On the design of a DEA-based device to pot entially assist lower leg disorders: an analytical and FEM investigation accounting for nonlinearities of the leg and device deformations

Abstract

BackgroundOne of the recommended treatments for disorders associated with the lower extremity venous insufficiency is the application of external mechanical compression. Compression stockings and elastic bandages are widely used for the purpose of compression therapy and are usually designed to exert a specified value or range of compression on the leg. However, the leg deforms under external compression, which can lead to undesirable variations in the amount of compression applied by the compression bandages. In this paper, the use of an active compression bandage (ACB), whose compression can be regulated through an electrical signal, is investigated. The ACB is based on the use of dielectric elastomer actuators. This paper specifically investigates, via both analytical and non-linear numerical simulations, the potential pressure the ACB can apply when the compliancy of the human leg is taken into account. The work underpins the need to account for the compressibility of the leg when designing compression garments for lower extremity venous insufficiency.MethodsA mathematical model is used to simulate the volumetric change of a calf when compressed. Suitable parameters for this calf model are selected from the literature where the calf, from ankle to knee, is divided into six different regions. An analytical electromechanical model of the ACB, which considers its compliancy as a function of its pre-stretch and electricity applied, is used to predict the ACB’s behavior. Based on these calf and ACB analytical models, a simulation is performed to investigate the interaction between the ACB and the human calf with and without an electrical stimulus applied to the ACB. This simulation is validated by non-linear analysis performed using a software based on the finite element method (FEM). In all simulations, the ACB’s elastomer is stretched to a value in the range between 140 and 220 % of its initial length.ResultsUsing data from the literature, the human calf model, which is examined in this work, has different compliancy in its different regions. For example, when a 28.5 mmHg (3.8 kPa) of external compression is applied to the entire calf, the ankle shows a 3.7 % of volume change whereas the knee region undergoes a 2.7 % of volume change. The paper presents the actual pressure in the different regions of the calf for different values of the ACB’s stretch ratio when it is either electrically activated or not activated, and when compliancy of the leg is either considered or not considered. For example, results of the performed simulation show that about 10 % variation in compression in the ankle region is expected when the ACB initially applies 6 kPa and the compressibility of the calf is first considered and then not considered. Such a variation reduces to 5 % when the initial pressure applied by the ACB reduced by half.ConclusionsComparison with non-linear FEM simulations show that the analytical models used in this work can closely estimate interaction between an active compression bandage and a human calf. In addi...

Intermittent Calf Compression Delays the Onset of Presyncope in Young Healthy Individuals

“…We envision that this device would rapidly (<1 s) engage, applying 4 pulses at 0-60 mmHg of pressure per minute (4 s on -11 s off). The device might utilize dielectric elastomer actuators (Pourazadi et al, 2015) or shape memory alloys (Moein and Menon, 2014;Moein et al, 2017) to enable intermittent compression, and would contain accelerometers, allowing compression to be activated during motionless standing and deactivated during ambulation (when the skeletal muscle pump helps offset hemodynamic deficits) or during sitting/supine postures (when orthostatic stress is negligible), incorporated into a comfortable and portable garment.…”

Flexible Actuators for Soft Robotics

“…Flexible actuators have been widely researched in the auxiliary medical field to achieve controllable compression. For instance, Pourazadi et al . designed an active compression bandage for lower extremity venous insufficiencies, which was based on dielectric elastomer actuators.…”

“…a) The calf and its several different regions to closely evaluate the interaction between an active compression bandage and the calf. Reproduced under the terms of the CC‐BY 4.0 License . Copyright 2015, The Authors.…”

Active Compression Bandage Made of Electroactive Elastomers

“…As mentioned above, prior to this work other investigators have reported on the use of DE actuators to develop active bandages [10], [11]. The peculiarities of the approach described here are: 1) two active layers were stacked together to increase the strength of the system; 2) the active layers were made of an acrylic elastomer film showing one of the highest electromechanical transduction performance, in terms of maximum achievable strains and stresses; 3) stiffening sticks were used to maximise actuation along the radial direction; 4) two thick and soft passive layers were used as interfaces with suitable properties in terms of mechanical compliance and electrical safety.…”

“…An alternative solution to address these issues comes from the use of Dielectric Elastomer (DE) actuators, which were proven to be effective for interacting with soft bodies [9]. In particular, their use for electro-mechanically active bandages was recently proposed [10], [11]. The device was conceived as a stretchable bandage consisting of a single layer of a silicone elastomer with compliant electrodes on both sides.…”