David Kohn

Publications of David Kohn

• The bone diagnostic instrument III: testing mouse femora.

  Authors: Connor Randall, Phillip Mathews, Eugene Yurtsev, Nadder Sahar, David Kohn, Paul Hansma

  The Review of scientific instruments. 07/2009; 80(6):065108.

  Here we describe modifications that allow the bone diagnostic instrument (BDI) [P. Hansma et al., Rev. Sci. Instrum. 79, 064303 (2008); Rev. Sci. Instrum. 77, 075105 (2006)], developed to test humanHere we describe modifications that allow the bone diagnostic instrument (BDI) [P. Hansma et al., Rev. Sci. Instrum. 79, 064303 (2008); Rev. Sci. Instrum. 77, 075105 (2006)], developed to test human bone, to test the femora of mice. These modifications include reducing the effective weight of the instrument on the bone, designing and fabricating new probe assemblies to minimize damage to the small bone, developing new testing protocols that involve smaller testing forces, and fabricating a jig for securing the smaller bones for testing. With these modifications, the BDI was used to test the hypothesis that short-term running has greater benefit on the mechanical properties of the femur for young growing mice compared to older, skeletally mature mice. We measured elastic modulus, hardness, and indentation distance increase (IDI), which had previously been shown to be the best discriminators in model systems known to exhibit differences in mechanical properties at the whole bone level. In the young exercised murine femora, the IDI was significantly lower than in young control femora. Since IDI has a relation to postyield properties, these results suggest that exercise during bone development increases post yield mechanical competence. We were also able to measure effects of aging on bone properties with the BDI. There was a significant increase in the IDI, and a significant decrease in the elastic modulus and hardness between the young and old groups. Thus, with the modifications described here, the BDI can take measurements on mouse bones and obtain statistically significant results.

• The tissue diagnostic instrument.

  Authors: Paul Hansma, Hongmei Yu, David Schultz, Azucena Rodriguez, Eugene A Yurtsev, Jessica Orr, Simon Tang, Jon Miller, Joseph Wallace, Frank Zok [......] Carol Chen, Mathilde Peters, David Kohn, Jenni Buckley, Xiaojuan Li, Lisa Pruitt, Adolfo Diez-Perez, Tamara Alliston, Valerie Weaver, Jeffrey Lotz

  The Review of scientific instruments. 06/2009; 80(5):054303.

  Tissue mechanical properties reflect extracellular matrix composition and organization, and as such, their changes can be a signature of disease. Examples of such diseases include intervertebral diskTissue mechanical properties reflect extracellular matrix composition and organization, and as such, their changes can be a signature of disease. Examples of such diseases include intervertebral disk degeneration, cancer, atherosclerosis, osteoarthritis, osteoporosis, and tooth decay. Here we introduce the tissue diagnostic instrument (TDI), a device designed to probe the mechanical properties of normal and diseased soft and hard tissues not only in the laboratory but also in patients. The TDI can distinguish between the nucleus and the annulus of spinal disks, between young and degenerated cartilage, and between normal and cancerous mammary glands. It can quantify the elastic modulus and hardness of the wet dentin left in a cavity after excavation. It can perform an indentation test of bone tissue, quantifying the indentation depth increase and other mechanical parameters. With local anesthesia and disposable, sterile, probe assemblies, there has been neither pain nor complications in tests on patients. We anticipate that this unique device will facilitate research on many tissue systems in living organisms, including plants, leading to new insights into disease mechanisms and methods for their early detection.

• Nanostructural analysis of trabecular bone.

  Authors: Sun Hong, Soon Hong, David Kohn

  Journal of materials science. Materials in medicine. 04/2009;

  The mechanical properties of bone are dictated by the size, shape and organization of the mineral and matrix phases at multiple levels of hierarchy. While much is known about structure-functionThe mechanical properties of bone are dictated by the size, shape and organization of the mineral and matrix phases at multiple levels of hierarchy. While much is known about structure-function relations at the macroscopic level, less is known at the nanoscale, especially for trabecular bone. In this study, high resolution transmission electron microscopy (HRTEM) was carried out to analyze shape and orientation of apatite crystals in murine femoral trabecular bone. The distribution and orientation of mineral apatites in trabecular bone were different from lamellar bone and the c-axis of the tablet-like mineral apatite crystals in trabecular bone was arranged with no preferred orientation. The difference in the orientation distribution of apatite crystals of trabecular bone in the present study compared with that of lamellar bone found in the literature can be attributed to the more complex local stress state in trabecular bone. Apatite crystals were also found to be multi-crystalline, not single crystalline, from dark field image analysis. From the observations of this study, it is suggested that Wolff's law can be applicable to the nanostructural orientation and distribution of apatite crystals in trabecular bone. It was also found that small round crystalline particles observed adjacent to collagen fibrils were similar in size and shape to the apatite crystals in biomimetically nucleated synthetic amorphous calcium phosphate, which suggests that they are bone mineral apatite nuclei.

• The bone diagnostic instrument II: Indentation distance increase.

  Authors: Paul Hansma, Patricia Turner, Barney Drake, Eugene Yurtsev, Alexander Proctor, Phillip Mathews, Jason Lelujian, Connor Randall, Jonathan Adams, Ralf Jungmann, Federico Garza-de-Leon, Georg Fantner, Haykaz Mkrtchyan, Michael Pontin, Aaron Weaver, Morton B. Brown, Nadder Sahar, Ricardo Rossello, David Kohn

  The Review of scientific instruments. 07/2008; 79(6):064303.

  The bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. SuchThe bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. Such measurements could contribute to the overall assessment of bone fragility in the future. Here, we describe an improved BDI, the Osteoprobe IItrade mark. In the Osteoprobe IItrade mark, the probe assembly, which is designed to penetrate soft tissue, consists of a reference probe (a 22 gauge hypodermic needle) and a test probe (a small diameter, sharpened rod) which slides through the inside of the reference probe. The probe assembly is inserted through the skin to rest on the bone. The distance that the test probe is indented into the bone can be measured relative to the position of the reference probe. At this stage of development, the indentation distance increase (IDI) with repeated cycling to a fixed force appears to best distinguish bone that is more easily fractured from bone that is less easily fractured. Specifically, in three model systems, in which previous mechanical testing and/or tests reported here found degraded mechanical properties such as toughness and postyield strain, the BDI found increased IDI. However, it must be emphasized that, at this time, neither the IDI nor any other mechanical measurement by any technique has been shown clinically to correlate with fracture risk. Further, we do not yet understand the mechanism responsible for determining IDI beyond noting that it is a measure of the continuing damage that results from repeated loading. As such, it is more a measure of plasticity than elasticity in the bone.

• Publisher’s Note: “The bone diagnostic instrument II: Indentation distance increase” [Rev. Sci Instrum. 79, 064303 (2008)]

  Authors: Paul Hansma, Patricia Turner, Barney Drake, Eugene Yurtsev, Alexander Proctor, Phillip Mathews, Jason Lulejian, Connor Randall, Jonathan Adams, Ralf Jungmann, Federico Garza-de-Leon, Georg Fantner, Haykaz Mkrtchyan, Michael Pontin, Aaron Weaver, Morton B. Brown, Nadder Sahar, Ricardo Rossello, David Kohn