# High-Speed Cell Assembly with Piezo-Driven Two-Finger Microhand
## 3 Methods of Grasping and Releasing Cells
### Determination of the Optimal Grasping and Releasing Condition  
Due to significant variations among individual cells, different cell sizes and shapes can affect grasping and releasing. Therefore, conducting experiments directly on cells to determine the optimal manipulation parameters is challenging and cumbersome owing to large result variances. Therefore, borosilicate glass microspheres with dimensions close to those of cells and more regular shapes serve as better experimental objects. In this study, 50 \(\upmu\)m microspheres were used as the operating objects, and, in 200 repetitions of grasping and transporting experiments, the success rates of grasping and transporting with the hemispherical end-effector both reached 100%. As for the releasing effect of the vibration-based release method combined with a gel coating, the amplitude and frequency of vibration still need to be determined. The small amplitude and frequency can lead to failure in overcoming adhesive forces, while the large amplitude and frequency can result in significant deviation from the desired position after release. Table 1 presents the experimental results of the release success rate under different vibration amplitudes and frequencies. From Table 1, it can be observed that when the frequency is 5 \(\upmu\)m and the amplitude is 25 Hz, the release success rate has already reached 98%. When the amplitude is greater than 15 \(\upmu\)m or the frequency is higher than 75 Hz, the release success rate could reach 100%. Next, multiple release experiments were conducted under different frequencies and amplitudes to analyze the release accuracy under different experimental conditions statistically. The results indicate that whether maintaining a constant frequency or amplitude, the post-release position consistently remains in the upper-left direction from the pre-release position. This suggests the presence of a consistent horizontal leftward and vertical upward displacement and the displacement shows systematic variation with changes in amplitude and frequency. The accuracy graphs in the horizontal and vertical directions after release are shown in Figure 4a and Figure 4b, respectively. The vertical deviation is generated by repeated vertical vibrations. While ensuring a high release success rate, the optimal amplitude and frequency values that minimize the vertical deviation can be determined easily through these repeated experiments. The vertical release deviation graph in Figure 4b shows that the optimal release accuracy, at 2.4 \(\upmu\)m, is achieved at a frequency of 25 Hz and an amplitude of 5 \(\upmu\)m.  
The horizontal deviation is caused by the unique shape of the hemispherical end-effector, resulting in microflow motion towards the left. According to the experimental results in Figure 4a, under different frequency and amplitude conditions, the initial release position has been adjusted to the right by the corresponding deviation to compensate. The compensated horizontal deviation results are shown in Figure 4c. The compensated horizontal release accuracy remains stable within 0.3 \(\upmu\)m.  
Based on the above experiments, we selected the release condition with an amplitude of 5 \(\upmu\)m and a frequency of 25 Hz according to the vertical deviation test as this resulted in the smallest vertical deviation. For the horizontal direction, we chose a compensation of 5.4 \(\upmu\)m to the right based on the horizontal deviation test results. Under this condition, we achieved optimal release accuracy and applied it as an ideal universal parameter for cell release. Through experiments, we found that the release accuracy of cells under this condition also reached its optimum. Therefore, this release condition was selected for subsequent cell array experiments.