Micromechanical and structural properties of a pennate diatom investigated by atomic force microscopy

Abstract

SummaryThe mechanisms behind natural nanofabrication of highly structured silicas are increasingly being investigated. We have explored the use of a standard Nanoscope III Multimode atomic force microscope (AFM) to study the silica shell of diatoms. The delicate structures of the shell surface of the diatom Navicula pelliculosa (Bre Âb.) Hilse were imaged and the shell's micromechanical properties were measured semi-quantitatively with a resolution down to approximately 10 nm. The technique to measure elasticity and hardness with the AFM was demonstrated to be useable even on these hard glass-like surfaces. Different experimental configurations and evaluation methods were tested. They gave a consistent result of the shell micromechanical properties. The first results showed that the diatom shell's overall hardness and elasticity was similar to that of known silicas. However, regions with different mechanical properties were distinguished. The elastic modulus varied from 7 to 20 GPa, from 20 to 100 GPa and from 30 to hundreds of GPa depending on the location. In general, the hardness measurements showed similar spatial differences. The hardness values ranged from 1 to 12 GPa but one specific part of the shell was even harder. Hence, certain localized regions of the shell were significantly harder or more elastic. These regions coincide with known characteristic features and mechanisms appearing at the different stages of the shell's growth. These results show that this method serves as a complementary tool in the study of silica biomineralization, and can detect eventual crystalline phases.

Structure and mechanical properties of selected protective systems in marine organisms

“…12b) [89,114,115]. The teeth themselves mineralize in a four-step process: (1) forming a pure chitin scaffold tooth, (2) precipitating crystals of an intermediate and Adapted from: (a) [118], (b) [79], (c) [124]. [127], (c) [128].…”

“…As there is an immense number of different profiles [122], it has been theorized that diatom species have evolved to defend against specific local predators [121]. The strength of the frustule itself varies by up to an order of magnitude along the diatom surface with the maximum strength approaching that of pure silica [123][124][125]. This variation has been associated with different regions of the exoskeleton's growth, with the highest strength region running along the center of the body, effectively creating a load-bearing beam of harder material (Fig.…”

“…This variation has been associated with different regions of the exoskeleton's growth, with the highest strength region running along the center of the body, effectively creating a load-bearing beam of harder material (Fig. 13c) [124].…”

Probing nanomechanical properties from biomolecules to living cells

“…However, owing to the hierarchical structure of collagen, it has been difficult to pinpoint the relative contributions of different organizational levels to the mechanical behavior of the polymer as a whole. This circumstance accounts for the broad range of reported values for Young's modulus (1)(2)(3)(4)(5)(6)(7)(8). In an attempt to streamline the system, Yang et al [101] deposited unfixed and glutaraldehyde-fixed collagen fibers upon a microfabricated substrate and made AFM indentation measurements on the suspended fragment.…”

“…to image and measure the mechanical properties of these microscopic structures, and several investigators have applied the technique either to measure their Young's moduli [4,62] or to explore the mechanical properties of the extracellular polymeric substances that are involved in their adhesion and motility [31,32].…”