Deformable synthetic microgel particles bearing molecular-recognition motifs for fibrin fibres are shown to augment clotting in vitro and mimic in vivo clot contraction, thus recapitulating the functions of natural platelets. Efforts to create platelet-like structures for the augmentation of haemostasis have focused solely on recapitulating aspects of platelet adhesion1; more complex platelet behaviours such as clot contraction2 are assumed to be inaccessible to synthetic systems. Here, we report the creation of fully synthetic platelet-like particles (PLPs) that augment clotting in vitro under physiological flow conditions and achieve wound-triggered haemostasis and decreased bleeding times in vivo in a traumatic injury model. PLPs were synthesized by combining highly deformable microgel particles with molecular-recognition motifs identified through directed evolution. In vitro and in silico analyses demonstrate that PLPs actively collapse fibrin networks, an emergent behaviour that mimics in vivo clot contraction. Mechanistically, clot collapse is intimately linked to the unique deformability and affinity of PLPs for fibrin fibres, as evidenced by dissipative particle dynamics simulations. Our findings should inform the future design of a broader class of dynamic, biosynthetic composite materials.

An effective approach to separating shaped particles is needed to isolate disease-causing cells for diagnostics or to aid in purifying nonspherical particles in applications ranging from food science to drug delivery. However, the separation of shaped particles is generally challenging, since nonspherical particles can freely rotate and present different faces while being sorted. We experimentally and numerically show that inertial fluid-dynamic effects allow for shape-dependent separation of flowing particles. (Spheres and rods with aspect ratios of $3:1$ and $5:1$ have all been separable.) Particle rotation around a conserved axis following Jeffery orbits is found to be a necessary component in producing different equilibrium positions across the channel that depend on particle rotational diameter. These differences are large enough to enable passive, continuous, high-purity, high-throughput, and shape-based separation downstream. Furthermore, we show that this shape-based separation can be applied to a large range of particle sizes and types, including small, artificially made $3\mathrm{\text{−}}\mu \mathrm{m}$ particles as well as bioparticles such as yeast. This practical approach for sorting particles by a previously inaccessible geometric parameter opens up a new capability that should find use in a range of fields.

One of the vital functions of naturally occurring cilia is fluid transport. Biological cilia use spatially asymmetric strokes to generate a net fluid flow that can be utilized for feeding, swimming, and other functions. Biomimetic synthetic cilia with similar asymmetric beating can be useful for fluid manipulations in lab-on-chip devices. In this paper, we demonstrate the microfluidic pumping by magnetically actuated synthetic cilia arranged in multi-row arrays. We use a microchannel loop to visualize flow created by the ciliary array and to examine pumping for a range of cilia and microchannel parameters. We show that magnetic cilia can achieve flow rates of up to 11 μl/min with the pressure drop of ~1 Pa. Such magnetic ciliary array can be useful in microfluidic applications requiring rapid and controlled fluid transport.

Using three-dimensional computer simulations, we examine hovering aerodynamics of flexible planar wings oscillating at resonance. We model flexible wings as tilted elastic plates whose sinusoidal plunging motion is imposed at the plate root. Our simulations reveal that large-amplitude resonance oscillations of elastic wings drastically enhance aerodynamic lift and efficiency of low-Reynolds-number plunging. Driven by a simple sinusoidal stroke, flexible wings at resonance generate a hovering force comparable to that of small insects that employ a very efficient but much more complicated stroke kinematics. Our results indicate the feasibility of using flexible wings driven by a simple harmonic stroke for designing efficient microscale flying machines. DOI: http://dx.doi.org/10.1103/PhysRevE.81.056304 © 2010 The American Physical Society