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

How do monocytes penetrate

Ley et al…Immunology 2007

Why bifurcations

Fox & Hugh, Heart 1966 Ku et al. Atherosclerosis. 1985

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

QuickTime™ and aAnimation decompressor

are needed to see this picture.

Investigation of flow• Ran initial flow experiments with 6um beads

• Ran with 30º and 120º bifurcations

• Analyze flow

Sarvepalli

QuickTime™ and aAnimation decompressor

are needed to see this picture.

2uL/min

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Distance from center um

Velocity um/s

6um 2uL/min 120deg6um 2uL/min 30deg10um 2uL/min 120deg

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Distance from center um

Velocity in um/s

5um 5uL/min 120deg5um 5uL/min 30deg10um 5uL/min 120deg

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Distance from center um

Velocity um/s

6um 10uL/min 120deg6um 10uL/min 30deg10um 10uL/min 120deg

QuickTime™ and aAnimation decompressor

are needed to see this picture.

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

Acknowledgments• Dr. Schmidtke

• Travis Spain

• Phillip Coghill

• Alex

• Dr. Johnson

• Dr. Keay

Questions?

QuickTime™ and aTIFF (Uncompressed) decompressor

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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

How do monocytes penetrate

Ley et al…Immunology 2007

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

In vivo• Uses mice to study adhesion

• Advantages–Genetically tailored–Real results

• Disadvantages–Cannot watch in real

time–Fluid mechanics not

observed–More variability