A New Portable Device for Acute Ankle Rehabilitation with SMA-Based Actuation

The physical rehabilitation of the lower limb after brain damage is very important because it is connected to the possibility of recovering an effective gait. The need for an initial stabilisation of the patients’ general conditions often leads to postponing the start of that process until the patients can be moved from their beds, but such a delay can have adverse effects in the development of disabling sequelae, e.g. muscular contracture, and hypertone.

A new device was developed to allow early passive ankle mobilisation. It is based on a specially-designed SMA-based actuator, which endows the apparatus with light weight, portability, and ultimately the characteristics for a safe use by bed-ridden individuals.

The actuator is composed of a quadruple arrangement of 0.25mm NiTi wires. Those wires are electrically connected in series two-by-two, but produce a total force of four (max. 30N) by pulling in parallel. The actuator is powered from the mains via a transformer/rectifier (56Vdc) lodged within the ankle device case. The device is being tested in the clinical environment and is very well accepted by both the patients and their therapists.