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# Manufacture of Energy Storage and Return Prosthetic Feet Using Selective Laser Sintering

[+] Author and Article Information
Brian J. South, Nicholas P. Fey

Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712

Gordon Bosker

Department of Rehabilitation Medicine, The University of Texas Health Science Center, San Antonio, TX 78229

Richard R. Neptune1

Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712rneptune@mail.utexas.edu

1

Corresponding author.

J Biomech Eng 132(1), 015001 (Dec 18, 2009) (6 pages) doi:10.1115/1.4000166 History: Received May 07, 2009; Revised August 18, 2009; Posted September 04, 2009; Published December 18, 2009; Online December 18, 2009

## Abstract

Proper selection of prosthetic foot-ankle components with appropriate design characteristics is critical for successful amputee rehabilitation. Elastic energy storage and return (ESAR) feet have been developed in an effort to improve amputee gait. However, the clinical efficacy of ESAR feet has been inconsistent, which could be due to inappropriate stiffness levels prescribed for a given amputee. Although a number of studies have analyzed the effect of ESAR feet on gait performance, the relationships between the stiffness characteristics and gait performance are not well understood. A challenge to understanding these relationships is the inability of current manufacturing techniques to easily generate feet with varying stiffness levels. The objective of this study was to develop a rapid prototyping framework using selective laser sintering (SLS) for the creation of prosthetic feet that can be used as a means to quantify the influence of varying foot stiffness on transtibial amputee walking. The framework successfully duplicated the stiffness characteristics of a commercial carbon fiber ESAR foot. The feet were mechanically tested and an experimental case study was performed to verify that the locomotor characteristics of the amputee’s gait were the same when walking with the carbon fiber ESAR and SLS designs. Three-dimensional ground reaction force, kinematic, and kinetic quantities were measured while the subject walked at 1.2 m/s. The SLS foot was able to replicate the mechanical loading response and locomotor patterns of the ESAR foot within $±2$ standard deviations. This validated the current framework as a means to fabricate SLS-based ESAR prosthetic feet. Future work will be directed at creating feet with a range of stiffness levels to investigate appropriate prescription criteria.

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## Figures

Figure 1

Mechanical testing of the HighlanderTM CF foot during the (a) toe-only, (b) heel-only, and (c) foot-flat conditions

Figure 2

Steps in deriving the CAD model for SLS fabrication from CF foot geometry: (a) HighlanderTM (FS 3000) CF foot (Freedom Innovations, Inc.), (b) centerline spline curve of sagittal plane CF geometry with keel and heel thicknesses used to modify foot stiffness, (c) extruded geometry, (d) cut and trimmed CAD model ready for SLS fabrication, and (e) resulting prototype

Figure 3

Stiffness data for SLS versus CF feet in the toe-only, foot-flat, and heel-only conditions. Measurement data (light gray) was fit with a linear regression line. All data were truncated at 0.6 cm displacement for ease of comparison.

Figure 4

Comparison of the intact and residual leg ground reaction forces between the SLS and CF (±2 standard deviations, shaded area) feet. The mean of the SLS foot was nearly always within two standard deviations, shaded area of the CF foot mean.

Figure 5

Comparison of the intact leg joint angles, moments, and powers between the SLS and CF (±2 standard deviations, shaded area) feet. The mean of the SLS foot was nearly always within two standard deviations of the CF foot mean.

Figure 6

Comparison of the residual leg joint angles, moments and powers between the SLS and CF (±2 standard deviations, shaded area) feet. The mean of the SLS foot was nearly always within two standard deviations of the CF foot mean.

Figure 7

The application of topology optimization techniques to develop novel prosthetic foot designs for manufacture using SLS technology. The example above sought to replicate the stiffness characteristics of the CF foot while minimizing the material used: (a) sagittal plane optimization solution, (b) corresponding 3D CAD model, and (c) resulting SLS prototype.

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