Ultrahigh frequency transducer for intracellular delivery of macromolecules
Research Description
Targeted intracellular delivery of macromolecules is fundamental to investigate the cell behavior and modulate the cell function for research. Besides, single cell level observation could be critical to see how the cell behaves (e.g. induced pluripotent stem cells (iPSC) generated by delivering reprogramming factor into them) with a variety of macromolecules such as DNA plasmids, proteins, and even Ca2+ ions. Ultrahigh frequency ultrasound (UHFUS) should be suitable for such single cell intracellular delivery and modulation of the targeted cells due to the high spatial resolution comparable to the single cell. Higher frequencies of the ultrasonic transducer have a lower mechanical index (MI), meaning that it is possible to investigate bioeffects without any contrast agents causing the cavitation. The first thing to do for intracellular delivery using UHFUS is to measure acoustic radiation force (ARF) applied to the targeted cell to estimate the effect. However, commercial hydrophones cannot measure ARF of UHFUS transducer with frequencies higher than 60MHz. Thus, our research focuses on a model based approach to estimate ARF by comparing theoretical and measured displacements of micrometer-sized spheres at the focus of UHFUS in gelatin phantom. In our research, the micrometer-sized sphere was placed in a block of gelatin. As shown in Figure 1, A pushing ultrasonic transducer (PUT, center frequency 150 MHz, aperture size 1.2 mm, and f-number 1) and tracking ultrasonic transducer (TUT, center frequency 150 MHz, aperture size 1.5 mm, and f-number 1) were focused to the sphere. PUT transmitted a pulse to generate ARF with various peak-to-peak voltages (Vpp) and pulse duration (tp) to verify the theory. TUT tracked the movement of the sphere. The data was post-processed to find the displacement of the sphere in response to ARF. The best fit between the theoretical calculation and the measured time to reach the maximum displacement (Umax) of the sphere was compared to estimate ARF of PUT in figure 2. To implement more accurate single cell intracellular delivery, UHFUS transducer with frequencies around 500MHz would be fabricated with our transducer fabrication protocol.
Targeted intracellular delivery of macromolecules is fundamental to investigate the cell behavior and modulate the cell function for research. Besides, single cell level observation could be critical to see how the cell behaves (e.g. induced pluripotent stem cells (iPSC) generated by delivering reprogramming factor into them) with a variety of macromolecules such as DNA plasmids, proteins, and even Ca2+ ions. Ultrahigh frequency ultrasound (UHFUS) should be suitable for such single cell intracellular delivery and modulation of the targeted cells due to the high spatial resolution comparable to the single cell. Higher frequencies of the ultrasonic transducer have a lower mechanical index (MI), meaning that it is possible to investigate bioeffects without any contrast agents causing the cavitation. The first thing to do for intracellular delivery using UHFUS is to measure acoustic radiation force (ARF) applied to the targeted cell to estimate the effect. However, commercial hydrophones cannot measure ARF of UHFUS transducer with frequencies higher than 60MHz. Thus, our research focuses on a model based approach to estimate ARF by comparing theoretical and measured displacements of micrometer-sized spheres at the focus of UHFUS in gelatin phantom. In our research, the micrometer-sized sphere was placed in a block of gelatin. As shown in Figure 1, A pushing ultrasonic transducer (PUT, center frequency 150 MHz, aperture size 1.2 mm, and f-number 1) and tracking ultrasonic transducer (TUT, center frequency 150 MHz, aperture size 1.5 mm, and f-number 1) were focused to the sphere. PUT transmitted a pulse to generate ARF with various peak-to-peak voltages (Vpp) and pulse duration (tp) to verify the theory. TUT tracked the movement of the sphere. The data was post-processed to find the displacement of the sphere in response to ARF. The best fit between the theoretical calculation and the measured time to reach the maximum displacement (Umax) of the sphere was compared to estimate ARF of PUT in figure 2. To implement more accurate single cell intracellular delivery, UHFUS transducer with frequencies around 500MHz would be fabricated with our transducer fabrication protocol.
Figure 1. Experimental setup and pulse sequences from both transducers. Pushing ultrasonic transducer (PUT) located on the bottom transmits a pulse to generate the transient acoustic radiation force applied to the sphere embedded in the gelatin block. Tracking ultrasonic transducer (TUT) located on top tracks the movement in every constant period of the sphere displaced under the ARF. Figure 2. (A) ultrahigh frequency ultrasound (UHFU) transducer, needle type suitable for single cell intracellular delivery (B) Displacement of the sphere under acoustic radiation force (ARF) with various pulse time duration (tp) of 5, 10, and 15 μs and peak-to-peak voltage (Vpp) of 15V from theory (Top) and measurement (Bottom). (C) Estimated ARF of the PUT using our model based approach