Investigation Of The Mechanical Characterization, Dynamic Responses And Applications Of Functional Contrast Agent Microbubbles

Malignant neoplasms and cardia-cerebrovascular disease have become the two serious threats to human beings, thus early diagnosis and effective therapy have attracted increasing research and clinic interests. With developments in nano-biotechnology, medical imaging and targeted gene/drug delivery, ultrasound (US)/magnetic resonance imaging (MRI)-guided clinical diagnosis and therapy have been regarded as one of the most promising non-invasive protocol in various strategies. US imaging is a most popular nonionic imaging modality, which has a long safety record and can provide real-time images at low cost. With the help of US contrast agents (encapsulated microbubbles), the sensitivity and accuracy of cancer detection in clinical applications have been greatly improved. Beyond the well-known imaging contrast enhancement effect, increasing body of literatures have also reported that ultrasound contrast agent (UCA) microbubbles (MBs) can serve as good therapeutic agents to facilitate targeted gene/drug delivery, tumor ablation and radiation treatment.Magnetic nanoparticles can be used as powerful contrast agents for MRI, which is capable to provide functional information with high spatial resolution and great soft-tissue contrast. Superparamagnetic iron oxide nanoparticles (SPIOs) have been particularly popular in biomedical applications, because they possess unique magnetic property, good biocompatibility with tissue and great potential as magnetic nonviral vector. Thus, many efforts have been made to design multifunctional diagnostic/therapeutic agents by integrating SPIOs to UCA microbubbles. However, the embedding of SPIOs to MB shell structures would result in the modulation of MB mechanical properties (e.g., size distribution, shell thickness and elasticity), which could significantly affect MB dynamic responses (e.g, resonance frequency, subharmonic/harmonic responses, acoustic absorption coefficient, nonlinear oscillation and cavitation activity).In this work, how the SPIOs impact on the mechanical properties and dynamical behavior of albumin-shelled perfluorocarbon MBs were emphatically studied. First of all, a type of multifunctional agent was systhesized by loading SPIO to albumin-shelled perfluorocarbon MBs. Secondly, the physical properties were investigated by ultraviolet spectrophotometer, magnetometer, transmission electron microscopy (TEM), X-ray energy spectrum and AFM 3-D imaging technology. The results showed that SPIO particles had been successfully coupled to albumin-shelled MBs instead of leaving in the suspension as free residues and had influence on the microstructure and morphology of the MBs. Then a comprehensive technique was proposed to assess the mechanical properties and acoustic properties and improve the evaluation accuracy and uncertainty. Combined AFM technology, single particle light sensor technology, acoustic attenuation and the dynamics simulation for coated bubbles, the size distribution, shell thickness and viscoelastic properties were confined one by one. How the SPIO concentrations affect the mechanical properties and acoustic properties were systematically studied. It is concluded that based on AFM technology and shelled-bubble dynamic models, the viscoelastic properties could be assessed accurately. The elastic coefficient decreased and the viscosity coefficient increased with SPIO concentration increasing. In addition, studies on the application of multifunctional MBs to ultrasound imaging, magnetic resonance imaging and ultrasound-assisted VEGF transfection were presented. Studies have shown that the ultrasound imaging and MRI effect, the sensitivity and accuracy were improved after adding SPIOs. Moreover, an optimized US-facilitated VEGF transfection outcome would be achieved by adopting SPIO-albumin MBs with an appropriate concentration of 114.7 μg/ml. Finally, the mechanism underlying the enhanced porosity and permeability of the 3-D alginate scaffolds by using LIPUS with varied acoustic pressures was examined in detail. The porosity and permeability of the 3-D alginate scaffolds were quantitatively tested with scanning electron microscopy examination, in vivo fluorescence image observation, and laser confocal image observation. The results indicated that the porosity and permeability of the scaffolds were enhanced by the microstreaming generated by ultrasound-driven microbubble oscillations, and increased as the LIPUS exposure intensity increases. This study will provide a theoretical basis for multifunctional micro/nano particles in the uncreasing improvement and development of the clinical noninvasive diagnosis and therapy, and propose characterization methods.