Mechanical and structural response of a hybrid hydrogel based on chitosan and poly(vinyl alcohol) cross-linked with epichlorohydrin for potential use in tissue engineering

Electrovalent effects of sodium carboxymethyl cellulose and hydroxyethyl cellulose on regeneration of empty fruit bunch cellulose to a superabsorbent hydrogel

The hydrogel regeneration process, involving various cellulose types, results in distinct chemical bonding patterns. Even minor variations in chemical interactions among polymers during regeneration significantly impact properties like hydrogel-forming ability, hydrophilicity, and swelling capacity. This study focuses on regenerating a superabsorbent hydrogel from the interplay of native empty fruit bunch cellulose (EFBC), sodium carboxymethyl cellulose (NaCMC), and hydroxyethyl cellulose (HEC) using epichlorohydrin (ECH) as a crosslinker. The hydrogel was formed from dissolved EFBC solutions in an aqueous NaOH/urea solvent, supplemented with different NaCMC and HEC weight ratios, and ECH chemically assisted the crosslinking process. EFBC provides the hydrogel's supporting skeletal structure, while NaCMC and HEC play vital roles in enhancing forming ability and its physical and mechanical properties through diverse chemical interactions based on their electrovalent properties. Notably, NaCMC imparts hydrophilicity, while HEC indirectly improves superabsorbent properties through the enhancement of the elastic network's retraction force. Hydrogels combining NaCMC and HEC show a remarkable water absorption capacity exceeding 30,000 %, surpassing those regenerated solely with EFBC and NaCMC. The highest swelling, over 130,000 %, is achieved with 0.75 % NaCMC and 0.25 % HEC. Regarding thermal stability, hydrogels with a higher NaCMC proportion outperform those with increased HEC content. The study highlights the critical role of tailored chemical interactions in successfully regenerating an improved superabsorbent hydrogel with enhanced water absorption properties.

Sponge-like porous polyvinyl alcohol/chitosan-based hydrogel with integrated cushioning, pH-indicating and antibacterial functions

Developing a packaging material with integrated cushioning, intelligent and active functions is highly desired but remains challenging in the food industry. Here we show that a sponge-like porous hydrogel with pH-indicating and antibacterial additives can meet this requirement. We use polyvinyl alcohol and chitosan as the primary polymers to construct a hydrogel with hierarchical structures through a freeze-casting method in combination with salting-out treatment. The synergy of aggregated polymer chains and the sponge-like porous structure makes the hydrogel resilient and efficient in energy absorption. It also enables rapid movement of molecules/particles and fast reaction due to the large specific surface area of the pore structures and the large amount of free water in it, leading to a sensitive pH-indicating function. The hydrogel shows an obvious color variation within a wide pH range in 3 min. The silver nanoparticles are fixed in the dense polymer networks, enabling a lasting release of silver ions. The porous structure makes the silver ion reach the protected item in a short time, achieving an antibacterial effect against S. aureus and E. coli with little cytotoxicity. This work paves the way for fabricating multifunctional hydrogels for diverse advanced packaging systems.

Copper-zinc/chitosan complex hydrogels: Rheological, degradation and biological properties

