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Research Papers

[+] Author and Article Information
Oluseeni A. Komolafe

School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104

Todd C. Doehring1

School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104tcdoe@drexel.edu

1

Corresponding author.

J Biomech Eng 132(2), 021004 (Jan 07, 2010) (5 pages) doi:10.1115/1.4000696 History: Received July 11, 2008; Revised September 03, 2009; Posted November 24, 2009; Published January 07, 2010; Online January 07, 2010

## Abstract

Although the overall bulk properties of the Achilles tendon have been measured, there is little information detailing the properties of individual fascicles or their interactions. The knowledge of biomechanical properties at the fascicle-scale is critical in understanding the biomechanical behavior of tendons and for the construction of accurate and detailed computational models. Seven tissue samples $(∼15×4×1 mm3)$ harvested from four freshly thawed human (all male) tendons, each sample having four to six fascicles, were tested in uniaxial tension. A sequential sectioning protocol was used to isolate interaction effects between adjacent fascicles and to obtain the loading response for a single fascicle. The specimen deformation was measured directly using a novel polarized light imaging system with digital image correlation (DIC) for marker-free deformation measurement. The modulus of the single fascicle was significantly higher compared with the intact fascicle group (single: 226 MPa (SD 179), group: 68 MPa (SD 33)). The interaction effect between the adjacent fascicles was less than 10% of the applied load and evidence of sub- and postfailure fascicle sliding was clearly visible. The DIC direct deformation measurements revealed that the modulus of single fascicles could be as much as three to four times the intact specimen. The consistently higher moduli values of the single (strongest) fascicle indicate that the overall response of the tendon may be dominated by a subset of “strongest” fascicles. Also, fascicle-to-fascicle interactions were small, which was $<10%$ of the overall response. This knowledge is useful for developing computational models representing single fascicle and/or fascicle group mechanical behavior and provides valuable insights into fascicle-scale Achilles tendon material properties.

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## Figures

Figure 1

Human Achilles tendon with insert of excised intact specimen samples

Figure 2

Figure 3

Sequential sectioning protocol: (A) intact specimen, (B) split between fibers, (C) lower fibers cut and split between remaining upper two fibers, and (D) final remaining fiber

Figure 4

First frame (left) and last frame (right) for the video tracked technique on the intact specimen (top) and the single fascicle specimen (bottom). The nodes are distributed in the first frame using a simple 2D triangulation algorithm. The last frame shows the displacement path of each node tracked from the first frame to the last.

Figure 5

Load response curve for a typical specimen with (A) intact specimen and first split. The small difference in carried load shows that there are minimal interaction effects between adjacent fibers. (B) Loading curve of intact specimen and remaining load curve after two cuts. The decrease in carried load with each cut is clearly visible.

Figure 6

Mean and single standard deviation stress-strain curve for the intact specimens and individual fascicle specimens

Figure 7

Specimen failure and adjacent sliding of fascicles is shown using the polarized light technique in the above images. The top figure shows the relative movement of features after initial failure. Approximately 25% of the maximum load is retained in most instances after specimen failure.

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