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Identifier 000446214
Title Biodegradable polyesters with Upper Critical Solution Temperature (UCST) behavior in aqueous salt solutions
Author Καρούζου, Μαρία
Thesis advisor Βαμβακάκη Μαρία
Reviewer Χατζηνικολαϊδου, Μαρία
Aseyen, Vladimir
Abstract Thermo-responsive polymers have attracted great attention for use in biomedical applications, including controlled drug delivery, tissue engineering and others. They are classified into two main types: polymers which phase separate in water upon heating, and are characterized by the so-called lower critical solution temperature (LCST), and those which become soluble in water when increasing the solution temperature, and display the so-called upper critical solution temperature (UCST). UCST polymers are much less studied compared to their LCST counterparts1, whereas UCST-type biodegradable polymers are scarce in the literature2. In the present work, we have synthesized main chain biodegradable polyesters bearing ionizable primary amine side groups, which exhibit a UCST in water in the presence of hydrophobic counterions. The polymers were synthesized by the polycondensation of a vinyl functionalized diol with a diacid chloride, followed by the post-polymerization modification of the alkene side groups of the polymer with cysteamine hydrochloride using photo-induced thiol-ene click chemistry. In the first part of the thesis, functional polyester homopolymers exhibiting pH-responsive properties in aqueous solution and a thermo-responsive behavior in the presence of tetrafluoroborate anions, which act as counterions to the charged amine groups, were prepared. The cloud point temperature (Tc) was tuned between 2 °C and 52 °C, following a linear dependence on the salt concentration, whereas it first increased and then decreased when varying the polymer concentration at a constant salt content, which was attributed to intra- and/or inter-molecular ionic interactions. The biodegradability of the polyester in phosphate buffered saline at pH 7.4 was studied. Finally, the primary amine side groups of the polyester were modified to ureido functionalities to obtain a thermo-responsive behavior in the absence of added salt in the solution. However, the ureido-derivatized polyester did not exhibit a thermo-responsive behavior even when systematically tuning the ureido content of the polyester. In the second part of this thesis, functional poly(ethylene glycol)-b-polyester (PEG-b-polyester) diblock copolymers were synthesized by attaching a poly(ethylene glycol) block onto the chain end of the polyester homopolymer bearing the alkene side groups via a Steglich esterification reaction. Thermo-responsive diblock copolymers were obtained following the post-polymerization modification of the alkene side groups of the copolymer with cysteamine hydrochloride, using photo-induced thiol-ene click chemistry. After anion exchange with the hydrophobic tetrafluoroborate counter-anion, the thermo-responsive diblock copolymer self-assembled into nanoparticles of a hydrodynamic radius, RH = 27 nm, in aqueous media at room temperature. At higher temperatures (>30 °C) the polymeric nanoparticles were disrupted indicating a UCST-type phase transition of the copolymers. The encapsulation and release of a hydrophobic dye (Nile Red) in the polymeric nanoparticles, as a function of the solution temperature, was also studied. Overall, the tunable transition temperature and excellent biodegradability of these novel smart polyesters render them promising biomaterials for use in drug delivery and tissue engineering applications.  
Language English
Subject Polymers
Thermoresponsive polymers
Issue date 2022-03-18
Collection   School/Department--School of Sciences and Engineering--Department of Materials Science and Technology--Post-graduate theses
  Type of Work--Post-graduate theses
Permanent Link https://elocus.lib.uoc.gr//dlib/e/5/1/metadata-dlib-1646047110-544707-30388.tkl Bookmark and Share
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