Pumping by flapping in a viscoelastic fluid

Department of Mechanical and Aerospace Engineering, University of California-San Diego, 9500 Gilman Drive, La Jolla, California 92093-0411, USA.
Physical Review E (Impact Factor: 2.29). 03/2010; 81(3 Pt 2):036312. DOI: 10.1103/PhysRevE.81.036312
Source: PubMed


In a world without inertia, Purcell's scallop theorem states that in a Newtonian fluid a time-reversible motion cannot produce any net force or net flow. Here we consider the extent to which the nonlinear rheological behavior of viscoelastic fluids can be exploited to break the constraints of the scallop theorem in the context of fluid pumping. By building on previous work focusing on force generation, we consider a simple, biologically inspired geometrical example of a flapper in a polymeric (Oldroyd-B) fluid, and calculate asymptotically the time-average net fluid flow produced by the reciprocal flapping motion. The net flow occurs at fourth order in the flapping amplitude, and suggests the possibility of transporting polymeric fluids using reciprocal motion in simple geometries even in the absence of inertia. The induced flow field and pumping performance are characterized and optimized analytically. Our results may be useful in the design of micropumps handling complex fluids.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Diffusio-phoresis --the motion of a particle or a macromolecule in a solute concentration gradient-- is an interfacially-driven transport phenomenon. Physically, it results from an osmotic pressure imbalance within the thin (ca. 1-10nm) diffuse layer located at the particle surface. Quite remarkably, it appears to be an efficient means of driving and manipulating colloidal particles. In this contribution, we present the results of our experimental study of this largely unexplored phenomenon. The thorough study of the diffusio-phoretic motility of colloids, as well as biological macromolecules, requires the building up of a spatially and temporally controlled solute gradient. Accordingly, a hydrogel microfluidics device was developed to generate a convection-free and spatiotemporal gradient. Particle migration is characterized and found to be in agreement with theoretical predictions. Furthermore, novel patterning mechanisms of particles are unveiled: trapping by rectification of concentration oscillations and particles localization by osmotic shock. They originate in the specific logarithmic sensing of the diffusio-phoretic velocity with electrolyte: non linear and logarithmic. Both observations are rationalized by numerical and theoretical predicitions. Analogies with positioning mechanisms in biology are finally discussed in an iconoclast questioning. Additionally we take advantage of diffusio-phoresis as an energy transduction mechanism to produce self-propelled particles. Inducing solute gradients by an asymmetric catalysis on the colloidal surfaces themselves, the namely Janus particles are chemically powered in the presence of fuel. In other words, they exhibit self-diffusio-phoretic propulsion. Through hydrodynamics and chemical interactions, these active particles are used as toy-models in the study of collective behavior and out-of-equilibrium statistical physics. The dynamics of individuals is carefully characterized as a persistent random walk. It is then connected to the statistical properties of an active suspensions of swimmers under gravity, reminiscent of Perrin's historic experiment. Our study tests the validity of the Fluctuation-Dissipation Theorem allowing the measurement of an effective temperature for the active system. This, in turn, is linked with the microscopic properties of the active suspension defining a Peclet number for the swimmers.
    Preview · Article · Oct 2010
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Locomotion on small scales is dominated by the effects of viscous forces and, as a result, is subject to strong physical and mathematical constraints. Following Purcell's statement of the scallop theorem which delimitates the types of swimmer designs which are not effective on small scales, we review the different ways the constraints of the theorem can be escaped for locomotion purposes.
    Preview · Article · Nov 2010 · Soft Matter
  • [Show abstract] [Hide abstract]
    ABSTRACT: Translating advances in the laboratory into sound clinical practice presents a series of formidable conceptual and technical challenges. One of them is our inability to maintain large grafts of living cells upon transfer from in vitro conditions into the host in vivo. This is due mainly to diffusion limitations within the grafting material. We embrace the well-known hypothesis of the "Diamond Concept" in bone tissue regeneration, which includes four key factors. Based on the understanding of basic elements of tissue engineering constructs, prefabrication and conditioning techniques and the nano-vascularisation of the scaffold, we furthermore hypothesize that combinations of cells, solid multipolymeric scaffold as the "core element" working as the extracellular matrix (ECM), growth factors and nano-vascularisation setting may eventually generate a large "ready-to-use"in vitro/in vivo graft. We are confident and think that growth factors will help in the construction of a step-by-step organisation of the bone tissue engineering construct (BTEC). A medical device, named in vitro/in vivo Bone Bioreactor Tissue Engineering Construct (IV2B2TEC), is proposed to fulfil the hypothesis. Soon, we hope to test the above hypothesis on a non-union bone defect in an animal model. This novel strategy will likely open new options for reconstructing extended bone defects and facilitate clinical translation of bone tissue engineering. As compared with conventional reconstructive methods, the strategy has four key advantages and might prove to be a novel armamentarium for clinicians in regenerative medicine.
    No preview · Article · Dec 2010 · Medical Hypotheses
Show more