Polymer hydrogels crosslinked by therapeutic metal ions have attracted increased interest in recent years due to their unique and versatile properties. Chitosan hydrogels are widely investigated for various biomedical applications such as tissue engineering and drug delivery. Copper and zinc ions are considered as therapeutic metal ions, that have important roles in bone regeneration. The aim of this study was to investigate the physicochemical and biological properties of bimetallic-chitosan complex hydrogels with different cupric and zinc ions content. Scanning electron microscopy (SEM) revealed changes in the morphology from the microstructure with larger, tubular pores for aerogels with higher Zn content, to the sheets-like structure with long pores for samples with higher Cu content. FTIR analysis indicated the formation of bimetallic-chitosan aerogels. The obtained X-ray diffraction patterns showed a broadening of chitosan's characteristic diffraction maximum, while characterization of physical properties showed decreased swelling ability and increased shear modulus with higher Cu content. ICP-MS results showed a negligible amount of copper and zinc ions released under physiological conditions during 24 h indicating a strong physical crosslink between metal ions and chitosan chains. Furthermore, accelerated in vitro degradation showed that hydrogels maintained good stability during four weeks of lysozyme activity. The MTT assay indicated that the cytotoxicity of Cu2+-Zn2+/chitosan complexes could be adjusted by the amount of cupric ions. All results imply that Cu2+ and Zn2+ ions act as physical crosslinkers of the polymer network. Also, results are in agreement with the prediction of density functional theory (DFT) which indicated stronger chitosan-Cu tetrahedral aqua complex interactions in comparison to the chitosan-[Zn(H2O)4]2+ interactions.

Lecithin as an Effective Modifier of the Transport Properties of Variously Crosslinked Hydrogels

Transport properties are one of the most crucial assets of hydrogel samples, influencing their main application potential, i.e., as drug carriers. Depending on the type of drug or the application itself, it is very important to be able to control these transport properties in an appropriate manner. This study seeks to modify these properties by adding amphiphiles, specifically lecithin. Through its self-assembly, lecithin modifies the inner structure of the hydrogel, which affects its properties, especially the transport ones. In the proposed paper, these properties are studied mainly using various probes (organic dyes) to effectively simulate drugs in simple release diffusion experiments controlled by UV-Vis spectrophotometry. Scanning electron microscopy was used to help characterize the diffusion systems. The effects of lecithin and its concentrations, as well as the effects of variously charged model drugs, were discussed. Lecithin decreases the values of the diffusion coefficient independently of the dye used and the type of crosslinking. The ability to influence transport properties is better observed in xerogel samples. The results, complementing previously published conclusions, showed that lecithin can alter a hydrogel's structure and therefore its transport properties.

Computation of Binding Energy of MCS and GO-Grafted MCS with Waterborne Epoxy Resin Using Density Functional Theory Method: Investigating the Corrosion Resistance of the Composite Coatings

In order to overcome the problems of poor corrosion resistance and low hydrophobicity of water-based coatings. Two corrosion-inhibiting materials, graphene oxide (GO) and modified chitosan (MCS), were added to the coatings to obtain a new type of coating with comprehensive properties. The composite material formed by PVA cross-linked waterborne epoxy resin was named "substrate". The density functional theory (DFT) calculation was used to explore the binding ability of MCS and GO-grafted MCS to the substrate, respectively. The results showed that the complex cross-linked network structure formed by the grafting of GO and MCS not only improved the intermolecular interaction force but also improved the binding ability to the substrate, and the coating is denser, effectively delaying the erosion to the coating by the corrosive medium. The composite coating exhibited excellent dual functional properties of hydrophobicity and corrosion resistance at the coating-metal interface, and a stronger protective effect was formed upon the steel plate. Studies showed that this composite coating has good hydrophobic properties. (The contact angle of the composite waterborne coating reaches 87°.) It also has low self-corrosion current (0.28/cm^-2) and high corrosion voltage (-0.45 V). The maximum inhibition efficiency of the coating is 99.97%.

Synthesis, characterization, and biological activities of new conjugates of Guanosine grafted on polyvinyl alcohol, carbohydrate chitosan, and cellulose

