Manna Raj Kumar, Shklyaev Oleg E, Stone Howard A, Balazs Anna C
Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA.
PNAS Nexus. 2022 Jun 8;1(2):pgac072. doi: 10.1093/pnasnexus/pgac072. eCollection 2022 May.
The intertwining of strands into 3D spirals is ubiquitous in biology, enabling functions from information storage to maintenance of cell structure and directed locomotion. In synthetic systems, entwined fibers can provide superior mechanical properties and act as artificial muscle or structural reinforcements. Unlike structures in nature, the entwinement of synthetic materials typically requires application of an external stimulus, such as mechanical actuation, light, or a magnetic field. Herein, we use computational modeling to design microscale sheets that mimic biology by transducing chemical energy into mechanical action, and thereby self-organize and interlink into 3D spirals, which spontaneously rotate. These flexible sheets are immersed in a fluid-filled microchamber that encompasses an immobilized patch of catalysts on the bottom wall. The sheets themselves can be passive or active (coated with catalyst). Catalytic reactions in the solution generate products that occupy different volumes than the reactants. The resulting density variations exert a force on the fluid (solutal buoyancy force) that causes motion, which in turn drives the interlinking and collective swirling of the sheets. The individual sheets do not rotate; rotation only occurs when the sheets are interlinked. This level of autonomous, coordinated 3D structural organization, intertwining, and rotation is unexpected in synthetic materials systems operating without external controls. Using physical arguments, we identify dimensionless ratios that are useful in scaling these ideas to other systems. These findings are valuable for creating materials that act as "machines", and directing soft matter to undergo self-sustained, multistep assembly that is governed by intrinsic chemical reactions.
在生物学中，链相互缠绕形成三维螺旋结构的现象无处不在，它实现了从信息存储到维持细胞结构以及定向运动等多种功能。在合成系统中，缠绕的纤维可以提供卓越的机械性能，并可作为人造肌肉或结构增强材料。与自然界中的结构不同，合成材料的缠绕通常需要施加外部刺激，如机械驱动、光或磁场。在此，我们利用计算模型设计出微尺度薄片，它们通过将化学能转化为机械作用来模仿生物学，从而自组织并相互连接形成自发旋转的三维螺旋结构。这些柔性薄片浸没在一个充满流体的微腔中，该微腔的底壁上有一块固定的催化剂片。薄片本身可以是被动的或主动的（涂有催化剂）。溶液中的催化反应产生的产物与反应物占据不同的体积。由此产生的密度变化对流体施加一个力（溶质浮力），从而引起运动，进而驱动薄片的相互连接和集体涡旋。单个薄片不会旋转；只有当薄片相互连接时才会发生旋转。在没有外部控制的合成材料系统中，这种自主、协调的三维结构组织、缠绕和旋转程度是出乎意料的。通过物理论证，我们确定了无量纲比率，这些比率有助于将这些概念扩展到其他系统。这些发现对于制造充当“机器”的材料，以及引导软物质进行由内在化学反应控制的自持多步组装具有重要价值。
