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Investigation of Fluid Behavior in Bifurcated Microfluidic
Chambers
Joel Ramey
Advisor: Dr. David Schmidtke
Outline• Motivation
• Making the apparatus
• Experiments
• Results
• Implications
• Future work
http://www.ladinfo.org/wbc-rbc-large-B.jpg
8um diameter
Motivation• What is a Leukocyte?
–White blood cell
• Why is adhesion important?–Inflammation–Thrombosis–Atherosclerosis
•~1 million deaths/year
Endothelial cells
Smooth muscle cells
Monocytes
Pool of fat
David W. Schmidtke http://en.wikipedia.org/wiki/Image:Carotid_Plaque.jpg
Research Aim• Take advantage of established microfabrication
techniques to study fluid dynamics with different geometries.–Easy to implement–Plethora of available geometries
David W. Schmidtke
Photolithography Procedure
• Substrate Cleaning (glass slide)
• Layer of Photoresist (negative photoresist)
• UV Exposure
• Develop
• Aligning the Mask
Transfer of a geometric shape from a photomask to a substrate
David W. Schmidtke
PDMS stamps• Clean pattern
• Pour PDMS over
over pattern–Cure PDMS
• Peal from pattern
http://faculty.washington.edu/afolch/images/Project_3DPDMS0.jpg
1st semester• Created new masks
–Initially transparencies–Inherent limitations
• Flow experiments–Bead adhesion shows
promise
• More new masks–Chrome
Apparatus
Monitor VCR
Video Camera Microscope
Flow chamber
SyringePump
Controls shear stress
Computer
Bead suspension (100 x 103 beads/mL)
Polystyrene beads. 6, 10, 20 um diameters
Schmidtke
Investigation of flow• Ran initial flow experiments with 6um beads
• Ran with 30º and 120º bifurcations
• Analyze flow
Sarvepalli
2uL/min
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Distance from center um
Velocity um/s
6um 2uL/min 120deg6um 2uL/min 30deg10um 2uL/min 120deg
5uL/min
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Distance from center um
Velocity in um/s
5um 5uL/min 120deg5um 5uL/min 30deg10um 5uL/min 120deg
10uL/min
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Distance from center um
Velocity um/s
6um 10uL/min 120deg6um 10uL/min 30deg10um 10uL/min 120deg
Future• Look more closely at fluid dynamics in main
branch
• Run computational fluid dynamics for actual pattern
• Analyze flow with beads at apex
• Run experiments with leukocytes
• Look into using pulsatile flow
Disorder of the large arteries.
AtherosclerosisAtherosclerosis
Atheroma formation: accumulation of fatty substances, cholesterol and cellular waste products.
Major cause of morbidity in the United States:
Affects close to 60 million Americans
Contributes to 33% of all deaths in U.S each year.
Endothelial cells
Smooth muscle cells
Monocytes
Pool of fat
In vitro• Advantages
–Watch experiment in real time–Process has high degree repeatability–Control over variables
• Disadvantages–Geometric constraints–Not an actual artery–Different surfaces
DeBakey et al. Ann. Surg. 1985
Predominant human anatomic sites for Predominant human anatomic sites for the localization of atherosclerotic the localization of atherosclerotic
lesionslesions
Ku et al. Atherosclerosis. 1985
High Shear Region (15-50dyn/cm2)
Low Shear Region (0-4dyn/cm2)
Stagnation Point
Carotid artery
Cross section of the carotid sinus
Schematic sudden expansion flow chamber. H, chamber height downstream of expansion; h chamber height upstream of expansion; S, gasket thickness; x coordinate parallel to glass slide; y, coordinate normal to glass slide.
Research AimResearch AimResearch AimResearch Aim
Take advantage of the microfabrication technologies to study the pattern of cell adhesion and rolling at bifurcated geometries
Techniques easy to implement Many different geometries are available
Computational simulation
In vivo Models
Malek et al. J.A.M.A 1999
Berger et al. Ann. Rev. Fluid Mech. 2000
Previous StudiesPrevious Studies
Glass models of bifurcations
Karino et al. J. Biomechanics 1990
Pedersen et al. Biomechanics 1992
Malinauskas et al. Atherosclerosis 1998
Sudden Expansion Flow ChambersBarber et al. Am. J. Physiology 1998
Skilbeck et al. Biorheology 2001
Skilbeck et al. Arterioscler Thromb Vasc Biol. 2001
Ramos et al. Circ Res. 1999
Westrick et al. Circulation 2001
Skilbeck et al. Biorheology 2001
Malek et al. J.A.M.A 1999