Guanosine (GU) is a purine nucleoside that has different biological applications. This study aimed to synthesize, characterize, and enhance the biological activities of GU through its covalently grafting on polyvinyl alcohol (PVA), chitosan (CS), and cellulose (CL). In this regard, the conjugation was constructed by different linkers such as chloroacetyl chloride, 2-bromopropionyl bromide, and epichlorohydrin (EPCH). The resulted novel conjugates were characterized by FT-IR, 1H-NMR, GPC, and TGA techniques. FT-IR spectra revealed the main characteristic groups, O–H, N–H, C=O and C=N of GU moieties. Furthermore, 1H-NMR spectra showed the aromatic C–H, O–H, and N–H protons of the grafted GU moieties. Two decomposition stages of grated polymers with high thermal stability are illustrated by TGA. GU showed no antifungal activity against Aspergillus fumigatus and Candida albicans. However, its conjugates: P-1A, P-1B, P-2A, P-2B, P-3A, and P-3B displayed significant antifungal effect with inhibitory zones in the range 8–11 mm. As compared to GU group, most of GU-polymer conjugates showed significant in vivo antitumor activity against EAC-bearing mice via the reduction in total tumor volume. In summary, these conjugates are biologically active macromolecules and may act as candidate carrier systems for other applications such as drug delivery.

Preparation, characterisation and comparison of glabridin-loaded hydrogel-forming microneedles by chemical and physical cross-linking

Poly(vinyl alcohol) (PVA) and carbomer were used as the hydrogel system to fabricate glabridin-loaded hydrogel-forming microneedles (HFMNs) by chemical cross-linking (CCMNs) and physical cross-linking (PCMNs). The properties and drug permeation effect of glabridin-loaded HFMNs with different methods were compared. They both owned excellent shape, mechanical and insertion properties. PCMNs showed a collapsed shape during swelling due to the low cross-linking rate and high porosity, probably resulting in resealing of skin pores during transdermal delivery. However, CCMNs could rapidly swell within 2 h with slightly bending. The infrared spectra indicated that CCMNs and PCMNs might form the hydrogel network by generating hydrogen and covalent bonds, respectively. The in vitro release studies showed that cumulative permeation amount within 24 h (1654 μg/cm²) of CCMNs, significantly higher than that (372 μg/cm²) achieved by PCMNs and that (118 μg/cm²) achieved by glabridin-loaded gel. The skin barrier recovery test suggests the desirable security of both microneedles (MNs), notwithstanding the presence of mild erythema in the mouse skin applied CCMNs. These results indicated that CCMNs were more desirable for glabridin delivery using PVA and carbomer as a skeleton of the hydrogel network.

Novel Hydrogel Material with Tailored Internal Architecture Modified by “Bio” Amphiphilic Components—Design and Analysis by a Physico-Chemical Approach

Nowadays, hydrogels are found in many applications ranging from the industrial to the biological (e.g., tissue engineering, drug delivery systems, cosmetics, water treatment, and many more). According to the specific needs of individual applications, it is necessary to be able to modify the properties of hydrogel materials, particularly the transport and mechanical properties related to their structure, which are crucial for the potential use of the hydrogels in modern material engineering. Therefore, the possibility of preparing hydrogel materials with tunable properties is a very real topic and is still being researched. A simple way to modify these properties is to alter the internal structure by adding another component. The addition of natural substances is convenient due to their biocompatibility and the possibility of biodegradation. Therefore, this work focused on hydrogels modified by a substance that is naturally found in the tissues of our body, namely lecithin. Hydrogels were prepared by different types of crosslinking (physical, ionic, and chemical). Their mechanical properties were monitored and these investigations were supplemented by drying and rehydration measurements, and supported by the morphological characterization of xerogels. With the addition of natural lecithin, it is possible to modify crucial properties of hydrogels such as porosity and mechanical properties, which will play a role in the final applications.

Chitosan-silica with hops β-acids added films as prospective food packaging materials: Preparation, characterization, and properties

In this study, silica (SiO₂) and β-acids were added to the chitosan films in order to improve the film's properties. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD) were used to explore the structure of film. The results of mechanical test indicated that the film containing SiO₂ (0.3%) and β-acids (0.3%) could obtain a significant tensile strength (10.04 MPa). The complex films possessed a good inhibitory effect on three types of bacteria, and good antioxidant activity (>56%, DPPH). The release mechanism of β-acids from the films exhibited Fickian diffusion (n < 0.45). During the storage of soybean oil, the films could well control the changes of the peroxide value, acid value and thiobarbituric acid reactant content. Overall, the biofilms not only possess good physical and chemical properties, but also prolongs the time of food storage.

