经颅聚焦超声联合微泡开放血脑屏障的数值仿真研究

近年大鼠等动物实验表明经颅聚焦超声联合微泡技术可无创开放血脑屏障实现药物递送,但在临床治疗时由于人体头颅非均质结构及其高声衰减特性,需优化超声经颅聚焦参数和微泡参数。本文基于人头颅CT数据、82阵元相控换能器和血管建立了三维数值仿真模型,研究超声及微泡参数对机械指数和靶区声发射的影响,评估血脑屏障开放程度及组织损伤的可能性。结果表明,声功率和微泡初始密度增大,机械指数和宽带噪声强度增大;频率增大,稳态空化强度增大;当微泡初始半径大于5μm时,稳态空化显著增强。该研究结果为经颅聚焦超声联合微泡技术诱导可控的BBB开放及安全有效递送治疗药物提供了理论数据和技术参考。     

超声造影剂微泡非线性动力学响应的机理及相关应用

随着生命科学及现代医学的发展, 一体化无创精准诊疗已经日益成为人们关注的焦点问题, 而关于超声造影剂微泡的非线性效应的相关机理、动力学建模及其在超声医学领域中的应用研究也得到了极大的推动. 本文对下列课题进行了总结和讨论, 包括: 1)基于Mie散射技术和流式细胞仪对造影剂微泡参数进行定征的一体化解决方案; 2)通过对微泡包膜的黏弹特性进行非线性修正, 构建新的包膜微泡动力学模型; 3)探索造影剂惯性空化阈值与其包膜参数之间的相关性; 以及4)研究超声联合造影剂微泡促进基因/药物转染效率并有效降低其生物毒性的相关机理.     

包膜超声造影微泡次谐波特性的优化设计与实验研究

基于包膜超声造影微泡在超声场中的理论振动模型,对其次谐波特性进行优化设计,从理论上计算和分析了微泡粒径、膜弹性及声压等对微泡次谐波响应的影响,以期获得其用于非破坏性次谐波成像的最佳条件。另外通过改变膜材料的配比, 制备了具有不同膜弹性的超声造影微泡,对其声学特性进行了体外声学实验测定。仿真计算和实验结果表明,在合适的膜材料配比条件下,制得的平均粒径为3μm左右的包膜微泡,可获得满意的次谐波响应,并且其用于非破坏性次谐波成像时的最佳工作声压约200-400 kPa。     

超声微泡低频动力学特性及其生物效应

理论上利用有耗散函数的Lagrange方程,建立了有壳微泡的R(t)运动方程,开展了自由空间中有壳微泡动力学特性的研究,表明微泡内外半径增量随声压的增大、超声频率的降低、初始内径的增大及壳厚的减薄而迅速增大。实验上,利用Mie散射技术在80°散射角和前向Mie散射检测新技术实验测量了微泡R(t)曲线;利用体视显微镜,实时观察了超声微泡对动物活体微血管损伤,开展了超声微泡生物效应的动物和细胞试验研究。结果表明:(1)超声作用下,微泡引起肿瘤中微血管壁周期性膨胀收缩而发生管壁破裂,形成血栓和微血管栓塞,抑制了肿瘤生长;(2)超声联合微泡可以破坏微血管内皮生长因子(VEGF)和肝癌细胞,可以减少肿瘤血管和癌细胞再生,因此,低频超声联合微泡技术是一种值得探索抑制肿瘤生长的新技术。     

非球形包膜微泡近场局部高压研究

基于流体力学,导出了超声驱动下的非球形包膜微泡的外部流体压强的解析表达式.数值模拟表明,虽然包膜微泡的非球形状对远场流体压强没有明显影响,但会造成近场局部位置有极大的流体压强,其明显高于同等条件下的球形包膜微泡周围相应位置上的流体压强.这一现象对包膜微泡的实际应用,如强超声治疗、靶向给药和细胞微穿孔等有着重要的意义.随着驱动频率向包膜微泡本征频率的靠近或微泡偏离球形程度的增大,所产生的近场局部高压也越大.     

