Name: fragility assessment of bovine cortical bone using scratch tests
Uploaded: 2017-11-30T13:00:00
Description: Watch this Scientific Journal Video about Fragility Assessment of Bovine Cortical Bone Using Scratch Tests at JoVE.com

This work was supported by the Department of Civil and Environmental Engineering and the College of Engineering at University of Illinois at Urbana Champaign. We acknowledge the Ravindra Kinra and Kavita Kinra Fellowship for supporting the graduate studies of Kavya Mendu. Scanning Electron Microscopy investigation was carried out at the facilities of the Frederick Seitz Material Research Laboratory and Beckman Institute at the University of Illinois at Urbana Champaign.

NOTE: The protocol described here, follows the animal care guidelines of the Illinois Institutional Animal Care and Use Committee.
1. Specimen Procurement
<ol>
	<li>Collect freshly harvested bovine femurs from a United States Department of Agriculture (USDA)-certified slaughterhouse and transport them in plastic air tight bags in a cooler. 
	NOTE: For the study conducted here, femurs were collected from animals that were 24 - 30 months old, corn-fed, and weighed about 1,000 - 1,100 poun...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+technique+for+characterizing+the+fracture+toughness+via+scratch+test+experiments.">An improved technique for characterizing the fracture toughness via scratch test experiments.</a> Wear. 313 (1-2), (2014).</li><li>Akono, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Energetic+size+effect+law+at+the+microscopic+scale:+Application+to+progressive-load+scratch+testing.">Energetic size effect law at the microscopic scale: Application to progressive-load scratch testing.</a> J of Nanomech and Micromech. 6 (2), (2016).</li><li>Kataruka, A., Mendu, K., Okeoghene, O., Puthuvelil, J., Akono, A. -. 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Micro scratch tests induce a mixed-mode fracture3. Furthermore, in the short longitudinal bovine cortical bone specimens, fracture processes are activated as the probe digs deeper. For a 3-mm long scratch, the prismatic volume probed is around 3,600 &#181;m long, 600 &#181;m wide, and 480 &#181;m deep. This large volume helped in predicting a homogenized response. A non-linear fracture mechanics model enabled us to extract the fracture resistance based on the J-integral calculation<sup cl...

In this study, we measure the fracture toughness of bovine compact bone from the mesoscale (osteons) to the microscale (lamellar level) using a novel micro scratch technique1,2,3,4,5. Fracture processes including crack initiation and crack propagation in bone are directly influenced by length scales owing to the different structural constituents and organization at different levels of hierarchy. Therefore, assessing bone fracture at smaller length scales is essential to yielding a fundamental understanding of bone fragility. On the one hand, conventional tests such as three-point bending, compact tension, and flexure tests are commonly conducted on bovine femur and tibia for fracture characterization at the macroscopic scale6,7,8. On the other hand, to measure the fracture toughness at the microscopic scale, Vicker&#39;s indentation fracture was proposed9. Micro indentation was performed using the Vicker&#39;s indenter to generate radial cracks. Furthermore, the Oliver Pharr nanoindentation fracture toughness method was performed using a sharp cube corner indenter10.
In the above nanoindentation based fracture toughness studies, the lengths of the cracks thus generated were measured by the observer and a semi-empirical model was used to calculate the fracture toughness. However, these methods are irreproducible, subjective, and the results are highly dependent on the observer&#39;s skill due to the need to measure the crack lengths using optical microscopy or scanning electron microscopy. Moreover, scratch tests were conducted at the nano-scale, but the underlying mathematical model is not physics-based as it does not account for the reduction in strength due to cracks and defects11. Thus, a gap of knowledge exists: a method for fracture assessment at the microscopic level based on a physics-based mechanistic model. This gap of knowledge motivated the application of micro scratch tests to compact bone by focusing first on porcine specimens5. The study has now been further extended to understand bovine cortical bone.
Two different orientations of the specimens are possible: longitudinal transverse and short longitudinal. Longitudinal transverse corresponds to fracture properties perpendicular to the longitudinal axis of the femur. Whereas, short longitudinal corresponds to the fracture properties along the longitudinal axis of femur5. In this study, we apply scratch testing to bovine cortical bones to characterize the bone&#39;s fracture resistance in the short longitudinal direction.

