1. Micro-Technologies for Implantable Strain Gauge Arrays
Anais Sahabian
William C. Tang
Gloria Yang

2. Implantable Bone Strain Gauges
Advantages:
Better understanding of types of strain bones undergo when affected by conditions such as osteoporosis or a tumor
Better understanding of the musculoskeletal system
Help create better orthopedic implants

3. Fabrication of Parylene-Based Strain Gauge
Taken from “Parylene-Based Strain Sensors for Bone”
Taken from “Parylene-Based Strain Sensors for Bone”

4. Thermal Distribution Simulation

5. Thermal Distribution: Cross-Sectional View

6. Results
The results were used as a qualitative analysis as opposed to a quantitative one. The simulation could not be done using the actual size of the device because of the lack of memory needed to compute the solutions.
In the real strain gauge, the gold is actually 9 times thinner and the current applied is magnitudes smaller. This means that the strain gauge will only slightly increase in temperature and the tissue and bone surrounding the parylene C will not feel the heat from the gold strain gauge.

7. Polypyrrole Deposition
Polypyrrole (PPy) is a naturally conductive polymer
Its conductivity changes with strain
Goal: To understand PPy properties so we can make a strain gauge using polypyrrole as the sensing mechanism

8. PPy Deposition Setup Reference Electrode Silicon Wafer
Counter Electrode

9. After the Deposition

10. Preliminary Results
After measuring the thicknesses of the PPy-coated wafers a correlation can be seen between amount of current applied and the thickness of the wafer.
Specifically, as the current increases the thickness of PPy deposited onto the wafer increases.
This correlation must be tested further to better understand exactly what currents give rise to certain thickness.

11. Carbon Black Doped PDMS
PDMS is not naturally conductive, while carbon black is.
When the two are mixed together the PDMS becomes conductive.
This is useful because it can be used as the sensing mechanism in strain gauges.

12. Compression Tests
A compression device was created to test the conductive properties of carbon black doped PDMS

13. Components of Setup

14. Stress vs. Strain Curve

15. Resistance vs. Strain Curve

16. Preliminary Results
As expected, when strain increases, the resistance of the PDMS decreases.
This shows that carbon black doped PDMS is sensitive enough to be used in a strain gauge.
The PDMS piece might become deformed after the first cycle, which would explain the decrease in resistance after each cycle.

17. Future Work
Characterize PPy deposition parameters and resistivity change with strain.
Conduct compression tests to characterize carbon black doped PDMS.

18. Acknowledgements National Science Foundation and UROP
Prof. William C. Tang
Gloria Yang
IM-SURE Fellows
Said Shokair