University of Notre Dame BIO Group

Glen L. Niebur
Associate Professor
Aerospace and Mechanical Engineering

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Anisotropic Damage of Cancellous Bone
Cancellous bone is a highly porous, anisotropic, cellular solid that serves several functions in the skeleton. Primarily it provides a structure to distribute loads from the surface of articulating diarthroidal (cartilage covered) joints to the main bone structure. This region of bone is commonly affected by osteoporosis and osteoarthritis causing it to weaken and become susceptible to fracture. Statistically, a woman who lives past the age of fifty has a one in seven chance of having a hip fracture due to osteoporosis. The annual medical expenditures for treatment of these fractures is over 10 billion dollars.

The goal of this project is to investigate the changes in the material properties of cancellous bone as a result of over loading. It has been demonstrated that loading beyond the linear elastic range results in a decrease in the effective elastic modulus of cancellous bone for subsequent loading. However, this has only been shown for uniaxial loading. The goal of this project is to investigate the effects of overloading in various states of uniaixal and multiaxial loading to determine a constitutive law for anisotropic damage. This information will be gathered for both normal and osteoporotic bone in order to determine how the damage mechanics change with the development of osteoporosis. The results will be applied to the diagnosis and treatment of osteoporosis, and to eventually improve our understanding of the mechanical and biological causes of osteoporosis. The project will involve experimental, computational, and theoretical components.

Microdamage Detection Using Computed Tomography
In cooperation with Ryan Roeder, we are developing techniques to label microdamage in bone using contrast agents. This technique will enable much better understanding of the evolution of microdamage during loading, its spatial correlation to loading, and its relationship to predicted loads.

Continuum Properties of Cellular Solids
Porous cellular materials are common in nature, for example cancellous bone, cork, and wood are all highly porous (solid volume fraction less than 50%). These materials have macroscopic material properties that depend on both the arrangement of the solid phase of and on the mechanical properties of the bulk material that makes up the solid phase. Knowledge of the relationships between these two factors and the macroscopic properties can be used in the development of computational analysis tools, and in the design of foamed and cellular materials. The long-term goal of this project is to relate the geometry of the cellular material and the properties of the constitutive solid to its macroscopic properties, and to investigate how variations of the cell geometry, or various inclusions affect the macroscopic properties. A continuum level model that incorporates the behavior of the cell geometry will be developed. Eventually, non-linear material properties and large deformations of the cell walls will be used to determine properties such as the yield stress, ultimate strength, and energy absorption capabilities. This project involves, experimental, computational and theoretical aspects.

Effects of Fusion Mass on Lumbar Inter-body Fusion Strength
Spinal fusion is a common procedure for treatment of herniated discs in the lumbar spine. This procedure involves removing the injured disc and fusing the adjacent vertebrae with a bone graft or other hardware. The goal of this project is to investigate the effects of variations on the mechanical properties of the resulting fusion mass on the strength of the final fusion and kinematical changes in the spine behavior following surgery.

The long-term goal of this project is to develop tools that can be used by surgeons and orthopaedic device manufacturers to improve the design and selection of surgical approaches and hardware constructs for spinal fusion.

Liu, X., Wang, X., Niebur, G.L., 2003, "Effects of damage on the orthotropic material symmetry of bovine tibial trabecular bone," Journal of Biomechanics vol. 36, no. 12, pp. 1753-1759.

Wang, X., Liu, X., Niebur, G.L., 2004, "Preparation of on-axis cylindrical trabecular bone specimens using micro-CT imaging", Journal of Biomechanical Engineering, vol 126. no. 1, pp. 122-125.

Wang, X., Guyette, J., Liu, X., Roeder, R.K., and Niebur, G.L., 2005, "Axial-Shear Interaction Effects on Microdamage in Bovine Tibial Trabecular Bone," The European Journal of Morphology, vol. 42, no. 1/2, pp. 61-69.

Wang, X. and Niebur, G.L., 2006, "Microdamage propagation in trabecular bone due to changes in loading mode," Journal of Biomechanics, vol. 39, no. 5, pp. 781-890.