Dynamic Fracture Response of a Synthetic Cortical Bone Simulant
This work characterizes the fracture response of a composite material designed to mimic the response of human cortical bone. We have identified additive manufacturing, more generally known as 3-D printing, as a means of reproducing the curvature, variatio
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Dynamic Fracture Response of a Synthetic Cortical Bone Simulant Thomas Plaisted, Allan Gunnarsson, Brett Sanborn, and Tusit Weerasooriya
Abstract This work characterizes the fracture response of a composite material designed to mimic the response of human cortical bone. We have identified additive manufacturing, more generally known as 3-D printing, as a means of reproducing the curvature, variation in thickness, and gradient in porosity characteristic of the human bone between the cortical and trabecular regions. As the base material for developing bone surrogates via additive manufacturing, we evaluate a photocurable polymer with a high loading of ceramic particulate reinforcement that is compatible with stereolithographic additive (SLA) manufacturing. Specimens were printed in two orientations to measure fracture response perpendicular and parallel to the direction of deposition of the layer-by-layer manufacturing process. Mode I fracture behavior of the material was measured in four point bending configuration at high rate via modified split Hopkinson pressure bar for both orientations. In this paper, the fracture behavior of the bone simulant are presented and are compared to the mode I fracture behavior of human cortical bone perpendicular to the long axis of the human femur characterized under the same conditions. Keywords Tissue simulant • Bio-mimicry • Fracture toughness • Cortical bone
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Introduction
Dynamic loading to the human body often results in bone fracture. The study and prevention of these injuries requires bio-fidelic representation of bone in order to understand the kinematics of injury and make accurate assessments of protection schemes. Post Mortem Human Surrogates (PMHS) may be used in these studies, although the bone tissue frequently comes from older donors and may not represent the mechanical characteristics of the general population, particularly if the target population is that of a typical athlete or soldier. Moreover, there can be large variations in the mechanical response of the tissue depending on the age and health of the donor. Developing a synthetic material to mimic the mechanical response of human bone alleviates a number of these concerns. The response of a surrogate material can be tailored to represent a particular age population and specific bone within the human skeleton. Human bone is a complex hierarchical composite material with variable mechanical properties throughout the different regions of the body. The basic constituents of human bone remain the same however: collagen fibers, hydroxyapatite mineral, and water. Each of these constituents are present in the hard outer cortical layer as well as the porous inner trabecular region of the bones. Long bones such as the femur exhibit increased strength and stiffness along the primary loading direction, whereas cranial bones are less stiff and exhibit transverse isotropy in directions tangent to the outer layer due to the absence of a predominant loading direction on the cranium [1]. Additive manufacturing offers an
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