Simulation and Experimental Studies of Biomechanics at

the Micro-Scale

Elizabeth Nettleton, Undergraduate: Chemistry, University of South Dakota

IM SURE Fellow, 2006

Dr. William C. Tang, Professor and Mentor: Biomedical Engineering,

University of California, Irvine Gloria Yang, Graduate Student:

Electrical Engineering, University of California, Irvine

Outline• The Work of the Tang Lab• My Role in the Project• My Work• Results• Conclusion• Acknowledgements

The Big Picture—My Lab’s Goals

• Heart Valve– Prosthetic valves weaken over time– Use a sensor to provide measurements of

strain within a valve • Bone Strain

– Bone tumors and osteoporosis lead to a decrease in skeletal density

– Monitoring bone strain could track skeletal remodeling and disease progression

Device Designs

Cantilever Beam: Heart Valve Strain Gauge: Bone

Photos Courtesy of Gloria Yang

My Role in the Project

• Heart Valve Investigation– Use COMSOL to find the values of the spring consta

nt, k, and resonant frequency, ω, of our device– Use a probe station to characterize the device– Characterize the effects of adhesives on heart valve

s – Use our device to find the compliance over the surf

ace of the heart valve tissue

My Role, Cont.

• Bone Investigation– Use COMSOL to model heat transfer of a device to s

urrounding tissue• Work Applicable to Both Projects

– Research adhesives• Biocompatibility, faithful transmission of surface tension t

o sensor, etc• Ethicon: Johnson & Johnson

MicrovalBD HealthsciencesCryolife

Edwards Lifesciences

• Learned about prosthetics

• Use their bovine pericardium valves

• Use their equipment to test adhesion effectsCarpentier-Edwards PERIMOUNT Pericardi

al Bioprosthesis Aortic Model 2700

Example of COMSOL Simulation—Cantilever

Example of Physical DataB4-Delta R (MM)

y = 2.160E-04x

y = 2.333E-04x

y = 2.417E-04x

y = 2.149E-04x

y = 2.210E-04x

y = 2.196E-04x

y = 2.263E-04x

y = 2.005E-04x

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 50 100 150 200 250 300

Displacement (micrometers)

Del

ta R

(o

hm

s)

Linear (Trial One) Linear (Trial Two) Linear (Trial Three) Linear (Trial Four)

Linear (Trial Five) Linear (Trial Six) Linear (Trial Seven) Linear (Trial Eight)

Example of COMSOL Simulation—Heat Transfer

Dermabond—Adhesive • Manufactured by

Ethicon, a Johnson & Johnson Company

• Attached sensor prototype to a foam block simulating the skin’s surface

• In the process of monitoring adhesive properties for seven days

Results

• Cantilever Modeling– Spring Constants

• COMSOL vs. Theoretical Values: Percent Difference for each length <1.32%

– Resonant Frequencies: forthcoming?– As of yet, our simulations have not been

successful. We have no data to compare to the theoretical values.

Results, Cont.

• Probe Station—Device Characterization– Multimeter vs. Wheatstone Bridge

• Graphed resistance changes vs. probe displacement• Results similar for both• Data best when lines of best fit forced through zero• Multimeter-lower standard deviation• Repeating Wheatstone bridge measurements, changin

g technique

Results, Cont.

– Heat Transfer Modeling– Have the model completed, working to appl

y boundary conditions– Adhesive Testing

– Currently monitoring Dermabond on foam block

Conclusions• What I’ve achieved:

– Providing theoretical data for the spring constant of our device

– Characterizing the device—its changing resistance with changing deflection

• I’ve also provided initial data on:– Modeling the resonant frequency of our

device– Modeling the heat transfer in an implanted

device– Monitoring the adhesion of Dermabond

Conclusions, Cont.

• Future Work– Currently the heart valve project is

focused on prosthetic valves– Eventually, apply research to living

heart valves, in vivo• Real-Time measurements• Wireless Communication System

Acknowledgements

• I would like to thank the following people and organizations for making this experience possible:– My mentor, William C. Tang– My graduate student, Gloria Yang– The Tang Lab, as a whole– UROP and the IM-SURE Program– National Science Foundation