TECHNICAL PAPERS: Fluids/Heat/Transport

Bioheat and Mass Transfer as Viewed Through a Microscope

[+] Author and Article Information
Kenneth R. Diller

Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX 78712e-mail: kdiller@mail.utexas.edu

J Biomech Eng 127(1), 67-84 (Mar 08, 2005) (18 pages) doi:10.1115/1.1835354 History: Received February 24, 2004; Revised October 07, 2004; Online March 08, 2005

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Measured thermal history in a cell suspension frozen and thawed in a multistep process on a convection cryostage under feedback control of a simple analog programming circuit
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(Color online) Human erythrocytes frozen in normal saline solution and imaged via polarized light brightfield microscopy. (a) Cells entrapped in channels of concentrated solute solution (blue) within a matrix of extracellular ice (red), resulting in extensive dehydration. The cooling rate was considerably less than the threshold for intracellular ice formation. (b) Cells following the nucleation of intracellular ice. A coarse crystalline texture is visible in both the intracellular and extracellular spaces, with the red and blue regions distributed much more homogeneously. Scale bar is 10 μm.
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Threshold cooling rate and nucleation supercooling combinations for effecting intracellular ice formation in human erythrocytes suspended in normal saline as detected by direct observation of the freezing process on a convection cryomicroscope 21
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Image sequences showing the development of partial IIF within the cells of a pancreas islet in 2M Me2SO cooled at 50°C/min (adapted from 65). The first image (a) is a prefreezing state, the second (b) is growing EIF (extracellular ice formation) and initiation of IIF, and the third (c) is completion of the freezing process. Intracellular freezing is biased toward cells located in the islet interior, and cells on the periphery do not show darkening caused by the presence of small internal ice crystals. Note that there is a delay between EIF and IIF and that the total islet volume is constant during freezing. Scale bar is 100 μm.
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Freezing sequence for a pair of HeLa cells imaged via phase contrast microscopy, producing a pronounced halo surrounding the cells and at the ice–liquid solution boundary. Images (a)–(d) were taken at progressively lower temperatures and depict two phenomena clearly: substantial loss of cell volume as the solute concentration in the extracellular solutions increases with decreasing temperature; and mechanical deformation of the cells as they are trapped between growing extracellular ice masses. Scale bar is 10 μm. Image (e) is taken from a video monitor during a digitizing process for which the gray scale histogram along the central vertical scan line is superimposed to the right side.
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Serial micrographs (a)–(g) from a freeze/thaw sequence for yeast cells on a convection cryomicroscope in isotonic solution (adapted from 73). Cell boundaries were isolated from the image of frozen cells with a digital algorithm 69 (h), and the size was normalized to the prefreezing value for each image and plotted as a function of temperature (i).
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(Color online) Flow of two colored solutions into the Y-junction on the stopped flow osmotic challenge stage. Cells were suspended in one solution and a different chemical concentration in the second. Cells at the interface where the two flows meet would experience an osmotic challenge by diffusion between the two merged streams 43.
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Progressive dehydration of a pancreas islet following step-wise exposure to a 1000 mOsm saline solution on the perfusion cryomicroscope (adapted from 65). Scale bar is 100 μm.
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Comparison of osmotic model simulations and experimental data at (a) 25°C, (b) 15°C, and (c) −3°C for C. texanum algal cells exposed to 500 mOsm sucrose (t=0 s) and then (t=1700 s for 25°C),(t=1900 s for 15°C),(t=3000 s for −3°C) to a solution containing 200 mOsm methanol and 300 mOsm sucrose (adapted from 78).
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Pancreas islets were exposed to 2M Me2SO on the perfusion cryomicroscope and imaged via laser scanning confocal microscopy. Volumes were measured from digital reconstruction of serial scan planes. (a) Shows normalized volumes of the islet initially and at sequential times during the osmotic response process. (b) and (c) are stereo pair images of reconstructed voxels representing the islet volume at times t=0 and t=236 min, respectively. Comparison of the sequential images shows the structural distortion associated with osmotic flows throughout the islet volume.
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Images of a freezing process on the optical axis cryomicroscope. The left image is a Phi-Z reconstruction of serial scans of the freezing of a physiological saline and 9.5% glycerol solution with 1 ppm Na–Fl, using 20× objective on a scanning confocal microscope. The ice phase is white, and concentrated solution is dark, with the gray scale proportional to the concentration of fluorescein. Vertical scale is compressed such that the vertical edge is 2.4 mm and horizontal edge is 0.7 mm. Vertical stage travel was 0.475 mm. The right image is an X–Y scan through the phase interface. Cooling rate at the base of the stage=5°C/min. (Adapted from 83.)
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Mushy zone during the freezing of an aqueous sodium permanganate solution. (a) A micrograph of a physiological concentration solution being frozen to produce a cellular ice interface structure in the mushy zone from the tips of the cells to the base of the cells in the interstitial region. (b) Gray scale scans orthogonal to the growth direction of the phase interface showing the variations in solute concentration laterally across the ice cells and intercellular regions and longitudinally from the base of the interstitial region to the ice free region ahead of the interface. (c) Gray scale scans showing the solute concentration profiles along the center of an ice cell and the centerline of the interstitial region between cells. (Adapted from 87.)
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Digital image analysis of phase interface morphology during the freezing of aqueous solutions. Examples of (a) planar, (b) cellular, and (c) dendritic interface structures are shown as captured on a cryomicroscope. The micrographs were digitized and subjected to serial processing and analysis algorithms to identify the phase boundary from all other image elements. The resulting phase boundary for the dendritic structure is shown in (d). Statistical feature cluster analysis was then applied to separate the three types of interface (e). The three types of geometric structure is clearly distinct when more than 30 cryomicrographs are compared. (Adapted from 8990.)
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En face refractive index DPC-OCT images of a human epithelial cell (a) 0 s, (b) 23 s, and (c) 35 s after the application of anhydrous glycerol in the extracellular medium. Each video frame represents a 100×100 μm2 area.
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Sequential coagulation of blood flow through a venule in the hamster cheek pouch following thermal insult.
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Extravasation of FITC dextran 70000 from venules in the hamster cheek pouch following mild thermal insult to the central area of the field of view. The upper left image is preburn, and the next is at the time of the burn (t=0). Subsequent images are at two minute intervals, to a total observation period of 12 min.
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Time series data for vasomotion in an arterial in the dermal circulation as observed and measured in a rat dorsal skin flap chamber. A periodic pattern of constriction and relaxation are seen in the control data. After mild local thermal stress the vasoactive function disappears as the vessel diameter increases to a steady state diameter larger than occurs at any time under normal control function.
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(Color online) Dermal vascular bed in a rat dorsal skin flap chamber following focal laser irradiations indicated by the arrows. Blood flow at the irradiation sites is stopped.




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