Kuziv Y. Branched thermosensitive polymers and hybrid nanocomposites based on them for biotechnology and medicine.

The thesis is devoted to the synthesis of thermosensitive star-shaped copolymers with dextran core and poly-N-isopropylacrylamide branches, hybrid nanocomposites with different composition based on them, and their detailed characteristics at physiological temperatures. All studies have been conducted by modern physicochemical methods: gel permeation chromatography, dynamic light scattering, transmission electron microscopy, IR-, UV-visible-, Raman and fluorescence spectroscopy, holographic interferometry. The biological activity of the obtained nanocomposites has been tested experimentally in vitro using MTT test, analysis of living/dead cells, confocal laser scanning microscopy, cytofluorimetric analysis. Branched copolymers with a dextran core with a molecular weight of 6,000 and 70,000 and 30 grafted poly-N-isopropylacrylamide chains, as well as with 15 short and long poly-N-isopropylacrylamide grafted chains have been synthesized. In all synthesized copolymers, the conformational transition occurs at a higher temperature than for linear poly-N-isopropylacrylamide. It is shown that with increasing number of poly-N-isopropylacrylamide grafts on a dextran core with a molecular weight of 6000, the stiffness of the macromolecule increases due to steric obstacles and the change in hydrodynamic size during the conformational transition is less visible. Stable gold and silver nanoparticles have been synthesized in situ in copolymer matrices. It has been established by Raman spectroscopy that the interaction of gold nanoparticles with the polymer matrix occurs through oxygen atoms of poly-N-isopropylacrylamide chains. It has been also investigated that when the nanosystem is heated from 18 to 40 оС, there are no significant changes in the interaction of AuNPs with macromolecules. For the first time, anomalous hysteresis is shown during heating and subsequent cooling of the binary nanocomposite Polymer/gold nanoparticles. Analyzing the direct hysteresis for the D-PNIPAA copolymer solution and the inverse hysteresis for the D-PNIPAA/AuNPs nanosystem, we can conclude that the difference in behavior mainly depends on the effect of gold nanoparticles. Probably, this effect can be caused by the surface charge of AuNPs, which leads to the repulsion of gold nanoparticles and complicates the phase transition of the macromolecule.