Designing cellulose hydrogels from non-woody biomass

Hydrogels are an attractive system for a myriad of applications. While most hydrogels are usually formed from synthetic materials, lignocellulosic biomass appears as a sustainable alternative for hydrogel development. The valorization of biomass, especially the non-woody biomass to meet the growing demand of the substitution of synthetics and to leverage its benefits for cellulose hydrogel fabrication is attractive. This review aims to present an overview of advances in hydrogel development from non-woody biomass, especially using native cellulose. The review will cover the overall process from cellulose depolymerization, dissolution to crosslinking reaction and the related mechanisms where known. Hydrogel design is heavily affected by the cellulose solubility, crosslinking method and the related processing conditions apart from biomass type and cellulose purity. Hence, the important parameters for rational designs of hydrogels with desired properties, particularly porosity, transparency and swelling characteristics will be discussed. Current challenges and future perspectives will also be highlighted.

Chitosan/alginate/hyaluronic acid polyelectrolyte composite sponges crosslinked with genipin for wound dressing application

Wound dressing composed of polyelectrolyte complexes (PECs), based on chitosan/alginate/hyaluronic acid (CS/ALG/HYA) crosslinked by genipin, was prepared by freeze-dried molding. Genipin as excellent natural biological crosslinker was chose for high biocompatibility and improving mechanical properties of materials. The CS/ALG/HYA sponges (CAHSs) were characterized by FTIR, XRD, DSC and SEM. Porosity, swelling behavior and mechanical properties and in vitro degradation of CAHSs were investigated. The cytotoxicity assay was carried out on HUVEC cells in vitro and the result proves the good biocompatibility of CAHSs. Hemolysis tests indicated that the prepared CAHSs were non-hemolytic material (hemolysis ratio < 5%, no cytotoxicity). PT and aPPT coagulation tests demonstrated that CAHS2 and CAHS3 could both activate the extrinsic and intrinsic coagulation pathway and thus accelerated blood coagulation. Further, in a rat full-thickness wounds model, the CAHS2 sponge significantly facilitates wound closure compared to other groups. CAHSs exhibited adjustable physical, mechanical and biological properties. Thus, the chitosan-based polyelectrolyte composite sponges exhibit great potential as promising wound dressings.

Preparation of chitosan aerogel crosslinked in chemical and ionical ways by non-acid condition for wound dressing

Herein, the dual-crosslinked chitosan aerogel was prepared using 1-butyl-3-methylimidazolium chloride, an ionic liquid, as a solvent. The hydroxyl groups were covalently crosslinked by epichlorohydrin (ECH), while the amino groups were ionically crosslinked by itaconic acid (IA). The chemical and ionic crosslinkings of the aerogels were analyzed using FT-IR and NMR. Both the types and the degree of crosslinking gave significant influences on the structures of the aerogels. The dual crosslinked aerogel with proper chemical crosslinking dose had the excellent swelling behavior. The prepared aerogel shows potential as a wound healing matrix, with low toxicity and antibacterial function.

Structure-property of crosslinked chitosan/silica composite films modified by genipin and glutaraldehyde under alkaline conditions

In this study, genipin and glutaraldehyde in varied concentrations were utilized in chitosan crosslinking under alkaline condition. A UV/Vis analysis was used to investigate the molecular structure of genipin and glutaraldehyde in an aqueous alkaline solution. The results showed the formation of glutaraldehyde dimer and polymerized genipin. The FTIR-ATR, SEM, DSC, XRD, mechanical properties, crosslinking degree and swelling ratio of chitosan based films crosslinked by genipin and glutaraldehyde were determined. The results indicated that the hydrogen bonds formed between genipin and chitosan enabled the films crosslinked by genipin (1 and 5 mmol/L) to have a higher degree of crosslinking, but a lower swelling ratio than glutaraldehyde (1 and 5 mmol/L). Genipin enabled the chitosan-based film to possess better mechanical properties and crystallinity than glutaraldehyde. The polymerization of genipin had a substantial effect on the network structure and swelling behavior of chitosan-based films crosslinked by genipin.

