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Cell penetration is a typical micromanipulation technique widely utilized in many cell biological applications. The significant cell deformation generated during penetration can mechanically damage the cell and even cause the death of the cell. Measuring the intracellular displacement resulting from cell deformation can provide a quantitative evaluation of the mechanical harm done to cells during penetration. The existing labeled intracellular displacement measurement approaches have limitations in spatial resolution and must introduce markers, which cause further harm to the cell. Moreover, label-free methods, such as traditional optical flow methods, are not suitable for measuring the inconsistent intracellular displacement distribution due to cell penetration. This paper presents a label-free noncontact method for measuring the intracellular displacements during penetration. First, based on a finite element simulation, the uneven distribution of intracellular displacements due to penetration was modeled by a quadratic model. Then, by combining the obtained displacement model with the Farnebäck dense optical flow method, a model-based optical flow method was developed to measure intracellular displacements. Finally, the method was used to ascertain the intracellular displacement in porcine oocyte penetration experiments. The forward-backward error of the proposed detection method is less than 0.5 pixels, lower by 49.3% and 26.1%, respectively, compared with two typical Farnebäck optical flow methods. This method could be used to analyze cell damage during penetration. With an appropriate extension, the method may be suitable for measuring the intracellular displacement due to cell manipulations other than penetration. [ABSTRACT FROM AUTHOR]

In this paper, we proposed an oocyte orientation selection method based on the minimum strain position in the penetration process in order to maximize the developmental potential of the operated oocytes. Considering the symmetry of an oocyte during the penetration process, we analyzed only the intracellular strain of the lower half of the oocyte (from 3 o'clock to 9 o'clock). Firstly, the strain distribution in the penetration process was calculated using the finite element analysis method. The influences of penetration force, zona pellucida thickness, oocyte radius, Young's modulus of the cytoplasm, and zona pellucida on the strain distribution were studied. The simulation results showed that the strain values at the 4 o'clock and 9 o'clock areas were significantly smaller than those at the 5 o'clock, 6 o'clock, 7 o'clock, and 8 o'clock areas. Secondly, the experimental strain distribution during penetration was evaluated for the first time using an optical flow method. The experimental strain distribution was strongly positively correlated to the aforementioned simulated results. Finally, the developmental potential of the penetrated porcine oocyte with different orientations was evaluated using the cleavage rate (48 h after penetration and parthenogenetic activation). The cleavage rate was strongly negatively correlated to the intracellular strain. We inferred that a smaller strain on the polar body areas in the penetration process caused less potential damage, which leads to a higher developmental potential of the penetrated oocyte. The optimized oocyte orientations, with the polar body at the 4 o'clock and 9 o'clock areas, are determined based on the minimum strain position in the penetration process. [ABSTRACT FROM AUTHOR]