Abstract—In this study the inhomogeneity in energy dissipation during tensile deformation of cortical bone was analyzed with the help of toughness and plastic work parameters. The compositional parameters were also determined for corresponding locations of bone diaphysis to observe their effect on elastic and plastic part of energy dissipation. The plastic part of energy dissipation was found to be mainly influenced by the compositional parameters of cortical bone. This study suggests that the locational variation in energy dissipation along bone diaphysis is mainly controlled by the deformation mechanisms that take place during the plastic deformation of cortical bone. Index Terms—Bone composition, Bone diaphysis, Inhomogeneity, Plastic work, Toughness I. INTRODUCTION ONE, a mixture of ductile protein polymer (collagen) and brittle calcium phosphate ceramic (hydroxyapatite), is considered as a remarkable natural material that has the ability to repair itself and to adapt to its mechanical environment. The mechanical properties of cortical bone are found to be significantly correlated to its compositional parameters such as minerals, organics, water, and density [1-7]. The locational variation in these compositional parameters along bone diaphysis is the main cause of mechanically heterogeneous nature of bone. Various earlier studies have been conducted to analyze the elastic heterogeneity in bone material [8-13]. These studies are somewhat useful for the development of numerical models used in the design of orthopedic implants and study of adoptive bone remodeling. However, bone material is considered to have sufficient amount of nonlinearity during deformation and failure [14-17]. Therefore, for the development of improved prosthetic implants and detailed study of bone remodeling, it is essential to incorporate plastic inhomogeneity to the numerical modeling and for the mechanical assessment of cortical bone. Different other studies and numerical models are also Manuscript received March 23, 2013. N.K. Sharma is with the Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India (phone: +91-9310664161; e-mail: enksharma@yahoo.com). Swati Sharma is with the Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India (phone: +91-8744868155; e-mail: swati.2517@gmail.com). D. K. Sehgal is with the Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India (e-mail: drofsehgal@yahoo.com). R. K. Pandey is with the Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India (e-mail: rkpiitd@yahoo.com). used to assess the failure of cortical bone [18,19]. This assessment is important from both the engineering and clinical point of view in order to understand the quality of bone. Failure of bone is characterized by dissipation of stored energy from an applied load and since the bone material is mechanically heterogeneous the amount of energy dissipation may be different at different anatomic locations. The locational effect of bone compositional parameters and apparent density to energy dissipation is also obvious. In view of this, the investigation regarding the effect of bone composition and density to quantitative assessment of variation in energy dissipation at different locations of cortical bone diaphysis is important for detailed analysis of overall bone quality. Toughness has been a key measure of bone quality [20] and is used to analyze the effect of compositional parameters on bones of different groups (according to age, gender, species etc) [21,22]. While toughness incorporates the total energy (elastic as well as plastic) until failure, the plastic work measures the energy dissipated during post- yield deformation of bone. These two parameters can be used together for detailed investigation of bone deformation behavior. In the present work toughness and plastic work parameters are used to provide an estimate of inhomogeneity in energy dissipation along cortical bone diaphysis for tensile deformation of bone. Further, the influence of bone density and composition (mineral, organic and water content) on the locational variation in the amount of energy dissipation has been investigated. II. MATERIALS AND METHOD The present study has been conducted in the tibiae cortical bones obtained from young bovine of age about 36 months. After removal of bone tissue from the body the surrounding soft tissue was removed and bone tissue was wrapped in gauze, soaked in normal saline, wrapped with plastic wrap and placed in sealed, airtight plastic bags. These plastic bags were placed in freezer and stored at -20°C within 1 hr after the bone tissues had been harvested. The bones were kept hydrated in saline upon removal from the freezer and during all stages of tissue preparation. For specimen preparation the epiphyses ends of the long bone were removed using vertical band saw leaving only the diaphysis section. The round cylindrical edges of the diaphysis were flattened into flat rectangular prismatic edges with the help of a belt sander. After flattening, the whole diaphysis of the cortical bone was sectioned into three equal segments namely; upper, middle and lower parts of the bone diaphysis. Effect of Bone Composition and Apparent Density on Inhomogeneity in Energy Dissipation during Tension N.K. Sharma, Swati Sharma, D.K. Sehgal, and R.K. Pandey B Proceedings of the World Congress on Engineering 2014 Vol II, WCE 2014, July 2 - 4, 2014, London, U.K. ISBN: 978-988-19253-5-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) WCE 2014