Research ArticleNEUROREHABILITATION

A soft robotic exosuit improves walking in patients after stroke

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Science Translational Medicine  26 Jul 2017:
Vol. 9, Issue 400, eaai9084
DOI: 10.1126/scitranslmed.aai9084
  • Fig. 1. Overview of a soft wearable robot (exosuit) designed to augment paretic limb function during hemiparetic walking.

    Exosuits (A) use garment-like functional textile anchors worn around the waist and calf (B) and Bowden cable-based mechanical power transmissions to generate assistive joint torques as a function of the paretic gait cycle (C). Integrated sensors (load cells and gyroscopes) are used to detect gait events and in a cable position–based force controller that modulates force delivery. The contractile elements of the exosuit are the Bowden cables located posterior and anterior to the ankle joint. Exosuit-generated PF and DF forces are designed to restore the paretic limb’s contribution to forward propulsion (GRF) and ground clearance (ankle DF angle during swing phase)—subtasks of walking that are impaired after stroke. Poststroke deficits in these variables are demonstrated through a comparison of paretic (black) and nonparetic (gray) limbs. Means across participants are presented (n = 7).

  • Fig. 2. Illustration of experimental setup.

    Ground reaction force and kinematic data were collected concurrently with metabolic data as participants walked on an instrumented treadmill with the exosuit worn either powered (delivering forces generated by an off-board actuation unit) or unpowered. Participants were harnessed, but no body weight was supported. Participants were allowed to hold a side-mounted handrail if necessary for safety.

  • Fig. 3. Exosuit-induced changes in poststroke gait mechanics and energetics.

    Changes in (A) peak paretic ankle DF angle during swing phase (n = 9; P < 0.001, paired t test), (B) interlimb propulsion asymmetry (perfect symmetry = 0%; n = 7; P = 0.002, paired t test), and (C) walking economy (normal walking economy = 0%; n = 7; P = 0.009, paired t test) during walking with the exosuit powered versus unpowered. Relationship between (D) relative changes (%Δ) in propulsion symmetry and walking economy (correlation: n = 7, P = 0.001) and (E) participants’ usual walking speed and relative change in propulsion symmetry (correlation: n = 7, P = 0.03). Means and SE are presented in (A) to (C). *P < 0.05.

  • Fig. 4. Overview and assessment of exosuit controller.

    (A) Commanded position trajectories (blue) translate to exosuit-generated forces (red) based on the exosuit-human series stiffness. This parameter reflects the interaction of the cable position command with the compliance inherent to the textiles, cables, and human tissue. On a step-by-step basis, the timing of exosuit-generated force delivery is controlled as a function of gait subphases identified using shoe-mounted gyroscope sensors (GY). The amplitude of force produced by the exosuit is measured by load cells (LC) that measure the force delivered at the ankle—one for each PF and DF (only PF is shown). The delivered force is continuously monitored, and adjustments are made by the controller to maintain specific features of the delivered force profile. (B) Average exosuit-generated PF forces as a function of the paretic gait cycle (x axis). Two ankle PF force delivery onset timings were evaluated. PF forces were delivered during terminal stance or about 10% earlier in the paretic gait cycle, during midstance. (C) Variability in commanded force parameters (x axis). The force features prescribed by the controller on a step-by-step basis included the onset timing of PF force (PF onset), the peak amplitude of PF force (PF peak)—constrained to 25% bw, the onset timing of DF force (DF onset), and the off time of DF force (DF offset). (D) Relative changes (%Δ) in participants’ interlimb propulsion symmetry based on the onset timing of exosuit-generated PF forces. Four participants benefited more from a late onset of PF force timing, two participants benefited more from an early onset, and one participant (#1) benefited equally from both timings. Means and SE are presented in (C) and (D). *P < 0.05.

  • Fig. 5. Overview of an untethered, unilateral, ankle-assisting exosuit adapted for overground walking.

    (A) Mechanical power generated by a 2.63-kg actuator mounted posteriorly on the waist belt is transmitted to the wearer via cable-based transmissions. A 0.56-kg battery is attached anteriorly on the waist belt. The contractile elements of the exosuit are located anterior and posterior to the ankle joint and assist ankle DF and PF, respectively. Improvements in (B) peak paretic ankle DF during swing phase (n = 9; P = 0.002, paired t test) and (C) interlimb propulsion asymmetry (n = 9; P = 0.045, paired t test) during overground walking are presented. Means and SE are presented. *P < 0.05.

