Assessing heat-treatment effects on bovine cortical bones by nanoindentation

Among different sterilization methods, heat-treatment of bone is recognized as one of the simple and practical methods to lower the human immunodeficiency virus (HIV) infection and overcome the risks of rejection and disease transfer from allograft and xenograft during bone transplantation. In order to best characterize the micro-structural mechanical property of bone after heat treatment, the nanoindentation technique was applied in this study to measure the localized elastic modulus and hardness for interstitial lamellae and osteons lamellae of bovine cortical bones at temperature 23degrees C (room temperature- pristine specimen), 37degrees C, 90 degrees C, 120 degrees C and 160 degrees C, respectively. The elastic modulus (E) and hardness (H) of interstitial lamellae obtained higher values as compared with osteons lamellae which show that interstitial lamellae are more stiff and mineralized than osteons. Moreover, as a specimen pre-heat treated at 90 degrees C, the E and H values of interstitial lamellae and osteons were closed to a pristine specimen. For a specimen pre-heat treated at 120 degrees C, both interstitial lamellae and osteons obtained an increase in E and H values. As a specimen pre-heat treated at 160 degrees C, the interstitial lamellae and osteons obtained a slight decrease in E and H values. These findings are correlated to results reported by other researchers [1, 2] that calcified collagen molecules starts to degenerate at about 120 degrees C and complete at 160 degrees C. Interestingly, when a specimen was pre-heat treated at 37 degrees C, both interstitial lamellae and osteons obtained significant decreases in E values of 57% and 40%, respectively as compared to the pristine specimen; while in H values, there was a decrease of 27.4% and 15%, respectively. Thus, this paper will investigate the mechanical properties of bovine cortical bones under various temperature ranges by nanoindentation technique

Measurements of heat treatment effects on bovine cortical bones by nanoindentation and compression testing

Heat treatment of bone is one of the reliable and simple sterilization methods to overcome the risk of rejection and disease transfer from allograft and xenograft, in particular for the prevention of human immunodeficiency virus (HIV) infection. However, the mechanical property of the micro-structural level after heat treatment is not well characterized. To address this issue, this study was carried out to compare the localized mechanical properties of micro-structural tissue with those at the global structural level. Nanoindentation technique has been well accepted as an accurate technique to measure mechanical property of small and heterogeneous specimen nondestructively, as well as the complex bio-material of micro-structural level, often with a resolution of better than 1 µm. In this study, nanoindentation was conducted to measure the localised elastic modulus and hardness values of bones at temperature of 23˚C (room temperature – non- heated sample), 90˚C and 150˚C, respectively. All experiments were conducted at room temperature (~23˚C). The elastic modulus (E) and nanoindentation hardenss (H) values in the longitudinal direction of bones heated at 150˚C were recorded as 23.43 GPa and 0.73 GPa, respectively; as in transverse direction, the E and H values were 12.77 GPa and 0.54 GPa, respectively. It showed significant increases of 44% and 43% in the longitudinal direction as compared to those of the non heat-treated bones. In addition, E and H values in transverse direction also showed increases of 23% and 38%, respectively as compared to those of the non heat-treated bones. Furthermore, heat-treated bones at 90˚C in longitudinal direction also appeared to have significant increases of 18% and 31% in E and H values, respectively. However, the E and H values in transverse direction increase only by 0.4% and 12.8%, respectively. In addition, compressive test is employed to measure the global stiffness (E) of the bone samples. When heated at 150˚C, the bone specimen showed an increase of 60% in stiffness (E) and an increase of 26% in yield stress. On the other hand, when heated at 90˚C, a slight increase of 11.4% in stiffness (E) and 21.5% in yield stress were recorded respectively. Furthermore, energy dispersive X-ray spectroscopy (EDX) which integrated with Backscattered Electron (BSE) imaging was conducted to examine the relationship between mineral content and mechanical strength within the nanoindentation regions. The data demonstrated that the non heat-treated bones obtained the highest calcium wt% amongst the three groups; as temperature increased, there was a slight decrease in calcium wt%; however, the changes were not severe in this study