According to the National Center for Biotechnology Information, approximately 60% of community dwelling subjects aged 80 or above experience gait disorder. Common causes of gait disorders are osteoarthritis in the hip and knee, as well as achilles tendon tears and injury to other cartilage, tendons or ligaments in the knee, hip, or ankle. These injuries put stress on the quadricep, the muscle that extends the knee and is responsible for support of the knee and forward propulsion of the knee during gait. In healthy knee locomotion, knee extension assistance can help reduce fatigue and risk of knee related injuries. Passive orthotics —generally used in clinics— are limited in how they assist the knee. Knee-ankle-foot-orthoses (KAFO), lower extremity orthotics that are used to control instabilities in the knee, create an uncomfortable and aesthetically unpleasing gait due to the rigid locking and unlocking mechanism of the device. The unnatural locking and unlocking process has inspired research and development to create a lightweight, non-restrictive knee assistant to replace KAFOs, insert a combination knee and hip exoskeleton.
To address some of these needs, Professor Walsh's Research Group at Harvard has explored exosuits -- technological orthotics designed to remedy gait disorder. The exosuit provides knee extension assistance by tensioning a bowden cable that crosses in front of the knee. The cable is connected to the body by a semi-rigid wrap around the thigh and and a calf wrap, and when the cable retracts, the two wraps pull closer together, causing the knee to extend. The calf-part of the exosuit is made of a cushioning base layer and a wrap that attaches to the cushion and is tightened using two adjustment dials.The frame is made of hollow carbon fiber tubing and other plastic components. The thigh part of the exosuit is a flexible plastic material and a textile wrap connected to a waist belt through a webbing strap connected to the hip. This exosuit was designed to be able to fit any wearer regardless of waist circumference, thigh size, or any other factors: because of this goal, all parts of the exosuit are highly adjustable and comfortable for users of all different shapes and sizes.
The exosuit is connected to an offboard cart with power actuation and control hardware. The mechanical power of the suit is created using a custom actuation unit made of two brushless DC motors. The actuation unit also includes a custom electronics board with built-in low-level firmware protections and a servomotor driver that tracks a velocity command.
The exosuit was tested using six healthy individuals with no musculoskeletal injuries. Each participant came in for two visits on separate days. On both days, each individual walked at a comfortable speed on a 10 degree decline and incline in order to increase loading on the knee while not fatiguing the participant. On the 10 degree decline, the total average negative knee biological power was decreased by about 11.4% on the right side, and it decreased by about 6.73% on the left. The total average positive knee biological power decreased by about 9.7% on the right side and about 6.67% on the left. On the 10 degree incline, the total average positive knee biological power decreased by about 17.5% on the left side and about 23.2% on the right. These responses varied greatly depending on the participant and that may be because instead of reducing quadricep usage, some participants may have changed their walking pattern to adjust to the exosuit.
Prior to this research, I was not familiar with exosuits. I find this topic extremely interesting and I believe mechanisms like the exosuits can have a great impact on society. In the future, I envision an even smaller lightweight apparatus used by athletes and elderly alike to prevent injury and eliminate gate disorders.
Park et al.(2020 May). A Hinge-Free, Non-Restrictive, Lightweight Tethered Exosuit for Knee Extension Assistance During Walking. Harvard Library, 2.
Comments