Effects of Moisture Content and Loading Profile on Changing Properties of Bone Micro-Biomechanical Characteristics

Abstract

BACKGROUND Our study explored the influences of hydration conditions and loading methods on the mechanical properties of cortical bones and cancellous bones. MATERIAL AND METHODS Elastic modulus and hardness of human cortical bones and cancellous bones that contained different moisture levels (20%, 30%, 40%, 50%, and 60%) were measured with nanoindentation with different peak loads and loading rates. Cortical bones with 20% and 60% moisture were tested with 30 nm, 40 nm, and 50 nm peak loads at 6 nm/s, 8 nm/s, and 10 nm/s loading rates, respectively. Cancellous bones with 5% or 40% moisture percentages were tested with 600 μN, 750 μN, and 1000 μN peak loads at 200 μN/s, 250 μN/s, and 333 μN/s loading rates, respectively. RESULTS Under the same loading condition, specimens with higher moisture contents showed decreased elastic modulus and hardness. Under different loading conditions, the loading modes had little influence on elastic modulus and hardness of cortical bone and cancellous bone with low moisture, but had significant influence on specimens with higher moistures. CONCLUSIONS The elastic modulus and bone hardness were affected by the moisture content and the loading conditions in cortical and cancellous bones with high hydration condition but not in those with low hydration condition.

Figure 1

Preparation of the specimens required for experiments. (A) Representative cortical bone specimens (a) and cancellous bone specimens (b) with a thickness of 5 mm were photographed and are presented here. (B) The change in moisture content in cortical bone (a, b) and cancellous bone (c, d) after heating.

Figure 2

Increased moisture content decreased elastic modulus and hardness of cortical bone and cancellous bone. (A, B) Elastic modulus and hardness of cortical bone decreased with increased moisture content. ** P<0.01, compared with the group with 20% moisture; ^# P<0.05, ^## P<0.01, compared with the group with 30% moisture; ^aa P<0.05, compared with the group with 40% moisture. (C, D) Elastic modulus and hardness of cancellous bone decreased with increased moisture content. ** P<0.01, compared with the group with 5% moisture; ^## P<0.01, compared with the group with 15% moisture; ^aa P<0.01, compared with the group with 25% moisture; ^b P<0.05, compared with the group with 35% moisture.