Delaine-Smith R M, Burney S, Balkwill F R, Knight M M
School of Engineering and Materials Science, Institute of Bioengineering, Queen Mary University of London, Mile End, London E1 4NS, UK; Centre for Cancer and Inflammation, Barts Cancer Institute, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, UK.
School of Engineering and Materials Science, Institute of Bioengineering, Queen Mary University of London, Mile End, London E1 4NS, UK.
J Mech Behav Biomed Mater. 2016 Jul;60:401-415. doi: 10.1016/j.jmbbm.2016.02.019. Epub 2016 Feb 17.
Mechanical characterisation of soft biological tissues using standard compression or tensile testing presents a significant challenge due to specimen geometrical irregularities, difficulties in cutting intact and appropriately sized test samples, and issues with slippage or damage at the grips. Indentation can overcome these problems but requires fitting a model to the resulting load-displacement data in order to calculate moduli. Despite the widespread use of this technique, few studies experimentally validate their chosen model or compensate for boundary effects. In this study, viscoelastic hydrogels of different concentrations and dimensions were used to calibrate an indentation technique performed at large specimen-strain deformation (20%) and analysed with a range of routinely used mathematical models. A rigid, flat-ended cylindrical indenter was applied to each specimen from which 'indentation moduli' and relaxation properties were calculated and compared against values obtained from unconfined compression. Only one indentation model showed good agreement (<10% difference) with all moduli values obtained from compression. A sample thickness to indenter diameter ratio ≥1:1 and sample diameter to indenter diameter ratio ≥4:1 was necessary to achieve the greatest accuracy. However, it is not always possible to use biological samples within these limits, therefore we developed a series of correction factors. The approach was validated using human diseased omentum and bovine articular cartilage resulting in mechanical properties closely matching compression values. We therefore present a widely useable indentation analysis method to allow more accurate calculation of material mechanics which is important in the study of soft tissue development, ageing, health and disease.
使用标准压缩或拉伸测试对柔软生物组织进行力学表征面临重大挑战，这是由于样本几何形状不规则、切割完整且尺寸合适的测试样本存在困难，以及夹具处的滑动或损坏问题。压痕测试可以克服这些问题，但需要将模型拟合到所得的载荷-位移数据中以计算模量。尽管该技术被广泛使用，但很少有研究通过实验验证其选择的模型或补偿边界效应。在本研究中，使用不同浓度和尺寸的粘弹性水凝胶来校准在大样本应变变形（20%）下进行的压痕技术，并使用一系列常用的数学模型进行分析。将一个刚性的、平头圆柱形压头应用于每个样本，从中计算“压痕模量”和松弛特性，并与无侧限压缩获得的值进行比较。只有一种压痕模型与从压缩获得的所有模量值显示出良好的一致性（差异<10%）。样本厚度与压头直径之比≥1:1以及样本直径与压头直径之比≥4:1对于实现最高精度是必要的。然而，并非总是能够在这些限制范围内使用生物样本，因此我们开发了一系列校正因子。该方法通过使用人类患病大网膜和牛关节软骨进行了验证，结果表明力学性能与压缩值密切匹配。因此，我们提出了一种广泛可用的压痕分析方法，以允许更准确地计算材料力学，这在软组织发育、衰老、健康和疾病研究中很重要。
