Subash, Niharikha

Abstract On-body compressive therapy is an essential treatment for a variety of health conditions. Traditional compression methods like pneumatics and knit stockings offer quality compression, but present issues with user experience (donning/doffing challenges or bulk/mass issues). This paper covers two studies related to active compression stockings, which utilize knitted shape memory alloy (SMA) wire to produce dynamic compression forces on the body. When these SMA knit panels are heated with an at-home heating pad, the knit contracts and creates dynamic compression. The first study characterizes the forces produced on the body by a new iteration of an SMA knit stocking. The second study compares two versions of the SMA knit garment with a commercially available knit compression garment. The results show that SMA knit compression garments are able to produce medical grade compression on the body, but that sizing and material properties can greatly impact the forces produced. In a comparison of different compression stockings, the user experience of the SMA compression garment was preferred over the alternative garments. Overall, the potential of SMA knit compression is further highlighted, with a clear need for further development to ensure consistent medical grade compression.

Abstract Advancements in the design of knitted Shape Memory Alloy (SMA) actuators have produced highly functional and easy-to-wear advanced textiles with variable fit/stiffness properties. Annealing SMA at high temperatures can alter their thermomechanical properties; however, heat treatments of SMA knitted actuators have yet to be systematically studied. This study investigates the relationship between annealing temperatures and the resultant SMA knit thermomechanical behavior (maximum force and actuator transformation temperature). Twelve SMA knitted samples were manufactured using Dynalloy Flexinol® 70°C (0.012″). Nine samples were annealed at three different temperatures (350°C, 450°C, 550°C), with the remaining samples acting as controls. The blocked force mechanical performance was characterized by varying the thermal load across various applied structural strains. The samples were thermally cycled between 20°C and 90°C at each strain level. The results indicate that samples annealed while stretched along the knit-course direction enabled large-force actuation at smaller displacements than the control samples. Annealed samples showed higher peak force than control samples as annealing temperature increased until the 450°C condition; however, the 550° samples showed a dip in force. The actuator transformation temperatures showed reduced Austenite start (As) temperature compared to the control sample, enabling actuation at a lower temperature while also reducing the Martensite Finish (Mf) temperatures. This work allows for greater tuning of knitted SMA actuators to meet the needs of researchers and product developers.