Rehabilitation and assistance enabled by electrical motors

Over the last two decades, a number of soft robotic powered exosuits have been developed at the Harvard Biodesign Lab. These soft systems have demonstrated an ability to augment strength and reduce the level of loading experienced by the wearer. The exosuits use pneumatically actuated and electrical motor actuated systems. The pneumatic-driven exosuit is constructed using McKibben muscles which are attached to the exosuit using a virtual anchor technique (see Figure 2c) to assist hip, knee, and ankle movement [30]. The core device is lightweight and weighs 3.5 kg without peripherals.
An alternative actuation approach uses high-power electrical motors driving Bowden cables, which enables the development of untethered exosuits [50]. The exosuits used garment-like functional textile anchors that are worn around the waist and calf and Bowden cable-based mechanical power transmissions to generate assistive joint torques as a function of the paretic gait cycle, as shown in Figure 5. A force-based control system was developed for real-life exosuits, with wearable strain sensing elements for human walking and running motion measurements [51][52]. An investigation and evaluation of the first-generation multi-articular, portable, and fully autonomous soft exosuit was conducted by Asbeck et al [53]. The results showed that an exosuit can provide a net metabolic increase of 9.3%. A breakthrough in the development of a soft robotic powered exosuit for post-stroke patients was presented by Awad et al [54]. The overall mass of the exosuit was approximately 0.9 kg and the light exosuits can effectively reduce interlimb propulsion asymmetry, increase ankle dorsiflexion, and reduce the energy required during walking. The exosuits were able to function synchronously with a wearer’s paretic limb to facilitate an immediate 5.33 ± 0.91° increase in the paretic ankle’s swing phase dorsiflexion and a 11 ± 3% increase in the paretic limb’s generation of forward propulsion (P < 0.05). This resulted in a 20 ± 4% reduction in forward propulsion interlimb asymmetry and a 10 ± 3% reduction in the energy cost of walking, which is equivalent to a 32 ± 9% reduction in the metabolic burden associated with poststroke walking. To optimise device performance, Ding et al. optimised the control of a soft exosuit developed for hip assistance during walking using a human-in-the-loop Bayesian optimisation method [55]. When wearing the optimised exosuit, the metabolic energy can be reduced by 17.4 ± 3.2%, which showed a significant improvement of more than 60% on metabolic reduction compared with state-of-the-art hip assistive devices. The relationship between assistance magnitude from the exosuit, the metabolic cost during walking and the gait mechanics was investigated by Quinlivan et al. [56]. The results show that the net metabolic rate of walking decreased by 22.83 ± 3.17% at a maximum exosuit assistance. Soft exosuits driven by electrical motors have great potential to assist our daily activities and increase walking efficiency, as well as demonstrating future potential for rehabilitation applications. Such systems are lightweight, textile-based, untethered and have integrated sensing elements and controllers, which are ideal for applications related to mobility assistance.