The rheology of hydrogels based on chitosan–gelatin (bio)polyelectrolyte complexes

Tunable Oxidized-Chitin Hydrogels with Customizable Mechanical Properties by Metal or Hydrogen Ion Exposure

This study focuses on the optimization of chitin oxidation in C6 to carboxylic acid and its use to obtain a hydrogel with tunable resistance. After the optimization, water-soluble crystalline β-chitin fibrils (β-chitOx) with a degree of functionalization of 10% were obtained. Diverse reaction conditions were also tested for α-chitin, which showed a lower reactivity and a slower reaction kinetic. After that, a set of hydrogels was synthesized from β-chitOx 1 wt.% at pH 9, inducing the gelation by sonication. These hydrogels were exposed to different environments, such as different amounts of Ca2+, Na+ or Mg2+ solutions, buffered environments such as pH 9, PBS, pH 5, and pH 1, and pure water. These hydrogels were characterized using rheology, XRPD, SEM, and FT-IR. The notable feature of these hydrogels is their ability to be strengthened through cation chelation, being metal cations or hydrogen ions, with a five- to tenfold increase in their storage modulus (G'). The ions were theorized to alter the hydrogen-bonding network of the polymer and intercalate in chitin's crystal structure along the a-axis. On the other hand, the hydrogel dissolved at pH 9 and pure water. These bio-based tunable hydrogels represent an intriguing material suitable for biomedical applications.

Rheology of Gels and Yielding Liquids

In this review, today's state of the art in the rheology of gels and transition through the yield stress of yielding liquids is discussed. Gels are understood as soft viscoelastic multicomponent solids that are in the incomplete phase separation state, which, under the action of external mechanical forces, do not transit into a fluid state but rupture like any solid material. Gels can "melt" (again, like any solids) due to a change in temperature or variation in the environment. In contrast to this type of rheology, yielding liquids (sometimes not rigorously referred to as "gels", especially in relation to colloids) can exist in a solid-like (gel-like) state and become fluid above some defined stress and time conditions (yield stress). At low stresses, their behavior is quite similar to that of permanent solid gels, including the frequency-independent storage modulus. The gel-to-sol transition considered in colloid chemistry is treated as a case of yielding. However, in many cases, the yield stress cannot be assumed to be a physical parameter since the solid-to-liquid transition happens in time and is associated with thixotropic effects. In this review, special attention is paid to various time effects. It is also stressed that plasticity is not equivalent to flow since (irreversible) plastic deformations are determined by stress but do not continue over time. We also discuss some typical errors, difficulties, and wrong interpretations of experimental data in studies of yielding liquids.

Evaluation of chitosan/xanthan gum polyelectrolyte complexes potential for pH-dependent oral delivery of escin

Escin is an amphiphilic and weakly acidic drug that oral administration may lead to the irritation of gastric mucosa. The entrapment of escin into chitosan (CH)/xanthan gum (XG)-based polyelectrolyte complexes (PECs) can facilitate controlled drug release which may be beneficial for the reduction of its side effects. This study aimed to investigate the influence of escin content and drying method on the formation, physicochemical, and controlled, pH-dependent drug release properties of CH/XG-based PECs. Measurements of transmittance, conductivity, and rheological characterization confirmed the formation of CH/XG-based PECs with escin entrapped at escin-to-polymers mass ratios 1:1, 1:2, and 1:4. Ambient-dried PECs had higher yield, entrapment efficiency, and escin content in comparison with spray-dried ones. FT-IR spectra confirmed the interactions between CH, XG, and escin, which were stronger in ambient-dried PECs. PXRD and DSC analyses showed the amorphous escin character in all dry PECs, regardless of the drying method. The most promising controlled and pH-dependent in vitro escin release was from the ambient-dried PEC at the escin-to-polymers mass ratio of 1:1. For that reason and due to the highest yield and entrapment efficiency, this carrier has the potential to prevent the irritation of gastric mucosa after oral administration of escin.

