Acoustic tweezers for studying intracellular calcium signaling in SKBR-3 human breast cancer cells

Abstract

Extracellular matrix proteins such as fibronectin (FNT) play crucial roles in cell proliferation, adhesion, and migration. For better understanding of these associated cellular activities, various microscopic manipulation tools have been used to study their intracellular signaling pathways. Recently, it has appeared that acoustic tweezers may possess similar capabilities in the study. Therefore, we here demonstrate that our newly developed acoustic tweezers with a high-frequency lithium niobate ultrasonic transducer have potentials to study intracellular calcium signaling by FNT-binding to human breast cancer cells (SKBR-3). It is found that intracellular calcium elevations in SKBR-3 cells, initially occurring on the microbead-contacted spot and then eventually spreading over the entire cell, are elicited by attaching an acoustically trapped FNT-coated microbead. Interestingly, they are suppressed by either extracellular calcium elimination or phospholipase C (PLC) inhibition. Hence, this suggests that our acoustic tweezers may serve as an alternative tool in the study of intracellular signaling by FNT-binding activities.

Quantification of Inter-Erythrocyte Forces with Ultra-High Frequency (410 MHz) Single Beam Acoustic Tweezer

“…Previously, several cellular SBAT applications were demonstrated. The SBAT was used to study the mechanical properties of human breast cancer cells including MCF-7, 9 SKBR-3, 10 and MDA-MB-231. 8 Also, the SBAT was shown to be capable of manipulating cell-sized microparticles inside of an excised blood vessel.…”

“…9,10 One of the reasons is that the measurement of the acoustic trapping force at frequency over 60 MHz is not possible due to the technical constraints of hydrophone and system. 15 Recently, the trapping force of 110 MHz transducers was successfully calibrated using a micropipette aspiration technique.…”

“…For these reasons, to date, the SBAT have been used to study the mechanical property of the cancer cell membrane 9 and intracellular calcium signaling properties of cancer cells. 10 Previous studies were carried out with transducers at frequencies under 200 MHz, which produced a spatial resolution in the range from tens to hundreds of micrometers. This is because the fabrication of a UHF transducer is challenging and time consuming process requiring the precise control of fabrication parameters.…”

Impedance matching network for high frequency ultrasonic transducer for cellular applications

“…There has been a growing interest in transducers in the frequency range higher than 100 MHz for applications in single cell analysis, acoustic trapping, and studying mechanotransduction with improved lateral resolution [8-12]. In these applications, a highly focused acoustic beam is required [13].…”

“…Therefore, an impedance matching network (IMN) is essential for the optimization of power transfer and efficiency by minimizing reflections between the ultrasonic transducer and the excitation source. This is particularly acute in applying large aperture high frequency transducers, which have extremely low electrical impedance at the resonance frequency, to a number of cellular applications [8-13] given that popular and highly sensitive piezoelectric materials typically have fairly high dielectric constants, which are unfavorable for the design of large aperture devices.…”