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

Active-contracting fabrics are a developing innovation that could revolutionize compression garment technology, notably aerospace orthostatic intolerance garments (OIG), by contracting on demand. Traditional fabric structures exhibit surface-wide distributed and/or functionally graded contractile actuation through the integration of materials with shape memory (SM) properties. Prior research has found that active-contracting fabrics, specifically weft knit garter fabric architectures constructed with shape memory alloy (SMA) filaments, can apply 8-30 mmHg on the body (single-layer construction) or 15-65 mmHg (double layer construction), depending on body radius (i.e. average ankle girth, SizeUSA women; average torso girth, SizeUSA men). Prior garment prototyping and performance validation efforts have been conducted with commercially available Flexinol wire with an actuation finish temperature of 90°C, a temperature that is not appropriate proximal to the human body. While other chemistries of SMA having lower actuation temperatures commonly used for medical devices inside the human body (T ≈ 37°C) are available, SMA material is currently not designed specifically for actuation control against the human skin (T ≈ 31°C). This research characterizes and validates a novel SMA material designed in collaboration with Fort Wayne Metals specifically for actuation adjacent to the surface of the body. Through traditional SMA material testing paired with experimental temperature-force-displacement testing, we present data validating material functionality in the design of a future OIG. The manuscript presents evidence for a future OIG that is donned in an oversized and compliant state, heated momentarily above ambient skin temperature to initiate actuation, and remains actuated post-applied heat indefinitely. The result is an OIG that requires almost no operating power that could be doffed through zipper releases and placed in a sub-zero chamber to return to the “off” state before reuse. Preliminary findings will be presented to characterize the performance of the material in future aerospace compression systems.