RESULTS OF RESEARCH OF THERMOSENSITIVE PROPERTIES OF COMPOSITIONS BASED ON CHITOSAN LACTATE

Introduction. The development of stimulus-sensitive drug delivery systems ("in situ" systems) is one of the actively developing trends in pharmaceutical technology. First of all, such systems provide sustained and controlled release of the active substance due to a special sol-gel transition. "In situ" systems are solutions that under various physiological conditions transition into a hydrogel. The transition of a solution into a hydrogel depends on various factors such as temperature, pH change, UV radiation, presence of certain molecules or ions. Biopolymers such as chitosan are the basis for in situ systems. Chitosan is an economically available, biodegradable and biocompatible polymer, which makes it a promising raw material for hydrogels. Solutions of chitosan salts are claimed to have stimuli-responsive properties such as pH- and thermosensitivity, however, the composition of such systems usually includes crosslinking agents that may have intrinsic pharmacological and/or toxic activities. The aim of this study was to test the hypothesis of the thermosensitivity of chitosan lactate-based hydrogels made without crosslinking agents. Material and Methods. In accordance with the objective, screening experiments were performed to obtain and investigate the properties of chitosan lactate, during which prototypes were obtained to test the ability of hydrogels to thermosensitive transition without auxiliary crosslinking agents and to evaluate the properties of chitosan-based hydrogels at different temperature values. Results. As a result of the experiments carried out, it was found that the solutions studied are not capable of thermosensitive phase transition. However, it should be noted that during the experiments samples of hydrogels based on chitosan and lactic acid were obtained with different organoleptic and physical properties depending on the concentration of lactic acid. Conclusions. Based on the results of the screening study, the hypothesis about the thermosensitive transition ability of chitosan lactate solutions without the addition of crosslinking agents was refuted. This issue requires further study using methods that allow to evaluate the underlying changes in the molecular structure of the polymer during gelation when the solution temperature is changed. The experiments also proved the ability of chitosan to form hydrogels in aqueous solutions with low concentration of weak organic acids with pH in the range from 5 to 6.