The influence of water removal on the strength and toughness of cortical bone

Abstract

Although the effects of dehydration on the mechanical behavior of cortical bone are known, the underlying mechanisms for such effects are not clear. We hypothesize that the interactions of water with the collagen and mineral phases each have a unique influence on mechanical behavior. To study this, strength, toughness, and stiffness were measured with three-point bend specimens made from the mid-diaphysis of human cadaveric femurs and divided into six test groups: control (hydrated), drying in a vacuum oven at room temperature (21 °C) for 30 min and at 21, 50, 70, or 110 °C for 4 h. The experimental data indicated that water loss significantly increased with each increase in drying condition. Bone strength increased with a 5% loss of water by weight, which was caused by drying at 21 °C for 4 h. With water loss exceeding 9%, caused by higher drying temperatures (≥70 °C), strength actually decreased. Drying at 21 °C (irrespective of time in vacuum) significantly decreased bone toughness through a loss of plasticity. However, drying at 70 °C and above caused toughness to decrease through decreases in strength and fracture strain. Stiffness linearly increased with an increase in water loss. From an energy perspective, the water-mineral interaction is removed at higher temperatures than the water-collagen interaction. Therefore, we speculate that loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness.

The double cantilever beam test applied to mode I fracture characterization of cortical bone tissue

“…As can be seen, dehydration causes an appreciable reduction of fracture energy, accompanied by a slight increase of elastic modulus, in agreement with earlier works (Currey, 1988a;Lucksanasombool et al, 2001;Nyman et al, 2006;Wang and Agrawal, 1996). The vascular porosity (Table 3) can be used to estimate the content of free water.…”

X-ray diffraction as a promising tool to characterize bone nanocomposites

“…The interaction of mineral and collagen in bone is discussed from the concept of a mineral-reinforced collagen matrix, and there is an evidence for a mineral matrix with collagen inclusions [18][19][20][21][22]. The role of water in the overall behavior of bone is also considered important [23]; however, the underlying mechanism is still not clearly understood. The compressive strength of bulk cortical bone in humans is around 170 MPa for the femur, and the elastic compressive modulus is around 17 GPa [24].…”

Measurements of mobile and bound water by nuclear magnetic resonance correlate with mechanical properties of bone

“…A number of early studies demonstrated that dehydration decreases the strain at fracture and energy to fracture of cortical bone [6][7][8][9][10][11], and a recent study found that the contribution of water to bone toughness exists at multiple energy levels [12]. It has been shown that elevated drying of bone (70 °C) can cause significantly greater loss of bone toughness than moderate drying (room temperature), indicating that each of the hierarchical arrangements of water molecules bound to the collagen and mineral phases would likely influence the ability of bone to resist fracture.…”