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Micro-scale Transport as a Critical Link between Molecular-scale Absorption and Macro-scale Mixing in Gut Physiology an

MSM PI Meeting, NIH, 11 April 2007. Micro-scale Transport as a Critical Link between Molecular-scale Absorption and Macro-scale Mixing in Gut Physiology and Function. Investigators Jim Brasseur, PI - modeling/simulation Andrew Webb, co-PI - MRI, imaging

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Micro-scale Transport as a Critical Link between Molecular-scale Absorption and Macro-scale Mixing in Gut Physiology an

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  1. MSM PI Meeting, NIH, 11 April 2007 Micro-scale Transport as a Critical Link between Molecular-scale Absorption and Macro-scale Mixing in Gut Physiology and Function • Investigators • Jim Brasseur, PI - modeling/simulation • Andrew Webb, co-PI - MRI, imaging • Nadine Smith, co-PI - animal experiment • Yanxing Wang, postdoctoral fellow - modeling • Gino Banco, PhD student - modeling • Amit Ailiani , PhD student - MRI, image analysis • Thomas Neuberger, PhD - MRI researcher • Consultant • Jack Wood, PhD, Ohio State - GI neurophysiology

  2. macro mixing villi motion & micro mixing(~200-300 µm scale) The Importance of Macro-Micro Couplings micro mixing transport ofmolecules to/from epithelium micro mixing villus lumen contractions & macro mixing(~cm scale) Nutrient absorption requires multi-scale mixing in the transport of molecules to the epithelium

  3. Objectives and Methods • Modeling and Computer Simulation:Lattice-Boltzmann methods (LBM) • (1) macro-scale scalar mixing w/ LBM(~ cm scale) • (2) couple with micro-scale scalar mixing w/LBM (~ hundreds of microns) • (3) couple LBM with MD of individual molecules transported to epithelium through the micro-mixing layer • Physiology + Model Parameterizations: MRIof the rat small intestines • (1) imaging motility of the rat small intestines at the macro scale (~ mm-cm scale) • (2) imaging villi movements and motility at the micro scale (~ 100 mm ~ 1 mm scale)

  4. MRI ANALYSISAndrew Webb

  5. Multiscale Modeling and Macro-Micro Mixing- Objectives - • Develop 3D multi-scale lattice Boltzmann methods (LBM) to model macro-to-micro mixing and transport in the gut (currently 2D) • Compare macro mixing/transport for basic space-time patterns of lumen contraction* (motility) • Study multi-scale coupling between macro mixing (lumen contraction) and micro mixing* (villi motion) • Couple the LBM with MD simulations of different nutrient molecules (future work) • *coupling with MRI data

  6. Lattice-Boltzmann applied to Modeling Macro-scale Mixing with Moving Boundaries and Passive Scalar • Basic Lattice-Boltzmann Method • Moving Boundaries (Ladd 1994 + Aiden 1991) 2 6 5 e2 e6 e5 0 1 3 • Passive Scalar (Merks et al. 2002) 7 • Scalar Boundary Conditions • - fixed scalar or fixed scalar flux

  7. Lattice-Boltzmann applied to Modeling Macro-scale Mixing in a Modeled Rat Small Intestine (2-D)* Segmental + Peristaltic Contractions Pure Segmental Contractions Pure Peristalsis * parameterized with MRI data from small intestine of rat

  8. δxc δxf Multi-Scale simulations on coupled Multi-Grid Lattices with Passive Scalar (2-D) • Embed fine lattice within coarse • Coupling algorithm of Yu, Mei, Shyy (2002) • Time advance intermediate time steps on fine lattice, relatively complex • Passing scalar between grids • Modeling moving “villi”

  9. U = 2 mm/s c = 1 dc/dn = 0 dc/dn = 0 c = 0 Multi-Scale cavity flow with “villi” on coupled Multi-Grid Lattices with Passive Scalar (2-D) • Simulation: lid-driven cavity flow with “villi” on lower surface • Simulation with no “villi” • zero scalar lower boundary

  10. Φ=π/2 Φ=0 Φ=π/4 Φ=3π/4 Multi-Scale simulations of cavity flow with “villi”and Passive Scalar

  11. Future Evolution MODELING • Complete 2D analyses of macro and macro-micro mixing • Develop 3-D models • Develop methods to incorporate more detaileddata from rat experiments at macro and micro scales • Incorporate MD simulation within LBM framework EXPERIMENT • Complete data collection of macro motility • Complete principle component analysis • Develop and evaluate methods to detect villi motionin vivo

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