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			<td>Buehler Isomet 5000 Precision Cutter</td>
			<td>Buehler,41 Waukegan Rd, Lake Bluff, IL 60044</td>
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			<td>(Through) Grainger, Peoria, Illinois</td>
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			<td>Bransonic CPXH ultrasonic bath has a tank capacity of 2.5 gal</td>
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			<td>Buehler Ecomet 250 Grinder - Polisher</td>
			<td>Buehler,41 Waukegan Rd, Lake Bluff, IL 60044</td>
			<td>497250</td>
			<td>8 inch base plate with a speed range from 10-500 rpm</td>
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			<td>Anton Paar, CSM Instruments Micro scratch tester</td>
			<td>Anton Paar Switzerland AG</td>
			<td>163251</td>
			<td>Compact Platform, Acoutstic Emission Sensor</td>
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			<td>JEOL 6060LV general purpose scanning electron microscope</td>
			<td>JEOL USA, Inc., Peabody, MA</td>
			<td></td>
			<td>Environmental scanning electron microscope which enables imaging at low vacuum levels.</td>
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			<td>Philips XL30 ESEM FEG&#160;</td>
			<td>FEI Company</td>
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			<td>Wet mode working of the instrument enables imaging of non conductive samples without altering them&#160;</td>
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			<td>Consumables</td>
			<td></td>
			<td></td>
			<td></td>
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		<tr>
			<td>Bovine Femur</td>
			<td>L&#38;M Slaughter house, Georgetown, IL</td>
			<td></td>
			<td>Corn fed, 24-30 month old mature bovine specimens.</td>
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			<td>MicroCut Discs 800 grit, 8 inch, PSA backed</td>
			<td>Buehler,41 Waukegan Rd, Lake Bluff, IL 60044</td>
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			<td>Meta Di Supreme Polycrystalline Diamond Suspension, 1 &#181;m</td>
			<td>Buehler,41 Waukegan Rd, Lake Bluff, IL 60044</td>
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			<td>MasterPrep Polishing Suspension, 0.05&#181;m</td>
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fragility assessment of bovine cortical bone using scratch tests

Bone is a complex hierarchical material with five distinct levels of organization. Factors like aging and diseases like osteoporosis increase the fragility of bone, making it fracture-prone. Owing to the large socio-economic impact of bone fracture in our society, there is a need for novel ways to assess the mechanical performance of each hierarchical level of bone. Although stiffness and strength can be probed at all scales &#8211; nano-, micro-, meso-, and macroscopic &#8211; fracture assessment has so far been confined to macroscopic testing. This limitation restricts our understanding of bone fracture and constrains the scope of laboratory and clinical studies. In this research, we investigate the fracture resistance of bone from the microscopic to the mesoscopic length scales using micro scratch tests combined with nonlinear fracture mechanics. The tests are performed in the short longitudinal orientation on bovine cortical bone specimens. A meticulous experimental protocol is developed and a large number (102) of tests are conducted to assess the fracture toughness of cortical bone specimens while accounting for the heterogeneity associated with bone microstructure.

Atomic force microscopy was used to measure the roughness of the polished surface. As a rule of thumb, the specimen qualifies as a well-polished one if the surface roughness is an order of magnitude smaller than the surface features of interest. In this case, the measured surface roughness of 60 nm over a 40 &#181;m x 40 &#181;m area clearly falls within this criterion.
Figure 4 shows the force vers...

Watch this Scientific Journal Video about Fragility Assessment of Bovine Cortical Bone Using Scratch Tests at JoVE.com

Fragility Assessment of Bovine Cortical Bone Using Scratch Tests

This study assesses the fracture toughness of bovine cortical bone at the sub-meso levels using microscopic scratch tests. This is an original, objective, rigorous, and reproducible method proposed to probe fracture toughness below the macroscopic scale. Potential applications are studying changes in bone fragility due to diseases like osteoporosis.

Bone is a complex hierarchical material with five distinct levels of organization. Factors like aging and diseases like osteoporosis increase the ...

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