Mechanical characterization of nacre as an ideal-model for innovative new endoprosthesis materials
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To mimic the impressive mechanical behavior of natural ceramics for technical or biomedical applications, interest has been focused on nacre, a natural composite consisting of imbricated aragonite platelets embedded in a protein matrix. Nacre is an ideal model material for implants, since it possesses favorable strength and toughness properties compared to the component materials of which it is composed. The focus of the present study was to test standardized parameters which are good indicators of the material’s suitability as an implant material.
Materials and methods
A three-point bending test was performed on polished nacre samples according to international standards for Young’s modulus, bending strength and fracture toughness. A total of 60 nacre samples were tested, with 5 samples each in 4 states of hydration (dry, distilled water, 0.9% NaCl and sea water). As a basis for comparison, 10 samples of a newly developed bioceramic material were tested for fracture toughness.
The fracture toughness of nacre tended to be higher for specimens conditioned in 0.9% NaCl than for dry specimens (5.3 ± 0.6 vs. 4.3 ± 0.7 MPam1/2, p = 0.061). The fracture toughness of the bioceramic investigated was observed to be somewhat higher than nacre (5.8 ± 0.4 vs. 4.3 ± 0.7 MPam1/2, p ≤ 0.001).
Discussion and conclusion
The increase in fracture toughness of hydrated nacre was not as large as would be expected based on the difference in stiffness of the matrix material after hydration that has been reported. Modulus and toughness were similar to published values and the fracture toughness observed was somewhat higher than reported for alumina implant ceramics, which are in use in total hip arthroplasty. In a direct comparison, we found that a newly developed alumina bioceramic material can in fact match nature in terms of fracture toughness.
KeywordsNacre Pearl Biomimetics Bioceramics Implant material Fracture toughness Material property
We are grateful for the cooperation offered by the CeramTec AG, Medical Products Division, and in particular to Carsten Upmann, for providing us with bioceramic material samples. We further wish to thank Dennis Kundrat for his technical assistance, as well as the central research shop of the Hannover Medical School (Zentrale Forschungswerkstätten), and in particular J. Viering and M. Breyvogel for their support in manufacturing the fixtures used in this study. This research was funded by the Collaborative Research Centre 599 for Biomedical Technology, a Centre of the German Research Foundation (DFG).
Conflict of interest statement
The authors declare that they have no conflict of interest related to this study.
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