Abstract
Nano-technology is one of the most attention fields of technological area in 21 century, especially in medicine and bio-technology. In the recent year, mixed micelles have attracted many interests and attention in two kinds of polymer blending and assembling. The investigation of micellization from two or more kinds of copolymer is a promising candidate in both fundamental research and practical applications. The main goal of this study is to establish a template for preparing a novel mixed micelle from graft and diblock copolymers, and to use it in cancer therapy. This study is divided into three major topics, including (1) preparation an environmental sensitive micelle from graft copolymers for use in intracellular drug delivery, (2) investigation and discussion of a novel mixed micelle structure from graft-diblock copolymers system, and (3) application the mixed micelle in cancer theapy. (1) Investigation of Polymeric Micelles with a Temperature / pH Sensitive Structure for Application in Intracellular Drug Delivery. In this topic, a new thermo-responsive, pH-responsive, and biodegradable micelle comprised of poly(D,L-lactide)-graft-poly(N-isopropyl acrylamide-co- methacrylic acid) (PLA-g-P(NIPAm-co-MAA)) were developed by grafting biodegradable poly(D,L-lactide) onto N-isopropyl acrylamide and methacrylic acid. A core-shell type nano-structure was formed with a hydrophilic outer shell and a hydrophobic inner core, which exhibited a phase transition temperature above 37 ℃ suitable for biomedical application. Upon heating above the phase transition temperature, PLA-g-P(NIPAm-co-MAA) micelle showed a polarity increasing of pyrene in either buffer solution or intra hepato-carcinoma cells as determined by fluorescence measurement, indicating that the structure of micelles caused leakages from out shell copolymers aggregation and collapse. The drug loading level of 5-fluorouracil (5-FU) encapsulated in the PLA-g-P(NIPAm-co-MAA) micelles can be as high as 20 %. The release of 5-FU from micelles was strongly controlled by the pH in the aqueous solution. Based on these results, PLA-g-P(NIPAm-co-MAA) micelles can be used as a drug carrier for intracellular delivery of anti-cancer drug. (2) Investigation of Mixed Micelles from a Graft Copolymer and a Diblock Copolymer. In the second topic, a novel mixed micelle with multifunctions was prepared from a polyelectrolyte of PLA-g-P(NIPAAm-co-MAAc) graft copolymer and a nonelectrolyte of mPEG-PLA diblock copolymer. The behavior of micellization of graft and diblock copolymers was studied detail by dynamic light scattering, fluorescence, Doppler microelectrophoresis, and other techniques. The results indicate that the micellization of mixed micelle is controlled by the graft copolymer, which has the lowest CMC. As initial water added into graft / diblock copolymer solution, the hydrophobic interactions of graft copolymers were increased, and hydrogen bonding occured between MAAc and mPEG; graft copolymers associated to form a swollen core-shell like pre-structure, the hydrophobic segments of diblock copolymer tended to arrange with graft copolymers, and the unimers of diblock copolymer associated into the pre-structure forming a mixed micelle. Otherwise, micellization of mixed micelles was also compared with different molar ratios and composition ratios of graft / diblock copolymers. The results show that these factors only influence the particle diameters and size distributions. Besides, another diblock copolymer, PEOz-PLA was added to prepare three component mixed micelles. The results indicate that PLA-g-P(NIPAAm-co-MAAc) and PEOz-PLA have the same CMC to form a swollen core-shell like pre-structure. The hydrogen bonding between MAAc and mPEG, and the molar ratios of graft / diblock copolymers were only influenced the particle diameters and size distributions. (3) Evaluation of Mixed Micelle for Application in Cancer Therapy. In the last topic, the mixed micelle comprised PLA-g-P(NIPAAm-co-MAAc) with mPEG-PLA was incorporated with anticancer drug, doxorubicin (Dox) for application in cancer therapy. The mixed micelle had an multi-functional inner core of PLA-g-P(NIPAAm-co-MAAc) to enable intracellular drug delivery and an extended hydrophilic outer shell of mPEG to hide the inner core. Via pH changes, the structure of inner core caused deformation from P(NIPAAm-co-MAAc) aggregation and collapsed. This variation induced the release of a significant amount of Dox from mixed micelles. Clear differences between free Dox and Dox-mixed micelles were observed using confocal laser scanning microscopy (CLSM). Additionally, the efficiency of screening feature also displayed in cytotoxicities; mixed micelle exhibited higher drug activity and lower material cytotoxicity than micelle from graft copolymer. This study presents not only a new micelle structure for a graft-diblock copolymer system, but also a method for determining some of the limitations on biomaterials used in intravenous injection.