Small animal bone biomechanics

Abstract

Animal models, in particular mice, offer the possibility of naturally achieving or genetically engineering a skeletal phenotype associated with disease and conducting destructive fracture tests on bone to determine the resulting change in bone's mechanical properties. Several recent developments, including nano-and micro-indentation testing, microtensile and microcompressive testing, and bending tests on notched whole bone specimens, offer the possibility to mechanically probe small animal bone and investigate the effects of aging, therapeutic treatments, disease, and genetic variation. In contrast to traditional strength tests on small animal bones, fracture mechanics tests display smaller variation and therefore offer the possibility of reducing sample sizes. This article provides an analysis of what such tests measure and proposes methods to reduce errors associated with testing smaller than ideal specimens.

Bone fragility beyond strength and mineral density: Raman spectroscopy predicts femoral fracture toughness in a murine model of rheumatoid arthritis

“…1 h ). The anterior surface was chosen for notching based on findings suggesting that physiological loading is primarily tensile in the anterior quadrant of rat and mouse femora (Indrekvam et al, 1991; Ramasamy and Akkus, 2007; Vashishth, 2008). After notching, the bones were stored in PBS overnight at 4°C and then allowed to warm to room temperature prior to three-point bending, which was conducted using an Instron 8841 DynaMight™ Axial Testing System (Instron Corp.; Canton, MA) with a 6 mm support span and a 50 N load cell.…”

Bone Material Properties and Skeletal Fragility

“…The degree to which the propagation load is smaller than the expected un-notched fracture load reflects the fracture toughness of the material; a small fracture initiation toughness is associated with a small failure force of the notched specimen. Three-point bending toughness testing is used both with standard rectangular beam specimens [55-57] and with the whole bones of small animals [46]. Similar to the use of whole bones for strength testing, the whole bone fracture initiation toughness tests lose accuracy because of the uncontrolled shapes of the bones between animals, and other violations of the analytical assumptions; but sample preparation is much easier.…”

“…and analyze them as if the specimens were machined specimens with a uniform cross-section [46,47]. Whole bone testing in bending violates the specimen aspect ratio assumption, the uniformity of cross-section assumption, the assumption that the specimen is straight and other requirements of the mathematical models ordinarily used to convert force and displacement into stress and strain.…”

Simulated weightlessness and synbiotic diet effects on rat bone mechanical strength

“…The three point bending tester was capable of running multiple tests with good repeatability. The equations (Vashishth, 2008;Saffar et al, 2009) to calculate moment of inertia (I ), the elastic (Young's) modulus (E) and fracture or bending stress (σ ) are:…”