Matching textured surfaces to microwheel sizes and symmetries may lead to more efficient propulsion of microdevices. Microbot locomotion is challenging because of the reversible nature of microscale fluid flow, a limitation that can be overcome by breaking flowfield symmetry with a nearby surface. We have used this strategy with rotating wheel-shaped microbots, microwheels (μwheels), that roll on surfaces leading to enhanced propulsion and fast translation speeds. Despite this, studies to date on flat surfaces show that μwheels roll inefficiently with substantial slip. Taking inspiration from the mathematics of roads and wheels, we demonstrate that μwheel velocities can be significantly enhanced by changing microroad topography. Here, we observe that periodic bumps in the road can be used to enhance the traction between μwheels and nearby walls. Whereas continuous μwheel rotation with slip is observed on flat surfaces, a combination of rotation with slip and nonslip flip occurs when μwheels roll on surfaces with periodic features, resulting in up to fourfold enhancement in translation velocity. The unexpectedly fast rolling speed of μwheels on bumpy roads can be attributed to the hydrodynamic coupling between μwheels and road surface features, allowing nonslip rotation of entire wheels along one of their stationary edges. This road-wheel coupling can also be used to enhance μwheel sorting and separation where the gravitational potential energy barrier induced by topographic surfaces can lead to motion in only one direction and to different rolling speeds between isomeric wheels, allowing one to separate them not based on size but on symmetry.

中文翻译：

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微道路上的微轮：增强地形表面上的平移。

将纹理表面与微轮尺寸和对称性相匹配可能会更有效地推进微型设备。由于微尺度流体流动的可逆性，微型机器人的运动具有挑战性，这一限制可以通过打破与附近表面的流场对称性来克服。我们已将这种策略用于旋转轮形微型机器人、微型轮（μwheels），它们在表面上滚动，从而增强推进力和快速平移速度。尽管如此，迄今为止对平坦表面的研究表明，μ轮滚动效率低下，并且滑动很大。受道路和车轮数学的启发，我们证明可以通过改变微道路地形来显着提高 μwheel 速度。在这里，我们观察到道路上的周期性颠簸可以用来增强 μwheel 和附近墙壁之间的牵引力。虽然在平坦表面上观察到连续的 μwheel 旋转与滑动，但当 μwheel 在具有周期性特征的表面上滚动时，会发生旋转与滑动和非滑动翻转的组合，从而导致平移速度提高四倍。μwheel 在崎岖不平的道路上意外地快速滚动可归因于 μwheel 与路面特征之间的流体动力耦合，从而允许整个车轮沿着其固定边缘之一进行防滑旋转。这种负重轮耦合器还可用于增强 μwheel 的分选和分离，其中地形表面引起的重力势能垒可导致仅在一个方向上的运动以及异构轮之间不同的滚动速度，从而允许人们在不基于大小但对称。