脉冲占空比对磁性微泡介导的聚焦超声温升效应的影响

集合多种诊断和治疗功能的声/磁造影剂微泡的研究与开发已经成为当前医学超声、生物医学工程及临床应用领域共同关注的热点问题.超顺磁氧化铁纳米颗粒具有独特的磁性特征和良好的生物相容性,可被用作核磁共振造影剂来提升影像对比度、空间分辨率及临床诊断准确性.我们的前期工作表明,通过将超顺磁氧化铁纳米颗粒挂载于常规超声造影剂微泡表面,可以成功构建多模态诊断及治疗介质,显著改变超声造影剂微泡的尺度分布及包膜粘弹系数等物理特性,进而影响微泡造影剂的声散射特性及其声空化效应和热效应.然而,此前的研究仅考虑了声场强度和微泡浓度等影响因素,对于脉冲超声时间特性对磁性微泡造影剂动力学响应的影响的相关研究仍有所欠缺.本文通过热电偶对凝胶仿体血管模型中流动的双模态磁性微泡在不同占空比超声脉冲信号作用下,产生温升效应开展了系统的实验测量,并基于有限元模型对实验结果进行了仿真验证.结果显示,脉冲信号占空比的提升是增强血管中磁性微泡在聚焦超声作用下温升效果的关键性时间影响因素.本文的研究成果将有助于更好地理解不同超声作用参数对双模态磁性微泡的热效应的影响机制,对保障双模态磁性微泡在临床热疗应用中的安全性和有效性具有重要的...     

具有双重治疗机制的磁性纳米无定型氧化铁基药物递送系统（英文）

合成一种具有pH响应性的聚乙二醇(PEG)修饰无定形介孔氧化铁纳米粒子(AFe-PEG).这种纳米粒子可以高效负载药物分子如阿霉素(DOX),构成新型多功能AFe-PEG/DOX药物递送体系.DOX的负载率高达948 mg/g-纳米粒子.在酸性溶液中,AFePEG/DOX纳米粒子不仅可以有效释放DOX,同时可以释放Fe离子进行Fenton反应,将H_2 O_2转变成·OH自由基.体外实验结果表明,AFe-PEG/DOX纳米粒子对HeLa细胞同时具有化疗和化学动力学疗法的疗效.同时,由于AFe-PEG/DOX纳米粒子本身的磁性,使其在外部磁场中的细胞内化效率也得到了提高.     

超声药物释放空化动力学行为研究

以直径1 μm的脂质体为空化研究对象,从修正的Rayleigh空化方程入手,研究机械系数(MI)对300 kHz和1 MHz超声作用时空化效应的影响。脂质体的药物释放以超声作用前后脂质体中钙黄绿素的荧光强度为量度。模拟结果表明:在微泡振荡过程中,由超声波驱动产生的负向最大泡壁运动速度促使微泡半径从最大快速减小接近于零,微泡积聚到最大能量。对于300 kHz和1 MHz的激励超声,存在一个拐点(MI)值,当MI小于接近0.4时,1 MHz微泡半径变化幅度强于300 kHz;当MI>0.4时,300 kHz微泡半径变化幅度强于1 MHz。这一结果预示在此范围内,300 kHz的药物释放效果好于1 MHz。本研究为超声空化效应研究及超声药物释放应用提供了理论依据。     

多聚赖氨酸诱导的负电性磷脂巨囊泡形变

利用荧光显微技术表征了多聚赖氨酸诱导的负电性磷脂巨囊泡的动力学响应行为.研究发现,多聚赖氨酸可吸附至二油酰磷脂酰胆碱和二油酰磷脂酸混合磷脂巨囊泡的表面,诱导其发生粘连、出"绳"及破裂现象.分析认为,在低盐环境中,膜形变由多聚赖氨酸吸附于二油酰磷脂酸富集区引起的膜两叶应力不对称,以及静电相互作用等因素产生.研究结果对基于聚合物-巨囊泡体系的药物输运控释、细胞形变、微控反应和基因治疗等方面的研究提供有价值的支持.     

