Sperm selection in the female reproductive tract (FRT) is sophisticated. Only about 1,000 sperm out of millions in an ejaculate reach the fallopian tube and thus have a chance of fertilizing an oocyte. In assisted reproduction techniques, sperm are usually selected using their density or motility, characteristics that do not reflect their fertilization competence and, therefore, might result in failure to fertilize the oocyte. Although sperm processing in in vitro fertilization (IVF) and intrauterine insemination (IUI) bypasses many of the selection processes in the FRT, selection by the cumulus mass and the zona pellucida remain intact. By contrast, the direct injection of a sperm into an oocyte in intracytoplasmic sperm injection (ICSI) bypasses all natural selection barriers and, therefore, increases the risk of transferring paternal defects such as fragmented DNA and genomic abnormalities in sperm to the resulting child. Research into surrogate markers of fertilization potential and into simulating the natural sperm selection processes has progressed. However, methods of sperm isolation — such as hyaluronic acid-based selection and microfluidic isolation based on sperm tactic responses — use only one or two parameters and are not comparable with the multistep sperm selection processes naturally occurring within the FRT. Fertilization-competent sperm require a panel of molecules, including zona pellucida-binding proteins and ion channel proteins, that enable them to progress through the FRT to achieve fertilization. The optimal artificial sperm selection method will, therefore, probably need to use a multiparameter tool that incorporates the molecular signature of sperm with high fertilization potential, and their responses to external cues, within a microfluidic system that can replicate the physiological processes of the FRT in vitro.

女性生殖道 (FRT) 中的精子选择非常复杂。射精中的数百万个精子中只有大约 1,000 个到达输卵管，因此有机会使卵母细胞受精。在辅助生殖技术中，通常根据其密度或运动性来选择精子，这些特征不能反映其受精能力，因此可能导致卵母细胞无法受精。尽管体外受精 (IVF) 和宫内人工授精 (IUI) 中的精子处理绕过了 FRT 中的许多选择过程，但卵丘块和透明带的选择仍然完好无损。相比之下，在胞浆内精子注射 (ICSI) 中将精子直接注射到卵母细胞中绕过了所有自然选择障碍，因此，增加了将父亲缺陷（例如片段的 DNA 和精子中的基因组异常）转移给后代的风险。对受精潜力的替代标记和模拟自然精子选择过程的研究取得了进展。然而，精子分离方法——例如基于透明质酸的选择和基于精子策略反应的微流体分离——仅使用一个或两个参数，与 FRT 内自然发生的多步精子选择过程无法相比。受精能力强的精子需要一组分子，包括透明带结合蛋白和离子通道蛋白，使它们能够通过 FRT 进行受精。因此，最佳的人工精子选择方法将，