TEAM SR-AFO: WEARRACON 2020 INNOVATION CHALLENGE COMPETITION APPLICATION 1

Soft Robotic AFO for Active StrokeRehabilitation

Marielle Debeurre1, Carly M. Thalman2, Tiffany Hertzell2, and Hyunglae Lee3

Index Terms—Soft Robotics, Wearable Robotics, Mechatronics, Rehabilitation

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Fig. 1. This is the concept illustration of an ankle foot orthosis that helpsimpaired users walk again through active plantarflexion assistance, aswell as support for lateral ankle buckling for prevention of trips and falls.

Project Lead: Marielle Debeurre studies Mechanical Engineering (MS)at Arizona State University. 23867 N 73rd St, Scottsdale, AZ 85255.602.748.6369. mdebeurr@asu.edu.

Key Collaborator: Carly Thalman studies Systems Engineering (PhD)at Arizona State University and is funded by the National ScienceFoundation (GRFP). 602.628.7739. cmthalma@asu.edu.

Key Collaborator: Tiffany Hertzell studies Mechanical Engineering(BSE) at Arizona State University and is graduating from Barrett, theHonors College. 224.678.4193. thertzel@asu.edu.

Senior Collaborator: Dr. Hyunglae Lee is an Assistant Profes-sor for the School for Engineering of Matter, Transport and Energy(SEMTE) at Arizona State University, and director of the NeuromuscularControl and Human Robotics Laboratory (ASU Neurorobotics Lab).Hyunglae.Lee@asu.edu.

1 Project Lead2 Key Collaborator3 Senior Collaborator, Corresponding AuthorM. Debeurre, C.M. Thalman, T. Hertzell, and H. Lee are with the Neuromus-cular Control and Human Robotics Laboratory in the Ira A. Fulton Schools ofEngineering, Arizona State University, AZ , USA.

1 PROJECT SUMMARY

Our team presents a pneumatic soft robotic ankle-foot or-thosis (SR-AFO) to improve gait abnormalities in impairedindividuals treated using rehabilitation or ankle braces. Ournovel design is lightweight and operates in multiple degreesof freedom to provide active assistance in ankle plantarflex-ion and inversion/eversion support while walking.

2 IMPACT TO WEARABLE ROBOTICS INDUSTRY

Ankle-foot orthoses (AFOs) are the most commonly-usedorthoses available to patients, accounting for as many as26% of all orthoses provided to patients in the United States[1], [2]. In particular, AFOs are commonly prescribed forstroke victims suffering from hemiparesis, which affectsaround 80% of stroke survivors [1], [3], [4]. According tothe 2002 World Health Report, around 15 million peoplesuffer from strokes each year, yielding potentially as manyas 8 million survivors affected by hemiparesis [5], [6]. Whilethere are many versions of AFOs available on the market,they are largely made out of rigid materials like plasticsand carbon fiber [1], [2]. With the rise in popularity of thewearable robotic industry, new robotic devices are being cre-ated to replace existing rehabilitative technology. The fieldof soft robotics is rapidly becoming a trend for wearable andrehabilitative robotics due to the compliant, affordable, andcomfortable nature of the materials used.

The team working in Arizona State University’s Neuro-muscular Control and Human Robotics Laboratory presentsone such wearable robotic device to improve rehabilitationfor gait-impaired individuals using a soft robotic ankle-foot orthosis (SR-AFO). Traditional AFOs are designed toprovide ankle support to the impaired individuals withoutactive corrective action. This can subsequently lead to com-plications with mobility, increased risk of injuries, or paindue to gait adaptations attributable to limited ankle function[7], [8]. The SR-AFO integrates soft, pneumatic actuatorsmade from garment-like fabrics that simulate the behaviorof the soleus (SOL) and gastrocnemius (GA) muscles in thewalking gait cycle into the traditional rehabilitative AFOdesign, reducing the amount of muscle activation neededby the patient [9]. This novel design operates in multipledegrees of freedom (DoF), providing both assistance inankle plantarflexion and inversion and eversion support,two critical motions which occur at different points in thegait cycle [9], [10]. The SR-AFO is designed to provide

TEAM SR-AFO: WEARRACON 2020 INNOVATION CHALLENGE COMPETITION APPLICATION 2

Fig. 2. Logic control box for the SR-AFO exosuit, which controls thetiming of actuation, monitors pressure levels, and collects kinematicbehavioral data of the user through FSR sensors.

Fig. 3. (a) Side and posterior views of the SR-AFO attached over thewearer’s shoe and secured at the knee, actuator pressure at atmo-sphere (inactive). (b) Side and posterior views of the exosuit, actuatorpressure at 100 kPa (active).

safe, active assistance at the precise intervals where it isneeded while walking without impacting the comfort orrange of motion (ROM) of the wearer. Inversion/eversion(IE) actuation is required in the loading response right afterheel strike in order to improve ankle stability in the medi-olateral direction. In fact, IE actuation may even provide aslight assistance to prevent “foot slap“ in this gait phase.Plantarflexion actuation is required to assist push off in thelate stance phase [11].

The main goal of the project is to produce a wearablerobotic AFO that achieves a higher level of performancethan competing designs. A “higher performing” devicewould accomplish three main goals: (1) increase humancomfort and adaptability to the orthosis, (2) extend therehabilitative capabilities of current AFO designs, and (3)have a competitive market price. The team believes thatthe proposed SR-AFO project attains each of these goals,and therefore predicts that this project will greatly impacttraditional methods of gait rehabilitation.

