# High-Speed Cell Assembly with Piezo-Driven Two-Finger Microhand
## 1 Introduction  
Cells are the fundamental building blocks of the human body, and in-depth research on cells is crucial for revealing life's mechanisms and conquering major diseases like cancer. Due to the unique actuation precision, micromanipulation systems have been used for single-cell operations and analyses, such as measurement of cellular mechanical properties [1; 2] and in vitro fertilization (IVF) [3]. Furthermore, the manipulation of multiple cells also receives widespread attention, such as bottom-up tissue engineering, which is expected to regenerate human tissues and organs for transplantation [4; 5; 6; 7; 8]. Cell manipulation techniques are gradually translating from laboratory to clinical applications, but the current mainstream methods still fall short in terms of precision and efficiency due to the reliance on manual control. Researchers are exploring methods that can achieve high-precision and high-speed micromanipulation at the cellular level. The dimensions of cells typically range from a few micrometers to several tens of micrometers, posing a challenge to the precision of micromanipulation systems. Micromanipulation systems come in various types, primarily categorized as contact and noncontact. The latter includes optical tweezers [9; 10], magnetic control [11; 12], acoustical tweezers [13; 14], microfluidics [15; 16; 17], and others. Among different types of micromanipulation systems, mechanical contact manipulation occupies a significant position due to its high flexibility, controllable force, and ease of automation [18; 19; 20; 21; 22]. Firstly, these systems offer controllable forces, thus avoiding impact on the biological target's activity [23; 24]. Secondly, robotic contact manipulations exhibit high precision, stability, and repeatability. Thirdly, they are easily programmable and the position and force feedback information can be obtained through sensors and image processing algorithms for automation [25]. Traditional solutions, such as precision lead screws driven by servo motors, face difficulties in achieving spatial positioning at the micro or nanometer scale due to issues of thread clearance, friction, and dynamic response speed. Piezoelectric ceramics, characterized by fast response, high resolution, and substantial thrust, are suitable for high-precision and small-range micromanipulations [26; 27]. Moreover, in-series mechanisms exhibit low stiffness and error accumulation, resulting in reduced precision of the end-effector, while parallel mechanisms offer high stability and precision [28; 29]. Therefore, a parallel mechanism driven by piezoelectric ceramics can meet the precision requirements for micromanipulation at the cellular level, and researchers have conducted extensive studies on it. [PERSON] designed a flexible 6-SPS (6-spherical-prismatic-spherical) micro-positioning system, which was capable of positioning the wafer with a resolution of less than 0.01 \(\upmu\)m [30]. [PERSON] developed a high-bandwidth XY nano-positioning stage that utilized two capacitance sensors for closed-loop position control, with a travel range of 15 \(\upmu\)m and a precision of 1 nm [31]. [PERSON] also proposed a 3-DoF parallel mechanism driven by prismatic actuators composed of compliant joints and links and flexure hinges [32]. Traditional hinges primarily achieve rotation through physical contact and mutual friction, but they are prone to backlash, making high-precision operations challenging. The motion or force output from flexible hinges is generated through the elastic deformation of their flexible structures, thereby enhancing the precision and stability of operations. The improvement of cell manipulation speed is another challenge for clinical applications. One constraint on speed is the success rate of grasping and releasing. Currently, the most common end-effectors are needle-shaped microgrippers, which are prone to misalignment during grasping, leading to grasping failure or target dropping during transportation.