本研究主旨在探討大白鼠坐骨神經之拉伸、應力鬆弛等生物力學機械性質，實驗所使用的老鼠品種分別是Sprague-Dawley和Wistar，拉伸實驗之應變速率為0.02與0.2 s-1。實驗結果顯示，在應變速率為0.02 s-1之條件下，拉伸強度、彈性模數和破損應變分別為3.66 ? 1.20 MPa、6.58 ? 3.22 MPa與0.91 ? 0.18，在較高應變速率0.2 s-1之條件下，三項相對應之機械性質分別為4.72 ? 1.21 MPa、12.56 ? 4.11 MPa與 0.77 ? 0.27，此結果顯示較高的應變速率會造成較大的彈性模數，但拉伸強度與破損應變經由統計學檢定後在兩個不同應變速率下並無顯著差異，表示不受應變速率影響。此外，利用光學顯微鏡觀察坐骨神經拉伸試片的橫截面，可以發現神經束膜與神經外膜是決定坐骨神經強度的主要軟組織。 在應力鬆弛方面，主要探討起始應變速率對應力鬆弛現象的影響，實驗結果顯示較慢的起始應變速率在33%的固定應變之下，會造成較大的應力鬆弛程度，但是對50%的固定應變而言，所呈現的現象卻是相反的，而在66%的固定應變條件下，並沒有發現起始應變速率會造成明顯不同的應力鬆弛現象。另一方面，比較不同固定應變在相同起始應變速率下的差異，可以發現在較低的起始應變速率(0.02 s-1)之下，33%固定應變的鬆弛程度會比50%與66%固定應變還要大，但在較高的起始應變速率(0.2 s-1)之下，鬆弛程度在三個不同固定應變量之下並沒有發現顯著的差別。此外，本研究使用一黏彈性數學模型(Kelvin Model)來分析應力鬆弛現象，分析結果顯示Kelvin Model關係式對大白鼠坐骨神經之應力鬆弛現象有相當不錯的描述結果。 The present study was conducted to investigate the in vitro tensile properties and stress relaxation behavior of sciatic nerves of Sprague-Dawley (SD) and Wistar rats under two different initial strain rates, 0.02 and 0.2 s-1. Results showed that for a strain rate of 0.02 s-1 the ultimate stress, elastic modulus and failure strain are 3.66 ? 1.20 MPa, 6.58 ? 3.22 MPa and 0.91 ? 0.18, respectively. The corresponding values for 0.2 s-1 are 4.72 ? 1.21 MPa, 12.56 ? 4.11 MPa and 0.77 ? 0.27, respectively. Such results indicate that a higher strain rate would result in a greater elastic modulus but ultimate stress and failure strain level would not be affected by strain rate according to statistical analysis. In addition, microstructural analysis showed that perineurium and epineurium were responsible for the tensile strength of rat sciatic nerve. With regard to the effects of initial strain rate on the stress relaxation behavior, a slower initial stain rate would cause a greater extent of stress relaxation at a constant strain of 33%, but an opposite trend was found for a constant strain of 50%. However, no statistically significant effect of initial strain rate could be found on the stress relaxation behavior of rat sciatic nerve at a constant strain of 66%. It was also found that the extent of stress relaxation under a constant strain of 33% was greater than those under 50% and 66% at a low initial strain rate of 0.02 s-1. Nevertheless, the extents of stress relaxation at a high initial strain rate of 0.2 s-1 were comparable among the given three constant strain levels. Finally, the stress relaxation results at all given testing conditions could be well correlated by a viscoelastic model (the Kelvin model).
