Swirling Propulsion in Complex Fluids and Micro-Swimming Rheometry

微生物的运动往往因其所处流体的复杂性而变得复杂。这些生物体“游泳”的许多体液(例如粘液)中含有限制成功游泳的蛋白质等大分子。要游过这些粘稠的液体就更加困难了。最近有人从理论上提出，一种被称为“漩涡”的微生物游动可以在复杂的液体中产生推进力，而这在“简单”、粘度较低的液体中是不可能实现的。漩涡的特征是身体的某些部分绕着轴对称的物体的轴旋转。漩涡是许多微生物游泳时的一个重要特征。该奖项将开发一种新型微型机器人，它可以展示复杂流体中的涡流推进特性，并利用这种推进来测量周围流体的特性。因此，它是一种复杂流体性质的动态传感器或“游泳式流变仪”。标准流变仪是桌面设备，其中流体被带到设备中，流体应用的本地环境在设备中重现。复杂流体剪切流动中的应力状态要求测量至少三种材料性质作为流体中剪切速率的函数。本奖项的目标是通过设计、小型化和优化新开发的“旋转”机器人，将流变学转变为远程、现场传感科学。因此，人们将把流变仪带到流体应用中，而不是把流体样本带到固定的流变仪上。已经创建了一个网球大小的原型，并成功地演示了主要概念。该机器人已设计完成，并将继续通过大规模计算机模拟进行优化。这种微型机器人将立即具有医疗和生物应用，包括测量滑液的复杂流变性，作为对几种疾病情况的直接映射。此外，多个微型机器人将被用来检查这些微型旋涡的集体动力学。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The movement of micro-organisms is often complicated by the complexity of the fluids in which they reside. Many of the fluids (e.g., mucous) in which these organisms “swim” contain large macromolecules such as proteins that limit successful swimming. It is more difficult to swim through these “sticky” fluids. It has recently been suggested theoretically that a type of microbial swimming called “swirl” can create propulsion in complex liquids that would not be possible in “simple,” less sticky fluids. Swirl is characterized by parts of the body spinning around the axis of an axisymmetric body. Swirl is a key feature of the swim stroke of many micro-organisms. This award will develop a novel micro-robot that demonstrates the characteristics of swirl propulsion in complex fluids and uses that propulsion to measure the properties of the surrounding fluid. Thus, it is a dynamic sensor of complex fluid properties or a “swimming rheometer”. Standard rheometers are desktop devices where fluid is brought to the device and the native environment of the fluid application is reproduced in the device. The state of stress in the shear flow of complex fluids requires the measurement of at least three material properties as a function of the shear rate in the fluid. The goal in the present award is that through design, miniaturization, and optimization of a newly developed “swirling” robot, rheometry will be transformed to a remote, in situ sensing science. Thus, one will bring the “rheometer to the fluid application” rather than bringing a fluid sample to a fixed rheometer. A tennis ball-size prototype has already been created and the primary concepts are successfully demonstrated. The robot was designed and will continue to be optimized via large scale computer simulation. The miniaturized robot will have immediate medical and biological applications including measuring the complex rheological properties of synovial fluid as a direct mapping to several disease conditions. Moreover, multiple miniaturized robots will be used to examine the collective dynamics of these micro-swirlers.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.