Technical Brief

Development of a Soft Pneumatic Sock for Robot-Assisted Ankle Exercise

[+] Author and Article Information
Fan-Zhe Low

Department of Biomedical Engineering,
National University of Singapore,
Block E4, #04-08,
4 Engineering Drive 3,
Singapore 117583, Singapore
e-mail: low_fanzhe@u.nus.edu

Hong Han Tan

Department of Biomedical Engineering,
National University of Singapore,
Block E4, #04-08,
4 Engineering Drive 3,
Singapore 117583, Singapore
e-mail: a0087265@u.nus.edu

Jeong Hoon Lim

Department of Medicine,
National University of Singapore,
1E Kent Ridge Road,
NUHS Tower Block Level 10,
Singapore 119228, Singapore
e-mail: mdcljh@nus.edu.sg

Chen-Hua Yeow

Department of Biomedical Engineering,
National University of Singapore,
Block E4, #04-08,
4 Engineering Drive 3,
Singapore 117583, Singapore
e-mail: bieych@nus.edu.sg

1Corresponding author.

Manuscript received July 20, 2015; final manuscript received December 30, 2015; published online February 15, 2016. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 10(1), 014503 (Feb 15, 2016) (5 pages) Paper No: MED-15-1225; doi: 10.1115/1.4032616 History: Received July 20, 2015; Revised December 30, 2015

Deep vein thrombosis (DVT) is a severe medical condition that affects many patients around the world, where one of the main causes is commonly associated with prolonged immobilization. Current mechanical prophylaxis systems, such as the compression stockings and intermittent pneumatic compression devices, have yet to show strong efficacy in preventing DVT. The current study aimed to develop a soft pneumatic sock prototype that uses soft extension pneumatic actuators to provide assisted ankle dorsiflexion–plantarflexion motion, so as to prevent the occurrence of DVT. The prototype was evaluated for its efficacy to provide the required dorsiflexion–plantarflexion motion by donning and actuating the prototype on simulated ankle–foot models with various ankle joint stiffness values. Our results showed that the soft extension actuators in the sock prototype provided controllable assisted ankle plantarflexion through actuator extension and ankle dorsiflexion through actuator contraction, where in our study, the actuations extended to 129.9–146.8% of its original length. Furthermore, the sock was able to achieve consistent range of motion at the simulated ankle joint across different joint stiffness values (range of motion: 27.5 ± 6.0 deg). This study demonstrated the feasibility of using soft extension pneumatic actuators to provide robot-assisted ankle dorsiflexion–plantarflexion motion, which will act as an adjunct to physiotherapists to optimize therapy time for bedridden patients and therefore may reduce the risk of developing DVT.

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Grahic Jump Location
Fig. 1

(a) Soft extension pneumatic actuator fabricated using silicone rubber and (b) two soft actuators encased within a restraining fabric case to prevent overinflation while guiding actuator extension

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Fig. 2

Experimental setup of a simulated ankle–foot model, with green markers used to determine ankle joint dorsiflexion–plantarflexion angle and blue and red markers used to estimate the actuator length. The actuators are deflated and pull the ankle model into dorsiflexion. The angle θ measured represent the joint ankle which will be further used to determine the range of angular displacement of the device (range of motion). The combined length of the two lines on the actuators represent the estimated length of the actuators.

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Fig. 3

Average ankle joint dorsiflexion–plantarflexion profile of the three simulated ankle–foot models during sock actuation with varying stiffness values (model 1: 0.309 N · m/rad, model 2: 1.19 N · m/rad, and model 3: 2.39 N · m/rad). Dash and dotted lines represent the respective maximum plantarflexion and dorsiflexion angles measured during calibration of the simulated ankle–foot models. Increasing angle represents plantarflexion while decreasing angle represents dorsiflexion.

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Fig. 4

Estimated actuator length during inflation–deflation cycle of the soft actuators, as a percentage of original length, where the shaded portions of the graphs represent the standard deviation of the data

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Fig. 5

Mathematical model illustrating the relationship between actuator force, ankle resistance moment, and weight of the foot. Point A represents the knee joint, point B represents the ankle joint, and point C represents the metatarsal region on the foot. The segment AB represents the tibia–fibula section of the lower limb. The length of each given section is included in relation to the anatomical height of the subject, H, using anthropometry data [11].




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