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ABSTRACT: High doses of sodium fluoride in bones lead to severe softening, by weakening interfacial properties between the inorg. minerals and the org. components, while leaving mineralization unchanged. This leads to redn. of microdamage and assocd. stress-whitening pointing to a change in failure mode. Accordingly, elastic modulus, failure stress, and indentation-distance increase are decreased, whereas failure strain is increased. [on SciFinder (R)]
Advanced Materials 11/2008; 21(4):451 - 457. · 13.88 Impact Factor
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Paul Hansma, Patricia Turner,
Barney Drake,
Eugene Yurtsev,
Alexander Proctor,
Phillip Mathews,
Jason Lulejian,
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
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ABSTRACT: 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. 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.
Review of Scientific Instruments 07/2008; 79(6):064303. · 1.37 Impact Factor
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ABSTRACT: In the nanocomposite bone, inorganic material is combined with several types of organic molecules, and these complexes have been proposed to increase the bone strength. Here we report on a mechanism of how one of these components, human osteopontin, forms large mechanical networks that can repeatedly dissipate energy through work against entropy by breaking sacrificial bonds and stretching hidden length. The behavior of these in vitro networks is similar to that of organic components in bone, acting as an adhesive layer in between mineralized fibrils.
Nano Letters 09/2007; 7(8):2491-8. · 13.20 Impact Factor
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Georg E Fantner,
Emin Oroudjev,
Georg Schitter,
Laura S Golde,
Philipp Thurner,
Marquesa M Finch, Patricia Turner,
Thomas Gutsmann,
Daniel E Morse,
Helen Hansma,
Paul K Hansma
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ABSTRACT: Sacrificial bonds and hidden length in structural molecules and composites have been found to greatly increase the fracture toughness of biomaterials by providing a reversible, molecular-scale energy-dissipation mechanism. This mechanism relies on the energy, of order 100 eV, needed to reduce entropy and increase enthalpy as molecular segments are stretched after being released by the breaking of weak bonds, called sacrificial bonds. This energy is relatively large compared to the energy needed to break the polymer backbone, of order a few eV. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby additionally providing a "self-healing" property to the material. Due to the nanoscopic nature of this mechanism, single molecule force spectroscopy using an atomic force microscope has been a useful tool to investigate this mechanism. Especially when investigating natural molecular constructs, force versus distance curves quickly become very complicated. In this work we propose various types of sacrificial bonds, their combination, and how they appear in single molecule force spectroscopy measurements. We find that by close analysis of the force spectroscopy curves, additional information can be obtained about the molecules and their bonds to the native constructs.
Biophysical Journal 03/2006; 90(4):1411-8. · 3.65 Impact Factor
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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
