Potential Bone Replacement Materials Prepared by Two Methods
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Potential Bone Replacement Materials Prepared by Two Methods Steve Lee1, Michael Porter1, Scott Wasko2, Grace Lau3, Po-Yu Chen4, Ekaterina E. Novitskaya1, Antoni P. Tomsia3, Adah Almutairi2, Marc A. Meyers1,5 and Joanna McKittrick1,5 1 University of California, San Diego, Materials Science and Engineering Program, 9500 Gilman Dr., La Jolla, CA 92093 USA 2 University of California, San Diego, Skaggs School of Pharmacy, 9500 Gilman Dr., La Jolla, CA 92093 USA 3 Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720 USA 4 National Tsing Hua University, Department of Materials Science and Engineering, Hsinchu 30013, Taiwan, R.O.C. 5 University of California, San Diego, Dept. of Mechanical and Aerospace Engineering, 9500 Gilman Dr., La Jolla, CA 92093 USA
ABSTRACT Natural and synthetic hydroxyapatite (HA) scaffolds for potential load-bearing bone implants were fabricated by two methods. The natural scaffolds were formed by heating bovine cancellous bone at 1325°C, which removed the organic and sintered the HA. The synthetic scaffolds were prepared by freeze-casting HA powders, using different solid loadings (20–35 vol.%) and cooling rates (1–10°C/min). Both types of scaffolds were infiltrated with polymethylmethacrylate (PMMA). The porosity, pore size, and compressive mechanical properties of the natural and synthetic scaffolds were investigated and compared to that of natural cortical and cancellous bone. Prior to infiltration, the sintered cancellous scaffolds exhibited pore sizes of 100 – 300 μm, a strength of 0.4 – 9.7 MPa, and a Young’s modulus of 0.1 – 1.2 GPa. The freeze-casted scaffolds had pore sizes of 10 – 50 μm, strengths of 0.7 – 95.1 MPa, and Young’s moduli of 0.1 –19.2 GPa. When infiltrated with PMMA, the cancellous bonePMMA composite showed a strength of 55 MPa and a Young’s modulus of 4.5 GPa. Preliminary data for the synthetic HA-PMMA composite showed a strength of 42 MPa and a modulus of 0.8 GPa. INTRODUCTION Understanding the structure and mechanical properties of natural bone is vital for developing new bioinspired bone implants. Bone has a complex hierarchical structure from the nano- to macro-scale. Composed of two main types of osseous tissue, cortical and cancellous, bone is a composite material consisting of ~ 67 wt% carbonated apatite minerals, also known as hydroxyapatite (HA), embedded within an organic matrix of type I collagen [1]. Figure 1 illustrates the structural hierarchy of cortical and cancellous bone. Cortical bone is a dense (~ 2.0 g/cm3) collection of cylindrical lamellar sheets composed of aligned, mineralized collagen fibers (osteons) surrounding vascular channels (Haversian canals) necessary for blood flow. Cancellous bone, on the other hand, is a highly porous open cell, foam-like material with high surface area and low density (0.2 – 0.5 g/cm3) composed of lamellar sheets of mineralized collagen fibers. Unlike cortical bone, cancellous bone contains flat lamellae rather than cylindrical osteons [2].
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The porosity and pore size of cancellous bone is
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