Nonlinear oscillation characteristics of magnetic microbubbles under acoustic and magnetic fields

Microbubbles loaded with magnetic nanoparticles (MMBs) have attracted increasing interests in multimode imaging and drug/gene delivery and targeted therapy. However, the dynamic behaviors generated in diagnostic and therapeutic applications are not clear. In the present work, a novel theoretical model of a single MMB was developed, and the dynamic responses in an infinite viscous fluid were investigated under simultaneous exposure to magnetic and acoustic fields. The results showed that the amplitude reduces and the resonant frequency increases with the strength of the applied steady magnetic field and the susceptibility of the magnetic shell. However, the magnetic field has a limited influence on the oscillating. It is also noticed that the responses of MMB to a time-varying magnetic field is different from a steady magnetic field. The subharmonic components increase firstly and then decrease with the frequency of the magnetic field and the enhanced effect is related to the acoustic driving frequency. It is indicated that there may be a coupling interaction effect between the acoustic and magnetic fields.     

磁流体管内“泡对”在磁声复合场中的振荡行为

基于磁流体管内单泡的动力学模型,通过引入泡间次级声辐射并考虑磁流体黏度的磁场效应,建立了管内“泡对”系统在磁声复合场中的动力学方程,分析了磁场强度、泡对尺寸、泡间相互作用(包括次级Bjerknes力F_B和磁吸引力F_m)及流体特性等对双泡振动特性的影响.结果表明,磁场增大了泡对的振幅,对大泡的影响远大于对小泡的影响.当两泡中心间距一定、两泡相对尺寸越大时,或是当两泡尺寸一定、两泡表面间距越小时,双泡之间的相互作用越强.磁声复合场中,磁场会影响F_B, F_m,磁压P_m及黏滞阻力等,且影响程度各不相同; F_B和F_m及P_m和黏滞阻力之间均存在竞争关系,与作用在微泡上的所有力共同影响泡的运动.通过研究“泡对”系统的动力学行为,为实际应用中调节磁声场,提高微泡对生物组织的靶向调控治疗效果提供了一定的理论依据.