TABLE 1Go/No Go Decision Points and Constraints

Design Requirements Characteristics

Design Considerations and Criteria [12] [13]

Soft, compliant material Neoprene, Spandex and NylonLow profile ∼ 5mmEasy don/doff ≤ 30 sLight weight ≤ 200 g

Motion and Force Considerations [14], [15], [16], [17], [18]

Support Plantarflexion 1.6 Nm/kgPF Muscle Assistance GA, SOL musclesAssists Pre-Swing Active during late stanceMinimum ROM ≥ 30◦ Dorsiflexion-Plantarflexion (DP)Lateral Stiffness 70 Nm/rad

Controls Criteria [11], [19], [20]

Perturbation Timing + 10% natural weight on toeGait Cycle % Assisted 40% to 60% of gaitPressure Threshold 100 kPaWalk at a natural pace ≥ 0.8 m/s

3 NOVELTY OF DESIGN

Our soft robotic AFO is a novel advancement that extendsrehabilitative capabilities beyond the basic assistance pro-vided by rigid AFO designs. The SR-AFO is a lightweight,compliant alternative to traditional AFOs or heavy andexpensive exoskeletons, and can be worn as clothing duringuse. The SR-AFO is affordable and provides active assis-tance in multiple DoF without adding excessive weight tothe user’s leg or restricting natural motion [9], [10].

4 DESIGN PLAN

To achieve the final production of a higher-performingsoft robotic AFO, a five-year design timeline for productoptimization is proposed (Fig. 4). Key Go/No Go decisionpoints occur at each level of the design plan to reflectcritical design requirements (Table 1). Human subject ex-perimentation is integrated into the design process [21]. Theteam will partner with Dr. Carolyn Kinney and Dr. MeganEikenberry1, clinicians at Mayo Clinic and MidwesternUniversity, to ensure that the SR-AFO functions optimallyfor gait-impaired patients. Clinical trials are scheduled forSeptember 2020. Pending the success of the clinical trials, thefinal design will be moved to production, and permanentlyimplemented into rehabilitation facilities.

5 INTELLECTUAL PROPERTY AND FUNDING

The team will develop a method to make the systemportable as in previous work [22]. Portability allows cus-tomers to purchase the orthosis for at-home rehabilitation.Designing for personal comfort will naturally draw con-sumers to our product. The corrective ability of the SR-AFOacross many gait abnormalities cements its market demand.A patent has been filed for an early version of the prototype[23], and the team plans to file a second patent for the newdesign prior to commercialization.

1. Dr. C. Kinney, MD, Department of Physical Medicine and Rehabil-itation, Mayo Clinic, AZ, and Dr. M. Eikenberry, DPT, Department ofPhysical Therapy, Midwestern University, AZ

TEAM SR-AFO: WEARRACON 2020 INNOVATION CHALLENGE COMPETITION APPLICATION 3

Fig. 4. A detailed plan presenting current work done on the SR-AFOproject, as well as the continued plan project out until May of 2021,where future funding and partnerships will be critical in the success andvalidation of the SR-AFO.

6 ANTICIPATED USE OF $5,000The current SR-AFO prototype costs approximately $100.00to manufacture, as shown in Table 2, excluding the cost ofthe controller, electricity and compressor used to actuate theexosuit. The cost of the control and pneumatic system isoutlined in Table 3. The manufacturing cost of the currentprototype is comparable to the price of plastic AFOs thatdo not include any robotic components. Additionally, theteam’s SR-AFO project eclipses the cost of rigid roboticcompetitors, which can cost up to $80,000 to implement forsimilar rehabilitative studies [24].

The $5,000 research budget will allow the team to im-prove the final design, particularly by addressing the useof a tether between the control box and the AFO. A tetherhas been used to contain wiring necessary to read forcedata from toe and heel sensors within the shoe. The airsupply used to actuate the pneumatic system is also tiedto the tether. The team proposes several alternatives to theexisting tether, such as the integration of wireless inertialmeasurement unit (WIMU) sensors connected to a smallercontrol box that could be fixed to the patient. This alterna-tive would allow the SR-AFO and its controller to be moreportable, as it would only require a connection to housed airsupplies. The team also intends to investigate the integrationof an improved portable pneumatic system as used in earlyversions of the SR-AFO [22].

Additionally, the team is currently working on a de-sign iteration that would integrate plantarflexion assistanceand inversion/eversion support into the human gait cycle.Currently, the SR-AFO has the capacity to perform bothfunctions, particularly in the actuator design and timingof pneumatic actuation. The team’s next step is to inte-grate both functions together seamlessly, so that both inver-sion/eversion support and plantarflexion assistance occurat precisely the optimal moment for assistance within thegait cycle for individuals with abnormal or highly varied

TABLE 2SR-AFO Bill of Materials

TABLE 3Controller and Pneumatic System Bill of Materials

gait patterns.The team has not yet implemented such design changes

due to research budgeting, and therefore a $5,000 increasewould allow these design improvements to be realized.Such improvements ensure that the team’s SR-AFO incor-porates and refines many thoughtful design features thatwould prompt a customer to select our product over acompetitor’s.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Carolyn Kinney andDr. Megan Eikenberry for their partnerships with the ASUNeurorobotics Lab, and Varun Nalam for assistance in ex-perimental testing. C. M. Thalman is funded by the Na-tional Science Foundation, Graduate Research FellowshipProgram (NSF-GRFP) award #1841051.

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TEAM SR-AFO: WEARRACON 2020 INNOVATION CHALLENGE COMPETITION APPLICATION 4

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[23] P Polygerinos, J Hsu, S Moore, and CM Thalman. Soft dynamicankle-foot orthosis exosuit for gait assistance with foot drop,November 7 2019. US Patent App. 16/396,409.

[24] P Jonathan. Forward strides for stroke survivors.https://www.baltimoresun.com/health/bs-hs-anklebots-20130602-story.html, 2013. [Online]. Accessed: 22-January-2020.