stenosis presentation

Sampling of Research at the Advanced

Materials and Technologies Laboratory

Presented at the VBI Faculty Meeting • November 10, 2009

Ranga PitchumaniAdvanced Materials and Technologies Laboratory

Department of Mechanical Engineering

Virginia Tech

Blacksburg, Virginia 24061-0238

[email protected] • http://www.me.vt.edu/amtl • (540) 231-1776

Advanced Materials and Technologies LaboratoryProf. Ranga Pitchumani • [email protected] • http://www.me.vt.edu/amtl

Research focuses on the fundamentals of multiscale, multiphysics phenomena in

the fabrication of composite materials via liquid molding and other methods. The

emphasis is on filling gaps in understanding of the phenomena, bridging them

across a cascade of scales, and using computational physics-based models for real-

time sensing and control, design, optimization, and analysis under uncertainty.

Use of carbon nanotubes in structural fiber-reinforced composites is studied for

their damping characteristics for applications in vibrating and rotating structures

(such as rotorcraft and wind turbine blades). Related issues on characterizing the

complex rheology and cure kinetics of resin systems with carbon nanotubes are also

addressed.

Composite Materials and Nanocomposites

100%

A/W=1709 m2/g

Blood flows through stenosed carotid and coronary arteries with a

complete bypass graft are investigated by using computational fluid dynamics

tools. Different anastomotic angles, bypass graft length and locations of the

stenosis are analyzed as function of the extent of plaque occlusion in the artery.

The effects of type-II diabetes mellitus is also investigated. The results show that

the flow features, including pressure drop cross the stenosis and the shear stress on

artery walls, are all influenced by these parameters; a systematic analysis is

conducted to derive information on graft design so as to minimize the possibility of

the restenosis in the host artery with bypass graft implantation.

Bio Transport

Phenomena A novel process for replication of

electroforming micromolds for use

in high aspect ratio micropart

fabrication is being studied in

collaboration with Sandia National

Laboratories. A combined

computational and experimental study

on the fundamental phenomena

governing the fabrication process is

used to systematically elucidate the

effects of the various process, material,

and geometric parameters, including

the interactive effects of uncertainty

inherent in the materials and the

process toward predicting the resulting

process variability and the micropart

quality. Optimum processing conditions

are derived for robust and reliable

processing.

Microfabrication

Programs in the area of energy focus on fuel cells, hybrid systems,

photovoltaics and thermal energy storage. The projects on fuel cells are

aimed at designing the cell and the systems for uniformity of current density

through optimal design of the operating conditions as well as through novel

material designs such as graded material microarchitectures. Passive air-

breathing fuel cell designs are developed for reduced system complexity and

novel microfuel cells that combine microfabrication and fuel cell technologies

are investigated for micropower generation at high power density. Transient

operation of fuel cells and fuel cell/battery and fuel cell/gasoline hybrid

systems are also being investigated to design systems for tracking varying

power requirements in different applications. Research on photovoltaics is

on understanding the fundamentals of dye-sensitized solar cells (DSSC) or

Grätzel cells with a view to develop design maps for applications in different

terrestrial locations. Thermal energy storage technologies based on phase

change materials are being developed for concentrating solar power systems.

The novel approach involves embedding thermosyphons or heat pipes to reduce

the resistance to heat transfer between the location where phase change occurs

and the working fluid of the power cycle.

Energy

As microsystem technologies and

application prospects continue to grow,

it is of interest to fabricate high aspect

ratio microstructures from a broad

range of metals and ceramics. The

objective of the work is to investigate a

new technique based on capillary-

driven microcasting and curing of

an epoxy-based metallic or ceramic

nanoparticulate slurry into a sacrificial

plastic mold, and subsequent sintering

of the nanoparticulate ceramic or

metallic phase to form the micropart.

Fundamentals of microchannel filling,

nanoparticle settling during flow, and

nanoparticulate preform sintering are

investigated to arrive at operating

windows on slurry formulations, mold

design, mold filling parameters, and

sintering conditions so as to maximize

feature fidelity.

Advanced Materials and Technologies Laboratory

Blood Flow Through Stenosed Arteries with Complete Bypass

Atherosclerosis—the constriction of an artery

through plaque buildup—is a leading cause of

human mortality in developed countries. Bypass

surgery is used to improve blood flow around a

diseased artery.

The goal is to study blood flow in a stenosed

artery with bypass with the objective of

developing bypass design guidelines.

Bypass parameters were varied in a

computational simulation study to assess their

influence on the pressure drop and wall shear

stress

Anastomosis Angle: α, Anastomosis Length: L

Occlusion: 1Astenosis

Ahost

1d

D

2

r v 0

r v

r v p Ý

r v

r v T

Artery Carotid (D = 6 mm; 370

ml/min flux)

Coronary (D = 3 mm; 35

ml/min flux)

20%, 50%, 75% and 100%

15o, 30o, 45o, and 60o

L/D 4, 6 and 8

Carreau model:

Blood Rheology


L = 8D

Axial Velocity Profiles

45o = 75%

L = 4D

L = 6D

Carotid Artery

Coronary Artery

45o = 75% L 4D

Carotid Artery

Bypass Ratio

1.77

Bypass Ratio

1.61

Bypass Ratio

1.48


Axial Velocity Profiles in the Carotid Artery

= 20%

45o L = 4D

= 50%

= 75%

= 100%

= 15o

= 30o

= 45o

= 60o

75% L = 4D


Pressure Drop in the Carotid Artery


Minimum Wall Shear Stress in the Carotid ArteryM

inim

um

Wa

ll S

he

ar

Str

ess,

min

[Pa

]

Min

imum

Wall

Shea

r S

tress,

min

[Pa]

min


Bypass Design Plots

Carotid Artery

Coronary Artery

p po

p po

po 129.3Pa

p po

po 101.5Pa

p po

Carotid Artery

Coronary Artery

po is the pressure drop in a

healthy non-stenosed artery

without bypass


Bypass in Patients with Type 2 Diabetes Mellitus