Research On Cell Deformation And Stress During Micromanipulation Based On Micro-vision

Micromanipulation plays an important role in bioengineering research.During micromanipulation,the manipulated cells may suffer from excessive deformation and intracellular strain due to the force exerted by the manipulator.The deformation and strain may cause mechanical damage to cells,influence the development of the cells,and even cause the death of the cells.Thus,it's necessary to measure the intracellular stress and the force applied on the cell during manipulation to avoid cell damage.However,the existing approaches for detecting intracellular deformation and strain usually introduce fluorescent micro-objects into cells,which lead to low spatial resolution and may cause extra damage to the cells.Meanwhile,the measurement of applied force during micromanipulation is mainly carried out by force sensors,which is complicated in assembly and difficult to carry out simultaneously with micromanipulation.The vision-based deformation and force measurement methods are non-contact,unlabeled and easy to conduct,which can solve the problems of the existing force measurement approaches.Therefore,taking the cell penetration process as an example,vision-based cell deformation and stress measurement methods are studied in this paper.The main contents of this paper are listed as follows:Firstly,to solve the problem of intracellular strain measurement,a model-based intracellular displacement measurement method and a strain estimation method are proposed in this paper.According to the displacement data obtained by finite element simulation during the penetration process,a quadratic model was adopted to describe the relation between displacement and coordinate of intracellular points.Further,by combining the displacement model with Farneb?ck optical flow method,a model-based intracellular displacement measurement method was developed.The method was verified to be more reliable compared with two typical optical flow methods.Based on the displacement measurement method,the distribution of intracellular strain during penetration was estimated according to the relative position of intracellular points.Secondly,to solve the problem of applied force sensing,a vision-based cell morphology detection method and a vision-based force sensing method are proposed in this paper.According to the improved point-load model,a force sensing method based on the geometric parameters of the deformed cell was developed.Also,the geometric parameters were obtained by real-time image processing.The vision-based force sensing method was used to measure the applied force of zebrafish embryo and porcine oocyte,the detected applied force was basically consistent with the research results in other literatures.Finally,the deformation and force measurement experiments were conducted on the self-developed NK-MR601 micromanipulation system.The penetration experiments with injection velocity as 10,20,30,40 and 50?m/s were conducted,and the intracellular strain and applied force were counted.The results presented that the intracellular strain increased with the penetration force at various penetration velocities,and it's basically consistent with the same power function.Further,with the increase of the penetration velocity,the intracellular strain and applied force at the moment of puncture tended to decrease.In addition,there was a significant difference between the data of high penetration velocity and low penetration velocity.The deformation and force measurement method proposed in this paper can be applied to the control module of micromanipulation system in the further research to realize the real-time control of cell deformation and force during the penetration process,which can help avoid the large damage to cells.In addition,the force measurement method of combining cell model with image processing technology can also be extended to other micromanipulation processes such as cell stretching and cell extrusion.