrogels create a suitable scaffold for hASC culture. These findings offer another factor of tunability in creating biomimetic hydrogels for various tissue engineering applications including tissue repair, regeneration, wound healing, and controlled release of growth factors.

Physical Hydrogels of Oxidized Polysaccharides and Poly(Vinyl Alcohol) for Wound Dressing Applications

Two natural polymers, i.e., cellulose and water soluble pullulan, have been selectively oxidized employing the TEMPO-mediated protocol, to allow the introduction of C₆-OOH groups. Thereafter, the composite hydrogels of poly(vinyl alcohol) (PVA) and different content of the oxidized polysaccharides were prepared by the freezing/thawing method. The Fourier transform infrared spectroscopy (FTIR) has been used to discuss the degree of interaction between the hydrogels constituents into the physical network. The homogeneity of the prepared hydrogels as revealed by the SEM show an excellent distribution of the oxidized polysaccharides inside the PVA matrix. The samples exhibit self-healing features, since they quickly recover the initial structure after being subjected to a large deformation. The cell viability was performed for the selected hydrogels, all of them showing promising results. The samples are able to load L-arginine both by physical phenomena, such as diffusion, and also by chemical phenomena, when imine-type bonds are likely to be formed. The synergism between the two constituents, PVA and oxidized polysaccharides, into the physical network, propose these hydrogels for many other biomedical applications.