# Portable Ankle Robotics to Reverse Foot Drop After Stroke.

> **NIH NIH U44** · NEXTSTEP ROBOTICS, LLC · 2021 · $1,473,428

## Abstract

This proposal finalizes the design of a portable ankle robot as a therapeutic device to reverse foot drop and restore safer
independent walking after stroke, then conducts a rigorous randomized clinical trial to establish clinical proof for this new
market application. Currently, there are no therapeutic solutions for foot-drop, only assistive devices (braces, canes,
electrical stimulation) that don't reverse the underlying ankle deficits. In contrast to arm robotics, lower extremity robotics
have been largely unsuccessful in stroke patients to date, we posit because they do not emphasize volitional engagment for
mediating motor learning. We pioneered modular ankle robotics technology, enabling human-robotics cooperative
learning utilizing impedance control for deficit severity adjusted assist-as-needed in conjunction with adaptive control for
precise timing of assistance to sub-events across the gait cycle. Our five positive clinical studies using this tethered
research device show hemiparetic ankle motor learning that translates into improved over-ground gait. Most importantly,
our randomized study shows that 18 sessions of ankle robotics integrated treadmill training (but not seated robot training)
durably reverses foot drop, restores paretic leg propulsion, and promotes safer heel-first foot landing during unassisted
walking, enabling 85% to self-discard their ankle braces or switch to a less dependent assistive device. Inspired by our
findings that ankle robot mediated functional motor learning is most effectively conducted in the context of locomotor
task-oriented training, we pursue finalization of a lighter weight and ergonomic portable ankle robot (AMBLE) that
meets portability and clinical usability standards for untethered wear into regular mobility focused physical therapy (PT).
Phase I produces a commercial portable ankle robot with desired portability (device mass, battery life); hardware design
(FDA freeze)-microcontroller software (FDA compliant); and adequate clinical usability (client-therapist performance
report card, auto-adjustable assistance) that meets key safety, stability, and comfort metrics (don-disengage time,
slippage, part failure, skin abrasions/irritations) during over-ground walking and mobility tasks for full integration into
physical therapy. Commercial units meeting FDA requirements will reach design freeze the first year (Phase 1); feasibility
of which is supported by our precedent battery operated version already showing proof-of-function in stroke patients.
Using AMBLE as a therapeutic device, optimized by the robot's intrinsic measurement capacities, we shift the robotics
rehabilitation paradigm beyond repetitive robot guided exercise task practice, toward immersive PT integrated robotics
(PTR). Phase II (3-yrs) is a blinded, randomized clinical trial investigating the hypothesis that 9 weeks (18 sessions) of
PTR is more effective than PT alone to reverse foot drop as assessed by gait biomechanics (ankle an...

## Key facts

- **NIH application ID:** 10372555
- **Project number:** 4U44NS111076-02
- **Recipient organization:** NEXTSTEP ROBOTICS, LLC
- **Principal Investigator:** Bradley Hennessie
- **Activity code:** U44 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $1,473,428
- **Award type:** 4N
- **Project period:** 2021-05-01 → 2025-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10372555

## Citation

> US National Institutes of Health, RePORTER application 10372555, Portable Ankle Robotics to Reverse Foot Drop After Stroke. (4U44NS111076-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10372555. Licensed CC0.

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