Ryan K. Roeder
Associate Professor
Aerospace and Mechanical Engineering

Research Areas

Personal Web Page
Click images for full size graphics.
Contrast Agents for Micro-Computed Tomography of Microdamage in Bone
Funding: U.S. Army Medical and Materiel Command through the Peer Reviewed Medical Research Program
Postdoc: Mark Z. Zhang
Graduate Students: Matt Landrigan and Ryan Ross
Undergraduate Interns: Matthew Meagher, Carl Berasi and Jimmy Buffi
Collaborators: Glen L. Niebur

Fatigue fractures, or "stress fractures," are common in people undergoing intense physical activity such as military recruits, manual laborers and athletes. Stress fractures impose a significant burden on the health of military personnel and defense spending. The total cost of stress fractures is estimated to exceed $10M/year in medical costs and lost duty. Currently, clinical diagnosis of stress fractures is often delayed by weeks to months due to nonspecific symptoms, and the limited sensitivity and specificity conventional imaging techniques. Consistent with larger societal trends, the mean age of active duty U.S. military personnel is rising. Increases in the number of female personnel will also translate into increases in the number veterans with osteoporosis. In the United States, treatment costs for all osteoporotic fractures exceed $13B/year. Current clinical assessment of fracture risk relies on measurements of bone mass using dual-energy x-ray absorptiometry (DEXA) which results in a significant percentage of false negatives. Therefore, other factors of bone quality, such as microdamage, are also likely to be implicated in fracture susceptibility.

The objectives of this project are to 1) develop damage-specific contrast agents, with greater x-ray attenuation than bone, for micro-computed tomography (micro-CT) of microdamage; 2) evaluate the x-ray attenuation, deliverability and specificity of contrast agent formulations; and, 3) quantify the effects of the contrast agent on micro-CT images in damaged and undamaged bone, and correlate the measurements to conventional measures of microdamage. A damage-specific contrast agent for micro-CT would enable researchers to determine the effects of microdamage on bone strength and fracture susceptibility. Moreover, the development of non-destructive techniques for detecting microdamage in bone could eventually translate into in vivo and clinical applications for assessing bone quality and fracture risk. Thus, whether through improved understanding of the etiology of stress and osteoporotic fractures, or the development of improved clinical methods to diagnose fracture risk, this work is aimed at improving bone health in military personnel and civilians, ranging from new recruits and athletes to retired veterans and the elderly.

Hydroxyapatite Whisker Reinforced Biocomposites for Synthetic Bone Substitutes
Funding: Indiana 21st Century Fund and the U.S. Army Medical Research and Materiel Command
Graduate Students: Gabriel L. Converse, Robert J. Kane and Timothy Conrad
Undergraduate Intern: John Souder
Collaborators: JoEllen Welsh, Ph.D. (Biological Sciences, Notre Dame) and Stephen Smith, M.D. (North Central Neurosurgery, South Bend, IN)

In order to meet the challenges of the next century, new synthetic biomaterials must be developed that are able to interact synergistically with natural tissues and biological processes. The extracellular matrix of bone tissue is a collagen matrix reinforced with apatite mineral crystals that have an elongated c-axis and exhibit a preferred orientation along directions of principle stress. Hydroxyapatite (HA) is the closest synthetic equivalent to human bone mineral, and is biocompatible and bioactive in vivo. The overall objective of this project is to investigate processing-structure-property relationships in HA whisker reinforced biocomposites in order to mimic salient aspects of the structure and biomechanical function of human bone tissue. For example, HA whisker reinforced polyetheretherketone (PEEK) has been tailored to mimic the elastic moduli, ultimate tensile strength and anisotropy of human cortical bone. The fatigue life of HA whisker reinforced high density polyethylene (HDPE) was shown to be 4-5 times longer than that for conventional powder reinforcement. Micromechanical models are being developed to relate the effects of the reinforcement morphology, orientation, and volume fraction to the mechanical properties. The in vitro response of osteoblasts to HA whisker reinforced biomaterials is also being investigated with collaborators in Biological Sciences. In vivo studies in small animal models are planned in collaboration with a local surgeon.

