Physics of Nano- Micro-Bubbles and their Ultrasound Response

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1 S7-1 Physics of Nano- Micro-Bubbles and their Ultrasound Response Yoichiro Matsumoto, Kazuyasu Sugiyama, Shin Yoshizawa* and Shu Takagi Department of Mechanical Engineering, the University of Tokyo * Department of Electrical and Communication Engineering, Tohoku University Nano-Biotechnology is coming more important in a medical application. Nano- micro-bubble could have a significant role in this field, like delivery system of drug, enzymes gene and so on. Micro-bubble is utilized as a contrast agent for ultrasound imaging and there are many commercial agents like Levovist, Sonovue, Optison, Sonazoid and so forth. Nano-bubbles can be also used for such contrast agents if the ultrasound frequency is high enough. However, those tiny bubbles have short life time, for example, that of 1µm air bubble is about 10ms in pure water due to the internal high gas pressure caused by the surface tension. For the utilization of nano-bubble, we need some mechanism to stabilize the bubbles to elongate their life time. A surfactant, electrolyte or lipid, which covers the bubble surface, could reduce the surface tension and the diffusion of the internal gas to the surrounding liquid. Molecular Dynamics simulations of the bubble system including the electrolyte and surfactant solutes are conducted. The static and dynamic molecular properties across the interface are investigated. It is revealed that the surface tension is reduced by the surfactant and the surfactant covers the bubble surface to form a micelle, which stabilizes the nano-bubble. The stabilizing surfactant is modeled as a lipid layer covering the bubble. The ultrasound contrast imaging is governed by the motion of the stabilized bubbles, so that it is essential to understand the dynamics of the stabilized bubbles in pressure field. The bubble motion is simulated and it is revealed that the bubble motion is influenced by the internal thermal phenomena and also the stabilizing layer on the bubble surface. The lipid viscosity, µs, has a significant influence on the bubble response to the surrounding ultrasound field. The bubble motion is damped by the viscous dissipation in the lipid. Figure shows the pressure response curve of the bubble covered with the lipid whose thickness is 5nm. The applied ultrasound is 20 periods tone burst, whose frequency is 2MHz and amplitude is 100 kpa. Reference 1. Kikugawa, G., Takagi, S., Matsumoto, Y., A molecular dynamics study on liquid-vapor interface adsorbed by impurities, Computers and Fluids, Vol36(1), pp69-76, Yoichiro Matsumoto, John S. Allen, Shin Yoshizawa, Teiichiro Ikeda, Yukio Kaneko, Medical ultrasound with microbubbles, -78-

2 Experimental Thermal and Fluid Science 29, pp , Yoichiro Matsumoto and Shin Yoshizawa, Behaviour of a bubble cluster in an ultrasound field, Int. J. Num. Methods in Fluids, 47, pp , Masaharu Kameda and Yoichiro Matsumoto, Nonlinear oscillation of a spherical gas bubble in acoustic fields, J. Acoust. Soc. Am., Vol.106, No.6, pp ,

