Full-field strain measurements on medical devices using digital image correlation: Considerations and practical...

Area of Science:

• Biomedical Engineering
• Materials Science
• Optical Metrology

Background:

• Direct stress and strain measurements are crucial for implantable medical device development.
• Current methods for acquiring such data on medical devices are limited.
• Optical Digital Image Correlation (DIC) offers a potential solution for full-field strain characterization.

Purpose of the Study:

• To investigate the feasibility of using optical DIC for strain measurement on medical devices.
• To evaluate various speckle pattern application techniques for DIC analysis.
• To demonstrate DIC's capability in revealing material behavior under load.

Main Methods:

• Investigated multiple speckle pattern application methods: aerosol painting, transfer papers, airbrushing (low/high pressure), graphite powder deposition, and microstamping.
• Performed comparative studies to assess speckle pattern quality at different scales (millimeter and sub-millimeter).
• Applied full-field DIC to measure strains on nitinol components (wire, Z-specimens, stent rings) under bending loads.

Main Results:

• High-pressure airbrushing produced superior millimeter-scale speckle patterns.
• Monodisperse graphite powder and microstamping yielded optimal sub-millimeter scale patterns.
• DIC successfully identified Lüders-like phase transformation bands in nitinol under bending.

Conclusions:

• Optical DIC is a feasible technique for direct strain measurement on medical devices across various scales.
• Specific speckling methods are optimal for different field-of-view requirements.
• This technique provides valuable data for device design, durability assessment, and computational modeling.