Development of a high frequency ultrasound microbeam system for cancer cell manipulation and characterization

Abstract

Recently, many high frequency ultrasound microbeam techniques such as acoustic tweezers, acoustic mi-croscopy, and a single cell stimulator have been developed for various biomedical applications. In this the-sis, I developed a high frequency ultrasound microbeam system with a 30MHz single element lithium nio-bate (LiNbO3) ultrasound transducer for cancer cell manipulation and characterization. A single-element LiNbO3 ultrasound transducer with a center frequency of 30 MHz and an f-number of ~ 0.7 was employed to form highly-focused ultrasound microbeams at focus for manipulation of a cell. Sine-bursts from a func-tion generator were input to the transducer after amplification in a RF power amplifier of a home-built puls-er-receiver for generation of the high frequency ultrasound microbeams. The ultrasound transducer was integrated to x-, y-, and z- linear motorized stages and then attached to an inverted fluorescence microscope to manipulate and characterize a cancer cell. The motorized stages were here controlled by a program de-veloped for precise beam focusing to a target cell. Also, an electron multiplying charge coupled device was implemented to the microscope in order to perform live-cell fluorescence imaging for monitoring and char-acterizing of a target cell. To evaluate the performance of the high frequency ultrasound microbeam system I developed, the system was applied to trap a 10 μm polystyrene microbead in a highly-focused microbeam and the performance of acoustic trapping of the microbead in transparent and turbid media has been then compared. The results demonstrated that a 10 μm polystyrene microbead could be successfully trapped in the media by using the system. Interestingly, it was found that its trapping performance was degraded in the turbid media compared to the transparent media. Furthermore, the system was employed as acoustic twee-zers to manipulate and characterize a cancer cell for development of more useful biomedical applications. In particular, I investigated whether the degree of invasiveness of breast cancer cells with different pheno-types in suspension could be realized by quantification of morphological and calcium responses of cancer cells to acoustic trapping. The results showed that the highly-invasive breast cancer cell (MDA-MB-231) was likely to exhibit strong calcium responses at lower input voltages than the weakly-invasive breast cancer cell (MCF-7) during acoustic trapping as well as the highly-invasive breast cancer cell was largely deformed than the weakly-invasive breast cancer cell due to acoustic trapping at a certain input voltage. Altogether, these results suggested that breast cancer cells with different phenotypes in suspension might be discriminated by quantification of morphological and molecular responses of the cells to acoustic trapping using the high frequency ultrasound microbeam system I developed, thus demonstrating it potentials as a promising bio-physical tool for cancer cell manipulation and characterization. ⓒ 2016 DGIST