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Immobilization of a thyroid hormone substitute of L-thyroxine on chitosan-based smart hydrogel structure was performed to reduce the side effects of the required daily dose. The hydrogel was obtained by the Schiff reaction of chitosan with acetaldehyde and quaternization with methyl iodide then by ion exchange with NaCl salt. Finally, a hydrogel was obtained from the treatment of chitosan-based salt at -200C. The amount of levothyroxine immobilized by physical sorption on the hydrogel was determined by molecular electron spectroscopy on basis especially absorption peak at 227 nm. Results of IR- and UV-Vis spectroscopic analyses revealed that the interaction between levothyroxine and hydrogel occurs mainly due to hydrogen bonding and orientation forces of intermolecular interaction

In our study, new natural-synthetic, cross-linked copolymers were obtained by radical copolymerization of chitosan in the presence of to chitosan, the radical co-polymerization with azobisanobutyronitrile initiator were performed in the homogeneous phase in the presence of monomers. The combined effects of the major parameters to the cross-linked radical copolymerization were studied systematically. The cross-linking degree of the monomers to chitosan (G) and dependence of crosslinking effectiveness (E) upon temperature, amount of chitosan, concentration of inisiator, solvent ratio, reaction time and concentration of monomers were studied. It revealed that G = 258% and E = 17-19% were max. at 60-70 0 C, within 150 min., in the cross-linked copolymerization of 0.35 g chitosan with 2.4 mol/l of N-vinylpyrrolidone and 0.2 mol/l of 4-vinylpyridine in the presence of 75 ml 2% CH3COOH as a solvent, and the estimated degree of homopolymerization at minimum 18-20%. Through the use of 1 H NMR, FTIR, SEM, X-Ray and thermogravimetric analysis methods, the mechanism of radical crosslinked copolymerization was proposed on the basis of the cyclic breakdown of chitosan.

In order to reduce the side effects of thyroid hormone substitute levothyroxine sodium pentahydrate, its sorption with a quaternized salt of a new alkyl derivative of chitosan was studied. The drug amount in the salt (gel) is in micrograms, and the gel-levothyroxine is in the form of a complex that can show biological activity. With that end in view, a sorption process of levothyroxine sodium from an aqueous solution to the inside and surface of the hydrogel was carried out under static conditions. The capacity of the hydrogel depending upon the pH medium, the ionic strength, the hydrogel dose, the concentration of the drug and the temperature was studied. It was shown that the effective sorption of levothyroxine by chitosan-based hydrogel was optimal at pH of 6-8.5, at 50 mg/L concentration of levothyroxine in the presence of 10-50 mg of hydrogel dose but the sorption degree begins to decrease after T=40 °C. The isotherm results of sorption processes have been found to be subordinate mainly to Langmuir and to some extent Freundlich equations. It revealed that gel degradation in the oxidizing medium is about 70% within 2 weeks, and in the elastase and PBS medium is about 17-20%.