Preparation and characterization of hydrogen-bonded layer-by-layer polymer films containing magnetic nanoparticles

Khan, Muhammad Alyaan Ahmed
Stimuli responsive layer-by-layer (LbL) polymer films are promising materials as platforms for controlled release of functional biological molecules such as drugs, proteins, growth hormones, etc. from surfaces. Recently, there has been a growing interest for preparation of LbL polymer platforms containing superparamagnetic iron oxide nanoparticles for dual functionality, i.e. bioimaging and controlled delivery of biological molecules. Moreover, if superparamagnetic iron oxide nanoparticles are embedded into temperature-responsive polymer films, an external trigger mechanism, i.e. magnetothermal trigger can also be used to release functional biological molecules on demand from the surfaces. The study presented in this thesis presents a strategy to incorporate charged iron oxide nanoparticles into neutral hydrogen-bonded polymer LbL films. First, iron oxide nanoparticles with size smaller than 20 nm were synthesized by co-precipitation technique using ultrasonication during synthesis. Iron oxide nanoparticles were characterized using dynamic light scattering, zeta-potential measurements, Fourier Transform Infrared Microscopy (FTIR) Spectroscopy, X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) imaging. For multilayer assembly, polyvinyl caprolactam (PVCL) and tannic acid (TA) were used as polymer building blocks. PVCL is a hydrogen accepting neutral polymer whereas TA has hydrogen donating hydroxyl groups with a pKa of ~ 8.5. At moderately acidic conditions, TA carries both protonated and ionized hydroxyl groups, thus can interact with PVCL through hydrogen bonding interactions, whereas it associates with positively charged iron oxide nanoparticles through electrostatic interactions. LbL films were constructed at pH 4 by immersing the substrate into solutions of TA, PVCL, TA and iron oxide nanoparticles. This process is repeated in the same order of solutions until desired number of layers is deposited at the surface. Stability of multilayers against pH was examined in detail. Multilayer growth and pH-stability were followed by UV-Visible Spectroscopy. Morphology of the multilayers were characterized using Atomic Force Microscopy (AFM). Information about magnetic properties of multilayers was obtained using Magnetic force Microscopy (MFM). Multilayers of TA/PVCL/TA/iron oxide nanoparticles were highly stable at acidic and slightly basic conditions. Moreover, these multilayers were capable of releasing ciprofloxacin, an antibiotic used for treatment of different bacterial infections in the body, at neutral and slightly basic conditions at body temperature. Release of ciprofloxacin from the multilayers was followed using UV-Visible Spectroscopy. The work in this thesis presents the first example of preparation of temperature responsive hydrogen-bonded multilayers containing magnetic iron oxide nanoparticles. In addition to temperature response, multilayers were capable of releasing ciprofloxacin by a pH trigger. Results obtained in this study form a basis for the development of more advanced responsive multilayer films for theranostic (therapeutic and diagnostic) applications.


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Citation Formats
M. A. A. Khan, “Preparation and characterization of hydrogen-bonded layer-by-layer polymer films containing magnetic nanoparticles,” M.S. - Master of Science, Middle East Technical University, 2014.