On the Correlation between the Microscopic Structure and Properties of Phosphate-Cross-Linked Chitosan Gels

Composite hydrogels assembled from food-grade biopolymers: Fabrication, properties, and applications

Biopolymer hydrogels have a broad range of applications as soft materials in a variety of commercial products, including foods, cosmetics, agrochemicals, personal care products, pharmaceuticals, and biomedical products. They consist of a network of entangled or crosslinked biopolymer molecules that traps relatively large quantities of water and provides semi-solid properties, like viscoelasticity or plasticity. Composite biopolymer hydrogels contain inclusions (fillers) to enhance their functional properties, including solid particles, liquid droplets, gas bubbles, nanofibers, or biological cells. These fillers vary in their composition, size, shape, rheology, and surface properties, which influences their impact on the rheological properties of the biopolymer hydrogels. In this article, the various types of biopolymers used to fabricate composite hydrogels are reviewed, with an emphasis on edible proteins and polysaccharides from sustainable sources, such as plants, algae, or microbial fermentation. The different kinds of gelling mechanism exhibited by these biopolymers are then discussed, including heat-, cold-, ion-, pH-, enzyme-, and pressure-set mechanisms. The different ways that biopolymer molecules can organize themselves in single and mixed biopolymer hydrogels are then highlighted, including polymeric, particulate, interpenetrating, phase-separated, and co-gelling systems. The impacts of incorporating fillers on the rheological properties of composite biopolymer hydrogels are then discussed, including mathematical models that have been developed to describe these effects. Finally, potential applications of composite biopolymer hydrogels are presented, including as delivery systems, packaging materials, artificial tissues, wound healing materials, meat analogs, filters, and adsorbents. The information provided in this article is intended to stimulate further research into the development and application of composite biopolymer hydrogels.

Ionic Strength Impacts the Physical Properties of Agarose Hydrogels

Agarose is a natural polysaccharide known for its ability to form thermoreversible hydrogels. While the effects of curing temperature and polysaccharide concentration on mechanical properties have been discussed in the literature, the role of ionic strength has been less studied. In the present manuscript, we investigate the effects of supporting salt concentration and the role of cation (i.e. Na+ or Li+, neighbors in the Hofmeister series), on the setting and performance of agarose hydrogels. Compressive and rheological measurements show that the supporting salts reduce the immediate elastic response of agarose hydrogels, with Li+ showing a stronger effect than Na+ at high ionic strength, while they significantly increase the extent of linear stress-strain response (i.e., linear elasticity). The presence of increasing amounts of added supporting salt also leads to a reduction in hysteresis during mechanical deformation due to loading and unloading cycles, which is more pronounced with Li+ than with Na+. The combination of rheological measurements and NMR relaxometry shows a mesh size in agarose hydrogels in the order of 6-17 nm, with a thickness of the water layer bound to the biopolymer of about 3 nm. Of note, the different structuring of the water within the hydrogel network due to the different alkali seems to play a role for the final performance of the hydrogels.

Chitosan-Based Biomaterials: Insights into Chemistry, Properties, Devices, and Their Biomedical Applications

Chitosan is a marine-origin polysaccharide obtained from the deacetylation of chitin, the main component of crustaceans’ exoskeleton, and the second most abundant in nature. Although this biopolymer has received limited attention for several decades right after its discovery, since the new millennium chitosan has emerged owing to its physicochemical, structural and biological properties, multifunctionalities and applications in several sectors. This review aims at providing an overview of chitosan properties, chemical functionalization, and the innovative biomaterials obtained thereof. Firstly, the chemical functionalization of chitosan backbone in the amino and hydroxyl groups will be addressed. Then, the review will focus on the bottom-up strategies to process a wide array of chitosan-based biomaterials. In particular, the preparation of chitosan-based hydrogels, organic–inorganic hybrids, layer-by-layer assemblies, (bio)inks and their use in the biomedical field will be covered aiming to elucidate and inspire the community to keep on exploring the unique features and properties imparted by chitosan to develop advanced biomedical devices. Given the wide body of literature that has appeared in past years, this review is far from being exhaustive. Selected works in the last 10 years will be considered.

The effect of trisodium phosphate crosslinking on the diffusion kinetics of caffeine from chitosan networks

This work examines the relationship between microstructural properties of hot-moulded chitosan networks, crosslinked with trisodium phosphate, and diffusive behaviour from these networks. Analysis through infrared spectroscopy (FTIR) confirmed successful crosslinking of the polymer chains and bioactive entrapment, while X-ray diffraction (WAXD) and dynamic oscillation in-shear elucidated the higher order structural properties of each matrix, as they transitioned from solutions to amorphous gels to semi-crystalline matrices. The picture of molecular motion observed in these systems and consequent application of the Flory-Rehner theory further indicated that different extents of chitosan crosslinking yielded a distinct water infusion functionality seen in the levels of swelling. Diffusion of caffeine from these delivery vehicles showed that network structural properties (governed by crosslinker concentration) had a significant effect on the release kinetics of the entrapped bioactive. The relationship between network mesh characteristics and diffusion properties were further confirmed by correlating caffeine release rates and molecular pore size.

