Abstract
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.
Highlights
Autografts are commonly used for human bone replacement; they are limited in volume and additional surgery is needed [1]
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
Nanoindentation Results In total, 642 indentations were made within osteons and nearby interstitial regions of cortical bone along the longitudinal direction
Summary
Autografts are commonly used for human bone replacement; they are limited in volume and additional surgery is needed [1]. Heat-treated cortical bone has been proposed as a substitute for bone transplant material to overcome the risks of rejection and disease transfer from allograft and xenograft [2]. Tages obtained in biological and mechanical properties, it is believed that heat-treated bones can be excellent alternative material for bone grafts and synthetic bone substitutes. Extensive research has been conducted in the past decade to study the structural arrangements, material compositions and mechanical properties of bone [1,2,3,4,5,6,7,8,9,10] in order to understand the bone problems such as bone fracture. Bone remodeling and the design of bone-implant system have been carried out.
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