Collaborative Research: High Resolution Acoustic Manipulation of Single Cells with Integrated MEMS based Phased Arrays

细胞是生命的基本构件。在液体环境中高精度地单独操作单个细胞的能力将使许多关于细胞与细胞和细胞与环境相互作用的基础生物学研究成为可能，这是以前无法实现的。这些发现将为环境对细胞结构、功能和信号的影响提供关键的见解，并将在生命科学、农业和医学的多个学科中得到广泛应用。由于单个细胞体积小且质地柔软，用机械镊子等物理设备处理单个细胞而不对微妙的亚细胞结构造成损害是极其困难的。或者，可以利用聚焦电场、激光束和超声波在焦点处产生微尺度的力，作为单细胞操作的虚拟镊子。其中，由于细胞对电场和激光照射下的声压有更高的耐受性，声学镊子与细胞的兼容性最强。然而，与激光光束不同的是，激光可以通过玻璃透镜和旋转镜轻松聚焦和操纵，而超声波的灵活聚焦和操纵需要复杂而昂贵的换能器阵列和控制电子设备。这种情况阻碍了声学镊子在单细胞操作中的广泛使用。在现有的单细胞操作技术中，超声相控阵以其独特的能力实现电子波束的形成(无需物理扫描换能器(S))。与其他方法相比，使用这种独特的波束形成技术将超声波辐射聚焦到精确的位置显示出前所未有的操纵能力。然而，在当前的超声相控阵系统中，首先利用换能器元件阵列将多路超声信号转换为电子信号。然后在电子域中完成相移。随着工作频率和通道数量的增加，相控阵系统变得越来越复杂、体积越来越大、功耗越来越大、成本越来越高。因此，目前的声相控阵不适合用于单细胞操纵的片上微流控平台。针对这一问题，本研究旨在研制一种新型微机械超声相控阵。它将由一组微机械硅声延迟线组成，延迟长度可调，无需电子转换即可为多个超声信号创建所需的相移。这使得利用单元件换能器和单通道超声收发器形成超声波波束成为可能。凭借先进的微加工工艺，它可以很容易地制造出来，甚至可以与微流控部件集成在同一基板上，用于单芯片操作。为了实现研究目标，将完成以下三个研究任务：1)对声移相器进行声学和机电设计与优化；2)开发实现多通道集成的片上微制造工艺；3)利用超声相控阵实现对单个细胞的灵巧的声学操纵和定位。这项多学科研究有望为研究生和本科生提供独特的学习和培训机会。7-12年级的学生将通过工程夏令营和开放参观活动参与进来。研究成果将被纳入各级PI的课程开发中。他们还将通过出版物、外展活动、特邀讲座和一个项目网站进行传播。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Cells are fundamental building blocks of life. The ability to manipulate single cells individually in a liquid environment with high precision will enable many fundamental biological studies on cell-to-cell and cell-to-environment interactions that could not be achieved before. Such discoveries will provide key insights into the effect of the environment on cellular structure, function, and signaling, and would have wide applications across multiple disciplines in life sciences, agriculture and medicine. Due to their small size and also soft nature, it is extremely difficult to handle single cells with a physical device, such as mechanical tweezers, without causing damage to the delicate subcellular structures. Alternatively, focused electrical fields, laser beams, and ultrasound waves can be utilized to generate microscale forces at the focal point, serving as virtual tweezers for single cell manipulation. Among them, the 'acoustic tweezers' are the most compatible with the cells due to cell's higher tolerance of sound pressure over electrical field and laser illumination. However, unlike the laser beams that can be easily focused and steered with a glass lens and a rotating mirror, agile focusing and steering of ultrasound waves requires complex and expensive transducer arrays and control electronics. This situation has prevented the wide use of 'acoustic tweezers' in single cell manipulation. The proposed work is to develop an acoustic phased array to enable acoustic steering and focusing of ultrasound beams for their applications in high-resolution acoustic manipulation of single cells.Among all existing single cell manipulation techniques, the ultrasound phased array has the greatest potential due to its unique ability to achieve electronic beam forming (without physically scanning the transducer(s)). Using this unique beam forming technique to focus ultrasonic radiation at precise locations presents unprecedented manipulation capabilities compared with other methods. However, in current ultrasound phased array systems, multiple channels of ultrasound signals are first converted into electronic ones with an array of transducer elements. The phase shift is then accomplished in the electronic domain. As the operation frequency and the number of the channels increases, the phased array system becomes increasingly complex, bulky, power-consuming and costly. Therefore, current acoustic phased arrays are not suitable for on-chip microfluidic platforms for single cell manipulation. To address this issue, this research aims to develop a new micromachined ultrasound phased array. It will consist of an array of micromachined silicon acoustic delay lines with tunable delay lengths to create the desired phase shift for multiple ultrasound signals without the need for electronic conversion. This enables ultrasound beam forming with a single-element transducer and a single-channel ultrasound transceiver. With advanced micromachining processes, it can be readily fabricated and even integrated together with microfluidic components onto the same substrate for single-chip operation. To achieve the research objective, the following three research tasks will be accomplished: 1) Conduct acoustic and electromechanical design and optimization of the acoustic phase shifter; 2) Develop an on-chip microfabrication process to achieve multi-channel integration; and 3) Demonstrate dexterous acoustic manipulation and positioning of single cells using the ultrasound phased array. This multidisciplinary research is expected to provide unique learning and training opportunities for both graduate/undergraduate students. Students in grades 7-12 will be involved through Engineering Summer Camps and Open House activities. Research results will be incorporated into the PI's course development at all levels. They will also be disseminated through publications, outreach activities, invited talks, and a project website.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.