|M.Sc Student||Keren Massuri|
|Subject||Light-Triggered Self-Assembled System|
|Department||Department of Biotechnology and Food Engineering||Supervisor||Assistant Professor Mizrahi Boaz|
|Full Thesis text|
In recent years there has been a growing interest in using stimuli-responsive polymers in a variety of applications, owing to their ability to change their physical state in respond to external stimuli. Among the diverse stimuli existing, light is of particular interest since it possesses many advantages. Despite the potential, two major limitations of light limit their medical application to topical formulation. The inefficiency of the reaction, and the toxicity. The long irradiation time together with the toxicity of many light triggered groups makes these systems clinically irrelevant.
Self-assembly of amphiphilic molecules has always been an attractive topic as it spontaneously produces various structures. In recent years several groups have reported on the self-assembly of amphiphilic multi-armed molecules into multi-molecular aggregates.
In this research, we chose to combine the self-assembly process with light triggered molecule. We have hypothesized that a light triggered, hydrophobic moiety will allow self-assembly which will be followed by cross linking via irradiation of light. The hydrophilic core will be composed of a short four-armed Poly(ethylene glycol) (PEG4). Cinnamylidene acetic acid (CAA) will be utilized both as the hydrophobic moiety, and as the light sensitive group. . Under exposure to UV light at wavelengths above 300 nm, the cinnamate group undergoes  cycloaddition; the formed bonds are expected to cross-link the polymer, and contribute to the structure stability in water.
Here, we intend to synthesize and characterize a self-assembled polymer, which will be responsive to light in aqueous environment. The synthesis, the self-assembly process, the light effect on the formed particles and the particles' stability to salt will be examined. First, the conjugated polymer was synthesized and the products of the synthesis were verified using UV-Vis spectroscopy and 1H-NMR, and were compared to the literature. In addition the final product of the synthesis was examined in GPC. The results showed that each molecule of PEG4 was modified with three groups of CAA in average.
Next, the polymer ability to self-assembly in aqueous environment was evaluated by determination of the critical micelle concentration (CMC), and characterization of the obtained particles' size and morphology.
The polymer ability to response to light was evaluated by monitor the FT-IR spectrum and by UV-Vis spectrum during irradiation. The system showed response to light in both cases.
Finally, the light effect on the particles size was monitored using DLS during irradiation. It was found that larger particles were formed when the solution was irradiated. The particles stability was evaluated by monitoring the turbidity of the solution against increasing salt concentration using UV-Vis spectroscopy. The results showed that higher concentration of salt was required in order to disassemble the multi-molecular aggregates.
In this research we have successfully synthesized a particulate system that can be stabilized using UV light. The particles stability is a key factor that needs to be considered when designing a particulate system.