Ultrasonic Characterisation of Porous Biomaterials Across Different Frequencies

Abstract

Mechanical testing is the most common experimental technique to determine elastic stiffness of materials. In case of porous materials, especially such with very high porosity, the determination of material stiffness may be strongly biased by inelastic deformations occurring in the material samples, especially in the vicinity of the load transfer devices, such as loading platens. In contrast, ultrasonic waves propagating through a material generate very small stresses and strains (and also strain rates lying in the ‘quasistatic’ regime). Thus, they enable the direct determination of the components of elastic stiffness tensors of materials, and also of those with a very high porosity. We shortly revisit from the theoretical basis of continuum (micro)mechanics that, depending on the frequency of the employed acoustical signals, the investigated materials are characterised at different observation scales, e.g. the elasticity of the overall porous medium, or that of the solid matrix inside the material are determined. We here report the elastic properties of biomaterials and biological materials at different length scales, by using ultrasound frequencies ranging from 100 kHz to 20 MHz. We tested isotropic scaffolds for biomedical engineering, made up of porous titanium and two different bioactive glass–ceramics, and we also determined the direction‐dependent normal and shear stiffness components of the anisotropic natural composite ‘spruce wood’.

Bioactive glass and glass-ceramic scaffolds for bone tissue engineering

“…The large variations in compressive strength values of the scaffolds can be interpreted by different fabrication methods, glass compositions, pore morphologies, pore sizes, pore size distributions, shape and thickness of struts (leading to anisotropic mechanical properties), as well as by different compressive strength test parameters employed (sample geometry, size, loading speed). A linear correlation has also been found between porosity and elastic modulus of glass-ceramic scaffolds using ultrasonic wave propagation [112] (Figure 9). For human bone, different functional relationships between bone volume fraction (i.e., porosity) and mechanical properties have been observed.…”

Elastic characterization of wood by Resonant Ultrasound Spectroscopy (RUS): a comprehensive study

“…This method can be accurate for determining the Young's moduli and some of the Poisson's ratios, but is not so suitable for the determination of the shear moduli on a heterogenous material like wood, due mainly to a non-homogeneous stress field, and it is time-consuming (Hassel et al 2009). Faster measurements can be obtained by using different techniques based on the measurement of ultrasonic wave velocities (Bucur 2006;Kohlhauser et al 2009). Ultrasonic wave methods are largely employed for this kind of investigation, because they are cheap, easy to generate and to detect.…”

Unitary Bioresorbable Cage/Core Bone Graft Substitutes for Spinal Arthrodesis Coextruded from Polycaprolactone Biocomposites

“…For bone graft substitutes which exhibit open porosity and specimens with uneven free surfaces (like ours) the determination of the modulus is subject to myriad errors. 30 Other methods like the ultrasonic method utilized by Kohlhauser et al may be more appropriate for the uniaxial compression of such samples.…”