New avenues for characterizing individual mineralized collagen fibrils with transmission electron microscopy

TL;DR

This paper introduces a novel method for isolating and visualizing individual mineralized collagen fibrils in bone using transmission electron microscopy, revealing their nanoscale organization and mechanical properties to inspire bio-inspired material design.

Contribution

It presents a new dropcasting technique for isolating MCFs and combines 4D-STEM and in situ tensile testing to analyze their ultrastructure and mechanics.

Findings

Isolated MCFs show detailed organic and mineral phase arrangement.

Mineral crystals within MCFs exhibit specific orientations.

MCFs can sustain tensile strains of at least 8%.

Abstract

Bone serves as a remarkable example of nature's architectured material with its unique blend of strength and toughness, all at a lightweight design. Given the hierarchical nature of these materials, it is essential to understand the governing mechanisms and organization of its constituents across length scales for bio-inspired structural design. Despite recent advances in transmission electron miscoscopy (TEM) that have allowed us to witness the fascinating arrangement of bone at micro-down to the nano-scale, we are still missing the details about the structural organization and mechanical properties of the main building blocks of bone -- mineralized collagen fibrils (MCFs). Here, we propose a novel approach for extracting individual MCFs from nature's model material via a dropcasting procedure. By isolating the MCFs onto TEM-compatible substrates, we visualized the arrangement of organic and mineral phases within the individual MCFs at the nanoscale. Using a 4D-STEM approach, the orientation of individual mineral crystals within the MCFs was examined. Furthermore, we conducted first-of-its-kind in situ tensile experiments, revealing exceptional tensile strains of at least 8%, demonstrating the intricate relationship between structural organization and the mechanical behavior of MCFs. The capabilities of TEM allow us to resolve MCF organization and composition down to the nanoscale level. This new knowledge of the ultrastructure of the bone-building blocks and the proposed sample extraction and in situ mechanical testing opens up new avenues for research into nature's inspired material design.