基于多基因遗传规划的储层岩石静态模量预测

声发射技术作为一种动态无损检测手段,主要实现对材料产生的缺陷进行动态监测及损伤位置的预测。微机电系统声发射传感器在检测材料疲劳裂纹位置和扩展方向上应用广泛,实现其对材料裂纹的3-D动态位移检测,对于无损检测技术的发展具有重要意义。该文提出了一种新型3-D微机电系统声发射传感器,首先对3-D微机电系统声发射传感器进行了结构设计和性能分析,结构方面主要包括z方向响应传感单元和x、y方向响应传感单元设计;其次通过传感器的阻尼、谐振点处灵敏度计算,证明传感器的性能良好;最后采用有限元软件ANSYS对z方向响应传感单元做了模态和谐响应分析,x、y方向响应传感单元做了模态分析和谐响应分析,仿真结果与理论值吻合较好,验证了结构设计的合理性,对实现材料裂纹的三维动态检测具有一定的参考意义。     

Preparation and in vitro evaluation of an ultrasound-triggered drug delivery system: 10-hydroxycamptothecin loaded PLA microbubbles

10-Hydroxycamptothecin (HCPT) loaded PLA microbubbles, used as an ultrasound-triggered drug delivery system, were fabricated by a double emulsion-solvent evaporation method. The obtained microbubbles were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and confocal laser scanning microscope (CLSM). In addition, the effect of diagnostic ultrasound exposure on BEL-7402 cells combined with HCPT-loaded PLA microbubbles was evaluated using cytotoxicity assay, CLSM and flow cytometry (FCM). It was found that the HCPT-loaded PLA microbubbles showed smooth surface and spherical shape, and the drug was amorphously dispersed within the shell and the drug loading content reached up to 1.69%. Nearly 20% of HCPT was released upon exposure to diagnostic ultrasound at frequency of 3.5 MHz for 10 min. Moreover, HCPT fluorescence in the cells treated only with the HCPT-loaded PLA microbubbles was discernible, but less intense, while those treated with the microbubbles in conjunction with ultrasound exposure was evident and intense, indicating an increased cellular uptake of HCPT by ultrasound exposure. Cytotoxicity test on BEL-7402 cells indicated that the HCPT-loaded PLA microbubbles combined with ultrasound exposure were more cytotoxic than the microbubbles alone. The results suggest that the combination of drug loaded PLA microbubbles and diagnostic ultrasound exposure exhibit an effective intracellular drug uptake by tumor cells, indicating their great potential for antitumor therapy.     

Drug-loaded nano/microbubbles for combining ultrasonography and targeted chemotherapy

A new class of multifunctional nanoparticles that combine properties of polymeric drug carriers, ultrasound imaging contrast agents, and enhancers of ultrasound-mediated drug delivery has been developed. At room temperature, the developed systems comprise perfluorocarbon nanodroplets stabilized by the walls made of biodegradable block copolymers. Upon heating to physiological temperatures, the nanodroplets convert into nano/microbubbles. The phase state of the systems and bubble size may be controlled by the copolymer/perfluorocarbon volume ratio. Upon intravenous injections, a long-lasting, strong and selective ultrasound contrast is observed in the tumor volume indicating nanobubble extravasation through the defective tumor microvasculature, suggesting their coalescence into larger, highly echogenic microbubbles in the tumor tissue. Under the action of tumor-directed ultrasound, microbubbles cavitate and collapse resulting in a release of the encapsulated drug and dramatically enhanced intracellular drug uptake by the tumor cells. This effect is tumor-selective; no accumulation of echogenic microbubbles is observed in other organs. Effective chemotherapy of the MDA MB231 breast cancer tumors has been achieved using this technique.     