3 S7-2 GENE DELIVERY BY BUBBLE LIPOSOME AND ULTRASOUND Kazuo Maruyama 1, Ryo Suzuki 1, Tomoko Takizawa 1, Yoichi Negishi 2, Naoki Utoguchi 1, Yasuhiro Matsumura 3 1 Department of Biopharmaceutics, Teikyo University School of Pharmacy, Sagamiko, Sagamihara, Kanagawa , Japan 2 Department of Drug and Gene Delivery System, School of Pharmacy, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo, Japan 3 Investigative Treatment Division, Research Center for Innovative Oncology, National Cancer Center Hospital East, Kashiwa, Chiba, Japan Gene therapy has a potentiality for treatment of cancer and diseases owning to genomic defects. It is important to select a vector which has good potency in terms of gene transduction efficiency, safe and easy to apply. In this situation, non-viral vectors are drawing the attention. However, they suffer from low transduction efficiencies. To improve this problem, many researchers attempt to develop effective gene delivery carrier. Recently, it was reported that microbubbles, which were ultrasound (US) contrast agents, improved the transfection efficiency by cavitation with US exposure. However, microbubbles had some problems regarding stability and targeting ability. To solve these problems, we paid attention to liposomes that had many advantages such as stable and safe in vivo and easy to modify targeting ligand. Previously, we represented that liposomes were good drug and gene delivery carriers. In addition, we succeeded to prepare the liposomes ( Bubble liposomes (BLs)) entrapping perfluoropropane gas which was utilized for contrast enhancement in ultrasonography. In this study, we assessed the feasibility of BLs as gene delivery carrier utilized cavitation by US exposure. BLs could deliver plasmid DNA to various cell types such as sarcoma, T cell line and endothelial cell in vitro by combination with US without cytotoxicity. In addition, the transfection efficiency with BLs was not affected even for the existence of serum. It was thought that the ability of transfection with BLs was not lost because of not interacting serum component. We also assessed the ability of gene delivery in tumor bearing mice. BLs and luciferase coding plasmid DNA were intraperitoneally injected into the mice which had been inoculated S-180 cells in the peritoneal cavity. And the mice were immediately exposed with US to abdominal area from outside of body. After 2 days, the cells were collected from the mice and luciferase activity was measured. Luciferase expression was higher in the mice treated with BL and US exposure than conventional lipofection. These results suggested that BLs might be a non-invasive and effective carrier for gene delivery. Acknowledgements: This study was supported by Industrial Technology Research Grand Program (04A05010) from New Energy and Industrial Technology Development Organization (NEDO) of Japan and a Research on Advanced Medical Technology ( ) in Health and Labor Sciences Research Grants from Ministry of Health, Labor and Welfare -80-

4 S7-3 Site-specific contrast imaging with phase change nano particle Kawabata, Ken-ichi, 1 ; Asami, Rei 1, Azuma, Takashi 1, Yoshikawa, Hideki 1, and Umemura, Shin-ichiro 2 1 Central Research Laboratory, Hitachi, Ltd., Tokyo, Japan 2 Department of Electrical and Communication Engineering Tohoku University, Sendai, Japan Stabilized microbubbles show high echogenicity and characteristic non-linear acoustic responses and widely used as contrast agent for diagnostic ultrasound. Recently it has been revealed that they also work as sensitizers for HIFU (high intensity focused ultrasound) therapy. If microbubbles were selectively placed in targeted tissues, targeted diagnosis and therapy would be possible. However, microbubbles are too large to be delivered into tissues from blood vessels. For tumor detection and therapy, we propose the use of nano-sized liquid precursor of microbubbles (nano droplet) that are small enough to be delivered into tumor tissues yet acts as microbubbles once stimulated by ultrasound pulses. We have developed nano droplets containing perfluoropentane [1] and found that microbubbles can be generaged with ultrasound pulses from a medical ultrasound scanner (modified for this study) at negative peak pressure at about several MPa in water [2]. Figure 1 shows microscopic images of nano droplets in polyacrylamide gel in water before and after ultrasound pulse exposure. We also confirmed that such microbubbles generation induces brightness changes in ultrasound echography. Further, such echographic changes were observed in living biological tissues such as tumors and livers [2]. Such in situ generation of microbubbles would contribute to site specific contrast imaging with proper targeting mechanism. Furthermore, since bubbles amplify thermal effect of ultrasound at present region, it would also contribute to site specific minimally invasive therapy with the aid of therapeutic ultrasound. Fig. 1: Microscopic imaging of microbubbles generation from nano droplet. 100 µm a) Nano droplet b) Micorobubles c) Commercially generated from available microbubble nano droplet contrast agent Ultrasound exposure (7.8 MHz, 3 MPa) Keywords: contrast agent, microbubble, phase change, nano droplet [1] Kawabata et al. (2005) Jpn J Appl Phys [2] Kawabata et al. (2006), Proc IEEE Ultrasonics Symposium

