A Study of Cryostructuring of Polymeric Systems. 69. Physicomechanical and Thermophysical Properties of Poly(vinyl alcohol) Cryogels Formed in the Presence of Nonprotonated and Salt Forms of Basic α-Amino Acids

Abstract

Macroporous physical (noncovalent) cryogels have been prepared via freezing at –20°C for 12 h followed defrosting by heating at a rate of 0.03°C/min of aqueous poly(vinyl alcohol) (PVA) solutions without and with additives (0.1–0.5 mol/L) of basic α-amino acids (arginine, histidine, lysine, ornithine) in nonprotonated or salt forms, and the influence of such additives on the physicochemical properties of the gel materials formed in this way has been studied. It has been shown that additives of arginine, its hydrochloride, as well as histidine, exhibit a chaotropic action on the cryotropic gelation of PVA by hindering hydrogen bonding, thus leading to a decrease in the elasticity and heat endurance of the resultant cryogels, whereas additives of lysine, ornithine and their hydrochlorides, as well as histidine hydrochloride, act as kosmotropic agents causing an increase in the compressive elasticity modulus and the fusion temperature of the samples due to the promotion of hydrogen bonding. The kinetic study of releasing amino acid additives used in the work has shown that the hydrochlorides are released from a gel carrier into an external aqueous environment somewhat slower than are nonprotonated forms, but without noticeable diffusion hindrances in all cases. Taking into account that such amino acids are used in cosmetology, the results obtained in this study suggest that PVA cryogels loaded with amino acid additives may be of practical interest when developing carriers for cosmetics such as nourishing masks, coatings for problem areas of skin, “patches”, etc.