Chemical and Biological Engineering MS Thesis Defense by Uğur Bozüyük





Title: Design of Chitosan-Based Carriers for Biomedical Engineering Applications

Speaker: Ugur Bozuyuk

Time: 03.09.2018, 11:00

Place: ENG B29

Koç University

Rumeli Feneri Yolu

Sariyer, Istanbul

Thesis Committee Members:

Assoc. Prof. Dr. Seda Kizilel (Advisor, Koç University)

Dr. Erkan Senses (Koç University)

Prof. Dr. Kutlu Ulgen (Boğaziçi University)


Chitosan-based materials have gained enourmous attention due to unique properties of chitosan such as biodegrability, biocompatibility and cationic nature. Especially, chitosan-based drug/gene delivery systems became a promising alternative for the treatment of various diseases. This thesis includes studies about nanoparticle and microrobotic-based chitosan carriers. In the first part of the thesis, the main aim is to synthesize colloidally stable ionically crosslinked chitosan nanoparticles. Ionically-crosslinked chitosan nanoparticles have gained considerable attention due to their cationic nature and sub-100 nm size. However, low solubility of chitosan in neutral media restricts its potential clinical translation. PEGylation is a simple solution to increase solubility of chitosan and chitosan nanoparticles in neutral media. Yet, effect of PEG chain length and chitosan/PEG ratio on particle size and zeta potential of nanoparticles are not known. This chapter of the thesis presents a systematic analysis of the effect of PEG chain length and chitosan/PEG ratio on size and zeta potential of nanoparticles. PEGylated chitosan polymers were prepared before the nanoparticle synthesis with different PEG chain lengths and chitosan/PEG ratios. Effect of PEG chain length (2, 5 and 10 kDa), chitosan/PEG ratio (25 mg chitosan to 4, 12 and 20 μmoles of PEG) and pH (within 6.0-7.4) on nanoparticles were investigated. Having obtained the experimental size and zeta potential values, artficial neural networks were created to predict size and zeta potential values of different groups. Artificial neural networks is a modelling tool used in nanomedicine to optimize and predict inherent properties of the system. Inherent properties of a nanoparticle system such as size and zeta potential can be estimated based on previous experiment results. Namely, nanoparticles with desired properties can be synthesized using an ANN. We were able to estimate the size and zeta potential of nanoparticles under different experimental conditions. After that, we performed cell attachment experiments with different nanoparticle groups. Nanoparticle groups having higher zeta potentials had better adhesion ability to HEK293-T cells, which was estimated through ANN model prior to experiments. Overall, this chapter presents the PEGylation of chitosan, synthesis of PEGylated chitosan nanoparticles and the use of ANN model as a tool to predict important properties such as size and zeta potential. In the second part of the thesis, plasmid DNA loaded and tumor homing peptide (CREKA) modified stable chitosan nanoparticle carriers were synthesized for gene delivery applications. Peptide modification and DNA loading was confirmed with certain assays and these nanoparticles will be used for cancer therapy applications in the future. In the third part of the thesis, we propose a magnetically-actuated chitosan-based microrobotic system that can release the chemotherapeutic drug using external light stimulus. We fabricated the chitosan-based microswimmers by two-photon direct laser writing (TDLW) technique using of a photosensitive derivative of chitosan in the form of a magnetic polymer nanocomposite. Amino groups on the microswimmers were modified with doxorubicin using a photocleavable linker. Controlled moving ability of the microswimmers was shown under rotating magnetic field. 60% of doxorubicin was released from the microswimmers in 5 minutes with light stimulus at 365 nm wavelength and 30 mW laser output power. Enzymatic degradation of the microswimmers was shown in 204 hours. This part of the thesis presents the combination of light-triggered drug delivery with magnetically-powered microswimmer mobility. Overall, it was shown that chitosan-based carriers can be fabricated in various forms for different applications. Our results suggested that chitosan-based materials are promising for biomedical applications.