Controlled Liposome Delivery from Chitosan-Based Thermosensitive Hydrogel for Regenerative Medicine

This work describes the development of an injectable nanocomposite system based on a chitosan thermosensitive hydrogel combined with liposomes for regenerative medicine applications. Liposomes with good physicochemical properties are prepared and embedded within the chitosan network. The resulting nanocomposite hydrogel is able to provide a controlled release of the content from liposomes, which are able to interact with cells and be internalized. The cellular uptake is enhanced by the presence of a chitosan coating, and cells incubated with liposomes embedded within thermosensitive hydrogels displayed a higher cell uptake compared to cells incubated with liposomes alone. Furthermore, the gelation temperature of the system resulted to be equal to 32.6 °C; thus, the system can be easily injected in the target site to form a hydrogel at physiological temperature. Given the peculiar performance of the selected systems, the resulting thermosensitive hydrogels are a versatile platform and display potential applications as controlled delivery systems of liposomes for tissue regeneration.

Chitosan-based smart hybrid materials: a physico-chemical perspective

Chitosan is one of the most studied cationic polysaccharides. Due to its unique characteristics of being water soluble, biocompatible, biodegradable, and non-toxic, this macromolecule is highly attractive for a broad range of applications. In addition, its complex behavior and the number of ways it interacts with different components in a system result in an astonishing variety of chitosan-based materials. Herein, we present recent advances in the field of chitosan-based materials from a physico-chemical perspective, with focus on aqueous mixtures with oppositely charged colloids, chitosan-based thin films, and nanocomposite systems. In this review, we focus our attention on the physico-chemical properties of chitosan-based materials, including solubility, mechanical resistance, barrier properties, and thermal behaviour, and provide a link to the chemical peculiarities of chitosan, such as its intrinsic low solubility, high rigidity, large charge separation, and strong tendency to form intra- and inter-molecular hydrogen bonds.

Ionotropic Gelation of Chitosan Flat Structures and Potential Applications

The capability of some polymers, such as chitosan, to form low cost gels under mild conditions is of great application interest. Ionotropic gelation of chitosan has been used predominantly for the preparation of gel beads for biomedical application. Only in the last few years has the use of this method been extended to the fabrication of chitosan-based flat structures. Herein, after an initial analysis of the major applications of chitosan flat membranes and films and their usual methods of synthesis, the process of ionotropic gelation of chitosan and some recently proposed novel procedures for the synthesis of flat structures are presented.

Design of nanostructure chitosan hydrogels for carrying zinc phthalocyanine as a photosensitizer and difloxacin as an antibacterial agent

Here, we develop homogeneous hydrogel networks containing zinc tetraamino-phthalocyanine (ZnTAPc) as photosensitizer cross-linked with glutaraldehyde. The cross-linking process occurs via imine bond formation by reaction of NH₂ groups of ZnTAPc and chitosan with aldehyde groups of the glutaraldehyde. Insertion of ZnTAPc interestingly increases its solubility in water medium. 2.0% and 4% w/w of the ZnTAPc were used with respect to chitosan polymer to generate hydrogel photosensitizer. FT-IR and UV-Vis spectroscopy, scanning electron microscopy, and rheological measurements were applied to evaluate the properties of the prepared hydrogels. Finally, difloxacin HCl was selected as a fluoroquinolone drug for the assessment of the drug release features of the made hydrogels. The difloxacin release was affected by the amount of ZnTAPc and pH medium. The activity of the hydrogels in photosensitizing process was considered by computing the rate of 1,3-diphenylisobenzofuran adsorption reduction as a singlet oxygen chemical quencher.

PCL-Blended Chitosan Substrates for Patterning the Heterotypic Cell Distribution in an Epithelial and Mesenchymal Coculture System

Cell-cell and cell-substrate interactions in coculture systems are very important to the context of biomaterial scaffolds for tissue engineering applications. Understanding the cellular interactions and distribution of epithelial-mesenchymal microtissues on the controllable biomaterial surfaces is useful to study the organoid applications. The aim of the present study is to investigate the effects of chitosan/poly(ε-caprolactone) (PCL)-blended biomaterials on the distribution and spheroid formation of HaCaT and Hs68 cells in a coculture system. In this study, we demonstrated that the cocultured cells gradually changed their pattern from core/shell spheroid to monolayered morphology as the PCL content increased in the blended substrates. This indicates that the chitosan/PCL-blended substrates are able to regulate cell-substrate and cell-cell interactions to modify the distribution of HaCaT and Hs68 cells similar to various mesenchymal-epithelial organizations in biological tissues. Moreover, we also developed a two-dimension lattice model to elaborate the dependence of cell spheroid development on complex cell-cell interactions. This information may be helpful to develop appropriate biomaterials with appropriate properties to the applications of engineered epithelial-mesenchymal organoids.

