www.elsevier.com/locate/jmbbm Available online at www.sciencedirect.com Research Paper Indentation size effect of cortical bones submitted to different soft tissue removals A. Bandini a,b , D. Chicot b,n , P. Berry a , X. Decoopman b , A. Pertuz c , D. Ojeda d a Department of Civil, Environmental and Materials Engineering (DICAM), University of Bologna, via Terracini, 28, 40131, Bologna, Italy b University Lille Nord de France, USTL, LML, CNRS, UMR 8107, F-59650 Villeneuve d’Ascq, France c Central University of Venezuela, Mechanical Engineering School, Material Science Department, Caracas 1050, Venezuela d Biomechanical Center, Engineering Faculty, University of Carabobo, Valencia, Venezuela article info Article history: Received 23 April 2012 Received in revised form 14 February 2013 Accepted 17 February 2013 Available online 28 February 2013 Keywords: Bone Elastic modulus Martens hardness Creep Instrumented indentation test abstract Properties of elasticity, hardness and viscosity are determined for the study of the visco- elastoplastic behavior of bones. The mechanical properties are compared in two upright sections of the bone due to their anisotropy. Besides, influence of hydration treatments leading to structural modifications of collagen and ground substance contents of bones on the mechanical properties is studied on a femoral cortical bovine bone. The treatments applied to the bone are used by forensic anthropologists to remove the soft tissue and modifying the hydration degree coupled to the collagen content. From instrumented indentation experiments, the hardness is characterized by the macrohardness and a hardness length-scale factor stating the hardness-load dependence. The elastic modulus results from the application of the methodology of Oliver and Pharr (1992). The coefficient of viscosity is deduced from a rheological model representing the indenter time–displacement observed under the application of a constant load. As a result, all the mechanical properties are found to be lower in the transverse section in an extent depending on the hydration treatment, i.e. the different values are located between 5% and 25% for the hardness around 0.5 GPa, between 25% and 40% for the elastic modulus around 20 GPa and between 2% and 35% for the coefficient of viscosity around 60 GPa.s. Unexpectedly, the elastic modulus to coefficient of viscosity ratio is found to be independent on the hydration treatment. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction The bone structural system is very important in the human body for load transmission, mechanical resistance and vital organs protection (Cowin, 1989). For clinical aspects, the determination of the mechanical properties of bones is very helpful for the osteoporosis treatment and for other diseases associated with bone fragility (Currey, 1984). To study the mechanical properties of bones, the soft tissue should be removed without compromising the surface morphology or the overall bone integrity and without introducing a ‘‘cleaning damage’’. For this purpose, a number of acceptable methods can be used to clean the bones including macerating in water, simmering or boiling, soaking in ammonia. Each of this 1751-6161/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jmbbm.2013.02.011 n Corresponding author. Tel.: þ33 359 572 852; fax: þ33 320 677 321. E-mail address: didier.chicot@univ-lille1.fr (D. Chicot). journal of the mechanical behavior of biomedical materials20 (2013) 338–346