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

细胞是生命的基本组成部分。在液体环境中以高精度单独操纵单细胞的能力将使以前无法实现的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。这些发现将为环境对细胞结构，功能和信号传导的影响提供关键见解，并将在生命科学，农业和医学的多个学科中具有广泛的应用。由于它们的小尺寸和柔软的性质，很难用物理设备（如机械镊子）处理单细胞，而不对微妙的亚细胞结构造成损害。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力，作为用于单细胞操作的虚拟镊子。其中，“声镊”与细胞的兼容性最好，因为细胞对电场和激光照射的声压有更高的耐受性。然而，与可以容易地用玻璃透镜和旋转镜聚焦和操纵的激光束不同，超声波的敏捷聚焦和操纵需要复杂且昂贵的换能器阵列和控制电子器件。这种情况阻碍了“声镊”在单细胞操作中的广泛使用。本论文的主要工作是开发一种超声相控阵技术，使超声束能够在高分辨率的单细胞声学操纵中实现声学转向和聚焦，在现有的单细胞操纵技术中，超声相控阵技术由于其独特的电子波束形成能力（无需物理扫描换能器）而具有最大的潜力。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在精确的位置提供了前所未有的操纵能力。然而，在当前的超声相控阵系统中，超声信号的多个通道首先利用换能器元件的阵列被转换成电子通道。然后在电子域中完成相移。随着工作频率和通道数的增加，相控阵系统变得越来越复杂、体积庞大、功耗高和成本高。因此，目前的声学相控阵不适合用于单细胞操作的芯片上微流体平台。为了解决这个问题，本研究旨在开发一种新的微机械超声相控阵。它将由一个微加工硅声学延迟线阵列组成，具有可调延迟长度，可为多个超声信号产生所需的相移，而无需电子转换。这使得能够利用单元件换能器和单通道超声收发器进行超声波束形成。通过先进的微机械加工工艺，它可以很容易地制造，甚至与微流体组件一起集成到同一衬底上，用于单芯片操作。为达成研究目标，本研究将完成以下三项研究工作：1）进行声学移相器的声学和机电设计与优化; 2）开发一种片上微加工工艺，以实现多通道集成; 3）使用超声相控阵演示灵巧的声学操纵和单细胞定位。这项多学科研究预计将为研究生/本科生提供独特的学习和培训机会。7-12年级的学生将参加工程夏令营和开放日活动。研究结果将被纳入PI的各级课程开发。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.