Dynamic Observation of Lacy Pattern Formation in a Bone Tissue Model Using Liquid Phase Scanning Transmission Electron Microscopy

ABSTRACT Bone is a hierarchical composite in which carbonated hydroxyapatite platelets form a continuous mineral network within and between collagen fibrils. Although the nanoscale organization of mature bone is well characterized, how mineral precursors transform into this architecture remains unresolved because conventional electron microscopy provides only static images. Here, a low‐dose liquid‐phase scanning transmission electron microscopy (LP‐STEM) workflow is established to visualize collagen mineralization dynamically in hydrated bone tissue. Sub‐sampling 20% of the pixels in the image and inpainting‐based reconstruction reduce the electron dose five‐fold while preserving approximately 4 nm spatial resolution. Time‐resolved imaging reveals the deposition and growth of poorly‐defined mineral clusters, their development into spherulitic structures, and their subsequent reorganization into crystalline branches separated by unmineralized regions. Our observations demonstrate that the characteristic unmineralized areas in the lacy mineral pattern emerge during crystallization rather than through mineral deposition around a pre‐existing organic template. The workflow enables nanoscale investigation of beam‐sensitive hydrated biological materials and provides a platform for studying physiological and pathological mineralization processes.