On the Formation and Stability of Chitosan/Hyaluronan-Based Complex Coacervates

This contribution is aimed at extending our previous findings on the formation and stability of chitosan/hyaluronan-based complex coacervates. Colloids are herewith formed by harnessing electrostatic interactions between the two polyelectrolytes. The presence of tiny amounts of the multivalent anion tripolyphosphate (TPP) in the protocol synthesis serves as an adjuvant “point-like” cross-linker for chitosan. Hydrochloride chitosans at different viscosity average molar mass, Mv¯, in the range 10,000–400,000 g/mol, and fraction of acetylated units, F_A, (0.16, 0.46 and 0.63) were selected to fabricate a large library of formulations. Concepts such as coacervate size, surface charge and homogeneity in relation to chitosan variables are herein disclosed. The stability of coacervates in Phosphate Buffered Saline (PBS) was verified by means of scattering techniques, i.e., Dynamic Light Scattering (DLS) and Small-Angle X-ray Scattering (SAXS). The conclusions from this set of experiments are the following: (i) a subtle equilibrium between chitosan F_A and Mv¯ does exist in ensuring colloidal stability; (ii) once diluted in PBS, osmotic swelling-driven forces trigger the enlargement of the polymeric mesh with an ensuing increase of coacervate size and porosity.

Investigations of the Influences of Processing Conditions on the Properties of Spray Dried Chitosan-Tripolyphosphate Particles loaded with Theophylline

The preparation of chitosan-tripolyphosphate (chitosan-TPP) particles by the spray drying had been reported word widely for a sustained release of drugs to prevent rapid drug metabolism. Although the spray drying is a straightforward procedure turning a liquid feed into a well-defined dry powder, seldom research works were focusing on how the processing parameters and liquid feeding constitutions of spray drying system might affect the properties of spray-dried chitosan particles loaded with drugs, such as the particle size and morphologies, which would be very important to drug encapsulation and dissolution of the drug delivery design. This study thus prepared the chitosan particles with theophylline (TH) loaded as a model drug and TPP as cross-linker at various spray drying conditions. Our results indicate the diameter of the TH/chitosan-TPP particles made by customized spray drying apparatus spans from 424 to 497 nm with a geometric standard deviation of less than 2. The corresponding release of TH was tunable by the chitosan-TPP matrix density under the selected spray drying temperature and the carrying air flow rate. These results suggest an indeed need for optimized spray drying processing conditions to make the ideal spray-dried TH/chitosan-TPP particles for the desired drug delivery.

Chitosan Acetylation Degree Influences the Physical Properties of Polysaccharide Nanoparticles: Implication for the Innate Immune Cells Response

The aim of the present contribution is twofold as it reports (i) on the role played by chitosan acetylation degree for the stability of nanoparticles (NPs) formed with hyaluronan and (ii) on the effect of the interaction of such NPs with immune cells. Chitosans with similar viscosity-average molecular weight, [Formula: see text], (i.e., 200 000) and different fractions of acetylated units ( F_A) together with low-molecular-weight hyaluronan were chosen for developing a select library of formulations via electrostatic complex coacervation. The resulting NPs were analyzed in terms of size, polydispersity, surface charge, and stability in physiological-mimicked media by dynamic light scattering. Only medium acetylated chitosan ( F_A = 0.16) guaranteed the stability of NPs. To explore the effect of NPs interaction with immune cells, the release of proinflammatory cytokines and the reactive oxygen species production by human macrophages and neutrophils, respectively, were evaluated. Strikingly, a structure-function relationship emerged, showing that NPs made of chitosans with F_A = 0.02, 0.25, 0.46, and 0.63 manifested a proinflammatory activity, linked to the instability of the system. Conversely, NPs made of chitosan with F_A = 0.16 neither modified the functional response of macrophages nor that of neutrophils. Of note, such NPs were found to possess additional properties potentially advantageous in applications such as delivery of therapeutics to target inflamed sites: (i) they are devoid of cytotoxic effects, (ii) they avoid engulfment during the early stage of interaction with macrophages, and (iii) they are muco-adhesive, thereby providing for site-specificity and long-residence effects.

