Cryostructuring of Polymeric Systems †: Application of Deep Neural Networks for the Classification of Structural Features Peculiar to Macroporous Poly(vinyl alcohol) Cryogels Prepared without and with the Additives of Chaotropes or Kosmotropes

Abstract

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.

Cryostructuring of Polymeric Systems. 61. Physicochemical Properties of Poly(vinyl alcohol) Cryogels Prepared on the Basis of Urea-Containing DMSO-Solutions of the Polymer and Evaluation of the Resultant Gel Materials as Potential Drug Carriers

“…In this case, it is found that some low-molecular solutes influenced on the physico-chemical properties of the resultant cryogels oppositely in comparison to the effects observed in aqueous media [50,51]. Thus, it is revealed that such well-known chaotropes as urea or guanidine hydrochloride, the additives of which cause marked decrease in the gel strength and heat endurance of the PVACGs prepared from the aqueous polymer solutions [52,53], in the DMSO media exhibit the antichaotropic (so-called kosmotropic) influence on the respective cryogels causing the considerable increase in their rigidity and fusion temperatures [51]. The studies of such phenomenon show that its main reason consisted in the urea-induced decrease in the solvation ability of DMSO with respect to PVA.…”

“…The "secondary" water-swollen cryogels rather than the "primary" DMSO-swollen samples were investigated since the polymeric walls of macropores in the 'primary' cryogels were almost transparent, so the peculiarities of their texture in the thin sections were in fact indiscernible with an optical microscope. In addition, it turned out that the DMSO-swollen PVACGs were practically not stained with Congo red dye usually employed to contrast the thin sections of the water-swollen PVA cryogels [19,24,27,29,30,53]. Qualitatively, Figure 3 demonstrates clear differences between the character of macroporous morphology of the cryogels prepared from the urea-free (a) and the urea-containing (b, c) feed PVA solutions.…”

“…In the as-prepared "primary" cryogels, DMSO was replaced by pure water, and the resultant "secondary" cryogels were cut for the 10-µm thick sections orthogonally to the axis of cylindrical samples using a SM-1900 cryomicrotome (Leica, Germany). Each section was placed on the microscope glass, which was then immersed into a 1 % aqueous solution of Congo red (the standard dye used for painting PVA-based materials [61], including the PVA cryogels [19,24,29,30,35,36,[50][51][52][53]) for staining for 10 s, and then rinsed with pure water. The excess of liquid was removed with a filter paper.…”

“…First, this work confirms previous study [51] on kosmotropic-like "action" of urea additives on the PVA cryotropic gel-formation in the DMSO medium. If in the case of the formation of cryogels via the freezethaw processing of the aqueous urea-containing PVA solutions, the increase in the urea concentration gave rise to the crucial decrease in the gel strength because of the urea-induced inhibition of the interchain PVA-PVA H-bonding [52,53] while in the DMSO medium the effects were opposite. This result is stipulated by the competition of urea with PVA for the solvent, since the urea forms rather stable H-bonds with DMSO thus promoting the partial change of the PVA-DMSO solvate interactions for the additional interchain PVA-PVA H-bonding [51].…”

Design and Assessment of Biodegradable Macroporous Cryogels as Advanced Tissue Engineering and Drug Carrying Materials

“…Although cryogel scaffolds can be readily formed through physical cross-linking—for example, involving ionic interaction and hydrogen bonding—they are generally reversible, and the resultant porosity and mechanical properties will not always be satisfactory for all applications. Poly(vinyl alcohol) (PVA) is one of the most studied synthetic polymers that can be physically cross-linked to obtain cryogels [ 2 , 14 ]. PVA cryogels are formed as a result of the formation of microcrystalline zones and are thermally reversible.…”