Human Bone: Functionally Graded Material Structures with Complex Geometry and Loading

1. Human Bone: Functionally Graded Material Structures with Complex Geometry and Loading By: Albert Marin and Dr. Arturo A. Fuentes Department of Mechanical Engineering The University of Texas-Pan American Figure source: <http://www.biovere.com/cart/images/Real_bone_femur_left_s.jpg>.

2. What is a Functionally Graded Material? • A Functionally Graded Material (FGM) is: • A material which both its composition and structure gradually change over volume therefore changing the properties of the material in order to perform a certain function(s). Thus, material properties depend on the spatial position in the structure. The properties that may be designed/controlled for desired functionality include chemical, mechanical, thermal, and electrical properties. Note: Typical Solids Mechanics equations assume the use homogeneous materials have uniformed properties. Significant research is being done by Industry, Universities, National Labs, and Federal Agencies to take more FGMs to the marketplace. Source: Miyamoto, Y., W. A. Kaysser, B. H. Rabin, A. Kawasaki, and R. G. Ford. Functionally Graded Materials: Design, Processing and Applications. Dordrecht/Boston/London: Kluwer Academic.

3. Types of Graded Structures • Stepwise Graded Structures • An example is a spark plug which gradient is formed by changing its composition from a refractory ceramic to a metal • Continuous Graded Structures • An example is the human bone which gradient is formed by its change in porosity and composition • Change in porosity happens across the bone because of miniature blood vessels inside the bone Note: Desired properties gradients may designed by controlling crystal structure and crystal orientation, particulate diameter, bonding state, etc. Source: Miyamoto, Y., W. A. Kaysser, B. H. Rabin, A. Kawasaki, and R. G. Ford. Functionally Graded Materials: Design, Processing and Applications. Dordrecht/Boston/London: Kluwer Academic.

4. Advantages and Challenges of FGM’s • Advantages of FGMs • Provide multifunctionality • Provide ability to control deformation, dynamic response, wear, corrosion, etc. and ability to design for different complex environments • Provide ability to remove stress concentrations • Provide opportunities to take the benefits (pros) of different material systems [e.g. ceramics and metals such as resistance to oxidation (rust), toughness, machinability, and bonding capability] • Challenges of FGMs • Mass production • Quality control • Cost

5. Example of a FGM • The human bone is a an example of a FGM. It is a mix of collagen (ductile protein polymer) and hydroxyapatite (brittle calcium phospate ceramic). The yellow marrow consists of fat which contributes to the weight and the red marrow is where the formation of red blood cells occur. A gradual increase in the pore distribution from the interior to the surface can pass on properties such as shock resistance, thermal insulation, catalytic efficiency, and the relaxation of the thermal stress. The distribution of the porosity affect the tensile strength and the Young’s modulus Figure source: Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. By Donald L. Bartel, Dwight T. Davy, and Tony M. Keaveny. Upper Saddle River, New Jersey: Pearson Education, Inc, 2006.

6. Applications of FGMs • Current applications of FGMs include: • Structural walls that combine two or more functions including thermal and sound insulation • Enhanced sports equipment such as golf clubs, tennis rackets, and skis with added graded combinations of flexibility, elasticity, or rigidity • Enhanced body coatings for cars including graded coatings with particles such as dioxide/mica Source: Miyamoto, Y., W. A. Kaysser, B. H. Rabin, A. Kawasaki, and R. G. Ford. Functionally Graded Materials: Design, Processing and Applications. Dordrecht/Boston/London: Kluwer Academic.

7. More Applications of FGM’s Source: Miyamoto, Y., W. A. Kaysser, B. H. Rabin, A. Kawasaki, and R. G. Ford. Functionally Graded Materials: Design, Processing and Applications. Dordrecht/Boston/London: Kluwer Academic.

8. Human Bone: Functionally Graded Material Structure • The human bone has high strength at the surface as it gradually lowers toward the inside by altering the porosity • From an engineering perspective, the human bone is a remarkable material having unique material properties that has the ability to repair itself and to adapt to its mechanical environment

9. Multifunctionality of Bones • Natural • Hematopoiesis • Formation of red blood cells which occur in the spongy and porous ends of long bones such as the femur • Mineral Storage • 99% of calcium is stored in bones • Mechanical • Protection of vital organs • Such as the brain, heart, spinal cord, lungs • Developed to absorb large amounts of energy yet remain lightweight • Support and Motion • Bones provide a frame that is able to withstand huge amounts of forces during motion for mobility Source: Bartel, Donald L., Dwight T. Davy, and Tony M. Keaveny. Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. Upper Saddle River, New Jersey: Pearson Education, Inc., 2006. 7-9.

10. Support and Motion • Bones are links like those of a truss which enable the body to transmit large forces from link to link Figure source: Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. By Donald L. Bartel, Dwight T. Davy, and Tony M. Keaveny. Upper Saddle River, New Jersey: Pearson Education, Inc, 2006.

11. Figure source: Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. By Donald L. Bartel, Dwight T. Davy, and Tony M. Keaveny. Upper Saddle River, New Jersey: Pearson Education, Inc, 2006.

12. Complex Geometry of Bones • Bones usually have a complex optimized geometry. In fact, bones exhibit a piezoelectric effect used both for detecting an external stress and to remodel bone structures so that no peak stress is developed at any point Figure source: Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. By Donald L. Bartel, Dwight T. Davy, and Tony M. Keaveny. Upper Saddle River, New Jersey: Pearson Education, Inc, 2006. Source: Bartel, Donald L., Dwight T. Davy, and Tony M. Keaveny. Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. Upper Saddle River, New Jersey: Pearson Education, Inc., 2006. 1-213.

13. Complex Loading of Human Bone • The skeletal system is like a machine that allow us to perform all types of activities including physical work and playing sports • Many bones undergo combined loading (axial, torsion, and bending loading) • The skeletal system, as a machine, gets damaged. Under certain loadings, bones break and joints wear out. Our advantage is that our skeletal system is usually able to repair itself Source: Bartel, Donald L., Dwight T. Davy, and Tony M. Keaveny. Orthopaedic Biomechanics: Mechanics and Design in Musculoskeletal Systems. Upper Saddle River, New Jersey: Pearson Education, Inc., 2006. 18-21.

14. Final Remarks • By exploiting the possibilities in the FGM concept, it is anticipated that scientists and engineers will optimize the properties of material systems and new and novel multifunctionalities will be created

15. Questions?