Technical Briefs

A New Laser Reflectance System Capable of Measuring Changing Cross-Sectional Area of Soft Tissues During Tensile Testing

[+] Author and Article Information
Gabriel G. Pokhai, Michele L. Oliver, Karen D. Gordon

School of Engineering, University of Guelph, Guelph, ON, N1G 2W1, Canada

J Biomech Eng 131(9), 094504 (Aug 06, 2009) (5 pages) doi:10.1115/1.3194753 History: Received July 21, 2008; Revised June 12, 2009; Published August 06, 2009

Determination of the biomechanical properties of soft tissues such as tendons and ligaments is dependent on the accurate measurement of their cross-sectional area (CSA). Measurement methods, which involve contact with the specimen, are problematic because soft tissues are easily deformed. Noncontact measurement methods are preferable in this regard, but may experience difficulty in dealing with the complex cross-sectional shapes and glistening surfaces seen in soft tissues. Additionally, existing CSA measurement systems are separated from the materials testing machine, resulting in the inability to measure CSA during testing. Furthermore, CSA measurements are usually made in a different orientation, and with a different preload, prior to testing. To overcome these problems, a noncontact laser reflectance system (LRS) was developed. Designed to fit in an Instron 8872 servohydraulic test machine, the system measures CSA by orbiting a laser transducer in a circular path around a soft tissue specimen held by tissue clamps. CSA measurements can be conducted before and during tensile testing. The system was validated using machined metallic specimens of various shapes and sizes, as well as different sizes of bovine tendons. The metallic specimens could be measured to within 4% accuracy, and the tendons to within an average error of 4.3%. Statistical analyses showed no significant differences between the measurements of the LRS and those of the casting method, an established measurement technique. The LRS was successfully used to measure the changing CSA of bovine tendons during uniaxial tensile testing. The LRS developed in this work represents a simple, quick, and accurate way of reconstructing complex cross-sectional profiles and calculating cross-sectional areas. In addition, the LRS represents the first system capable of automatically measuring changing CSA of soft tissues during tensile testing, facilitating the calculation of more accurate biomechanical properties.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 1

Photograph of the laser reflectance system installed on an Instron 8872 servohydraulic testing machine. The bearing has a central aperture large enough for the tissue clamps of the Instron to pass through, permitting simultaneous area measurement and tensile testing.

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Figure 2

Sample result from metallic specimen validation showing three measurement methods. (a) Reconstructed cross-sectional profile obtained using laser reflectance system. (b) Photograph of casting mold. (c) Photograph of specimen.

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Figure 3

Sample result from soft tissue specimen validation showing three measurement methods. (a) Reconstructed cross-sectional profile obtained using laser reflectance system. (b) Photograph of casting mold. (c) Photograph of destructive transverse slice of specimen.

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Figure 4

Representative stress strain curve illustrating the difference between true and engineering stresses

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Figure 5

Average decrease in bovine tendon cross-sectional area with increasing strain (n=6). Error bars show standard deviation.



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