Transport of fluid through a pipe is essential for the operation of macroscale machines and microfluidic devices. Conventional fluids only flow in response to external pressure. We demonstrate that an active isotropic fluid, comprised of microtubules and molecular motors, autonomously flows through meter-long three-dimensional channels. We establish control over the magnitude, velocity profile and direction of the self-organized flows, and correlate these to the structure of the extensile microtubule bundles. The inherently three-dimensional transition from bulk-turbulent to confined-coherent flows occurs concomitantly with a transition in the bundle orientational order near the surface, and is controlled by a scale-invariant criterion related to the channel profile. The non-equilibrium transition of confined isotropic active fluids can be used to engineer self-organized soft machines.One Sentence Summary: An isotropic fluid composed of nano-sized motors organizes into an autonomous machine that pumps fluid through long channels. Recent studies have revealed emergence of diverse complex patterns in synthetic systems of active matter (21-24). The next step is to elucidate conditions that transform chaotic dynamics of these systems into coherent long-ranged motion that can be used to harvest energy and thus power various micromachines (25-29).Here, we study 3D active fluids and demonstrate an essential difference with their conventional counterparts. The Navier-Stokes equations dictate that a conventional fluid comprised of inanimate constituents will flow only in response to an externally imposed body force, or stress and pressure gradients (29). This is no longer true for active fluids. Indeed, in living organisms, the entire cellular interior can assume large-scale coherent flows in absence of any externally imposed stresses, a phenomenon known as cytoplasmic streaming (30-32). Despite recent advances using living bacterial suspensions (13,14,33,34), creating tunable synthetic active 3 fluids that exhibit autonomous long-ranged flows on length scales large compared to constituent units remains a challenge. We use a 3D microtubule-based isotropic active fluid whose bulk turbulent flows are driven by continuous injection of energy through the linear motion of the constituent kinesin motors (24, 35). We find that confinement robustly transforms locallyturbulent dynamics of such active fluids into globally-coherent flows that persist on meter scales.Our experiments demonstrate that non-equilibrium transitions of synthetic active materials can be used to engineer self-organized machines in which nanometer sized molecular motors collectively propel fluid on macroscopic scales. Microtubule-based active isotropic fluids:The active fluid we study is comprised of microtubule filaments, kinesin motor clusters and depleting polymer (Fig. 1A) (24, 35). Kinesin motors are bound into synthetic clusters with tetrameric streptavidin (36, 37). The depleting polymer induces microtubule bundling (38), while the kinesin c...

As demonstrated by means of DNA nanoconstructs[1], as well as DNA functionalization of nanoparticles[2-4] and micrometre-scale colloids[5-8], complex self-assembly processes require components to associate with particular partners in a programmable fashion. In many cases the reversibility of the interactions between complementary DNA sequences is an advantage[9]. However, permanently bonding some or all of the complementary pairs may allow for flexibility in design and construction[10]. Here, we show that the substitution of a pair of complementary bases by a cinnamate group provides an efficient, addressable, UV light-based method to covalently bond complementary DNA. To show the potential of this approach, we wrote micrometre-scale patterns on a surface via UV light and demonstrate the reversible attachment of conjugated DNA and DNA-coated colloids. Our strategy enables both functional DNA photolithography and multi-step, specific binding in self-assembly processes.

Microtubule-based active matter provides insight into the self-organization of motile interacting constituents. We describe several formulations of microtubule-based 3D active isotropic fluids. Dynamics of these fluids is powered by three...

DNA is increasingly used as an important tool in programming the self-assembly of micrometer-and nanometer-scale particles. This is largely due to the highly specific thermoreversible interaction of cDNA strands, which, when placed on different particles, have been used to bind precise pairs in aggregates and crystals. However, DNA functionalized particles will only reach their true potential for particle assembly when each particle can address and bind to many different kinds of particles. Indeed, specifying all bonds can force a particular designed structure. In this paper, we present the design rules for multiflavored particles and show that a single particle, DNA functionalized with many different "flavors," can recognize and bind specifically to many different partners. We investigate the cost of increasing the number of flavors in terms of the reduction in binding energy and melting temperature. We find that a single 2-μm colloidal particle can bind to 40 different types of particles in an easily accessible time and temperature regime. The practical limit of ∼100 is set by entropic costs for particles to align complementary pairs and, surprisingly, by the limited number of distinct "useful" DNA sequences that prohibit subunits with nonspecific binding. For our 11 base "sticky ends," the limit is 73 distinct sequences with no unwanted overlaps of 5 bp or more. As an example of phenomena enabled by polygamous particles, we demonstrate a three-particle system that forms a fluid of isolated clusters when cooled slowly and an elastic gel network when quenched. multifunctional | thermodynamicsA defining feature of DNA nanotechnology is the ability of DNA single strands to bind selectively only with complementary strands (1-8). Identical particles coated with identical DNA strands can be joined together by adding to the suspension a linker strand that attaches to the two coatings (9, 10). Such structures have been used for immunoassays (11), particle aggregation, and formation of crystalline structures, typically Face Centered Cubic (FCC) (12). Use has also been made of different particles, A and B, functionalized with cDNA strands (13). This configuration, where A-A and B-B bonds do not occur but A-B bonds do (14-16), has been exploited to form more complex crystals, such as BCC or CsCl structures (12,17). Over the past several years, there has been a great deal of progress in modeling the DNA-mediated interparticle interaction and making quantitative comparisons with experiments (16,(18)(19)(20)(21)(22)(23). Although nanoscale particles are typically coated with tens to hundreds of DNA molecules, and micrometer-scale colloids can be coated with 10 4 -10 5 DNA strands, there has been little work on coating particles with more than one type of DNA sequence on the same particle. Allowing these particles to be "polygamous," to specifically bind to a particular set of other particles, enables not only the fabrication of more complex crystals but the design of more general programmed structures. For rigid structures,...