Abstract
Bone fragility is a concern for aged and diseased bone. Measuring bone toughness and understanding fracture properties of the bone are critical for predicting fracture risk associated with age and disease and for preclinical testing of therapies. A reference point indentation technique (BioDent) has recently been developed to determine bone's resistance to fracture in a minimally invasive way by measuring the indentation distance increase (IDI) between the first and last indentations over cyclic indentations in the same position. In this study, we investigate the relationship between fracture toughness KC and reference point indentation parameters (i.e. IDI, total indentation distance (TID) and creep indentation distance (CID)) in bones from 38 mice from six types (C57Bl/6, Balb, oim/oim, oim/+, Phospho1−/− and Phospho1 wild type counterpart). These mice bone are models of healthy and diseased bone spanning a range of fracture toughness from very brittle (oim/oim) to ductile (Phospho1−/−). Left femora were dissected, notched and tested in 3-point bending until complete failure. Contralateral femora were dissected and indented in 10 sites of their anterior and posterior shaft surface over 10 indentation cycles. IDI, TID and CID were measured. Results from this study suggest that reference point indentation parameters are not indicative of stress intensity fracture toughness in mouse bone. In particular, the IDI values at the anterior mid-diaphysis across mouse types overlapped, making it difficult to discern differences between mouse types, despite having extreme differences in stress intensity based toughness measures. When more locations of indentation were considered, the normalised IDIs could distinguish between mouse types. Future studies should investigate the relationship of the reference point indentation parameters for mouse bone in other material properties of the bone tissue in order to determine their use for measuring bone quality.
Highlights
Bone quality is a concern for aged and diseased bone
In this study, we investigate the relationship between fracture toughness KC and indentation distance indentation distance increase (IDI), total indentation distance (TID) and creep indentation distance (CID) in mouse bones chosen from several mouse models of healthy and diseased bone, and spanning a range of fracture toughness
Bones considered for this study were from four mouse strains and six mouse types (C57Bl/6, Balb, oim/oim, oim/+, Phospho1 wild type (WT) and Phospho1−/−), chosen to represent a spectrum of bone toughness, from very brittle to ductile (Phospho1−/−) [1,18,19,20]
Summary
Bone quality is a concern for aged and diseased bone. Ageing and disease degrade the mechanical and structural properties of bone, increasing its vulnerability to fracture and compromising its function. Bone toughness is expressed in terms of work to fracture, Wf, which measures the bone's capacity to dissipate energy before final failure These measurements are highly dependent on the specimen geometry, the bone matrix structure, and the distribution of defects within the sample. Recent studies, using notched samples described the fracture mechanics of bone in terms of linear elastic stress intensity factor, KC, a critical value of the toughness characterizing complete fracture of the bone [11,12]. This fracture mechanics approach significantly improves measurements of toughness as it accounts for geometric characteristics of the sample and reduces the effects of microstructural defects by introducing a notch to represent a worst-case pre-crack
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