Nanofibril-mediated fracture resistance of bone
Abstract
Natural hard composites like human bone possess a combination of strength and toughness that exceeds that of their constituents and of many engineered composites. This augmentation is attributed to their complex hierarchical structure, spanning multiple length scales; in bone, characteristic dimensions range from nanoscale fibrils to microscale lamellae to mesoscale osteons and macroscale organs. The mechanical properties of bone have been studied, with the understanding that the isolated microstructure at micro- and nano-scales gives rise to superior strength compared to that of whole tissue, and the tissue possesses an amplified toughness relative to that of its nanoscale constituents. Nanoscale toughening mechanisms of bone are not adequately understood at sample dimensions that allow for isolating salient microstructural features, because of the challenge of performing fracture experiments on small-sized samples. We developed an in-situ three-point bend experimental methodology that probes site-specific fracture behavior of micron-sized specimens of hard material. Using this, we quantify crack initiation and growth toughness of human trabecular bone with sharp fatigue pre-cracks and blunt notches. Our findings indicate that bone with fatigue cracks is two times tougher than that with blunt cracks. In-situ data-correlated electron microscopy videos reveal this behavior arises from crack-bridging by nanoscale fibril structure. The results reveal a transition between fibril-bridging (~1µm) and crack deflection/twist (~500µm) as a function of length-scale, and quantitatively demonstrate hierarchy-induced toughening in a complex material. This versatile approach enables quantifying the relationship between toughness and microstructure in various complex material systems and provides direct insight for designing biomimetic composites.
Additional Information
© 2021 IOP Publishing Ltd. Received 23 August 2020; Revised 11 November 2020; Accepted 19 January 2021; Published 5 April 2021. The authors thank Bill Johnson, Katherine Faber, Carlos Portela, Xiaoxing Xia, and Eric Luo for helpful discussions. The authors thank Matthew Sullivan and Carol Garland for assistance with experiments and instruments. The authors gratefully acknowledge the facilities and infrastructure provided by the Kavli Nanoscience Institute at Caltech. O.A.T would like to thank the National Science Foundation for financial support through the Graduate Research Fellowship Program (NSF GFRP). J.R.G. gratefully acknowledges financial support from the U.S. Department of Basic Energy Sciences under Grant DE-SC0006599. Data availability: The data that supports the findings of this study is available from the corresponding author upon reasonable request.Attached Files
Submitted - 2008.09955.pdf
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Additional details
- Eprint ID
- 107654
- Resolver ID
- CaltechAUTHORS:20210122-082128326
- NSF Graduate Research Fellowship
- Department of Energy (DOE)
- DE-SC0006599
- Created
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2021-01-22Created from EPrint's datestamp field
- Updated
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2022-07-12Created from EPrint's last_modified field
- Caltech groups
- Kavli Nanoscience Institute