Fluorescent microscope system to monitor real-time interactions between focused ultrasound,echogenic drug delivery vehicles,and live cell membranes

Rapid development in the field of ultrasound triggered drug delivery has made it essential to study the real-time interaction between the membranes of live cells and the membranes of echogenic delivery vehicles under exposure to focused ultrasound. The objective of this work was to design an analysis system that combined fluorescent imagining, high speed videography, and definable pulse sequences of focused ultrasound to allow for real time observations of both cell and vehicle membranes. Documenting the behavior of the membranes themselves has not previously been possible due to limitations with existing optical systems used to understand the basic physics of microbubble/ultrasound interaction and the basic interaction between microbubbles and cells. The performance of this new system to monitor membrane behavior was demonstrated by documenting the modes of vehicle fragmentation at different ultrasound intensity levels. At 1.5 MPa the membranes were shown to completely fragment while at intensities below 1 MPa the membranes pop open and slowly unfold. The interaction between these vehicles and cell membranes was also documented by the removal of fluorescent particles from the surfaces of live cells out to 20 μm from the microbubble location. The fluid flow created by microstreaming around ensonated microbubbles was documented at video recording speeds from 60 to 18,000 frames per second. This information about membrane behavior allows the chemical and physical properties of the drug delivery vehicle to be designed along with the ultrasound pulse sequence to cause the most efficient drug delivery.     

Ultrasound thrombolysis

Ultrasound energy for thrombolysis dates back to 1976. Trubestein et al. demonstrated first in vitro that a rigid wire delivery low frequency ultrasound energy could disrupt clot. These investigators also showed that this system had potential for peripheral arterial clot dissolution in vivo in animal studies [G. Trubestein, C. Engel, F. Etzel, Clinical Science 51 (1976) 697s-698s]. Subsequently, four basic approaches to ultrasonic thrombolysis have been pursued - two without pharmacological agents: (1) catheter-delivered external transducer ultrasound, (2) transcutaneous-delivered HIFU external ultrasound without drug delivery and ultrasound in conjunction with thrombolytic drugs and/or microbubbles or other agents, (3) Catheter-delivered transducer-tipped ultrasound with local drug delivery, and (4) transcutaneous-delivered low frequency ultrasound with concomitant systemic (intravenous) drug delivery for site specific ultrasound augmentation. This article reviews recent data on therapeutic ultrasound for thrombolysis in vitro, in vivo, in animal studies, as well as in human clinical trials.     

Activation of microbubbles by low-intensity pulsed ultrasound enhances the cytotoxicity of curcumin involving apoptosis induction and cell motility inhibition in human breast cancer MDA-MB-231 cells

Ultrasound and microbubbles-mediated drug delivery has become a promising strategy to promote drug delivery and its therapeutic efficacy. The aim of this research was to assess the effects of microbubbles (MBs)-combined low-intensity pulsed ultrasound (LPUS) on the delivery and cytotoxicity of curcumin (Cur) to human breast cancer MDA-MB-231 cells. Under the experimental condition, MBs raised the level of acoustic cavitation and enhanced plasma membrane permeability; and cellular uptake of Cur was notably improved by LPUS–MBs treatment, aggravating Cur-induced MDA-MB-231 cells death. The combined treatment markedly caused more obvious changes of cell morphology, F-actin cytoskeleton damage and cell migration inhibition. Our results demonstrated that combination of MBs and LPUS may be an efficient strategy for improving anti-tumor effect of Cur, suggesting a potential effective method for antineoplastic therapy.     

Combined optical and acoustical detection of single microbubble dynamics

A detailed understanding of the response of single microbubbles subjected to ultrasound is fundamental to a full understanding of the contrast-enhancing abilities of microbubbles in medical ultrasound imaging, in targeted molecular imaging with ultrasound, and in ultrasound-mediated drug delivery with microbubbles. Here, single microbubbles are isolated and their ultrasound-induced radial dynamics recorded with an ultra-high-speed camera at up to 25 million frames per second. The sound emission is recorded simultaneously with a calibrated single element transducer. It is shown that the sound emission can be predicted directly from the optically recorded radial dynamics, and vice versa, that the nanometer-scale radial dynamics can be predicted from the acoustic response recorded in the far field.     

