Previous Research

Internship 2004

I worked under Dr. Stefan Judex analyzing the effects of omega-3 fatty acids and dietary fibers on rapidly growing rat bones.

Diploma Thesis 2005/2006

The topic of my thesis was "The Influence of Chemical Modifications on Bone's Chemical and Mechanical Properties. I conducted my research at the National Synchrotron Light Source at Brookhaven Laboratories, and at the Center for Biotechnology at Stony Brook University.

Abstract:

Bone loss and osteoporosis are a major health problem, already affecting 44 million people in the US alone. Osteoporosis is a disease characterized by an accelerated loss of bone. The loss of mineral in bones and thus, loss of bone mineral density significantly increases fracture risk. In osteoporosis and various bone diseases, the chemical composition of bone differs from healthy bones. Bone is primarily composed of mineral and collagen, which together provide its mechanical strength. It is well known that both the mineral and organic phase have a significant influence on the strength of bone. Mineral contributes for stiffness and compressive strength, whereas collagen provides tensile strength and elasticity.
The goal for this study was to chemically induce different, controlled levels of mineralization and collagen structure without changing the other components of bone and measure the mechanical properties on specific regions of the sample. We want to demonstrate the changes that occur due to the chemical modifications at the microscopic level. It was hypothesized that gradual demineralization and collagen digestion will enable the correlation of certain levels of mineralization and collagen structure with the mechanical strength. Briefly, femoral bone from an adult rat and one adult dog was chemically modified to specifically eliminate the mineral or collagen, respectively, without altering the other components of bone. Specifically, bone pieces were soaked in EDTA solution for up to 10 days and collagenase solution for up to 48 h. Subsequently, samples were analyzed for chemical composition using synchrotron infrared microspectroscopy and nanoindentation to assess the mechanical properties. Results show that the process of demineralization is an all-or-nothing process; it does not proceed gradually. Regions that have not been reached by EDTA are still completely mineralized. When determining the level of mineralization by calculating the ratio of mineral to protein, no significant differences were found between the mineralized regions of the different time points. Also, no differences were found in the collagen cross-linking ratio amongst the different time points in the remaining mineralized regions. However, the collagen cross-linking ratio was significantly higher in the demineralized edge of the samples, indicating that EDTA does change the organic matrix. Yet, the exact changes in collagen structure need to be determined more precisely. Elastic modulus and the level of mineralization were relatively constant over all regions investigated.
Digesting bone collagen by exposing bone to collagenase type I solution did not show any differences in the amount of collagen and the collagen cross-links compared to the control sample, suggesting that the collagen did not get degraded.
The hypothesis of gradual demineralization and collagen digestion could not be verified by our results. The resulting small range of mineralization within the remaining mineralized regions offered no correlation with the elastic modulus. In future experiments, other demineralizing and collagen digesting agents should be analyzed to obtain a gradual demineralization and collagen digestion and hence enable us to correlate chemical and mechanical properties to study the precise influence of bone’s chemical composition on its mechanical strength.