Simulation and Experimental Studies of Biomechanics at the Micro-Scale

1. 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

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

3. 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

4. Device Designs Cantilever Beam: Heart Valve Strain Gauge: Bone Photos Courtesy of Gloria Yang

5. My Role in the Project • Heart Valve Investigation • Use COMSOL to find the values of the spring constant, k, and resonant frequency, ω, of our device • Use a probe station to characterize the device • Characterize the effects of adhesives on heart valves • Use our device to find the compliance over the surface of the heart valve tissue

6. My Role, Cont. • Bone Investigation • Use COMSOL to model heat transfer of a device to surrounding tissue • Work Applicable to Both Projects • Research adhesives • Biocompatibility, faithful transmission of surface tension to sensor, etc • Ethicon: Johnson & JohnsonMicrovalBD HealthsciencesCryolife

7. Edwards Lifesciences • Learned about prosthetics • Use their bovine pericardium valves • Use their equipment to test adhesion effects Carpentier-Edwards PERIMOUNT Pericardial Bioprosthesis Aortic Model 2700

8. Example of COMSOL Simulation—Cantilever

9. Example of Physical Data

10. Example of COMSOL Simulation—Heat Transfer

11. 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

12. 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.

13. 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, changing technique

14. Results, Cont. • Heat Transfer Modeling • Have the model completed, working to apply boundary conditions • Adhesive Testing • Currently monitoring Dermabond on foam block

15. 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

16. 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

17. 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