Measurement of Cortical Bone Strain Distribution by Image Correlation Techniques and from Fracture Toughness

Abstract

Bone fracture toughness has been well studied, however, it is also important to investigate the effect of preservative treatment on the mechanical properties of bones. It is necessary to evaluate crack initiation and propagation after fracture because this process may be different in the case of injured bone tissues. In this study, we attempted to analyze the strain distribution on bone tissue surface by using image correlation techniques in order to elucidate the relationship between microscopic bone damage and strain distribution. Bovine femoral cortical bone was employed as the bone specimen and the three-point bend test method was used to determine the fracture toughness, in accordance with the ASTM E399 guidelines. An Instron type machine was used in the fracture toughness test and the loading rate was set to 1 mm/min. Black and white spray paint was applied in a random pattern to the surface of the specimens, and the specimens were loaded until they were ruptured. Bone surface strain analysis was performed using image correlation techniques and the changes were recorded in a digital image. In order to evaluate the effects of preservative treatment on the mechanical properties of bone, we categorized the specimens into 4 groups: the control group included the specimens that were submitted for testing immediately after machining and the preservation group comprised specimens that were analyzed after preservative treatment with different method (formalin, ethanol and physiological saline solution). A strain analysis performed using image correlation techniques allowed the visualization of the increased strain at the forward end of the slit of the specimens. The strain value at the forward end of the slit (the longitudinal direction of specimens) measured at the time of rupture in the control group was approximately 4 times larger than that in the formalin preservation group, thereby suggesting the embrittlement of bone organic constituents due to preservative treatment.

Ex vivo determination of bone tissue strains for an in vivo mouse tibial loading model

“…These methods are clearly limited in their scope to provide direct measurements of strain across an entire bone surface and so more recently, digital image correlation (DIC) has been used to overcome these limitations offering a viable method for measuring high resolution full-field strains on the whole bone surface ( Sztefek et al, 2010 ). Although being an ex vivo technique, DIC is particularly suitable for biological applications, as it reveals strains in inhomogeneous, anisotropic and non-linear materials, like bone, which has also a complex morphology ( Nicolella et al, 2001, Verhulp et al, 2004, Nicolella et al, 2005, Hoc et al, 2006, Yang et al, 2007, Sztefek et al, 2010, Yamaguchi et al, 2011 ). Furthermore, DIC provides only surface strain measurements and not volumetric measurements as FE models.…”

A review on experimental and numerical investigations of cortical bone fracture

“…31 Numerous experimental studies determined the effect of several parameters, that is, sugar, age, hydration, mineralization, preservative method, fatigue loading, strain rate, porosity, anisotropy, demineralization, deproteinization, type of specimen, indentation, shear deformation, bone composition, etc., on fracture parameters of cortical bone. 21–23,32–64 Many researchers have validated their numerically predicted results with the experimental analysis as well. 22,40,42,47,51,62…”

“…21–23,32–64 Many researchers have validated their numerically predicted results with the experimental analysis as well. 22,40,42,47,51,62…”

Experimental multiscale measurements for the mechanical identification of a cortical bone by digital image correlation

“…The identification procedure of the prior stochastic model of this apparent elasticity field is detailed in Nguyen (2013); Nguyen et al (2015) for which the measurements of the displacement field are required both at the macroscopic scale and at the mesoscopic scale. The implementation of the experimental methodology by optical measurements of mechanical fields, the development of a measuring bench, the specimen preparation, the experimental measurements, and the DIC method, have already been the object of research in the context of biological materials Bertolino et al (2007); Bornert et al (2010); Chauvet et al (2010); Gusachenko et al (2012); Heripre et al (2007); Houssen et al (2011); Kalouche et al (2010); Yang et al (2012Yang et al ( , 2010; Yamaguchi et al (2011). In this paper, new advances are proposed to circumvent the difficulties induced by the complex nature of the cortical bone and the need to observe for the same loading two very different scales.…”