Effect of the Leg Volume Change on the Performance of an Active Compression Brace Based on Shape Memory Alloys

Abstract

In this paper, the effect of calf deformation on the performance of an active compression brace (ACB) due to external pressure is investigated experimentally and analytically. The ACB, actuated by shape memory alloy wires, was designed and prototyped for potentially being used in future clinical studies to prevent or mitigate symptoms of lower extremity disorders. In this work, an analytical model is presented to simulate the ACB when wrapped around a calf assumed to be either incompressible or compressible. Furthermore, a physical calf model synced with a controllable syringe pump with a LabVIEW code was used to perform cyclic tests to evaluate the performance of the ACB experimentally in both cases of having a simplified incompressible calf or, more realistically, a compressible calf. The collected experimental data was compared with simulation results obtained from the analytical model. The experimental results showed a significant drop in the actuation pressure produced by the ACB on a deformable calf model compared to an incompressible calf model. The analytical model that was developed accurately predicted such a behavior. In fact, for an initial wrapping pressure of 10 mmHg the maximum deviations between the experimental and analytical results were 1.66 and 0.54 mmHg respectively for the cases of an incompressible and compressible calf. Similarly, for the initial wrapping pressure of 15 mmHg the maximum deviations were found to be 0.52 and 0.73 mmHg respectively. A two-dimensional finite element (FE) model of the leg was also developed to investigate the effect of the applied external pressure on the internal tissue. FE analyses were conducted using different geometrical parameters of the leg including calf, tibia and fibula sizes.