Polyvinyl alcohol-based hydrophilic monoliths from water-in-oil high internal phase emulsion template

Herein, we report a new approach to fabricate polyvinyl alcohol (PVA) based hydrophilic monoliths by alcoholysis of porous emulsion-templated polyvinyl acetate (PVAc). The precursory PVAc-based monolith is obtained by polymerization of a W/O high internal phase emulsion (HIPE) containing vinyl acetate as the external phase while water as the internal phase. As an alcoholysis-stable tri-functional commonomer, triallyl isocyanurate is chosen as the crosslinking agent to prevent possible collapse of the polymeric skeleton and the consequent losses in mechanical properties during the alcoholysis step. By alcoholysis of the resulting PVAc-based monolith, the PVA-based monoliths are successful prepared as confirmed by FTIR analysis. BET analysis and SEM observation confirm the formation of open-cell and highly interconnected porous structures of PVA-based monoliths with surface areas of around 16m²/g. Stemming from the intrinsic hydrophilicity of hydroxyl and morphology, PVA-based monoliths exhibit great enhancement in hydrophilicity with a much lower water contact angles than that of PVAc-based monoliths.

Engineering muscle constructs for the creation of functional engineered musculoskeletal tissue

Volumetric muscle loss (VML) is a disabling condition in which current clinical procedures are suboptimal. The field of tissue engineering has many promising strategies for the creation of functional skeletal muscle in vitro. However, there are still two key limitations that prevent it from becoming a solution for treating VML. First, engineered muscle tissue must be biocompatible to facilitate muscle tissue regrowth without generating an immune response. Second, engineered muscle constructs must be scaled up to facilitate replacement of clinically relevant volumes of tissue (centimeters in diameter). There are currently no tissue engineering strategies to produce tissue constructs that are both biocompatible and large enough to facilitate clinical repair. However, recent advances in tissue engineering using synthetic scaffolds, native scaffolds, or scaffold-free approaches may lead to a solution for repair of VML injuries.

Design of 2D chitosan scaffolds via electrochemical structuring

Chitosan (CS) is a versatile biopolymer whose morphological and chemico-physical properties can be designed for a variety of biomedical applications. Taking advantage of its electrolytic nature, cathodic polarization allows CS deposition on electrically conductive substrates, resulting in thin porous structures with tunable morphology. Here we propose an easy method to obtain CS membranes with highly oriented micro-channels for tissue engineering applications, relying on simple control of process parameters and cathodic substrate geometry.

 

Cathodic deposition was performed on two different aluminum grids in galvanostatic conditions at 6.25 mA cm⁻² from CS solution [1g L⁻¹] in acetic acid (pH 3.5). Self-standing thin scaffolds were cross linked either with genipin or epichlorohydrin, weighted, and observed by optical and electron microscopy. Swelling properties at pH 5 and pH 7.4 have been also investigated and tensile tests performed on swollen samples at room temperature. Finally, direct and indirect assays have been performed to evaluate the cytotoxicity at 24 and 72 h.

Thin scaffolds with two different oriented porosities (1000µm and 500µm) have been successfully fabricated by electrochemical techniques. Both cross-linking agents did not affected the mechanical properties and cytocompatibility of the resulting structures. Depending on the pH, these structures show interesting swelling properties that can be exploited for drug delivery systems. Moreover, thanks to the possibility of controlling the porosity and the micro-channel orientation, they should be used for the regeneration of tissues requiring a preferential cells orientation, e.g., cardiac patches or ligament regeneration.