Abstract
Wide-pore cryostructurates were prepared via freezing sodium alginate aqueous solutions with subsequent ice sublimation from the frozen samples, followed by their incubation in the ethanol solutions of calcium chloride or sulfuric acid, rinsing, and final drying. Such sequence of operations resulted in the calcium alginate or alginic acid sponges, respectively. The swelling degree of the walls of macropores in such matrices decreased with increasing polymer concentration in the initial solution. The dependence of the degree of swelling on the cryogenic processing temperature had a bell-like character with a maximum for the samples formed at −20 °C. According to 1H NMR spectroscopy, the content of mobile (non-frozen) water in the frozen water-sodium alginate systems also depended on the initial polymer concentration and freezing temperature. The cryostructurates obtained did not lose their integrity in water, saline, in an acidic medium at pH 2 for at least three weeks. Under alkaline conditions at pH 12 the first signs of dissolution of the Ca-alginate sponge arose only after a week of incubation. Microbiological testing of the model depot form of the antibiotics entrapped in the Ca-alginate cryostructurate demonstrated the efficiency of this system as the antibacterial material.
Highlights
Polymeric cryostructurates are the macroporous materials of spongy morphology, which are formed as a result of freezing the solutions of macromolecular precursors or certain gels with subsequent removal of the crystallized solvent phase without thawing the system as a whole [1]
Cryostructuring systems exerts afraction, significant influence on theoftexture of the resulting we studied the features of the macroporous morphology of alginate cryostructurates formed heterophase matrices, as well as on the volume fraction, size, and shape of their macropores. at the,temperatures we studied theoffeatures of the macroporous morphology of alginate with cryostructurates same freezing the polysaccharide solutions in comparison the samples the formed at the same freezing temperatures of the polysaccharide solutions in comparison with5 the osmotic characteristics of which (Figure 3) were discussed above
Of a certain scientific and applied interest is the preparation of alginate materials using the methods of cryostructuring of macromolecular systems. This is because such approach allows obtaining the wide-pore polymer matrices with a developed system of interconnected large pores. This method was used to create spongy alginic acid and calcium-alginate cryostructurates that were prepared by freezing at −10 . . . −30 ◦ C sodium alginate aqueous solutions (10–50 g/L), followed by sublimation of ice from the frozen samples, the treatment of freeze-dried spongy matrices with, respectively, ethanol solution of sulfuric acid or calcium chloride, washing the resultant sponges and their final drying in vacuum
Summary
Polymeric cryostructurates are the macroporous materials of spongy morphology, which are formed as a result of freezing the solutions of macromolecular precursors or certain gels with subsequent removal of the crystallized solvent phase without thawing the system as a whole [1]. The physico-chemical properties and macroporous morphology of various cryostructurates are determined by many factors, including the nature of the precursors, their concentration in the feed system (before cryogenic processing), the conditions of freezing, and removal of the crystalline phase, the methods of imparting insolubility to cryostructurates of the above-indicated type (I) [1,2,3,4,7,8,9,10,11] These polymeric matrices include polyelectrolyte cryostructurates formed according to a three-stage scheme: freezing a solution of polyelectrolyte—removing the crystallized solvent phase—transforming the polymer into an insoluble form (either using the crosslinking counterions or by recharging the ionogenic groups of macromolecular chains) [5,12,13]. Such research was the goal of this work, and we mainly interested in the properties of wet and swollen alginate sponges since upon their use as the wound dressings, where the materials operate in aqueous media
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