Ultrasound mediated destruction of multifunctional microbubbles for image guided delivery of oxygen and drugs

We synthesized multifunctional activatible microbubbles (MAMs) for ultrasound mediated delivery of oxygen and drugs with both ultrasound and fluorescence imaging guidance. Oxygen enriched perfluorocarbon (PFC) compound was encapsulated in liposome microbubbles (MBs) by a modified emulsification process. DiI dye was loaded as a model drug. The ultrasound targeted microbubble destruction (UTMD) process was guided by both ultrasonography and fluorescence imaging modalities. The process was validated in both a dialysis membrane tube model and a porcine carotid artery model. Our experiment results show that the UTMD process effectively facilitates the controlled delivery of oxygen and drug at the disease site and that the MAM agent enables ultrasound and fluorescence imaging guidance of the UTMD process. The proposed MAM agent can be potentially used for UTMD-mediated combination therapy in hypoxic ovarian cancer.     

Correlation between microbubble-induced acoustic cavitation and hemolysis in vitro

Microbubbles promise to enhance the efficiency of ultrasound-mediated drug delivery and gene therapy by taking advantage of artificial cavitation nuclei.The purpose of this study is to examine the ultrasound-induced hemolysis in the application of drug delivery in the presence of microbubbles.To achieve this goal,human red blood cells mixed with microbubbles were exposed to 1-MHz pulsed ultrasound.The hemolysis level was measured by a flow cytometry,and the cavitation dose was detected by a passive cavitation detecting system.The results demonstrate that larger cavitation dose would be generated with the increase of acoustic pressure,which might give rise to the enhancement of hemolysis.Besides the experimental observations,the acoustic pressure dependence of the radial oscillation of microbubble was theoretically estimated.The comparison between the experimental and calculation results indicates that the hemolysis should be highly correlated to the acoustic cavitation.     

Modeling photothermal and acoustical induced microbubble generation and growth

Previous experimental studies showed that powerful heating of nanoparticles by a laser pulse using energy density greater than 100 mJ/cm², could induce vaporization and generate microbubbles. When ultrasound is introduced at the same time as the laser pulse, much less laser power is required. For therapeutic applications, generation of microbubbles on demand at target locations, e.g. cells or bacteria can be used to induce hyperthermia or to facilitate drug delivery. The objective of this work is to develop a method capable of predicting photothermal and acoustic parameters in terms of laser power and acoustic pressure amplitude that are needed to produce stable microbubbles; and investigate the influence of bubble coalescence on the thresholds when the microbubbles are generated around nanoparticles that appear in clusters.

We develop and solve here a combined problem of momentum, heat and mass transfer which is associated with generation and growth of a microbubble, filled with a mixture of non-vaporized gas (air) and water vapor. The microbubble’s size and gas content vary as a result of three mechanisms: gas expansion or compression, evaporation or condensation on the bubble boundary, and diffusion of dissolved air in the surrounding water. The simulations predict that when ultrasound is applied relatively low threshold values of laser and ultrasound power are required to obtain a stable microbubble from a single nanoparticle. Even lower power is required when microbubbles are formed by coalescence around a cluster of 10 nanoparticles. Laser pulse energy density of 21 mJ/cm² is predicted for instance together with acoustic pressure of 0.1 MPa for a cluster of 10 or 62 mJ/cm² for a single nanoparticle. Those values are well within the safety limits, and as such are most appealing for targeted therapeutic purposes.     

Mechanisms underlying sonoporation: Interaction between microbubbles and cells

The past several decades have witnessed great progress in “smart drug delivery”, an advance technology that can deliver genes or drugs into specific locations of patients’ body with enhanced delivery efficiency. Ultrasound-activated mechanical force induced by the interactions between microbubbles and cells, which can stimulate so-called “sonoporation” process, has been regarded as one of the most promising candidates to realize spatiotemporal-controllable drug delivery to selected regions. Both experimental and numerical studies were performed to get in-depth understanding on how the microbubbles interact with cells during sonoporation processes, under different impact parameters. The current work gives an overview of the general mechanism underlying microbubble-mediated sonoporation, and the possible impact factors (e.g., the properties of cavitation agents and cells, acoustical driving parameters and bubble/cell micro-environment) that could affect sonoporation outcomes. Finally, current progress and considerations of sonoporation in clinical applications are reviewed also.