Hydrogel Nanoarchitectonics: An Evolving Paradigm for Ultrasensitive Biosensing

The integration of nanoarchitectonics and hydrogel into conventional biosensing platforms offers the opportunities to design physically and chemically controlled and optimized soft structures with superior biocompatibility, better immobilization of biomolecules, and specific and sensitive biosensor design. The physical and chemical properties of 3D hydrogel structures can be modified by integrating with nanostructures. Such modifications can enhance their responsiveness to mechanical, optical, thermal, magnetic, and electric stimuli, which in turn can enhance the practicality of biosensors in clinical settings. This review describes the synthesis and kinetics of gel networks and exploitation of nanostructure-integrated hydrogels in biosensing. With an emphasis on different integration strategies of hydrogel with nanostructures, this review highlights the importance of hydrogel nanostructures as one of the most favorable candidates for developing ultrasensitive biosensors. Moreover, hydrogel nanoarchitectonics are also portrayed as a promising candidate for fabricating next-generation robust biosensors.

Highly Stable CsSnCl3 Quantum Dots Grown in an Ionic Liquid/Gelatin Composite System through an In Situ Method

Lead halide perovskite quantum dots (QDs) are controversial due to their high lead content. Tin, a low-toxic element with an outer electronic structure similar to that of Pb, becomes a strong candidate for preparing lead-free perovskite QDs. However, tin-based perovskite QDs, especially CsSnCl₃ QDs, exhibit poor environmental stability. Herein, we proposed an strategy for highly stable CsSnCl₃ QDs using an ionic liquid as a solvent and antioxidant and gelatin as a multidentate ligand and coating material through an in situ method ([AMIM]Cl/gelatin-QDs). The results showed that the abundant active groups of gelatin served as the nucleation growth center for QDs and further passivated QDs. At the same time, the long molecular chain of gelatin can coat the QDs to isolate the environment and fully protect QDs, and the size of QDs grown in gelatin was 5-10 nm. In addition, the oxidation resistance of ionic liquids and the halogen-rich environment formed also played an important role. Even if [AMIM]Cl/gelatin-QDs were treated with water and ultraviolet light simultaneously, its remaining fluorescence intensity was still above 60% within 72 h. Meaningfully, QDs endowed the composite system mildew resistance, which can resist the erosion of gelatin by molds, thereby realizing the system's long-term protection toward CsSnCl₃ QDs.

Novel chitosan and bacterial cellulose biocomposites tailored with polymeric nanoparticles for modern wound dressing development

Dressing biomaterials play a key role in wound management keeping a moisture medium and protecting against external factors. Natural and synthetic materials could be used as dressings where chitosan and bacterial cellulose is one of the most important solutions. These biopolymers have been used for wound dressing based on their non-toxic, biodegradable, and biocompatible features. In this study, biocomposites based on bacterial cellulose and chitosan membranes tailored with antimicrobial loaded poly(N-isopropylacrylamide)/polyvinyl alcohol nanoparticles were prepared. Core-shell polymeric nanoparticles, bacterial cellulose/chitosan membranes, and biocomposites were independently loaded with silver sulfadiazine, a well-known sulfonamide antibacterial agent used in the therapy of mild-to-moderate infections for sensitive organisms. The chemistry, structure, morphology, and size distribution were investigated by Fourier transformed infrared spectroscopy (FTIR-ATR), RAMAN spectroscopy, Scanning electron (SEM) and Transmission electron microscopy (TEM), and Dynamic light scattering (DLS). In vitro release behaviors of silver sulfadiazine from polymeric nanoparticles and biocomposites were investigated. The biological investigations revealed good biocompatibility of both the nanoparticles and the biocomposites in terms of human dermal fibroblasts viability and proliferation potential. Finally, the drug-loaded polymeric biomaterials showed promising characteristics, proving their high potential as an alternative support to develop a biocompatible and antibacterial wound dressing.