Structural and Mechanical Anisotropy in Human Cortical Bone Tissue
Graduate Student: Justin Deuerling

Bone, as a biomaterial, consists of directional structural features across several unique hierarchical scales, ranging from nano-scale crystals and molecules to the macroscopic shape. However, the foundational structural unit across the hierarchical scales is a relatively simple two phase arrangement of anisometric bone mineral (apatite) preferentially oriented in a collagen matrix. Despite a growing database of measurements for the mechanical anisotropy of cortical bone, few efforts have been made to quantitatively measure influential structural features, e.g., the preferred orientation of bone mineral, and virtually no efforts have been made to correlate the anisotropy to structural measurements. Furthermore, the mechanical anisotropy in cortical bone is known to vary with anatomic location. Efforts to characterize and correlate structural features to mechanical anisotropy will also consider various anatomic sites, which will in turn provide data for clinically relevant anatomical sites (e.g., the proximal femur). The objectives of this work are to 1) characterize and quantitatively correlate anatomic variation in the mechanical anisotropy of human cortical bone with measurements of relevant structural features, 2) use this data to develop new micromechanical models which account for non-uniformity and anisotropy prior to hierarchical scaling, and 3) apply the knowledge gained in the design and synthesis of new orthopaedic biomaterials which can be tailored to function as a mechanical analog to human cortical bone.

Synthesis of Ceramic Powders of Tailored Size and Morphology
Funding:U.S. Army Medical and Materiel Command through the Peer Reviewed Medical Research Program and the Indiana 21st Century Fund
Postdoc: Mark Z. Zhang
Graduate Students: Gabriel L. Converse and Timothy Conrad
Undergraduate Intern: Matthew Meagher

Chemical solution syntheses include environmentally benign and highly controllable methods for precipitating inorganic crystals. Nanoparticles are of interest for use as contrast agents in biomedical imaging. The use of anisometric (e.g., whiskers or plate-like) and/or nano-scale reinforcement particles is well-known to enhance the mechanical properties in engineered composites. Many natural biocomposites, such as bone and teeth, use biochemical processes to control the size and shape of the mineral phase that reinforces an organic phase. The objectives of this work are to 1) examining processing effects on the size and morphology of precipitates and 2) delineate governing reaction mechanisms in order to improve process control.

H. Leng, X. Wang, R.D. Ross, G.L. Niebur and R.K. Roeder, “Micro-Computed Tomography of Fatigue Microdamage in Cortical Bone Using a Barium Sulfate Contrast Agent,” J. Mech. Behav. Biomed. Mater., 1 [1] 68-75 (2008).

X. Wang, D.B. Masse, H. Leng, K.P. Hess, R.D. Ross, R.K. Roeder and G.L. Niebur, “Detection of trabecular bone microdamage by micro-computed tomography,” J. Biomechanics, 40 [15] 3397-3403 (2007).

G. L. Converse, W. Yue and R. K. Roeder, "Processing the tensile properties of hydroxyapatite-whisker-reinforced polyetheretherketone," Biomaterials, 28 [6] 927-935 (2007).

W. Yue and R. K. Roeder, "Micromechanical model for hydroxyapatite whisker reinforced polymer biocomposites," J. Mater. Res., 21 [8] 2136-2145 (2006).

R. K. Roeder, G. L. Converse, H. Leng and W. Yue, "Kinetic Effects on Hydroxyapatite Whiskers Synthesized by the Chelate Decomposition Method," J. Am. Ceram. Soc., 89 [7] 2096-2104 (2006).

Copyright 2007 | Notre Dame Home | Notre Dame BIO Home | CoE Home | AME Home
To Notre Dame Homepage E-mail Us