An Enzyme-Free "ON-OFF" Electrochemiluminescence Biosensor for Ultrasensitive Detection of PML/RARα based on Target-Switched DNA Nanotweezer

Herein, an enzyme-free "ON-OFF" electrochemiluminescence (ECL) biosensor for ultrasensitive detection of fusion gene PML/RARα is constructed based on a simple target-switched DNA nanotweezer as hemin concentration controller. In this biosensor, the hemin concentration is primarily controlled by the conversion of "opened-closed" DNA nanotweezers and low concentration hemin is first used as electrochemically regenerable enhancer. In the absence of the target, the nanotweezers are in an opened state which lead to a low concentration of hemin in the solution, resulting in an enhanced Ru(bpy)₃²⁺ ECL signal. In the presence of the target, the closed nanotweezers absorbed onto the surface of electrode can capture the hemin, which achieves a high concentration of hemin and then quenches the ECL signal. The developed method achieves ultrasensitive detection of PML/RARα with a wide linear range from 1 fM to 1 nM and limit of detection as low as 0.125 fM. In addition, the ECL biosensor shows excellent specificity to the other subtypes of PML/RARα (subtype "S", "V"), "PML", and "RARα". Moreover, due to the high designable character of DNA nanotweezer, this method might provide a pragmatic Ru(bpy)₃²⁺ ECL platform for ultrasensitive detection of nucleic acid in the future.

Concepts for Developing Physical Gels of Chitosan and of Chitosan Derivatives

Chitosan macro- and micro/nano-gels have gained increasing attention in recent years, especially in the biomedical field, given the well-documented low toxicity, degradability, and non-immunogenicity of this unique biopolymer. In this review we aim at recapitulating the recent gelling concepts for developing chitosan-based physical gels. Specifically, we describe how nowadays it is relatively simple to prepare networks endowed with different sizes and shapes simply by exploiting physical interactions, namely (i) hydrophobic effects and hydrogen bonds-mostly governed by chitosan chemical composition-and (ii) electrostatic interactions, mainly ensured by physical/chemical chitosan features, such as the degree of acetylation and molecular weight, and external parameters, such as pH and ionic strength. Particular emphasis is dedicated to potential applications of this set of materials, especially in tissue engineering and drug delivery sectors. Lastly, we report on chitosan derivatives and their ability to form gels. Additionally, we discuss the recent findings on a lactose-modified chitosan named Chitlac, which has proved to form attractive gels both at the macro- and at the nano-scale.

Hydrogel Cross-Linked with Dynamic Covalent Bonding and Micellization for Promoting Burn Wound Healing

A novel hydrogel (HA-az-F127 hydrogel) formed by reacting hydrazide modified hyaluronic acid (HAAD) and benzaldehyde terminated F127 triblock copolymers (BAF127) was developed in this work. The hydrogel with dynamic covalent chemically and micellar physically double-cross-linked networks exhibited rapid gelation and shear thinning properties. Besides, the hydrogel possessed functions, such as adaptable mechanical strength, self-healability, liquid-absorption, or drainage and tissue adhesion, which are important for wound treatment. Studies on cytocompatibility and histopathology by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide tests, live/death staining, and cell counting kit 8 assay demonstrated excellent biocompatibility of the hydrogels. After it was applied in the deep partial-thickness burn model, the hydrogel contributed effectively in promoting burn wound repair. Therefore, the HA-az-F127 hydrogel combined multiple functions in one system, demonstrating potential application in promoting burn wound healing.

Study on hydrophilicity and degradability of chitosan/polylactide-co-polycaprolactone nanofibre blend electrospun membrane

Electrospinning is an interesting technique to produce polymer membranes made of entangled nanofibres. The technique is raising interest in pharmaceutical and biomedical areas. Either electrospun membranes are studied for tissue regeneration purposes, or incorporation of nanoparticles in electrospun membranes can be an opportunity to control the delivery of drug or to obtain dual drug delivery system. In this work suspensions of hydrochloride chitosan salt in copolymer polylactide-co-polycaprolactone (PLA-PCL) solution were electrospun in order to assess an advanced study for developing polymer nanofibre blend membrane loaded with chitosan polymer. The aim of the work was to investigate the properties and stability of chitosan/PLA-PCL electrospun membranes considering their application for tissue regeneration and drug delivery. The electrospun membranes were characterized for their physico-chemical (FT-IR) morphology (SEM) and in vitro biological properties (cytocompatibility and cells engraftment). Results show that homogeneous electrospun PLA-PCL/chitosan blend nanofibres in the range size 800 nm were obtained. Chitosan was loaded inside the nanofibres up to 27.2% (w/w) without modifying nanofibre shape, and only 6% of the loaded chitosan resulted to be on the nanofibre surface. The presence of chitosan in the nanofibres has shown to accelerate the electrospun membranes degradation in vitro.