Task Progress:
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SUPPLEMENTAL REPORTING SEPTEMBER 2013: All proposed aims and activities have been completed.
REPORTING JANUARY 2013: Micro-damage Analysis (in-progress): After mechanical testing, one half of each fractured beam was bulk stained in 1% basic fuchsin and embedded in polymethy-methacrylate (PMMA) using standard staining and embedding protocols. The plastic blocks were then cut to obtain 200 µm thick sections, transverse to the beam length. The sections were grounded to approximately 70 µm thickness, fine polished using alumina slurries (particle diameters 1.0 µm and 0.05 µm) on cloth wheel and mounted on plastic slides for imaging. Beam cross-sections were then imaged under an optical microscope (AxioImager, Carl Zeiss) equipped with a multichannel fluorescence acquisition system (Axiovision, Zeiss). Sections (n=3/beam) from the fracture edge were used to quantify load-induced damage. Preliminary results obtained from monotonically tested beams show evidence of micro-cracks ranging from 30 to 70 µm in length with smaller cracks observed in the drug treated groups and at lower density. Work is underway to correlate toughness and fatigue-life with extent of microdamage in beams.
Fatigue Crack Growth (in-progress): Miniature compact tension (CT) specimens (6x4x1 mm3) were prepared from the posterior cortex of the radius using slicing equipment (Buehler, Isomet 5000). The specimen also comprised of a sharp notch and two precision holes to mount the specimen on a set of loading fixtures using stainless steel pins. Specimens are prepared such that the direction of crack extension is parallel to the long-axis of the osteons. A special setup was designed to monitor crack length, comprised of a fixed lens (200X) digital microscope (ProScope HR) that is attached to a manual XYZ translation stage for accurate positioning of the microscope. The entire assembly is mounted on an aluminum base plate attached to a microscope boom. Crack growth is conducted under cyclic fatigue at a frequency of 5 Hz and a stress ratio (R=smin/smax) of 0.1. The specimen geometry and crack length are used to calculate stress intensity distribution around the crack tip and the results are modeled according to Paris' Law, da/dN=C(delta K)m, where da/dN = rate of crack growth, delta K = stress intensity range, C = crack growth coefficient and m = crack growth exponent (brittleness index). Experiments are currently underway to quantify and compare m and C between all groups.
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Abstracts for Journals and Proceedings
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Bajaj D, Belman R, Fritton JC. "Evaluation of spatial variation in tissue-level mechanical properties of small animal cortical bone under diametral compression." Orthopaedic Research Society Annual Meeting 2012, San Francisco, CA, February 4–7, 2012. Orthopaedic Research Society Annual Meeting 2012, San Francisco, CA, February 4–7, 2012. Poster 0359. , Feb-2012
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Abstracts for Journals and Proceedings
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Bajaj D, Palacio-Mancheno PE, Patel M, Reyes G, Cardoso L, Schaffler MB, Fritton JC. "Remobilization following anti-resorptive treatment with risedronate decreases cortical tissue toughness." First Annual Musculoskeletal Repair and Regeneration Symposium, Albert Einstein College of Medicine, Bronx, NY, October 4, 2012. First Annual Musculoskeletal Repair and Regeneration Symposium, Albert Einstein College of Medicine, Bronx, NY, October 4, 2012. , Oct-2012
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Abstracts for Journals and Proceedings
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Bajaj D, Palacio-Mancheno PE, Schaffler MB, Cardoso L, Fritton JC. "Effects of bisphosphonate treatment and remobilization on the tissue-level quality of immobilized bone." 2012 NASA Human Research Program Investigators’ Workshop, Houston, TX, February 14-16, 2012. 2012 NASA Human Research Program Investigators’ Workshop, Houston, TX, February 14-16, 2012. , Feb-2012
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Abstracts for Journals and Proceedings
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Geissler JR, Bajaj D, Allen MR, Burr DB, Fritton JC. "Alendronate treatment elicits a reduction in fatigue-life of canine cortical bone." Orthopaedic Research Society Annual Meeting 2012, San Francisco, CA, February 4–7, 2012. Orthopaedic Research Society Annual Meeting 2012, San Francisco, CA, February 4–7, 2012. Abstract #0089, , Feb-2012
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Abstracts for Journals and Proceedings
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Bajaj D, Patel P, Schaffler MB, Fritton JC. "Cortical bone structure is completely recovered with remobilization after risedronate treatment while tissue-level cyclic fatigue life is not." 2013 NASA Human Research Program Investigators’ Workshop, Galveston, TX, February 12-14, 2013. 2013 NASA Human Research Program Investigators’ Workshop, Galveston, TX, February 12-14, 2013. , Feb-2013
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Abstracts for Journals and Proceedings
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Bajaj D, Palacio-Mancheno PE, Patel M, Reyes G, Cardoso L, Schaffler MB, Fritton JC. "Decreased Cortical Tissue Toughness Upon Remobilization after Anti-Resorptive Treatment with Risedronate." Orthopaedic Research Society Annual Meeting 2013, San Antonio, TX, January 26-29, 2013. Orthopaedic Research Society Annual Meeting 2013, San Antonio, TX, January 26-29, 2013. Poster 0693. , Jan-2013
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Articles in Peer-reviewed Journals
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Bajaj D, Geissler JR, Allen MR, Burr DB, Fritton JC. "The resistance of cortical bone tissue to failure under cyclic loading is reduced with alendronate." Bone. 2014 Jul;64:57-64. Epub 2014 Apr 1. http://dx.doi.org/10.1016/j.bone.2014.03.045 ; PubMed PMID: 24704262; PubMed Central PMCID: PMC4041841 , Jul-2014
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Articles in Peer-reviewed Journals
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Geissler JR, Bajaj D, Fritton JC. "American Society of Biomechanics Journal of Biomechanics Award 2013: Cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures." J Biomech. 2015 Apr 13;48(6):883-94. Epub 2015 Feb 2. Review. https://doi.org/10.1016/j.jbiomech.2015.01.032 ; PubMed PMID: 25683519; PubMed Central PMCID: PMC4380555 , Apr-2015
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Awards
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Bajaj D. "2nd Place, Poster Competition, 3rd Annual National Postdoc Appreciation Day Symposium. UMDNJ-RWJMS, Piscataway, NJ, September 2011." Sep-2011
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Awards
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Bajaj D. "USRA New Investigator Award for Outstanding Bone Research, Houston, Texas, February 2012." Feb-2012
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Books/Book Chapters
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Subramanian G, Bajaj D, Iyer S, Fritton JC, Quek SYP. "Osteonecrosis of the Jaw: A Spectrum Disorder?" in "Osteonecrosis: Diagnosis, Treatment and Management." Ed. G.I. Bianchi, P.C. Giordano. Hauppauge, NY : Nova Science Publishers, Inc., 2012. p. 1-44., Dec-2012
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