We have been studying sonoporation that promotes drug and gene delivery using ultrasound exposure in the presence of microbubbles. A sonoporation technique that utilizes drug-loaded microbubbles for efficient deliver is widely studied; however, their results showed low transduction rates of the technique. In this study, sonoporation phenomena under three types of exposure condition (continuous, repetitive, pulse) were observed in the presence of fluoresce dye-loaded microbubbles adjacent to cells using confocal microscopy. The results showed that different types of ultrasound exposure induce different types of membrane damage; however, the transduction was achieved only in one cell (3%), which was induced by exposure to pulsed ultrasound. In other cells, adhesion of the dye on cell membrane was frequently observed, suggesting that adhesion of bubble shell lipid to the cell bilayer lipid prevents the dye from transduction into cells. This suggests possibility for improving transduction rates by controlling affinity of microbubbles to cells.
We have proposed a simple optical technique for visualization of ultrasound fields using the focused shadowgraphy. To improve the quality of the field images, effects of coherency in the illuminating light source were investigated using a laser diode (LD) and a light-emitting diode (LED). An acoustic field of a 2.5-MHz ultrasound pulse was visualized. The results showed that the effect of noise in the LD beam, which was generated by interference of light diffraction, was not removed by the image subtraction, while the effect of noise in LED beam containing no interference noise was successfully removed. Also, the first order integration of the brightness waveform evaluated using the LED field image showed good agreement with the pressure waveform only in the case with the pinhole, indicating the possibility for evaluation of pressure waveform from an optical image of an ultrasound fields.
We have been studying adverse effect of ultrasound exposure on pulsation of the heart using cardiomyocytes isolated from neonatal rats. Our previous study used cardiac myocytes cultured on a cover slip scaffold; however, the stiffness of the underlying layer is very different from that in in vivo conditions. In this study, cardiomyocytes were cultured on a soft gel scaffold, and their mechanosensitivity was compared with those cultured on a coverslip scaffold. In the experimental results, significant difference was found in the shape indices that represent circularity of cells (gel, 0.29 ± 0.08; cover slip, 0.11 ± 0.04), indicating that cytoskeleton is less developed in the cells cultured on the gel scaffold. Furthermore, a threshold of cycle numbers to induce pulsation disruption is about 10 times higher in the cardiomyocytes culltured on gel scaffold, suggesting the dependence of mechanosensitivity of cardiomyocytes on development of their cytoskeleton.
The scattering effect in light propagation through random media can be suppressed with the phase-conjugate optics. We have applied this technique to the transillumination imaging of animal body using a digital phase-conjugate system. In the experiment, we attempted to restore various incident light patterns through a scattering medium. As a result, the feasibility of scattering suppression using digital phase-conjugate light was verified.
A high intensity focused ultrasound (HIFU) field of a transducer for ultrasound therapy was visualized using an image subtraction Schlieren technique. The transducer of 110 mm in diameter and 100 mm in focal length was driven by a burst pulse of 1.58 MHz in center frequency and of 10 W or 100 W in input electric power. 10 instantaneous HIFU fields were visualized at 10 different phases, and a beam profile was determined by superimposing the fields. FWHMs of the beam were 5.8 mm in a visualized field but was 7.3 mm in a field determined by hydrophone measurement.