CAREER: Establishing Swimming Sperm as a Model Active Matter System

非技术总结：游动的精子主动消耗能量并推动自己前进。同时，它们与邻近的精子相互作用，形成不同的相，类似于大量的水分子形成蒸汽或液相。在不同的条件下，精子可以单独游动（就像气体中的分子），也可以形成密集的集体运动，这被称为群集阶段（想象一群鸟，但用精子代替了鸟）。关注大量自我推进物体行为的研究领域被称为活性物质。在这个项目中，课题组的目标是产生实验数据来严格检验现有的理论模型，并建立游动精子作为活性物质的实验模型体系。在这个项目中回答的基本问题可以帮助生物学家理解精子是如何通过哺乳动物雌性生殖道的。工程师们还可以利用这些信息来利用精子作为载体，或者为自动推进的物体开发机械开关。在学术环境中，研究项目的成功取决于有才能的学生的贡献，首席研究员利用辅导活动派遣本科生到周围学校系统中指导学生。这一教育计划旨在提高现有本科生的表现，并加强未来学生的储备。该项目结合了涉及物理学、生物学和信息论的跨学科研究项目，旨在为北卡罗来纳农业和技术州立大学（历史上的黑人大学和学院之一）的学生创造一个智力刺激的环境。技术摘要：考虑微游泳者和周围流体之间动量守恒的理论模型表明，在低雷诺数游泳者（如精子）中不应看到群集阶段。然而，在适当的粘弹性流体和初始条件下，首席研究员观察到精子聚集。这些表现出的临界指数与干燥活性物质理论模型中预测的指数相似，该模型不考虑游泳者和流体之间的动量守恒。这个项目首先通过追踪单个精子游泳时产生的流体流动来测试动量守恒命题，这也将帮助我们更好地理解精子在粘弹性流体中的推进机制，它模拟了精子在女性生殖道中游动所需的粘液流变学。精子-精子和精子-侧壁的相互作用是由周围的液体和直接碰撞介导的。因此，研究小组接下来通过流动和细胞追踪来研究精子之间的相互作用规律以及游动精子碰撞在侧壁上产生的机械压力。这些研究可能有助于理解女性生殖道，特别是子宫输卵管连接处如何调节精子的运动，以及微流体系统中自推进物体的机械致动器的发展。最后，本项目采用信息论方法分析精子行为。具体来说，它考察了不同阶段的信息传递和信息熵，试图确定生命活性物质系统的组织原则。该项目由材料研究部的凝聚态物理项目和人力资源开发部的传统黑人学院和大学本科项目（HBCU-UP）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary:Swimming sperm actively consume energy and propel themselves. Meanwhile, they interact with neighboring sperm and form different phases, similar to a large number of water molecules forming either vapor or liquid phases. Under different conditions, sperm may swim individually (like molecules in a gas) or form dense, collective motion, which is called the flocking phase (think of a flock of birds but replacing birds with sperm). The research field that focuses on the behaviors of a large number of self-propelling objects is referred to as active matter. In this project, the research group aims to produce experimental data to rigorously test the existing theoretical models, and establish swimming sperm as an experimental model system for active matter. Fundamental questions answered in this project can be applied to help biologists understand how sperm pass through the mammalian female reproductive tract. Engineers can also use the information to utilize sperm as carriers or develop mechanical switches for the self-propelled objects. Success of a research project in an academic setting depends on the contribution of talented students, and the principal investigator utilizes tutoring activities to send undergraduate students to tutor students in the surrounding school systems. This education plan aims to boost both the performance of existing undergraduate students, as well as strengthening the pipeline for future students. Combined with the interdisciplinary research project that involves physics, biology, and information theory, the project aims to create an intellectually stimulating environment for students at North Carolina Agricultural and Technical State University, one of the Historically Black Universities and Colleges.Technical Summary:Theoretical models that consider momentum conservation between the microswimmers and the surrounding fluids suggest that the flocking phase should not be seen among low-Reynolds-number swimmers such as sperm. However, given the appropriate viscoelastic fluid and initial conditions, the principal investigator has observed flocking of sperm. These exhibit critical exponents similar to those predicted in the dry active matter theoretical model, which does not consider momentum conservation between swimmers and fluid. This project first addresses this by tracing the fluid flow generated by individual sperm swimming to test the momentum conservation proposition, which will also help us better understand sperm propulsion mechanism in viscoelastic fluid, which simulates the rheology of mucus that they need to swim through in the female tract. Sperm-sperm and sperm-sidewall interactions are mediated by the surrounding fluid and direct collisions. Thus, the research team next examines the interaction rules between sperm along with mechanical pressure generated on the sidewalls by swimming sperm colliding into them through the flow and cell tracing. These studies may lead to understanding how the female reproductive tract, particularly the uterotubal junction, regulates the movement of sperm, as well as the development of mechanical actuators for self-propelled objects in microfluidic systems. Finally, this project employs information theory approaches to analyze sperm behaviors. Specifically, it examines information transfer and the information/entropy of different phases, trying to identify organizational principles underlying living active matter systems. This project is co-funded by the Condensed Matter Physics program in the Division of Material Research and the Historically Black Colleges and Universities – Undergraduate Program (HBCU-UP) in the Division of Human Resource Development.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.