Design and Control of Reduced Power Actuation for Active-Contracting Orthostatic Intolerance Garments

Area of Science:

• Materials Science
• Biomedical Engineering
• Aerospace Engineering

Background:

• Active-contracting fabrics, particularly those using shape memory alloy (SMA) filaments, show promise for aerospace compression garments like orthostatic intolerance garments (OIG).
• Previous SMA applications used high actuation temperatures (90°C), unsuitable for direct skin contact (approx. 31°C).
• Existing medical-grade SMAs operate at core body temperatures (approx. 37°C), not optimized for surface skin application.

Purpose of the Study:

• To characterize and validate a novel SMA material designed for actuation adjacent to human skin.
• To explore SMA knitted actuator configurations for improved performance and reduced power consumption in OIGs.

Main Methods:

• Experimental temperature-force-displacement testing was performed on Dynalloy Flexinol® and Fort Wayne Metals SMA wires.
• SMA knitted actuator configurations were tested to evaluate performance differences.
• Characterization focused on low-temperature, nickel-rich SMA versus high-temperature, titanium-rich SMA.

Main Results:

• Certain SMA knitted actuator structures negate performance differences between low- and high-temperature SMAs.
• Some SMA knitted actuator configurations exhibit increased force upon cooling, enabling novel actuation control.
• The novel SMA material is suitable for actuation adjacent to the skin surface.

Conclusions:

• A novel SMA material and knitted actuator designs enable effective OIG function at skin-compatible temperatures.
• Future OIGs can be donned in a relaxed state, activated by brief heating, and maintain actuation via skin temperature equilibration.
• This approach minimizes power consumption and waste heat, allowing for low-power operation and easy doffing.