  • Table 1. Participant baseline characteristics and gait performance.

    AD, assistive device; P, paretic; NP, nonparetic; AGRF, anterior GRF; F, female; M, male; Y, yes; N, no.

    ParticipantSide of
    paresis
    SexAge
    (years)
    Chronicity
    (years)
    Regular
    orthosis
    Regular
    AD
    HandrailWalking
    speed
    (m/s)
    Peak P ankle
    angle (°)
    Peak P
    AGRF
    (% bw)
    Peak NP
    AGRF
    (% bw)
    Cost of
    transport
    (ml O2/kg/m)
    01RightF307.08AFONoneY1.05*−0.0212.8024.570.28
    02LeftM563.58NoneNoneN1.054.207.0920.320.20
    03LeftF520.75NoneCaneY0.530.303.8911.050.28
    04LeftM512.83AFOCaneY0.9314.739.4817.600.15
    05LeftF371.08AFOCaneN0.670.397.6417.430.33
    06RightM442.33NoneNoneN1.29−2.3418.7722.270.14
    07RightF464.25NoneNoneN1.3*−0.8020.0627.340.18
    08RightM6114.17AFONoneY0.92−7.52
    09LeftM673.33NoneCaneY0.813.85

    *The participant’s actual 10-m overground walk test speed was higher than the speed tested on the treadmill. Participant #01’s actual overground speed was 1.16 m/s, but this participant was not safe walking at this speed on the treadmill. Participant #07’s speed was 1.72 m/s, but this speed was beyond the capabilities of the electromechanical actuator used for this study.

    †Participant #04 typically used a foot-up brace. Participant #05 used a custom brace that supported frontal plane motion.

    ‡GRF data unavailable.

    • Table 2. Participant measurements used for exosuit fitting.

      IC, iliac crest; W, wide; R, right; L, left.

      ParticipantHeight (cm)Weight (kg)Paretic limb anthropometric measurements (cm)Shoe size (U.S.)Lateral
      support
      IC to
      ground
      Hip circumference
      (at IC)
      Thigh
      circumference
      Below knee
      circumference
      Calf
      circumference
      011624940.632.520.013.515.27WY
      021777343.035.319.014.014.8R-10.5 | L-11N
      031589036.348.022.014.515.59.5WN
      041737944.539.517.012.513.012WN
      05172739Y
      061868047.038.519.014.014.311WN
      071676040.538.318.314.014.39.5WN
      081819939.841.317.715.415.4R-11.5 | L-11N
      091829747.040.023.516.017.0R- 12.5W | L- 13WN

    Supplementary Materials

    • www.sciencetranslationalmedicine.org/cgi/content/full/9/400/eaai9084/DC1

      Materials and Methods

      Fig. S1. Effects of wearing a passive exosuit on poststroke propulsion and energy expenditure.

      Table S1. Tethered exosuit ankle PF assistive forces.

      Table S2. Additional individual subject-level data.

      Video S1. Video demonstration of exosuit-assisted treadmill walking.

    • Supplementary Material for:

      A soft robotic exosuit improves walking in patients after stroke

      Louis N. Awad, Jaehyun Bae, Kathleen O’Donnell, Stefano M. M. De Rossi, Kathryn Hendron, Lizeth H. Sloot, Pawel Kudzia, Stephen Allen, Kenneth G. Holt, Terry D. Ellis,* Conor J. Walsh*

      *Corresponding author. Email: tellis{at}bu.edu (T.D.E.); walsh{at}seas.harvard.edu (C.J.W.)

      Published 26 July 2017, Sci. Transl. Med. 9, eaai9084 (2017)
      DOI: 10.1126/scitranslmed.aai9084

      This PDF file includes:

      • Materials and Methods
      • Fig. S1. Effects of wearing a passive exosuit on poststroke propulsion and energy expenditure.
      • Table S1. Tethered exosuit ankle PF assistive forces.
      • Legend for video S1

      [Download PDF]

      Other Supplementary Material for this manuscript includes the following:

      • Table S2 (Microsoft Excel format). Additional individual subject-level data.
      • Video S1 (.mp4 format). Video demonstration of exosuit-assisted treadmill walking.

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