Technical developments of functional electrical stimulation to correct drop foot: Sensing, actuation and control strategies

•Functional electrical stimulation enables restoration of lost motor functions.•Drop foot individuals have benefited from such neuroprostheses over the years.•Open- and closed-loop control architectures to correct drop foot are discussed.•Muscles' response to electrical stimulation is nonlinear, time-varying and highly coupled.•Model-based closed-loop architectures provide enhanced performance and robustness.

This work presents a review on the technological advancements over the last decades of functional electrical stimulation based neuroprostheses to correct drop foot. Functional electrical stimulation is a technique that has been put into practice for several years now, and has been shown to functionally restore and rehabilitate individuals with movement disorders, such as stroke, multiple sclerosis and traumatic brain injury, among others. The purpose of this technical review is to bring together information from a variety of sources and shed light on the field's most important challenges, to help in identifying new research directions. The review covers the main causes of drop foot and its associated gait implications, along with several functional electrical stimulation-based neuroprostheses used to correct it, developed within academia and currently available in the market. These systems are thoroughly analyzed and discussed with particular emphasis on actuation, sensing and control of open- and closed-loop architectures. In the last part of this work, recommendations on future research directions are suggested.