Design and development of a soft brace for active correction of spine scoliosis.

Scoliosis is an abnormality of the spinal curvature that severely affects the musculoskeletal, respiratory, and nervous systems. Conventionally, it is treated using rigid spinal braces. These braces are static, rigid, and passive in nature, and they (largely) limit the mobility of the spine, resulting in other spinal complexities. Moreover, these braces do not have precise control over how much force is being applied by them. Over-exertion of force may deteriorate the spinal condition. This research presents a novel active soft brace that allows mobility to the spine while applying controlled corrective forces. The brace uses elastic bands to apply forces in the form of elastic resistance. These forces are regulated by varying the tensions in elastic bands using low-power, lightweight, twisted string actuators (TSAs). Use of TSAs and the elastic bands significantly reduces the weight and power consumption of the device. This results in higher comfortability and longer wear time. To realize the brace concept a finite element analysis was carried out. A FE model of the patient’s trunk was created and validated with in-vitro study from literature. The brace model was installed on the simulated trunk to evaluate in-brace correction in both sagittal and coronal planes. The brace was evaluated under various load cases by simulating the actuator action. The research also focused on the protype development which include the actuator and contact forces modeling of the active soft brace (ASB). The actuator modeling is required to translate the twisting of string in terms of contraction of the string’s length, whereas the contact force modeling helps in estimating the net resultant force exerted by the band on the body using single point pressure/force sensors. The actuators (TSAs) are modeled as helix geometry and numerical estimation was validated using a laser position sensor. The results showed that the model effectively tracked the position (contraction in length) with root mean square error (RMSE) of 1.7386 mm. The contact force is modeled using the belt and pulley contact model and validated by building a custom testbed. The actuator module is able to regulate the pressure in the range 0–6 Kpa, which is comparable to 0–8 Kpa pressure regulated in rigid braces. This makes it possible to verify and demonstrate the working principle of the proposed active soft brace. The use of stretch sensor to measure the stretch(tension) in the elastic bands is a crucial part of the brace. It is used as feedback to control the tension in the elastic bands using twisted string actuators. A few, fabric and silicon-based stretch sensors are analyzed to pick a suitable candidate for the active soft brace application. Two control modes were designed to control the amount of force being exerted by the brace. One using pressure sensors as feedback to keep the contact pressure at desired setpoint. Second mode using the stretch sensor to keep the tension in the bands at a desired setpoint. The active soft brace modules (TSA actuator, bands and stretch sensors, controller) were integrated and validated on the mannequin. This research concludes the preliminary part of conceptual design, construction, and validation of the demonstrator prototype, before going into the clinical trials. Clinical trials take longer duration to evaluate the effectiveness of the brace on real patients and were out of the scope of the project.