January 2019

3D-Printed Knee Brace To Aid Rehab, Elderly

Figure 1. A 3D-printed, flexible knee brace with adjustable stiffness and embedded magnetic angle sensor. Torsional stiffness of the brace is modified by applying elastic bands of varying thickness.

Researchers from the Georgia Institute of Technology recently detailed the successful benchtop testing and pilot human movement studies of a 3D-printed knee brace. The brace, which has an embedded magnetic angle sensor and whose torsional stiffness can be adjusted by applying varying sizes of elastic bands (Figure 1), is able to alter joint loading, joint kinematics, and user effort, according to the study published in the Conference Proceedings of the IEEE Annual Meeting of the Engineering in Medicine and Biology Society, 2018.

The purpose of any brace or orthosis is to control joint motion, typically to improve coordination or stability, reduce the risk of pain or injury, or correct for weak muscles. Braces should be designed for each user, based on anthropometrics and the specific condition being corrected or supported. The authors note that biomechanics researchers, clinicians, and patients are all interested in the development of knee orthoses with user-controllable mechanical properties and point to the increasing prevalence of prescriptions for such braces as support of their clinical relevance. Three-dimensional (3D) printing provides a technical answer to the clinical need.

The various parts of the custom brace, all made from thermoplastic polyurethane, were manufactured on a Lulzbot Taz 5 3D printer (Aleph Objects, Loveland, CO), as were the elastic bands used to modulate torsional stiffness, and the housing components for the non-contact magnetic angle sensor and disc magnet.

Figure 4. Results of benchtop testing for a range of elastic band thicknesses.

Researchers tested the mechanical behavior of the brace using a treadmill walking task, which showed that the device can selectively modulate joint kinematics in everyday activities, such as walking. During the flexion-extension task, the brace produced resistance-training-like effects in its ability to apply unique levels of torsional stiffness, thereby requiring the user to exert varying levels of effort.

The change in the slope of the torque-angle curve (Figure 4) demonstrates the brace’s ability to adjust torsional stiffness using elastic bands. The results of the flexion-extension task (Figure 7) reflect increased knee flexor EMG activity which means, the authors suggest, the “device could be used for resistance training exercises of varying intensity, perhaps for rehabilitation or strengthening purposes.”

Source: Bolus NB, Ganti VG, Inan OT. A 3D-Printed, Adjustable-Stiffness Knee Brace with Embedded Magnetic Angle Sensor. Conf Proc IEEE Eng Med Biol Soc. 2018 Jul;2018:1624-1627.

Figure 7. Knee flexor activity and device angle for one representative flexion-extension cycle at three different stiffness settings.

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