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

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 (E) 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 g (r=-0.780, p=.005) decreased with increasing collagen ratio (amide III/CH) 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 E, g and relaxation time τ 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.

Mechanical Heterogeneity in the Bone Microenvironment as Characterized by Atomic Force Microscopy

“…Numerous studies using a variety of techniques have characterised the mechanical properties of bone at multiple length scales. Elastic and viscoelastic studies on both cortical and trabecular bones generally give Young's/shear moduli in the GPa range, though the results vary due to different experimental conditions (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). The Young's/shear modulus of trabecular bone is slightly lower than that of the cortical bone and occasionally as low as 10s -100s MPa (23,24).…”

A Review on Recent Advances in the Constitutive Modeling of Bone Tissue

“…As expected, there was a significant change in the apparent response which goes back to the bone volume fraction. In the case of viscosity, Ojanen et al [30] found that bone tissue visco-elasticity may not fully be able to predict the macro-scale visco-elasticity in human trabecular bone.…”

Effect of Including Periodic Boundary Condition on the Fatigue Behaviour of Cancellous Bone

“…Moreover, the computational analyses would be longer in duration, as opposed to the computational method preferences; cost-effective, non-destructive and timesaving. Most FE analyses of trabecular bone accounted only the apparent properties [15,40,43] and only a few have implemented the periodic boundary on the models tested [44][45][46][47]. However, no comparison has ever been made in between uniaxial and multiaxial trabecular fatigue.…”