The Influence Of Residual Bioactivities On The Tribological Properties Of Bone Tissue

It is well know that skeleton systems are to support the necessary forces. To achieve this function, the skeleton systems have the excellent mechanical properties. The skeletal systems have many biotribological pairs (joint pairs). Due to disease or trauma, the joint pairs are often damaged resulting in failure of the original function, which is one of the serious problems threatening human health. For solve this problems in clinical medicine, application of artificial bone to repair and replace of human diseased or damaged tissue is an effective approach. Natural bone tissue and the implant are formed a typical biotribological pair. The interface exist the exchange of the living materials, such as water, protein, minerals, etc. This process has an important effect on the biotribological behavior, namely the biological activity of bone tissue on biotribological behavior have remarkable influence. At present, it has been studied that the changes of bioactive substances in bone tissue affect mechanical properties and viscoelasticity. However, there has been no reported about the biological activity of bone tissue itself impacting biotribological behavior. Therefore, carrying out the research about the influence of residual bioactivities on biotribological properties of bone tissue is innovative. This is helpful to understand the essential difference between the tribological properties of natural biological materials and engineering materials. It is provided an important theoretical basis for bone tissue repairing, as well as the innovation of artificial bone technology.In this work, bone tissue samples having different bioactivities were prepared by the process of dehydration, and the two groups of dried samples are soaked. While, artificial bone material is also studied. The influence of residual bioactivities on biotribological properties of bone tissue was studied in ball-on-flat configurations. It is also utilize finite element method to calculate the stress distribution of bone tissue. The main conclusion can be shown as following:(1) In the tribological experiment, it has an important influence of water content on biotribological properties of bone tissue, mainly for:the decrease of water content resulted in elastic modulus and nano-hardness of bone tissue increased but decreased toughness. Bone tissue become brittle and sensitive to the external loading. The water content also affects the viscoelasticity of bone tissue, the bone tissue after dehydration is prone to fatigue wear and spalling. The recovery of the water under infiltration could restore the viscosity and elasticity of the bone tissue at a certain extent, but the tribological properties is unrecoverable. The change of water contents affect the collagen and mineral of bone tissue too, leading to the variation of the biotribological behavior.(2) In this paper, the crystallization of water can be kept intact in the mineral phase. Under 60℃, flowing water and a small amount of affinity water were removed. Mass of affinity water was not removed until the temperature reach to 120℃. In addition, type I collagen which is the main component of bone matrix has thermally unstability, it is apt to melt. Furthermore, the removal of water will lead to collagen hardening or degeneration. All of these weaken the cross-link of collagen in bone tissue. Thus, denatured collagen was broken by extrusion or pulling easily, which generated delamination or spalling. The inactivation of collagen also causes the mineral crystals losing bound, thereby increasing wear. The inactivation of bioactivities has a significant impact on the tribological behavior of bone tissue.(3) FEM and the tribological behavior of artificial bone and its bioactive coating deepen the understanding of the importance of bioactivity. Based on FEM, the porosity of bone tissue increased obviously after dehydration, as well as the stress of the whole bone tissue, which resulted in bone tissue under the destructive stress. It is remarkable that the hole tends to stress concentration, and the hole impairs the protective effect of the special structure of Haversian system, this is the reason why bone tissue after dehydration is higher probability to injury. Artificial bone and its bioactive coating test show that polysaccharide play an important role similar to the collagen of nature bone. It can cross-link inorganic components so as to enhance the viscoelasticity and toughness and to improve the biotribological properties. The HA/Ag coating is resemble to the dehydrated bone tissue, and its tribological propertied turn to deterioration.