Rheological Properties of Fish Gelatin Modified with Sodium Alginate

Polyelectrolyte complexes of sodium alginate and gelatin obtained from cold-blooded fish were studied for potential application as structure-forming agents in food hydrogels. The mass ratio of sodium alginate to gelatin plays a decisive role in the sol-gel transition and rheological behavior of the complexes. Differences in the sol-gel transition temperature were observed upon heating and cooling, as is typical for such materials. We investigated the characteristics of this transition by measuring the isothermal changes in the elastic modulus over time at a constant frequency and the transition temperature at a range of frequencies. The kinetic nature of this transition depends on the composition of the complexes. A characteristic alginate-gelatin mass ratio is the ratio at which maximum transition temperature as well as elastic modulus and viscosity (rheological parameters) values are obtained; the characteristic mass ratio for these complexes was found to be 0.06. Calculation of the ionic group ratios in the biopolymers that form complexes and comparison of these data with the turbidimetric titration results clarified the origin of these maxima. Measuring the viscoelastic properties and the creep-elastic recoil of the samples allowed us to characterize these materials as viscoelastic media with a viscosity in the order of 103-104 Pa·s and an elastic modulus in the order of 102-103 Pa. These values drastically decrease at a certain stress threshold, which can be treated as the gel strength limit. Therefore, the observed rheological behavior of gels formed by fish gelatin modified with sodium alginate characterizes them as typical viscoelastic soft matter.

pH mediated rheological modulation of chitosan hydrogels

Chitosan (CS) hydrogels are used widely for multifarious applications in diverse fields due to the property of pH responsiveness. This study aims to explain the sensitivity of CS hydrogels to alteration in pH due to change in the concentration of acetic acid, which is a solvent for CS. Studies on changes in rheological properties in this regard are still scarce. The present study evaluated the change in rheological properties of the CS hydrogels by studying the flow behaviour, creep recovery and thixotropic property. The obtained data were used to fit mathematical models, like power law model and Herschel-Bulkley model to gain a vivid understanding of the rheological properties of CS hydrogel. Overall analyses revealed that the CS hydrogels, irrespective of the pH, were highly elastic in nature and exhibited significant creep recovery. However, the steady flow behaviour and thixotropy varied substantially with variation in pH.

Polyelectrolyte Polysaccharide-Gelatin Complexes: Rheology and Structure

General features of rheological properties and structural peculiarities of polyelectrolyte polysaccharide–gelatin complexes were discussed in this paper. Experimental results were obtained for typical complexes, such as κ-carrageenan–gelatin, chitosan–gelatin and sodium alginate–gelatin complexes. A rheological method allows us to examine the physical state of a complex in aqueous phase and the kinetics of the sol–gel transition and temperature dependences of properties as a result of structural changes. The storage modulus below the gelation temperature is constant, which is a reflection of the solid-like state of a material. The gels of these complexes are usually viscoplastic media. The quantitative values of the rheological parameters depend on the ratio of the components in the complexes. The formation of the structure as a result of strong interactions of the components in the complexes was confirmed by UV and FTIR data and SEM analysis. Interaction with polysaccharides causes a change in the secondary structure of gelatin, i.e., the content of triple helices in an α-chain increases. The joint analysis of the structural and rheological characteristics suggests that the formation of additional junctions in the complex gel network results in increases in elasticity and hardening compared with those of the native gelatin.

Cross-Linked Hydrogel for Pharmaceutical Applications: A Review

Hydrogels are promising biomaterials because of their important qualities such as biocompatibility, biodegradability, hydrophilicity and non-toxicity. These qualities make hydrogels suitable for application in medical and pharmaceutical field. Recently, a tremendous growth of hydrogel application is seen, especially as gel and patch form, in transdermal drug delivery. This review mainly focuses on the types of hydrogels based on cross-linking and; secondly to describe the possible synthesis methods to design hydrogels for different pharmaceutical applications. The synthesis and chemistry of these hydrogels are discussed using specific pharmaceutical examples. The structure and water content in a typical hydrogel have also been discussed.