Micro-Technologies for Implantable Strain Gauge Arrays

Anais Sahabian William C. Tang

Gloria Yang

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

Fabrication of Parylene-Based Strain Gauge

Taken from “Parylene-Based Strain Sensors for Bone”

Taken from “Parylene-Based Strain Sensors for Bone”

Thermal Distribution Simulation

Thermal Distribution: Cross-Sectional View

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.

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

PPy Deposition Setup

Silicon Wafer

Counter Electrode

Reference Electrode

After the Deposition

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.

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.

Compression Tests

A compression device was created to test the conductive properties of carbon black doped PDMS

Components of Setup

Stress vs. Strain Curve

Resistance vs. Strain Curve

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.

Future Work

Characterize PPy deposition parameters and resistivity change with strain.

Conduct compression tests to characterize carbon black doped PDMS.

Acknowledgements

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