Wood Materials Science, Institute for Building Materials, ETH Zürich, Stefano-Franscini-Platz 3, 8093, Zurich, Switzerland.
Applied Wood Materials, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600, Dübendorf, Switzerland.
Planta. 2018 May;247(5):1123-1132. doi: 10.1007/s00425-018-2850-9. Epub 2018 Jan 27.
AFM measurements on spruce sample cross-sections reveal that the structural appearance of the S 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 S 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.
在云杉样本横截面上进行的 AFM 测量表明，取决于切割角度，S 层的结构外观会从网络结构变为同心层状纹理。在过去的几十年中，木材次生细胞壁内的木材成分的结构组装一直是众多研究的主题，这导致了木材大分子的空间排列和取向的矛盾模型。在这里，我们使用多通道原子力显微镜通过定量成像，对大分子组装获得新的见解。研究了以 0°至 30°的不同角度切割的云杉木材的横截面。引人注目的是，取决于切割角度，S 层的结构外观从网络状结构变为明显的同心层状纹理。这使我们得出结论，次生细胞壁中经常观察到的层状组织不是连续固有环图案的结果，而是在较大切割角度下纤维素聚集体的特定表面横截面外观的结果。通过分析每个像素记录的力距离曲线，对次生细胞壁进行了纳米力学表征。与文献中报道的纳米压痕值相比，获得的压痕模量值明显较低。这可能是由于探针的相互作用体积较小，压痕深度要浅得多。
