The microstructure and micromechanics of the tendon–bone insertion

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Abstract

The exceptional mechanical properties of the load-bearing connection of tendon to bone rely on an intricate interplay of its biomolecular composition, microstructure and micromechanics. Here we identify that the Achilles tendon–bone insertion is characterized by an interface region of 500 μm with a distinct fibre organization and biomolecular composition. Within this region, we identify a heterogeneous mechanical response by micromechanical testing coupled with multiscale confocal microscopy. This leads to localized strains that can be larger than the remotely applied strain. The subset of fibres that sustain the majority of loading in the interface area changes with the angle of force application. Proteomic analysis detects enrichment of 22 proteins in the interfacial region that are predominantly involved in cartilage and skeletal development as well as proteoglycan metabolism. The presented mechanisms mark a guideline for further biomimetic strategies to rationally design hard–soft interfaces.

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Figure 1: The structure of tendon fibres changes before attaching to bone.
Figure 2: Micromechanical testing of enthesis samples.
Figure 3: Fibre composition changes from collagen type I to collagen type II before attaching to bone.
Figure 4: Quantitative proteome analysis of differences in expression between Achilles tendon enthesis (E) and Achilles tendon (T).
Figure 5: Fundamental structural and molecular components of the enthesis.

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Acknowledgements

Research was supported by the International Graduate School of Science and Engineering (L.R. and L.A.K.). The authors acknowledge the continuous support of the DFG via the Nanosystems Initiative Munich (NIM).

Author information

L.R. and L.A.K. contributed equally to this work. L.R., L.A.K., H.G., J.S.-S., F.P., S.A.S., R.B. and A.R.B. designed the research. L.A.K. and J.S. performed microcomputed tomography. L.R. and L.A.K. carried out micromechanical analysis, confocal microscopy and investigated fibre composition. L.A.K. and E.K. performed proteomics experiments. L.R., L.A.K., K.W.M., R.B. and A.R.B. analysed the data and wrote the paper. All authors reviewed and revised the manuscript.

Correspondence to R. Burgkart or A. R. Bausch.

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Rossetti, L., Kuntz, L., Kunold, E. et al. The microstructure and micromechanics of the tendon–bone insertion. Nature Mater 16, 664–670 (2017) doi:10.1038/nmat4863

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