Urea (URE) and guanidine hydrochloride (GHC) possessing strong chaotropic properties in aqueous media were added to DMSO solutions of poly(vinyl alcohol) (PVA) to be gelled via freeze–thaw processing. Unexpectedly, it turned out that in the case of the PVA cryotropic gel formation in DMSO medium, the URE and GHC additives caused the opposite effects to those observed in water, i.e., the formation of the PVA cryogels (PVACGs) was strengthened rather than inhibited. Our studies of this phenomenon showed that such “kosmotropic-like” effects were more pronounced for the PVACGs that were formed in DMSO in the presence of URE additives, with the effects being concentration-dependent. The additives also caused significant changes in the macroporous morphology of the cryogels; the commonly observed trend was a decrease in the structural regularity of the additive-containing samples compared to the additive-free gel sample. The viscosity measurements revealed consistent changes in the intrinsic viscosity, Huggins constant, and the excess activation heat of the viscosity caused by the additives. The results obtained evidently point to the urea-induced decrease in the solvation ability of DMSO with respect to PVA. As a result, this effect can be the key factor that is responsible for strengthening the structure formation upon the freeze–thaw gelation of this polymer in DMSO additionally containing additives such as urea, which is capable of competing with PVA for the solvent.

Poly(vinyl alcohol) (PVA) physical cryogels that contained the additives of o-, m-, and p-bis-phenols or phenol were prepared, and their physico-chemical characteristics and macroporous morphology and the solute release dynamics were evaluated. These phenolic additives caused changes in the viscosity of initial PVA solutions before their freeze–thaw processing and facilitated the growth in the rigidity of the resultant cryogels, while their heat endurance decreased. The magnitude of the effects depended on the interposition of phenolic hydroxyls in the molecules of the used additives and was stipulated by their H-bonding with PVA OH-groups. Subsequent rinsing of such “primary” cryogels with pure water led to the lowering of their rigidity. The average size of macropores inside these heterophase gels also depended on the additive type. It was found also that the release of phenolic substances from the additive-containing cryogels occurred via virtually a free diffusion mechanism; therefore, drug delivery systems such as PVA cryogels loaded with either pyrocatechol, resorcinol, hydroquinone, or phenol, upon the in vitro agar diffusion tests, exhibited antibacterial activity typical of these phenols. The promising biomedical potential of the studied nanocomposite gel materials is supposed.

Macroporous poly(vinyl alcohol) cryogels (PVACGs) are physical gels formed via cryogenic processing of polymer solutions. The properties of PVACGs depend on many factors: the characteristics and concentration of PVA, the absence or presence of foreign solutes, and the freezing-thawing conditions. These factors also affect the macroporous morphology of PVACGs, their total porosity, pore size and size distribution, etc. In this respect, there is the problem with developing a scientifically-grounded classification of the morphological features inherent in various PVACGs. In this study PVA cryogels have been prepared at different temperatures when the initial polymer solutions contained chaotropic or kosmotropic additives. After the completion of gelation, the rigidity and heat endurance of the resultant PVACGs were evaluated, and their macroporous structure was investigated using optical microscopy. The images obtained were treated mathematically, and deep neural networks were used for the classification of these images. Training and test sets were used for their classification. The results of this classification for the specific deep neural network architecture are presented, and the morphometric parameters of the macroporous structure are discussed. It was found that deep neural networks allow us to reliably classify the type of additive or its absence when using a combined dataset.

Macroporous physical poly(vinyl alcohol)-based (PVA) cryogels were prepared originating from the dimethylsulfoxide solutions of the polymer that contained urea additives. The variables of the cryotropic gel-formation process were its temperature and the concentration of the added urea, which caused the increase in the rigidity and heat endurance of the resultant cryogels, as well as promoted widening of the macropores in the gel matter. Subsequent rinsing of the DMSO-swollen cryogels with the water excess resulted in the water-swollen PVA cryogels with simultaneous further increase in their rigidity. These gel matrices were tested with respect of their potential to operate as the polymeric carriers in the drug delivery systems. Loading of such water-swollen cryogels with a model drug, ε-amino caproic acid, and then studies of its release kinetics revealed that urea content in the initial PVA solutions used for the freeze-thaw-induced formation of the DMSO-swollen cryogels played the key role for the release characteristics of the drug-loaded water-swollen gel carrier. Namely, PVA cryogels prepared in the presence of a higher concentration of urea possessed the larger pores and, as a result, the drug release occurred somewhat faster.

Physical (non-covalent) macroporous cryogels of poly(vinyl alcohol) (PVACGs) are formed as a result of the consecutive freezing of concentrated PVA solutions, their incubation in a frozen state and then thawing. In this study the influence of the additives of trehalose and the solvent used on the PVA cryotropic gel-formation, as well as on the properties of the respective PVACGs was explored. It was shown that both the rigidity and the heat endurance of cryogels formed in the DMSO medium in the presence of trehalose progressively increased with increasing the additive concentration. It turns, in the case of cryogels prepared in the aqueous medium in the presence of trehalose the dependences of the physicomechanical characteristics on the additive concentration were of a bell-like (concave) type, while the heat endurance of the samples grew monotonically.

Noncovalent (physical) macroporous poly(vinyl alcohol) cryogels (PVACGs) formed by the freezing–defrosting technique without the use of chemical cross-linking reagents are of significant interest as biomedical materials. For their safe use in medicine, it is necessary to ensure reliable sterility of the corresponding processes and products. In this study, PVACGs are prepared by freezing 100 g/L aqueous solutions of this polymer at –20°C for 12 h followed by defrosting at a heating rate of 0.03°C/min. Then, the resulting cryogels are treated with 1–4 N solutions of strong mineral acids (HCl, H₂SO₄, and H₃PO₄) and both the character of changes in the physicochemical properties and microstructure of the gel matrix caused by the action of these acids, as well as the possibility of their use for the sterilization of PVACGs, are assessed. It has been shown that HCl solutions cause significant swelling and softening of the gel matrix up to its complete dissolution in 4 N HCl. On the contrary, the treatment of the cryogels with aqueous solutions of H₂SO₄ or H₃PO₄ leads to an increase in the elasticity and heat endurance of these cryogels. Tests of the sterilizing properties of such acidic solutions with respect to the cells of microorganisms (bacteria, yeasts, mycelial fungi) incorporated into the cryogels have revealed the high efficiency of this approach, which is attractive especially from the viewpoints of both the simplicity of the treatment itself and the financial viability in the case of using aqueous solutions of sulfuric acid.