Strategic Research Program 17 (VUB Funding)

Amputation; Traumatic, Limb, Lower, Prosthesis User

AMPfoot, Prosthetics, gait, electro-encephalography, dual-task walking

Objectives: The main objectives are to determine neural dynamics during gait using electro-encephalography as well as brain sources and to investigate the attentional demand during walking in able-bodied individuals, and individuals with an amputation. Materials & Methods: 6 able-bodied individuals conducted one experimental trial, and 6 unilateral transtibial and 6 unilateral transfemoral amputees performed 2 experimental trials; the first with the current and the second with a novel powered transtibial prosthesis, i.e. the Ankle Mimicking Prosthetic foot 4.0. Each experimental trial comprised 2 walking tasks; 6 and 2min treadmill walking at normal speed interspersed by 5min of rest. During 6min walking the sustained attention to response (go-no go) task, with measures reaction time and accuracy, was performed. Electro-encephalographic (EEG) data were gathered when subjects walked 2min. Motor-related cortical potentials and brain activity during gait are extracted using EEG.

Detailed description of the novel device: The device mainly distinguishes itself from commercial prostheses thanks to its new type of actuation providing a compact and energy efficient solution to the challenge of ankle-foot actuation. This new actuation method consists of using springs, a servo motor and a locking mechanism, coupled with a sensory network providing intelligence to the robotic device. The AMPfoot 4.0 design is also based on previous research conducted on the AMP-Foot 2. However, it is important to note that in contrast with its preceding designs, the AMP-Foot 4.0 does not provide active propulsion at push-off. During walking, the AMP-Foot 4.0 working principle is divided into two main logic sequences, i.e. the stance and the swing phase. These two phases are detected by analyzing gyroscope and acceleration measurements from an Inertial Measurement Unit chip. During the stance phase, the ankle performs a dorsi-flexing movement while a plantar-flexing torque is applied at the ankle. The person's gravitational potential energy is stored into elastic potential energy by means of the used spring. It is this spring that provides the plantar-flexing torque required at the ankle as reaction to the movement of the user. Due to the use of a locking system, the prosthesis can adapt its so-called zero torque rest point depending on the slope or stride length of the user. This provides adaptability and therefore greater comfort compared to prostheses with a fixed zero torque rest point. During the swing phase, the locking mechanism unlocks to free the ankle movement. Parallel springs external to the stance system are then activated to reset the foot to its initial position. From that moment, the device is ready for a new step.

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Belgium