Mammalian embryos experience not only hormonal but also mechanical stimuli, such as shear stress, compression, and friction force, in the fallopian tube before nidation. In order to apply mechanical stimuli to embryos in a conventional IVF culture system, we developed the Tilting Embryo Culture System (TECS). The observed embryo images from the TECS suggest that the velocities and shear stresses of TECS embryos are similar to those experienced in the oviduct. Use of TECS enhanced the development rate to the blastocyst stage and significantly increased the cell number of mouse blastocysts (P<0.05). Although not significant, human thawed embryos showed slight improvement in development to the blastocyst stage following culture in TECS compared to static controls. Rates of blastocyst formation following culture in TECS were significantly improved in low quality embryos and those embryos cultured under suboptimal conditions (P<0.05). Here, we propose that the TECS could be a promising approach to improve embryo development and blastocyst formation by exposing embryos to mechanical stimuli similar to in the fallopian tube.

The microfluidic sperm-sorting (MFSS) device is a promising advancement for assisted reproductive technology. Previously, poly(dimethylsiloxiane) and quartz MFSS devices were developed and used for intracytoplasmic sperm injection. However, these disposable devices were not clinically suitable for assisted reproduction, so a cyclo-olefin polymer MFSS (COP-MFSS) device was developed. By micromachining, two microfluidic channels with different heights and widths (chip A: 0.3 × 0.5 mm; chip B: 0.1 × 0.6 mm) were prepared. Sorted sperm concentrations were similar in both microfluidic channels. Linear-velocity distribution using the microfluidic channel of chip B was higher than that of chip A. Using confocal fluorescence microscopy, it was found that the highest number of motile spermatozoa swam across the laminar flow at the bottom of the microfluidic channel. The time required to swim across the laminar flow was longer at the bottom and top of the microfluidic channels than in the middle because of the low fluid velocity. These results experimentally demonstrated that the width of microfluidic channels should be increased in the region of laminar flow from the semen inlet to the outlet for unsorted spermatozoa to selectively recover spermatozoa with high linear velocity.

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