Microfluidic Device Increases Sperm Concentration by Optimization of Chamber Structure

Intracytoplasmic sperm injection (ICSI) is an extremely timeconsuming and tedious procedure in cases of oligozoospermia, because it is difficult to obtain a sufficient number of motile sperms. To circumvent this difficulty, we previously developed a microfluidic device to increase sperm concentration and reduce time required for ICSI. Here, we improved this device by carefully optimizing its dimensions. We achieved a 10–13-fold enrichment ratio in non-motile human sperms (1.0 × 104 cells/ml) when a chamber height of 1.4 mm was used, and we described a mathematical model to explain the relationship between sperm concentration and enrichment ratio. However, this model was unable to explain the decrease in the enrichment ratio when a chamber height of 1 mm was used. Moreover, some sperms in the lower region of the chamber would return to the upper region and were then lost from the chamber as a result of fluid flow and/or internal force induced by the flow.