Utility of FEM and FEAUtility of FEM and FEA Evaluate possible designs without Evaluate possible designs without

manufacturing a prototypemanufacturing a prototype

Augment experimental capabilitiesAugment experimental capabilities– timetime– moneymoney

Heart DiseaseHeart Disease 4 million patients in the U.S. are victims of 4 million patients in the U.S. are victims of

heart failure, and nearly 400,000 new cases heart failure, and nearly 400,000 new cases are diagnosed each yearare diagnosed each year

2,800 receive heart transplants2,800 receive heart transplants

Heart disease is the leading cause of death Heart disease is the leading cause of death and disability in the U.S.and disability in the U.S.

Arrow LionHeartTMArrow LionHeartTM LVAD (Left Ventricular LVAD (Left Ventricular

Assist Device)Assist Device)– electric pulsatile blood pumpelectric pulsatile blood pump– fully implanted in upper fully implanted in upper

abdomenabdomen– 70 cc volume70 cc volume

8 L/min at beat rate of 135 = stroke volume of 60 cc

IntroductionIntroduction

TitaniumPump Case

Pusher-plate

Poly(urethaneurea)Blood Sac

IntroductionIntroduction

Design goal: 2 yrs @50,000,000 cycles/yr Design goal: 2 yrs @50,000,000 cycles/yr = 100,000,000 cycles = 100,000,000 cycles

FEA used to evaluate various pump designs and FEA used to evaluate various pump designs and their effectiveness at reducing the material their effectiveness at reducing the material stresses stresses

Finite Element ModelFinite Element Model Axisymmetric Axisymmetric Pusherplate and pump case treated as rigidPusherplate and pump case treated as rigid 8-node continuum elements8-node continuum elements Blood sac : homogeneous, Blood sac : homogeneous,

hyperelastic (non-linear)hyperelastic (non-linear) Frictionless contactFrictionless contact

0

1

2

3

4

0 50 100Stain (%)

Str

ees

(Pa)

2.86 in

0.9 in

Finite Element ModelFinite Element Model

Boundary ConditionsBoundary Conditions

Internal pressure = 100 mm HgInternal pressure = 100 mm Hg Rigid pump case was fixed in spaceRigid pump case was fixed in space Pusherplate displaced 0.8 inches Pusherplate displaced 0.8 inches

– 30 increments 30 increments – simulating ejection stroke of pumpsimulating ejection stroke of pump

Parametric StudyParametric Study 3 different thickness sacs 3 different thickness sacs

((0.015, 0.02, 0.025 inches0.015, 0.02, 0.025 inches))

2 pump case designs 2 pump case designs (tapered, not tapered)(tapered, not tapered)

2 radii of curvature for 2 radii of curvature for sac (3/16 and 7/16 inch)sac (3/16 and 7/16 inch)

Total of 12 casesTotal of 12 cases

3/16 inch of stroke

3/8 inch of stroke end of stroke

Small radius (3/16 in), Tapered pump case

0

10

20

30

40

50

0 0.2 0.4 0.6 0.8Displacement of pusherplate (inches)

Max

. P

rin

. S

trai

n (

%)

thickness=0.015 in

thickness=0.02 in

thickness=0.025 in

1

23

4

0.015 in. thick sac

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8Displacement of pusherplate (inches)

Max

. Prin

cipa

l St

rain

(%)

small, tapered

small, not tapered

large, tapered

large,not tapered

05

101520253035404550

0.01 0.015 0.02 0.025 0.03Thickness of Sac (inches)

Pe

ak

Pri

n.

Str

ain

(%)

small, taperedsmall, no taperlarge, taperedlarge, no taper

0

50

100

150

200

250

300

0.01 0.015 0.02 0.025 0.03Thickness of Sac (inches)

Pe

ak

Pri

n.

Str

es

s (

ps

i)

small, taperedsmall, no taperlarge, taperedlarge, no taper

ConclusionsConclusions

Material stresses and strains are sensitive to the Material stresses and strains are sensitive to the thickness of the blood sacthickness of the blood sac

Radius of curvature has little influence on the Radius of curvature has little influence on the peak stress in the blood sac, however, it does peak stress in the blood sac, however, it does affect when the peak stress occurs during the affect when the peak stress occurs during the stroke cyclestroke cycle

ConclusionsConclusions

Tapering the pump case can significantly Tapering the pump case can significantly alter blood sac stresses alter blood sac stresses

All stresses and strains were much lower All stresses and strains were much lower than the yield stress and strain for poly than the yield stress and strain for poly (urethaneurea)(urethaneurea)

News Release News Release (Feb. 28th, 2001)(Feb. 28th, 2001)

First fully implantable First fully implantable heart assist device heart assist device implanted implanted

As of March 12As of March 12thth, , Arrow LionHeartTM Arrow LionHeartTM recipient is stable and recipient is stable and recovering as expectedrecovering as expected

Total Artificial HeartTotal Artificial Heart

Fit into chest cavity Fit into chest cavity – 50 cc50 cc

Develop a model to Develop a model to predict and minimize predict and minimize stresses in biomaterials, stresses in biomaterials, so that the durability of so that the durability of a reduced-size device is a reduced-size device is not adversely affected not adversely affected by pump scalingby pump scaling