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TECHNICAL PAPERS: Soft Tissue

# Effects of the Frequency and Duration of Cyclic Stress on the Mechanical Properties of Cultured Collagen Fascicles From the Rabbit Patellar Tendon

[+] Author and Article Information
Ei Yamamoto1

Biomechanics Laboratory, Department of Mechanical Engineering and Biomimetics, School of Biology-Oriented Science and Technology, Kinki University, Naga, Wakayama 649-6493, Japanei@waka.kindai.ac.jp

Daisuke Kogawa

Mizuno Corporation, Osaka 559-8510, Japan

Susumu Tokura

Ishikawajima-Harima Heavy Industry, Yokohama, Kanagawa 235-8501, Japan

Kozaburo Hayashi

Biomechanics Laboratory, Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan and Research Institute of Technology, Okayama University of Science, Okayama 700-0005, Japan

1

Corresponding author. Telephone +81-736-77-0345, ext 4522; Fax: +81-736-77-4754.

J Biomech Eng 127(7), 1168-1175 (May 28, 2005) (8 pages) doi:10.1115/1.2073587 History: Received June 24, 2004; Revised May 28, 2005

## Abstract

The effects of frequency or duration of cyclic stress on the mechanical properties of collagen fascicles were studied by means of in vitro tissue culture experiments. Collagen fascicles of approximately $300μm$ in diameter were obtained from rabbit patellar tendons. During culture, cyclic stress having the peak stress of approximately $2MPa$ was applied to the fascicles at $1Hz$ for $1hour∕day$ ($1Hz-1h$ group), at $1Hz$ for $4hours∕day$ ($1Hz-4h$ group), or at $4Hz$ for $1hour∕day$ ($4Hz-1h$ group). The frequency of $4Hz$ and the duration of $1hour∕day$ are considered to be similar to those of the in vivo stress applied to fascicles in the intact rabbit patellar tendon. After culture for 1 or $2weeks$, the mechanical properties of the fascicles were determined using a micro-tensile tester, and were compared to the properties of non-cultured, fresh fascicles (control group) and the fascicles cultured under no load condition (non-loaded group). The tangent modulus and tensile strength of fascicles in the $4Hz-1h$ group were similar to those in the control group; however, the fascicles of the $1Hz-1h$ and $1Hz-4h$ groups had significantly lower values than those of the control group. There was no significant difference in the tensile strength between the $1Hz-1h$ and non-loaded groups, although the strength in the $1Hz-4h$ group was significantly higher than that of the non-loaded group. It was concluded that the frequency and duration of cyclic stress significantly affect the mechanical properties of cultured collagen fascicles. If we apply cyclic stress having the frequency and duration which are experienced in vivo, the biomechanical properties are maintained at control, normal level. Lower frequencies or less cycles of applied force induce adverse effects.

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## Figures

Figure 1

Apparatus for the culture of collagen fascicles under cyclic load condition (23). Four fascicles can be set up in parallel in a culture bath. Four load cells are used to measure load applied to each fascicle. A linear actuator was used for the application of displacement, and the load is continuously monitored during culture.

Figure 2

Stress-strain curves of control fascicles and the fascicles cultured for 1 (A) and 2 (B) weeks. There were no noticeable differences in the shape of the curves among the groups. The tangent modulus was calculated from the slope of each curve (linear regression) between 2% and 5% strain.

Figure 3

Tangent modulus of collagen fascicles. A two-way ANOVA was used to assess statistical differences with respect to experimental groups and culture periods, followed by Fisher’s PLSD test for comparisons among groups at each period. A two-way ANOVA showed significant differences among groups. The moduli in the non-loaded, 1Hz-1h, and 1Hz-4h groups were significantly smaller compared with the control group both at 1 and 2weeks. The moduli in the 4Hz-1h group were significantly larger than those in the control, non-loaded, 1Hz-1h, and 1Hz-4h groups except for at 2weeks; there was no significant difference between the 4Hz-1h and control groups at 2weeks. There were no significant differences in the modulus among these three groups except for the 1Hz-4h group at 2weeks.

Figure 4

Tensile strength of collagen fascicles. A two-way ANOVA was used to assess statistical differences with respect to experimental groups and culture periods, followed by Fisher’s PLSD test for comparisons among groups at each period. A two-way ANOVA showed significant differences among groups. The strength in the non-loaded, 1Hz-1h, and 1Hz-4h groups were significantly lower compared with the control group both at 1 and 2weeks. Although there was a significant difference in the strength between the 4Hz-1h and control groups at 1week, this difference disappeared at 2weeks.

Figure 5

Strain at failure of collagen fascicles. A two-way ANOVA was used to assess statistical differences with respect to experimental groups and culture periods, followed by Fisher’s PLSD test for comparisons among groups at each period. A two-way ANOVA showed significant differences among groups. The strain at failure was significantly larger in the 1Hz-1h and 1Hz-4h groups than in the control group except for the 1Hz-1h group at 1week, whereas there were no significant differences in the strain between the 4Hz-1h and control groups both at 1 and 2weeks.

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