Acoustic radiation force generated by ultrasonic standing wave is one of the forces with the ability of cell trapping. Cells can be trapped at either pressure nodes or anti-nodes depending on the properties of the cells and suspension medium.
A research team at the Suzhou Institute of Biomedical Engineering and Technology (SIBET) of the Chinese Academy of Sciences developed an acoustic trapping chip which can offer three dimensional trapping of cells in continuous flowing medium with circular resonance structure.
Cell trapping is of great importance in biomedical engineering because it allows clamping, separation, filtration and agglomeration of cells. Among different trapping approaches, acoustic trapping has been widely used in biological research because it can provide contactless and biosafe cell manipulation.
Ultrasonic standing waves can be further categorized into standing bulk acoustic waves(BAW), generated by a bulk piezoelectric transducer, or a standing surface acoustic waves(SAW), generated by singlecrystal lithium niobate (LiNbO3) etched with interdigitated electrodes. SAW can manipulate particles with very low energy consumption, but is generally used for sorting in flowing liquid and particle arrangement in stationary liquid due to its overall smaller clamping force compared with BAW.
On the other hand, the acoustic microstreaming vortex can also be applied to trap cells at the vicinity of the obstacle or microbubbles. The design of micropillars or obstacles plays an important role in trapping efficiency improvement. However, some of the trappers cannot release particles easily, and some of them cannot provide a fixed trapping position.
The trapping efficiency is basically determined by trapping force. In most previous studies, particles are usually trapped in a static fluid or a flowing fluid with extremely low speed, or the trapping process lasts for several seconds, which are mainly due to insufficient trapping force. This will reduce the trapping efficiency, as well as throughput, while high throughput cell manipulation is important in many biological applications such as Raman identification and nanoparticle capture.
The SIBET team established standing acoustic wave in the circular microstructure providing sufficient strength to clamp cells in the center of the chamber. Meanwhile, cells are clamped near the bottom surface of the micro channel under the radiation force formed in the depth direction.
Thus, a three dimensional trapping of cells is formed with special design of microchannels actuated by only one piezoelectric plate transducer. Experimental results show that the chip can provide nN (nanonewton) level trapping force and ms (millisecond) level trapping time for micron sized particles moving at velocity of mm/s level.
Fig.1 Schematic diagram of the chip design and its trapping performance on red blood cells and white blood cells. The cells aggregate to the center of the circular cavity within 60ms. (Image by SIBET)
Fig.2 Single particle with diameter of 10μm queuing up on the cavity array was delivered step by step to the detection spot, which can be applied to high throughput Reman spectra acquisition. (Image by SIBET)
Fig. 3 Chip successfully used for nanoparticle capture (a) Bright field image of seed cluster before nanoparticle capture; 10μm blank polystyrene beads aggregate in the circular cavity; (b) Fluorescent image of seed cluster; As the seed particles are blank, nothing can be seen. (c) Fluorescent image of 100nm green fluorescent nanoparticles captured in the region of the seed cluster. (Image by SIBET)
With this non-contact and biocompatible trapping method, the chip can be applied to a variety of biomedical engineering scenarios such as organ chips, cell culture, Raman analysis and nanoparticle capture.
The research results entitled “Acoustic 3D trapping of microparticles in flowing liquid using circular cavity” were published in Sensors and Actuators A:Physical. WANG Ce is the first author of the paper, and MA Yuting is the co-corresponding author.
The research was supported by the National Key R&D Program of China, Youth Innovation Promotion Association of Chinese Academy of Sciences, Equipment development project of Chinese Academy of Sciences.
Contact
XIAO Xintong
Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences (http://www.sibet.cas.cn/)
Phone: 86-512-69588013
E-mail: xiaoxt@sibet.ac.cn
