Taking into account the trends in the field of green chemistry and the desire to use natural materials in biomedical applications, (bio)polyelectrolyte complexes ((bio)PECs) based on a mixture of chitosan and gelatin seem to be relevant systems. Using the approach of self-assembly from the dispersion of the coacervate phase of a (bio)PEC at different ratios of ionized functional groups of chitosan and gelatin (z), hydrogels with increased resistance to mechanical deformations and resorption in liquid media were obtained in this work in comparison to a hydrogel from gelatin. It was found that at z ≥ 1 a four-fold increase in the elastic modulus of the hydrogel occurred in comparison to a hydrogel based on gelatin. It was shown that hydrogels at z ≈ 1 had an increased sorption capacity and water sorption rate, as well as increased resistance to the in vitro model environment of phosphate-buffered saline (PBS) solution containing lysozyme at 37 °C. It was also shown that in PBS and simulated gastric fluid (SGF) solutions, the effect of the polyelectrolyte swelling of the hydrogels was significantly suppressed; however, at z ≥ 1, the (bio)PEC hydrogels had increased stability compared to the samples at z < 1 and based on gelatin.

In this work, solutions of low molecular weight chitosan with the concentration of 4 and 5 wt.% were subjected to electrohydrodynamic forming at the feed rate of 0.1 and 0.2 ml/h. Using a statistical analysis of the electron scanning microscopy data, it was shown that at the concentration of 4 wt.%, spherical particles of two types are formed: most of the particles are with the average diameter about of 260 nm, and particles with a larger diameter of about 480 nm. A transition through the particle-to-fiber threshold was observed with an increase in the concentration of the solution to 5 wt.%. This led to the formation of both spherical particles with a monomodal distribution and average diameter of 207 nm and elongated particles of a fiber-like shape with diameter of 157 nm and length of 1401 nm. At the same time, an increase in the solution feed rate resulted in a strong decrease in the average diameter of spherical particles to 150 nm and an elongation of fiber-like objects by 1.5 times. The particle-to-fiber threshold can be observed when the dynamic viscosity of the solution changes in the range of about 10–14 cP. Graphical Abstract

In this work, three carboxymethyl starches (CMS) were obtained by the two-step reaction process of carboxymethylation with different degrees of substitution (0.16, 0.33, and 0.36). From these samples, (bio)polyelectrolyte complexes ((bio)PECs) were obtained with chitosan (Chit) by the mixing of individual solutions of polymers (0.25 wt.%) at different volume ratios. The effect of the biopolymer and ionized groups of z ratios, pH, and degree of substitution of CMS in the formation of PEC were evaluated by turbidimetry and dynamic light scattering. The results showed that increasing the amount of CMS samples (ratio of z) led to an increase in the efficiency of the formation of (bio)PEC using CMS with a high DS value. Using the turbidimetry method for the chitosan and CMS mixtures, it was observed that the formation of (bio)PEC is divided into four transition zones delimited by pH transition points, and the stoichiometric complexation (z = 1) is achieved at a pH that displayed morphological changes “pH_morph”, which is a single point for Chit:CMS 1, and for Chit:CMS 2 and Chit:CMS 3, this is a range of 4.9–6.4 and 4.3–6.4, respectively. Analysis of the structural properties of the structures of (bio)PECs by dynamic light scattering was characterized by monomodal distribution, and the main observed effect was associated with an increase in the value of D_avg with an increase in the ratio of Chit:CMS.

Biopolymeric films based on chitosan and starch offer an ecological alternative for food protection. Nevertheless, their practical application is often limited by their low mechanical properties and high solubility in aqueous solutions, due to weak interactions between the chains of the biopolymers. One approach to resolve this problem is to obtain biopolymeric films based on (bio)polyelectrolyte complex ((bio)PEC). These films exhibit stronger electrostatic interactions and homogeneous biopolymeric structure. In this study, films based on (bio)PEC were obtained by the casting method, using chitosan and carboxymethyl cassava starch with different degrees of substitution with a biopolymer concentration of 2.5 wt.% at pH = 6. The obtained films were analyzed using the optical and scanning microscopy, color method, ATR-FTIR spectroscopy, thermogravimetry, mechanical analysis under tension, solubility in water, simulated gastric fluid (SGF), and phosphate-buffered saline (PBS) solutions, and contact angle of water. The results demonstrated that the tensile strength and Young’s modulus of films based on (bio)PEC increased by 2–4 times, and the elongation at break by 20% compared to films based on a mixture chitosan and starch. This is due to the increase in the attraction between oppositely charged polyelectrolytes in (bio)PEC films. Additionally, the solubility of (bio)PEC films was reduced by ~40%, 35% and 70% in water, SGF and PBS solutions, respectively, when the carboxymethyl starch with highest degree of substitution was used, and z was near to 1.