Characteristics:

• Dyeing and scanning sample by confocal microscopy.
• Segmentation and Meshing in Simpleware ScanIP+FE.
• CFD simulation in Star-CCM+ from CD-adapco.
• Analysis of stresses and concentrations.

Image Processing

    Rat lymphatic vessels were isolated, loaded with fluorescent dye, and pressurized to ensure valve opening. Vessels were then imaged using confocal microscopy (Nikon) to obtain 2-D image slices 2.5 µm for the full depth of the vessel (~ 100 um).

    Stacks of images were imported into Scan IP/FE (Simpleware, Exeter, UK) and refined using primarily recursive Gaussian, mean and median, and discrete Gaussian filters. Extensions were added to either end to allow for ease in the application of boundary conditions.The surface mesh was then imported into the commercial computational fluid dynamics solver Star-CCM+ for volume meshing and flow analysis.

Meshing

     Following importation into the CFD solver, a surface wrapper was used to approximate the geometry and a volume mesh was created using the trimmer meshing module. This module produces a robust mesh that is primarily hexahedral with minimal cell skewness. The resulting mesh consisted of approximately 385,000 volumetric cells.

Simulations

   A fully developed parabolic velocity profile with an average velocity of 2.0 mm s-1 was implemented at the inlet. A shear stress-dependent function was applied at the wall of the vessel as the flux boundary condition of NO. Simulations revealed areas of high concentration near upper surface of the valve leaflet corresponding to areas of essentially zero shear (Figure 2 Upper Panel). Additionally, high areas of high wall shear stress (WSS) were observed at the inner surface of the lymphatic valve leaflet.

Thanks to

Department of Biomedical Engineering, Texas A&M University
J.T. Wilson • W. Wang • A.H. Hellerstedt • D.C. Zawieja • J.E. Moore Jr.

We gratefully acknowledge the Texas A&M University Supercomputing facility for providing computing resources useful in conducting the research reported in this outline.