Trowbridge E A, Crofts C E
J Biomech. 1986;19(12):1023-33. doi: 10.1016/0021-9290(86)90119-3.
Cyclic uniaxial load tests were performed on natural and chemically modified bovine pericardium which is used in the construction of heart valve substitutes. A template was employed to select specimens from the same sites in different pericardial sacs. When the pericardium was chemically modified by glutaraldehyde fixation as an entire sac the tissue showed increased extensibility after modification compared with the natural tissue. The undeformed stress-free length (gauge length) in both the natural and modified tissue was determined by a highly reproducible experimental method giving a coefficient of variation of less than 0.5%. Specimens excised from a natural pericardial sac demonstrated a significant increase (p less than 0.03) in length, 4.97 +/- 3.49%, after a single load cycle, compared with controls placed in isotonic saline but not mechanically tested. The test pieces had returned to their original length by 8.5 h after the mechanical test. After fixation the same specimens decreased significantly in length (p less than 0.001) by 11.18 +/- 4.28%. This shrinkage was not significantly different to that of the control specimens (11.09 +/- 2.47%) which had not been tested. Uniaxial loading of these chemically modified strips demonstrated a similar increase in tissue extensibility compared to the natural tissue if the undeformed length of the test specimen after shrinkage was used as the gauge length. After mechanical conditioning the chemically modified tissue also demonstrated a significant increase (p less than 0.001) in stress-free length (5.35 +/- 0.59% after 36 cycles, 8.92 +/- 1.50% after 2085 cycles). These deformations were not permanent. The tissue had returned to its original length after 38 h in its normal buffered glutaraldehyde storage medium. On the basis of these observations, recommendations for the clarification and standardisation of gauge length definitions were made in natural, chemically modified and mechanically conditioned tissue.
对用于构建心脏瓣膜替代品的天然和化学改性牛心包进行了循环单轴载荷试验。使用模板从不同心包囊中相同部位选取标本。当整个心包囊用戊二醛固定进行化学改性时，与天然组织相比，改性后的组织显示出更大的延展性。通过一种高度可重复的实验方法确定天然组织和改性组织中未变形的无应力长度（标距长度），变异系数小于0.5%。与置于等渗盐水中但未进行机械测试的对照相比，从天然心包囊中取出的标本在单个加载循环后长度显著增加（p<0.03），为4.97±3.49%。机械测试后8.5小时，试件恢复到原始长度。固定后，相同标本的长度显著减少（p<0.001），减少了11.18±4.28%。这种收缩与未测试的对照标本（11.09±2.47%）没有显著差异。如果将收缩后试件的未变形长度用作标距长度，这些化学改性条带的单轴加载显示出与天然组织相比类似的组织延展性增加。经过机械调节后，化学改性组织的无应力长度也显著增加（p<0.001）（36个循环后为5.35±0.59%，2085个循环后为8.92±1.50%）。这些变形不是永久性的。在其正常的缓冲戊二醛储存介质中放置38小时后，组织恢复到原始长度。基于这些观察结果，对天然、化学改性和机械调节组织中标距长度定义的澄清和标准化提出了建议。