5 S7-4 Preparation and Detection of Nanobubbles: Toward Ultrasonic Molecular Imaging Kazunori Itani 1), Takashi Itoh 1), Taketo Konno 1),Masahiko Abe 2), Hideki Sakai 2),Koji Tsuchiya 2),Kiyoshi Ohkawa 3), Yukio Miyamoto 3),Tomokazu Matsuura 3),Masato Kukizaki 4), 1) ALOKA Co Ltd, 2) Tokyo University of Science, 3 ) the Jikei University, School of Medicine, 4) Miyazaki Prefecture Industrial Technology Center We are developing ultrasonic molecular imaging technology for early detection of malignant tumors by ultrasonically detecting micro/nano bubbles conjugated with monoclonal antibodies against CD147 which is a target marker for malignant tumors. Downsizing bubbles, which are outstanding contrast agents for ultrasound, to nano-scale, is expected to have the following benefits for an ultrasound molecular probe. 1) Nanobubbles under 200nm could be delivered nearby tumors through endothelial cells. 2) Nanobubbles can be efficiently delivered into a micro structure (i.e. capillary or sentinel lymph node) 3) Nanobubble has much larger surface area than micro bubble per unit volume, so targeted nanobubbles, which are conjugated with antibody, are expected to improve its ability to trap object molecules. The abilities of bubbles for an ultrasound molecular probe are 1) biodegradability and safety 2) moderate stability 3) conjugation with antibody or something else 4) control of diameter and narrow distribution 5) escape from the biological defense mechanism. For preparation of a micro/nano bubble, we synthesized two kinds of new surfactants, cycloamylose-modified surfactant and polymerizable cationic gemini surfactant, which were excellent in biodegradability and safety. Polymerizable cationic gemini surfactant bubbles can form strong interfacial membranes after polymerization. As a result it is expected to improve stability on nanobubbles. Using method of ultrasonic irradiation we succeeded in generating 200 nm bubbles in diameter. Fig 1 shows FF-TEM image of Cycloamylose-modified surfactant bubbles. And using method of SPG (Shirasu Porous Glass) which was developed by Miyazaki Prefecture Industrial Technology Center, we succeeded in generating 600 nm bubbles in diameter with a narrow distribution, synthesized with polymerizable cationic gemini surfactant. Fig 2 shows particle size distribution of polymerizable anionic gemini surfactant bubbles. It is necessary to develop SPG which consists of smaller porous in order to generate 200 nm bubbles in diameter with a narrow distribution. Detection sensitivity on nanobubbles is anticipated to decline. Another problem of ultrasonic molecular imaging is developing a new technology for imaging nanobubbles at a high sensitivity. We compared echoes from commercial contrast agents Sonazoid (micro bubble) and polymerizable anionic gemini surfactant bubbles (nanobubble) and verified the detection sensitivity. On nanobubbles, the second harmonics appeared especially at a low frequency which is used in ultrasound diagnosis, and an amplitude of the second harmonics was only 5 db less than that of Sonazoid. Simulation and experiment results were in good agreement with each other (Fig.3). This result suggests that nanobubbles can be imaged in the second harmonics using low frequency transmission. Moreover, we are going to study the use of third and higher harmonics to detect nanobubbles at a high sensitivity. We would like to present our trial for imaging nanobubbles. -82-

500n Relative particle number Fig1 FF-TEM image of Cycloamylose-modified surfactant bubbles Particle size [µm] Fig2 Particle size distribution of polymerizable anionic gemini surfactant bubbles

6 500n Relative particle number Fig1 FF-TEM image of Cycloamylose-modified surfactant bubbles Particle size [µm] Fig2 Particle size distribution of polymerizable anionic gemini surfactant bubbles Fundamental Second 5dB (a) db (b) MHz Fig3 Comparison of bubble echoes experiment Acknowledgements : (a) and simulation (b) This study was supported in part by the Research and Development Project for Molecule Imaging Apparatus Supporting Medical Treatment for such as a Malignant Tumor, New Energy and Industrial Technology Development Organization,and Research fellowship for nanomedicine, Ministry of Health, Labour and Welfare -83-

Monitoring Of Adhesive Cure Process and Following Evaluation of Adhesive Joint Structure by Acoustic Techniques

ECNDT 006 - We... Monitoring Of Adhesive Cure Process and Following Evaluation of Adhesive Joint Structure by Acoustic Techniques Elena Yu. MAEVA, Ina SEVIARYNA, Gilbert B. CHAPMAN, Fedar M. SEVERIN University