Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/23709
Title: Synthesis and functionalization of micro/nano-particles for malicious cells detection and elimination
Authors: HU FEIXIONG
Keywords: magnetic nanoparticles, MRI, surface and bulk functionalization, composite nanoparticle, magnetic drug targeting, controlled release
Issue Date: 12-Jun-2009
Source: HU FEIXIONG (2009-06-12). Synthesis and functionalization of micro/nano-particles for malicious cells detection and elimination. ScholarBank@NUS Repository.
Abstract: Micro/nano size particles are very useful vehicles for surface and bulk functionalization due to their high surface/volume ratio and their ability to encapsulate other agents. In this thesis, different approaches of surface and bulk functionalization of micro/nanoparticles for diagnosing or eliminating malignant cells were developed. At the same time, other important properties of particles such as the cytotoxicity and cell uptake were investigated after the functionalization process. A simple technique was first developed for preparing polymeric microparticles for antimicrobial applications. Poly (4-vinyl pyridine)/poly (vinylidene fluoride) (P4VP)/(PVDF) microparticles prepared by the phase inversion technique were used as the substrate. P4VP contributed the antimicrobial groups while PVDF provided the mechanical strength of the beads. The N-alkylation of the P4VP was carried out with alkyl chains of different lengths since the length of the carbon side chains has been shown to affect the antibacterial efficacy of pyridinium-type polymers. Two microorganisms, a Gram-negative bacteria Escherichia coli (E. coli) and a fungi spore Aspergillus niger (A. niger), were chosen to test the antimicrobial efficacy of the microparticles. To obtain a better understanding of the difference in efficacy against these two microbial species, the effect of surface pyridinium groups on cellular components was studied. This technique for preparing antibacterial microparticles has the advantages of ease of mass production and scale up, and the microparticles possess stability for repeated usage. In the second part of the work, magnetic nanoparticles were developed for the detection and elimination of malignant mammalian cells. For in vivo applications, the particles to be introduced must be small enough, such that they do not clog the blood vessels through which they are guided to the target organ. A new magnetic targeted drug delivery carrier was developed by encapsulating magnetic Fe3O4 seeds and tamoxifen, a drug for human breast cancer, in a biodegradable polymer, poly(L-lactic acid) (PLLA), in the form of nanoparticles. These magnetic nanoparticles can also be used as contrast agents for magnetic resonance imaging (MRI), with which the distribution of the carrier can be visualized in vivo. The encapsulation of tamoxifen in the polymer matrix can extend the release profile over that of other reported methods. The anti-cancer activity of the nanoparticles was evaluated with MCF-7 breast cancer cells. Subsequently, a block polymer, poly(L-lactic acid)-block-poly(poly(ethylene glycol) monomethacrylate) (PLLA-b-PPEGMA), was synthesized for encapsulating the magnetic seeds, and the composite polymer-Fe3O4 nanoparticles were then surface functionalized with folic acid. The uptake of the folic acid functionalized nanoparticles by cancer cells was shown to be enhanced compared to that of nanoparticles without folic acid functionalization. Finally, a new PEGylation strategy was developed to increase the circulation time of magnetic nanoparticles in the blood stream via surface initiated atom transfer radical polymerization (ATRP). A silane initiator was first immobilized on the magnetic nanoparticles surface. Then, copper-mediated ATRP technique was used to graft polymerize poly(ethylene glycol) monomethacrylate (PEGMA) on the magnetic nanoparticles surface. The uptake of the PEGMA-functionalized magnetic nanoparticles by macrophage cells was used to evaluate the applicability of this technique for increasing in vivo half-life of magnetic nanoparticles.
URI: http://scholarbank.nus.edu.sg/handle/10635/23709
Appears in Collections:Ph.D Theses (Open)

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