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. 2015 Apr 6;12(105):20141326.
doi: 10.1098/rsif.2014.1326.

Extreme strength observed in limpet teeth

Asa H Barber  1 , Dun Lu  2 , Nicola M Pugno  3
Affiliations

Extreme strength observed in limpet teeth

Asa H Barber et al. J R Soc Interface. .

Abstract

The teeth of limpets exploit distinctive composite nanostructures consisting of high volume fractions of reinforcing goethite nanofibres within a softer protein phase to provide mechanical integrity when rasping over rock surfaces during feeding. The tensile strength of discrete volumes of limpet tooth material measured using in situ atomic force microscopy was found to range from 3.0 to 6.5 GPa and was independent of sample size. These observations highlight an absolute material tensile strength that is the highest recorded for a biological material, outperforming the high strength of spider silk currently considered to be the strongest natural material, and approaching values comparable to those of the strongest man-made fibres. This considerable tensile strength of limpet teeth is attributed to a high mineral volume fraction of reinforcing goethite nanofibres with diameters below a defect-controlled critical size, suggesting that natural design in limpet teeth is optimized towards theoretical strength limits.

Keywords: mechanics; mineralized tissue; nanoscale.

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Figures

Figure 1.
Figure 1.
Structure of the common limpet tooth (Patella vulgata). (a) Optical image of the tongue-like radula containing bands of teeth along a length of many centimetres. (b) Scanning electron micrograph of the teeth groupings with each tooth length approximately 100 μm. High-magnification electron microscopy images of the tooth cusp show (c) the changing orientation of the nanofibrous goethite in the chitin matrix and (d) the high anisotropy of the composite at the anterior and posterior edges owing to alignment of the goethite, note the mineral fibre length of approx. 3 μm, with (e) close-up of the tooth indicating the distinct phases of the goethite ‘reinforcing fibre’ and the chitin ‘matrix’ highlighting the structural resemblance to a fibre-reinforced composite material with an average fibre diameter of approx. 20 nm. Adapted from reference [12]. (Online version in colour.)
Figure 2.
Figure 2.
Failure of the limpet teeth structure was achieved by (a) embedded teeth in an epoxy resin and tensile testing to failure. Backscattered SEM images clearly indicated the nanofibrous structure. (b) Plot of the average length of the nanofibres during straining of the teeth embedded in epoxy resin, indicating failure of the nanofibre reinforcement that cause a fragmentation of the nanofibres to smaller lengths. (Online version in colour.)
Figure 3.
Figure 3.
Scanning electron micrographs showing (a) the limpet tooth prior to FIB milling, (b) FIB sectioning and attachment of the limpet tooth cusp to an AFM probe and (c) further FIB milling to thin the sample towards a ‘dog-bone’ geometry.
Figure 4.
Figure 4.
Scanning electron micrograph of (a) the limpet tooth sample attached to the AFM cantilever set-up and partially embedded within gripping glue and (b) failure at the sample free length mid-point after tensile testing.
Figure 5.
Figure 5.
Plot of the stress–strain behaviour of individual limpet tooth samples, with a variety of lengths, tensile tested to failure using AFM.
Figure 6.
Figure 6.
Plot of the tensile strength of limpet tooth material with varying sample length. The data fitting line shows the general trend of minimal strength variation with sample length.
See this image and copyright information in PMC

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