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J Biomech. 2017 Dec 8;65:96-105. doi: 10.1016/j.jbiomech.2017.10.002. Epub 2017 Oct 13.

Tissue viscoelasticity is related to tissue composition but may not fully predict the apparent-level viscoelasticity in human trabecular bone - An experimental and finite element study.

Author information

1
Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland. Electronic address: xiaowei.ojanen@uef.fi.
2
Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland.
3
Department of Biomedical Engineering, Lund University, POB 118, 221 00 Lund, Sweden.
4
Department of Applied Physics, University of Eastern Finland, POB 1627, FI-70211 Kuopio, Finland; Diagnostic Imaging Center, Kuopio University Hospital, POB 100, FI-70029 Kuopio, Finland.
5
SIB Labs, University of Eastern Finland, PO Box 1627, FI-70211 Kuopio, Finland.
6
Department of Physical Therapy, Bispebjerg Hospital, Denmark; Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
7
Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.

Abstract

Trabecular bone is viscoelastic under dynamic loading. However, it is unclear how tissue viscoelasticity controls viscoelasticity at the apparent-level. In this study, viscoelasticity of cylindrical human trabecular bone samples (n=11, male, age 18-78 years) from 11 proximal femurs were characterized using dynamic and stress-relaxation testing at the apparent-level and with creep nanoindentation at the tissue-level. In addition, bone tissue elasticity was determined using scanning acoustic microscope (SAM). Tissue composition and collagen crosslinks were assessed using Raman micro-spectroscopy and high performance liquid chromatography (HPLC), respectively. Values of material parameters were obtained from finite element (FE) models by optimizing tissue-level creep and apparent-level stress-relaxation to experimental nanoindentation and unconfined compression testing values, respectively, utilizing the second order Prony series to depict viscoelasticity. FE simulations showed that tissue-level equilibrium elastic modulus (Eeq) increased with increasing crystallinity (r=0.730, p=.011) while at the apparent-level it increased with increasing hydroxylysyl pyridinoline content (r=0.718, p=.019). In addition, the normalized shear modulus g1 (r=-0.780, p=.005) decreased with increasing collagen ratio (amide III/CH2) at the tissue-level, but increased (r=0.696, p=.025) with increasing collagen ratio at the apparent-level. No significant relations were found between the measured or simulated viscoelastic parameters at the tissue- and apparent-levels nor were the parameters related to tissue elasticity determined with SAM. However, only Eeq, g2 and relaxation time τ1 from simulated viscoelastic values were statistically different between tissue- and apparent-levels (p<.01). These findings indicate that bone tissue viscoelasticity is affected by tissue composition but may not fully predict the macroscale viscoelasticity in human trabecular bone.

KEYWORDS:

Collagen crosslink; Composition; Finite element modeling; Trabecular bone; Viscoelasticity

PMID:
29108850
DOI:
10.1016/j.jbiomech.2017.10.002
[Indexed for MEDLINE]

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