Using Self-Assembling Swimming Devices to Control Motion at the Nanoscale

《神奇之旅》等电影富有想象力地探索了开发能够在人体中导航并执行诸如切除肿瘤等任务的微型设备的想法。虽然这一愿景看起来很梦幻，但现实是研究人员正在向这一目标迈进。目前，人类头发宽度的一小部分人造机器可以在含有少量化学“燃料”的水中游泳，而不需要任何外部干预。通过为这些设备配备磁铁，它们也可以通过外部磁场手动引导货物，它们可以拾取，拖动然后释放。然而，这些成就还没有实现制造能够在体内自行导航、将药物输送到特定治疗目标的设备的最终目标。在这种情况下，使用外部转向是不切实际的，设备必须找到自己的方式。这是非常具有挑战性的，因为微型设备在液体环境中体验的方式。由于液体性质在小尺寸时的变化方式，设备将周围的流体体验为糖浆状；也就是说它们不能像我们熟悉的游泳运动那样产生运动。此外，这些装置不断受到周围分子的碰撞，导致它们随机改变位置和方向，而且在身体的某些部位还有湍流需要应对。这项研究的目的是克服这些挑战，建造微型游泳装置，使其能够在没有外部干预的情况下直接指向目标，从而实现包括靶向药物输送在内的一系列应用。为了使这成为可能，这些设备必须能够根据周围环境调整它们的运动。这将使用一系列新的材料来实现，这些材料根据某些信号化学物质的存在或不存在而膨胀和收缩。这些大小的变化会使游泳装置改变受随机撞击影响的程度，要么使它保持直线运动，要么促使它迅速改变方向。尺寸的变化也会改变设备的速度。通过这种方式，设备可以利用周围混乱的环境将它们带到特定的位置。还将发展以同样灵敏的方式附加和释放货物的能力。除了在药物输送方面取得重大进展外，该奖学金开发的运输系统还将用于运输用于医疗诊断设备内分析的材料。此外，将制造一类旋转而不是平移的游泳者，用于在这些诊断系统的小通道中混合诸如化学试剂之类的流体。游泳者的增强运动也可以用来加快化学过程中的反应速度，从而加快工业过程。为了制造出适合上述任务的游泳设备，并使其具有快速、直线移动等理想性能，研究人员将开发新的制造方法。将传统部件组合在一起制造设备，只需将它们定位在正确的位置并粘在一起就可以实现，但在小规模操作中，这种操作不切实际，而且需要昂贵的显微操作。一种更实际的方法是为单个组件配备“粘性标签”或其他功能，这些功能将使自组装偏向于优选结构。然而，一些变化将继续存在。这项工作的一个关键的新方法实际上是利用这种变化，通过应用“自然选择”，使用物理障碍路线来挑选具有最佳性能的设备来完成特定任务。通过这种方式，高效的游泳者可以在不需要外部干预的情况下利用随机过程进行自我组装。

Films such as the "Fantastic Voyage" imaginatively explore the idea of developing miniaturised devices capable of navigating through the body and performing tasks, such as removing tumours. While this vision may seem fantastical, the reality is that researchers are moving closer towards this goal. At present, man-made machines a fraction of the width of a human hair can swim around in water containing a small amount of chemical "fuel" without any external intervention. By equipping these devices with magnets, they can also be manually steered towards cargo using external fields, which they can pick up, drag and then release. However these achievements have not yet enabled the ultimate goal of making devices that can navigate themselves through the body to deliver a drug to a particular therapeutic target. In this case it is impractical to use external steering, and the devices must instead find their own way. This is very challenging because of the way in which liquid environments are experienced by miniaturised devices. Due to the way in which liquid properties change at small sizes, the devices experience the surrounding fluid as treacle like; meaning they cannot generate motion using the swimming motions that we are familiar with. Also the devices are constantly jostled by collisions from surrounding molecules, causing them to change their position and orientation randomly, and in some parts of the body there are turbulent flows to contend with.The aim of this Fellowship is to overcome these challenges to build miniaturised swimming devices that can direct themselves towards targets without external intervention, to enable a range of applications including targeted drug delivery. In order for this to be possible the devices must be able to adjust their motion according to their surroundings. This will be achieved using a new range of materials that expand and contract according to the presence or absence of certain signalling chemicals. These size changes will cause the swimming device to change the degree to which it is affected by the random knocks it receives, either keeping it moving in a straight line, or encouraging it to change direction rapidly. The size changes will and also alter the speed of the device. In this way devices can exploit the chaos of their surroundings to carry them to specific locations. The ability to attach and release cargo in a similarly responsive way will also be developed. As well as producing significant advances for drug delivery, the transport systems developed by the Fellowship will also be used to transport material for analysis within medical diagnostic devices. In addition, a class of swimmers that rotate rather than translate will be made and used to mix fluids such as chemical reagents in the small channels of these diagnostic systems. The enhanced motion of the swimmers can also be used to speed up reaction rates in chemical processes, resulting in faster industrial processes.To build swimming devices for the above tasks with desirable properties such as being fast, and moving in a straight line, the Fellowship will develop new manufacturing methods. Combining conventional parts together to make devices can simply be carried out by positioning them in the correct places and sticking them together, however at small scales such operations are impractically laborious and require expensive microscopic manipulations. A more practical approach is to instead equip the individual components with "sticky tags" or other features that will bias the self-assembly to make preferred structures. However some variations will remain. One of the key novel methodologies of the work will actually exploit this variation, by applying "natural selection" using a physical obstacle course to pick out devices with the best performance for a particular task. In this way efficient swimmers can assemble themselves by exploiting a random process without requiring external intervention.