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Planta

, Volume 247, Issue 5, pp 1123–1132 | Cite as

A close-up view of the wood cell wall ultrastructure and its mechanics at different cutting angles by atomic force microscopy

  • Kirstin Casdorff
  • Tobias Keplinger
  • Markus Rüggeberg
  • Ingo Burgert
Original Article

Abstract

Main conclusion

AFM measurements on spruce sample cross-sections reveal that the structural appearance of the S2 layer changes from a network structure to a concentric lamellar texture depending on the cutting angle.

The structural assembly of wood constituents within the secondary cell wall has been subject of numerous studies over the last decades, which has resulted in contradicting models on the spatial arrangement and orientation of the wood macromolecules. Here, we use multichannel atomic force microscopy by means of quantitative imaging, to gain new insights into the macromolecular assembly. Cross-sections of spruce wood, which had been cut at different angles ranging from 0° to 30° were investigated. Strikingly, depending on the cutting angle, the structural appearance of the S2 layer changed from a network-like structure to a distinct concentric lamellar texture. This makes us conclude that the often visualized lamellar organization of the secondary cell wall is not the consequence of a continuous inherent ring pattern, but rather a result of the specific surface cross-section appearance of cellulose aggregates at larger cutting angles. By analyzing the recorded force distance curves in every pixel, a nano-mechanical characterization of the secondary cell wall was conducted. Substantially lower indentation modulus values were obtained compared to nanoindentation values reported in the literature. This is potentially due to a smaller interaction volume of the probe with a by far less deep indentation.

Keywords

AFM Concentric lamellar structure Spruce Microfibril angle Quantitative imaging mode Indentation modulus 

Abbreviations

AFM

Atomic force microscopy

CML

Compound middle lamella

SNOM

Scanning near-field microscopy

TEM

Transmission electron microscopy

MFA

Microfibril angle

NI

Nanoindentation

QI™

Quantitative imaging

Notes

Acknowledgements

The authors thank Thomas Schnider for cutting the wood samples. Valuable discussion with John Berg is acknowledged.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

425_2018_2850_MOESM1_ESM.docx (132 kb)
Supplementary material 1 (DOCX 132 kb)

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Wood Materials Science, Institute for Building MaterialsETH ZürichZurichSwitzerland
  2. 2.Applied Wood MaterialsEmpa-Swiss Federal Laboratories for Materials Science and TechnologyDübendorfSwitzerland

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