Search for: All records

In the world of soft-robotic medical devices, there is a growing need for low profile, non-rigid, and lower power actuators for soft exoskeletons and dynamic compression garments. Advanced compression garments with integrated shape memory materials have been developed recently to alleviate the functional and usability limitations associated with traditional compression garments. These advanced garments use contractile shape memory alloy (SMA) coil actuators to produce dynamic compression on the body through selective heating of the SMA material. While these garments can create spatially- and temporally-controllable compression, typical SMA materials (e.g., 70°C Flexinol) consume considerable power and require considerable thermal insulation to protect the wearer during the heating phase of the SMA actuation. Alternative SMA materials (e.g., NiTi #8 by Fort Wayne Metals, Inc.) transform below room temperature and do so using no applied electrical power and generate no waste heat. However, these materials are challenging to dynamically control and require active refrigeration to reset to material. In theory, low-temperature SMA actuators made from materials like NiTi #8 may maintain additional dynamic actuation capacity once equilibrated to room temperature (i.e., the material may not fully transform), as the SMA phase transformation temperature window expands when the material experiences applied stress. This paper investigates this possibility: we manufactured and tested low-temperature NiTi coil actuators to determine the magnitude of the additional force that can be generated via Joule heating once the material has equilibrated to room temperature. SMA spring actuators made from NiTi #8 consumed 84% less power and stabilized at significantly lower temperatures (26.0°C vs. 41.2°C) than SMA springs made from 70°C Flexinol, when actuated at identically fixed displacements (100% nominal strain) and when driven to produce equal forces (∼3.35N). This demonstration of low-power, minimal-heat exposure SMA actuation holds promise for many future wearable actuation applications, including dynamic compression garments.

 

Many medical conditions, including sensory processing disorder (SPD), employ compression therapy as a form of treatment. SPD patients often wear weighted or elastic vests to produce compression on the body, which have been shown to have a calming effect on the wearer. Recent advances in compression garment technology incorporate active materials to produce dynamic, low bulk compression garments that can be remotely controlled. In this study, an active compression vest using shape memory alloy (SMA) spring actuators was developed to produce up to 52.5 mmHg compression on a child's torso for SPD applications. The vest prototype incorporated 16 SMA spring actuators (1.25 mm diameter, spring index = 3) that constrict when heated, producing large forces and displacements that can be controlled via an applied current. When power was applied (up to 43.8 W), the prototype vest generated increasing magnitudes of pressure (up to 37.6 mmHg, spatially averaged across the front of the torso) on a representative child-sized form. The average pressure generated was measured up to 71.6% of the modeled pressure, and spatial pressure nonuniformities were observed that can be traced to specific garment architectural features. Although there is no consistent standard in magnitude or distribution of applied force in compression therapy garments, it is clear from comparative benchmarks that the compression produced by this garment exceeds the demands of the target application. This study demonstrates the viability of SMA-based compression garments as an enabling technology for enhancing SPD (and other compression-based) treatment. 

This study explores efficient methods for production of customizable heated textiles. An electrical heating system using the Liberator40® conductive fiber, stitched in a serpentine pattern on stretch knit fabrics, was employed. Parameters including thread layers, pattern sizes, and different fiber-based substrates and covering were compared when analyzing resistance and temperature output. Results indicated that covered knit fabrics stitched with a 0.4cm serpentine spacing produced the most efficient measure of temperature.