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 ValveStrain Gauge: Bone Photos Courtesy of Gloria Yang

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

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 & Johnson Microval BD Healthsciences Cryolife

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

Example of COMSOL Simulation—Cantilever

Example of Physical Data

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, changing technique

Results, Cont. –Heat Transfer Modeling –Have the model completed, working to apply 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