Journal
JOURNAL OF BIOMECHANICS
Volume 47, Issue 11, Pages 2641-2646Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.jbiomech.2014.05.017
Keywords
Viscoelastic models; Dynamic mechanical analysis; Strain rate; Liver; Soft tissues
Categories
Funding
- European Union [304961 (ReLiver)]
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Understanding and modelling liver biomechanics represents a significant challenge due to the complex nature of this organ. Unfortunately, there is no consensus on liver viscoelastic properties, and results are strongly dependent on sample type and status, adopted testing method, and testing conditions. Standard force-triggered tests (e.g. step response or dynamic mechanical tests) necessitate an initial contact between sample and testing apparatus, which may result in significant pre-stress to very soft and highly hydrated samples. In a previous study we proposed the epsilon dot method ((epsilon) over dotM): a testing and analysis framework to address the drawbacks of standard mechanical tests. Focusing on ex-vivo unconfined bulk compressive tests, here we use both the (epsilon) over dotM and dynamic mechanical analysis (DMA) to derive liver viscoelastic parameters in the region of small strains or the linear viscoelastic region (LVR). As liver samples were visibly deteriorated at the end of frequency sweep tests, a modified approach was adopted to reduce DMA testing times. This approach, termed step-reconstructed DMA (SRDMA), is based on dynamic measurements around specific frequencies and then reconstruction of liver behaviour in the entire frequency range of interest. The instantaneous elastic modulus obtained from SRDMA tests (2.65 +/- 0.30 kPa) was significantly higher than that obtained with the (epsilon) over dotM (2.04 +/- 0.01 kPa). We show that the overestimation of stiffness is due to data acquisition in a local rather than an absolute LVR, highlighting the importance of using a rapid and zero pre-stress approach to characterise very soft and highly hydrated biological tissues. (C) 2014 Elsevier Ltd. All rights reserved.
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