Synthesis And Biomedical Application Of Multifunctional Nanocomposites Based On The Self-assembly Of Amiphiphilic Block Copolymer

Recently, with the rapid development in nanotechnology and biotechnology, multifunctional nanocomposites have attracted more and more attention, among which block copolymer-based multifunctional systems have been paid special attension owing to their potential biomedical applications in the various fields such as magnetic resonance imaging (MRI), drug delivery, absorption and separation of biomolecules, etc. In this thesis, following work has been conducted as listed below:(1) Novel amino- or thiol-functionalized superparamagnetic copolymer-silica nanosphere (NH2-SMCSNs/SH-SMCSNs), which consists of a magnetic core and a silica cross-linked block copolymer shell, have been fabricated. It was found that the diameter of these kind of superparamagnetic copolymer-silica nanospheres was around 150 nm and the magnetization intensity of NH2-SMCSNs was as high as 8.3 emu/g.(2) A sub-100 nm, thiol-functionalized and superparamagnetic copolymer-silica composite nanosphere material (SH-SSCNs) have been successfully fabricated through the self-assembly of Fe3O4 nanoparticles and polystyrene100-block-poly (acrylic acid) 16 and a subsequent sol-gel process. The size and magnetic properties of the SH-SSCNs could be easily tuned by simply varying the initial concentrations of the magnetite nanoparticles in the oil phase. By incorporating fluorescent dye molecules into the silica network, the composite nanospheres could be further fluorescent-functionalized. The toxicity of the SH-SSCNs was evaluated by choosing three typical cell lines (HUVEC、RAW264.7 and A549) as model cells, and no significant cytotoxicity was observed. It was also demonstrated that SH-SSCNs could be used as a new class of magnetic resonance imaging (MRI) probes, having a remarkably high spin-spin (T2) relaxivity (r2= 176.1 mM-1·S-1).(3) RhB-labelled silica cross-linked magnetic cluster micelles with tunable sizes (80 nm, 130 nm and 180 nm) were fabricated via the self-assembly of amiphiphilic block copolymer PS-b-PAA and magnetite nanoparticles in selective solvent and a subsequent cross-linking process by changing the initial magnetite concentration in oil phase. The application of the RhB-labelled silica cross-linked magnetic micelles as T2-weighted contrast agent was demonstrated both in vitro and in vivo. The in vitro MR tests showed that the relaxivity r2 increases with the increase of the nanoparticle sizes. We further examined the effect of particle size on MR imaging of normal liver in vivo, and found that the MRI contrast enhancement in liver by RhB-SCL-MMs was dependent on the size of the nanoparticles. The results indicated that RhB-SCL-MMs-130 with dynamic-diameter of 130 nm exhibited the highest contrast enhancement in liver. We also evaluated the effect of size on cytotoxicity and cellular uptake of macrophage cell line RAW264.7 and the results indicated that all three-sized micelles had no significant cytotoxicity and could be uptaken by cell line RAW264.7, which might provide potential application for cell imaging in the field of fluorescence imaging. Furthermore, the in vivo bio-distribution studies in combination with histological analysis proved that the RhB-SCL-MMs could be mainly uptaken by liver and spleen and neglectable tissue toxicities were observed in tissue slice tests.(4) A simple strategy was developed to fabricate a novel kind of uniform, biocompatible and PEGylated multifunctional hybrid micelles with multiple magnetite nanocrystals-loaded core and dye-doped silica cross-linked shell based on the self-assembly between poly (ε-caprolactone)-b-poly (acrylic acid) copolymer and inorganic nanoparticles. The loading of multiple magnetite nanoparticle in the core part of the hybrid micelles endows them with T2 weighted MR imaging functionality. Small dye molecules (Rhodamine B) were directly incorporated into the silica layer framework during the cross-linking process, imparting the hybrid micelles with fluorescent imaging modality. Poly (ethylene glycol) (PEG) was grafted to reduce the phagocytic capture of nanoparticles by cellular components of immune systems. Importantly, the potential application of magnetite incorporated PEGylated hybrid micelles as T2 contrast agents for MRI was demonstrated both in vitro and in vivo, with the passive targeting behavior via EPR effect due to the leaky vasculature and poor lymphatic drainage in tumors.(5) Hierarchically mesoporous structured silica materials have been successfully synthesized via a facile route using amphiphilic block copolymer polystyrene-b-poly (acrylic acid) (PS-b-PAA) and cetyl trimethyl ammonium bromide (CTAB) as dual templates. It was found that the dimension of spherical micelle-like aggregates of PS-b-PAA could be adjusted by changing the type of solvents. Selecting N, N-dimethylformamide (DMF) as a solvent, spherical micelle-like aggregates with an average diameter of 35 nm were obtained, and bimodal mesoporous materials (BMM) possessing large pores of 35 nm and small pores of 2.5 nm in diameters could be prepared. When the solvent was changed to N,N-dimethylformamide (DMF)/tetrahydrofuran (THF) (v/v=1:1), the average diameter of the spherical micelle-like aggregates of PS-b-PAA increased to 200 nm, and hollow mesoporous spheres (HMS) with 200-nm hollow cores and 25-nm shells were obtained.(6) Core-shell structured dual-mesoporous silica spheres (DMSS) that possess smaller pores (2.0 nm) in the shell and larger tunable pores (12.8-18.5 nm) in the core have been successfully synthesized by utilizing an amphiphilic block copolymer (polystyrene-b-poly (acrylic acid), PS-b-PAA) and cetyl trimethyl ammonium bromide (CTAB) as co-templates. The thickness of the shells and the larger pore size in the core could be easily tuned by changing the amounts of TEOS and the hydrophobic block (PS) length during synthesis, respectively. By encapsulating hydrophobic magnetite nanoparticles into the cores, superparamagnetic dual-mesoporous silica spheres were obtained. Drug storage and release testing results showed that the diffusion rate of the stored drug could be efficiently controlled by changing the shell thickness of DMSS.