Synthesis Of Novel PEG-Poly(Aspartic Acid)Derivatives For Drug Delivery And Analysis Of Biomedical Polymer By HPLC

Amphiphilic polymers containing poly(ethylene glycol)(PEG) as hydrophilic segments can self-assemble to form polymeric micelles for drug delivery, which not only provide with good stability of drug carrier, but also prolong circulation of the nanoparticles in the bloodstream and enhance drug efficacy. Polymers derived from poly(amino acid)s have attracted much attention in drug carrier, tissue engineering and other fields, due to the good biocompatibility, biodegradablity, non-toxicity of degradation products. In this work, the functional PEG derivatives with different end groups were separated and characterized by high performance liquid chromatography (HPLC). A series of novel PEG-poly(aspartic acid) derivatives were designed and synthesized for drug delivery and the properties of their drug-loading and drug-release were investigated. The aqueous size-exclusion chromatography (SEC) analysis of reduction-sensitive poly(ethylene imine)(PEI) derivatives used for gene delivery was optimized.In Chapter1, the development and application of the polymeric micelles for drug delivery were outlined. The synthesis of biodegradable poly(amino acid) materials and their development in controlled drug release were systematically presented. Meanwhile, the application of HPLC including SEC in the characterization of polymers was briefly introduced.PEGylation of drug and drug-carrier (PEG-modification) are widely used in modern medicine and controlled release system. The two terminal groups of linear PEG play an important role in the PEGylation of polymeric drug carrier. How to characterize accurately the end group structure of the functionalized PEG is one of the the main challenges in polymer characterization field. In Chapter2, a series of PEG derivatives modificated by carboxyl benzaldehyde as representative polymers were synthesized, and several kinds of chromatographic columns were used to separate and characterize the PEG derivatives accuratly by HPLC. Suitable conditions were found to separate the different PEG derivatives based on their end-groups. In addition, the different PEG derivatives could be separated rapidly in30seconds by using UPLC (Ultra High Performance Liquid Chromatography) system.In Chapter3, biodegradable Y-shaped amphiphilic ABC triblock copolymer mPEG-PBLA/PCL (MPBC) for drug delivery, containing hydrophilic PEG and hydrophobic poly(?-caprolactone) and poly(?-benzyl-L-aspartate) segments, were prepared by enzymatic polymerization, NCA-ring opening polymerization (NCA-ROP) and click reaction using endgroup-modificated PEG as initiator. The drug encapsulated in the Y-shaped polymeric micelles can be released slowly. Owing to the good biocompatibility, the resulted polymeric micelles were non-toxic and the DOX-loaded micelles displayed obvious anticancer activity similar to free DOX against HeLa cells. This work provides a new way to synthesize multi-functional non-linear polymers.In Chapter4, novel pH and reduction dual-sensitive biodegradable polymeric micelles for efficient intracellular delivery of anticancer drugs were prepared based on a block copolymer of methyloxy-poly-(ethylene glycol)-b-poly[(benzyl-L-aspartate)-co-(N-(3-aminopropyl)imidazole-L-aspartamide)][mPEG-SS-P(BLA-co-APILA), MPBA] synthesized by a combination of ring-opening polymerization and side-chain reaction used endgroup-modificated PEG as initiator. Because of the introduction of disulfide bond and imidazole groups, the obtained MPBA polymer exhibited pH and reduction sensitive behaviour. The polymeric micelles and DOX-loaded micelles could be prepared simply by adjusting the pH of the polymer solution without the use of any organic solvents. The drug release study indicated that the DOX-loaded micelles showed retarded drug release in PBS at pH7.4and a rapid release after exposure to weakly acidic or reductive environment. The polymeric micelles were non-toxic and the DOX-loaded micelles displayed obvious anticancer activity similar to free DOX against HeLa cells. Thus, the pH and reduction dual-responsive mPEG-SS-P(BLA-co-APILA) polymeric micelles are an attractive platform to achieve the fast intracellular release of anticancer drugs.The molecular weight and weight distribution are important parameters for polymers and usually are determined by size exclusion chromatography (SEC). However, because of the interaction between the functional groups of the polymers and the surface of the column packing materials which can affect the chromatographic behaviour of polymers, resulting in so-called non-size effects such as ion exclusion (sample elutes early), ion-interaction and hydrophobic interactions (sample elutes late), the molecular weight results measured by aqueous SEC are uaually inaccurate or even wrong. In Chapter5, the aqueous mobile phase was optimized in combination with Shodex OHpak SB columns for SEC analysis of reduction-sensitive disulfide-containing poly(ethylene imine)(PEI) derivatives used in gene delivery. Addition of acetonitrile in mobile phase was shown to be able to suppress the hydrophobic interactions between polymer analytes and the stationary phase. The absolute molecular weights and distributions of the cationic polymers were determined directly from online SEC-MALLS (multi-angle light scattering)/RI (refractive index) detection. The results demonstrate that a good SEC separation of reduction-sensitive disulfide-containing PEI derivatives used in gene delivery with little band broadening was achieved.