Synthesis Of Functional Poly(?-caprolactone)s And Their Applications In Drug Delivery

Poly(s-caprolactone) (PCL) has received great attention in recent years due to its biocompatibility, good mechanical properties and biodegradability through hydrolysis as well as enzyme catalytic degradation. However, because of the hydrophobic and semi-crystalline nature, low degradability, and especially the lack of functional groups, its biomedical applications are limited. The purpose of this dissertation is to introduce pendant functional groups to PCL through chemical modification. Taking the advantages of the improved physicochemical properties of modified PCL, we have prepared micellar nanoparticles with tunable sizes and properties, which have been applied for bioconjugation, fluorescent labeling and delivery of anti-cancer drugs.The main contents of this dissertation are summarized below:1. Benzyl chloro formate was firstly used to protect the amino group of trans-4-aminocyclohexanol. Then, the hydroxyl group of the resultant alcohol, benzyl 4-hydroxycyclohexanecarbamate, was oxidized into carbonyl group by the use of Jones' reagent. Finally, by a Baeyer-Villiger oxidation, the ketone, benzyl 4-oxocyclohexane carbamate was converted into the corresponding lactone y-(carbamic acid benzyl ester)-?-caprolactone (CABCL) by using m-chloroperoxybenzoic acid. The synthesis process was studied in detail and the structure of the product in each step was confirmed by NMR, FT-IR and Mass.2. A series of copolymers poly[?-caprolactone-co-y-(carbamic acid benzyl ester)-s-caprolactone] [P(CL-co-CABCL)] were prepared by ring-opening polymerization (ROP) of s-caprolactone (CL) and y-(carbamic acid benzyl ester)-s-caprolactone (CABCL) at varied ratios in bulk using stannous octoate [Sn(Oct)2] as catalyst. They were converted into deprotected copolymers poly(?-caprolactone-co-y-amino-s-caprolactone) [P(CL-co-ACL)] with free amino groups by hydrogenolysis in the presence of Pd/C. The pendant amino groups were further used for the attachment of biotin (PCL/Biotin). The structures of polymers were characterized by NMR, FT-IR, GPC and the thermal properties were studied by DSC.3. Better compatibility between DOX and P(CL-co-CABCL) than that between DOX and PCL calculated from Flory-Huggins interaction parameter motivates the synthesis of monomethoxy-poly(ethylene glycol)-b-poly[(?-caprolactone-co-y-(carbamic acid benzyl ester)-s-caprolactone] mPEG-b-P(CL-co-CABCL). mPEG-b-P(CL-co-CABCL) block copolymers with various CABCL contents were prepared via ring-opening polymerization (ROP) of CL with CABCL using monomethoxy-poly(ethylene glycol) (mPEG) as macroinitiator and characterized by 1H NMR, FT-IR, GPC, WAXD, and DSC techniques. Also, the micellar formation of the copolymer in aqueous solution was investigated with fluorescence spectroscopy, DLS and TEM. mPEG-b-P(CL-co-CABCL) had decreased crystallinity as well as lower critical micelle concentration (CMC) and improved stability of prepared micelles in comparison with mPEG-b-PCL. Notably, these micelles of mPEG-b-P(CL-co-CABCL) showed higher drug loading capacity and better sustained release profile. Furthermore, it was also evidenced that DOX-loaded micelles prepared with this copolymer were more readily internalized by HepG2 cells and mainly stayed in cytoplasm, while free DOX accumulated more in the nuclei. However, at the same drug dose, DOX-loaded micelles were less potent in inhibiting cell proliferation than free DOX.4. Using monomethoxy-poly(ethylene glycol) (mPEG) as macroinitiator and Sn(Oct)2 as catalyst, by controlling the feed ratio and sequence of s-caprolactone (CL) and y-methyl-s-caprolactone (MCL), a series of copolymers:mPEG-b-PCL, PEG-b-PCL-b-PMCL, mPEG-b-P(CL-co-MCL) and mPEG-b-PMCL were synthesized via ring-opening polymerization.1H NMR and GPC were used to characterize the structures of polymers. FT-IR, WAXD and DSC were used to study the crystallinity. Due to the introduction of MCL, polymers had decreased crystallinity, improved drug loading capacity and faster release profile. Furthermore, it was also evidenced that DOX-loaded micelles prepared with these copolymers could be internalized by HepG2 cells and the endocytic ability was mainly depended on the core structure of micelles.5. A family of novel amphiphilic block copolymers monomethoxy-poly(ethylene glycol)-b-poly[s-caprolactone-co-?-(carbamic acid benzyl ester)-s-caprolactone] mPEG-b-P(CL-co-CABCL) were synthesized via ring-opening polymerization (ROP) of s-caprolactone (CL) and y-(carbamic acid benzyl ester)-s-caprolactone (CABCL) at varied ratios using mPEG as macroinitiator and Sn(Oct)2 as catalyst. Subsequent deprotection upon removal of carbobenzoxy (Cbz) group yielded monomethoxy-poly(ethylene glycol)-b-poly(s-caprolactone-co-?-amino-?-caprolactone) (mPEG-b-P(CL-co-ACL)) copolymers bearing primary amine functional groups on the PCL block in the presence of 33 wt% HBr solution in glacial acetic acid. Furthermore, a proof-of-concept usage of amino groups for bioconjugation was illustrated by tagging the copolymer with a fluorophore, fluorescein isothiocyanate (FITC). The structures of polymers were characterized with NMR, FT-IR and GPC techniques, the self-assembling of these block copolymers into micellar structures was confirmed by FS, DLS and TEM, in vitro MTT and live/dead assays demonstrated that the micelles were nontoxic to human dermal fibroblasts, and the cellular uptake of FITC-labeled micelles were studied with human fibroblast cells using fluorescence microscopy.