Numerical simulation of two-stage sperm separation in a microfluidic chip

Due to increasing infertility in couples and impractical laboratory methods, the selection of healthy sperm with high DNA integrity is crucial to in vitro fertilization. Like the sperm selection process in nature and the female reproductive system, sperms with inherent motions and mobility can reach the egg and fertilize it. So, we need to select those with inherent swimming behavior with high motility. In this study, we designed a microfluidic chip that can trigger two inherent motions of motile sperms, rheotaxis, and crossing streamlines to separate them. First, we design the chip so that velocity field and shear rate are suitable for sperm rheotaxis and diffusion. After that, using the sperm rotation equation, or Adler equation, in a MATLAB code, the rotation of moving sperms particles capable of rotating and swimming in the opposite direction of the flow were tracked. For simulating the crossing streamlines section, diffusiophoresis force is defined as a force by which sperm diffusion can be defined thereby by coupling convection and diffusion mass transfer equations; crossing streamlines phenomenon can be seen. When the results were analyzed, it was observed that the separation efficiency due to rheotaxis is about 100% and through crossing streamlines is about 65%, indicating that high efficiency and precision two-stage separation can be achieved. As a result, these simulations show that this chip can select sperms with inherent motion and high mobility.