The Synthesis Of Different Sizes Of Hollow Silica Microspheres And Their Applications In Bi-functional Ultrasound/magnetic Resonance Imaging

Molecular imaging technology is combination of molecule/cell biology probesand modern instruments （PET, CT, NMR, US, etc.）. It could provide real-time andnon-invasive imaging of molecular or cellular activity in vivo, such as signaltransduction of intracellular, apoptosis, gene expression and tumor formation, etc.,which is significance for biological research, as well as diagnosis and treatment ofdisease. The most commonly used molecular imaging techniques include: nuclearmedicine imaging （NMI）, magnetic resonance imaging （MRI）, optical imaging （OI）,ultrasound imaging （US）, and CT imaging. NMI have high sensitivity and quantitative,but the low spatial resolution; optical imaging hardly used in clinical research for itslimited penetration; CT imaging can’t find lesions; MRI have the advantages of highspatial resolution and multiple sequence imaging; US imaging is safe, real-time andnon-invasive diagnosis. Ultrasound combined with NMI, MRI and OI has broadapplication. In this thesis, we investigated the synthesis of hollow silica microsphereswith different sizes and their applications in US. Then modified DTPA-Gd andtargeting molecule RGD onto the surface of hollow silica microspheres with adiameter of400nm to achieve bi-functional ultrasound/magnetic resonance imaging.We also study the biocompatibility, tissue distribution and metabolism of hollowmicrospheres. All the research contents and results are as follows:1. The synthesis of hollow silica microspheres with different sizes and theirapplications in ultrasound imagingBased on the previous studies by our group, hollow silica microspheres with different sizes were further synthesized and explored their ultrasound imaging in vitro.100nm PS were prepared by emulsifier-free emulsion polymerization using[2-（acryloyloxy） ethyl] trimethylammonium chloride （AETAC） as a stabilizer and2,2’-Azobis （2-methylpropionamidine） dihydrochloride （AIBA） as a initiator;200and400nm PS were prepared using polyvinylpyrrolidone （PVP） as a stabilizer and AIBAas a initiator;1.4m PS were synthesized via dispersion polymerization using PVP asa stabilizer and2,2’-azo-bisisobutyronitrile （AIBN） as a initiator. Then hydrolysis ofTEOS and APS were carried out in alcohol medium with PS template,amino-functionalized PS@SiO₂core/shell microspheres were obtained with ammoniacatalyzes. SiO₂hollow microspheres were prepared via remove the template byetching with THF under hydrothermal conditions. Finally, appropriate cavity andbiocompatible monodisperse SiO₂were synthesized by modified with polyethyleneglycol （mPEG-COOH）. The nanoscale SiO₂hollow spheres exhibit a strongultrasound signal （test condition: transducer frequency=6.0MHz, mechanical index=0.06）,400nm is the best size for ultrasound imaging. All results indicating thatSHS-PEG with different sizes have potential to be a novel ultrasound contrast agent.2. The preparation of ultrasound/MRI bi-functional hollow silica microspheresand their applications in targeted imagingOn the basis of the above studies, we modified DTPA-da onto the surface of400nm hollow silica microspheres so that it can be used in US and T1-weighted MRimaging, then coupling targeted molecule cyclic RGDfK peptide to obtained targetedultrasound/MRI bi-functional hollow silica microspheres. Finally, biocompatiblehollow SiO₂were synthesized by modified with mPEG-COOH and thus could beapplied to ultrasound/MRI bi-functional imaging in vivo. The formedSHS-Gd-RGD-PEG hollow microspheres showed highly hydrophilic property, goodblood compatibility, low toxicity to high/low expressing cells, normal cells, and evenin vivo. SHS-Gd-RGD-PEG exhibited significant T1-weighted imaging at0.5T, andthe relaxation rate is better than commercial Gd-DTPA, these results demonstrate thatSHS-Gd-RGD-PEG is a very good T1-weighted MR imaging agent. The microspheresshowed enhanced contrast effect on the tumor cells αvβ3high affinity over-expressing PC3, better than low-expressing HeLa cells. SHS-Gd-RGD-PEG can also be used inMRI and US in vivo. All of the heart, liver and kidney of the mouse exhibitedenhancement effect of signal after intravenous injection; and the presence ofmicrospheres in liver in vivo ultrasound experiment suggesting the potentialapplication of hollow microspheres for ultrasound/MRI bi-functional imaging agent invivo, thus could significantly improve the diagnosis accuracy. Moreover, tissuedistribution and metabolism indicating that the microspheres would be uptake by theheart and lung through blood, then went into the liver and spleen after pulmonaryretention, and then into the kidney, and mainly be excreted by hepatic metabolism tothe feces, as well as metabolized through the kidney into the urine.