Bone is a unique biological composite material made up of a highly structured collagen mesh matrix and mineral deposits. Bone deformability is governed by mineral stiffness and collagen organization-derived elasticity. When the bone is mechanically loaded or damaged, these forces are propagated through the highly sensitive network of osteocytes interspersed throughout the structure.  Nonlinear label-free imaging of these biological structures could provide live information about the tissue response in healthy bone and during states of disease or injury. Here, we perform second harmonic generation (SHG) and third harmonic generation (THG) microscopy to investigate the organization and health of bone. We have developed SHG polarimetric analysis of bone collagen assembly into lamellar sheet structures and have investigated the collagen role in intact cranial bone. By adjusting the polarization angle even in the highly scattering bone tissue we find increased contrast in aligned collagen regions, and confirm the retention of polarimetric contrast even with imaging through around 50 microns of highly scattering tissue. THG imaging finds osteocyte cell bodies are wrapped in collagen structures with lacunae extending between the cell bodies to form a three dimensional network. Using a hypophosphatasia mouse model with disrupted mineralization and an osteogenesis imperfecta mouse model with a disrupted collagen sequence, we find that the collagen mesh organization and osteocyte networks are impaired. We are currently exploring techniques to extend our imaging depth deeper into the bone by moving to the 1300 nm and 1700 nm excitation wavelengths, as well as by performing wavefront shaping to recover the imaging point spread function deep in the bone. Our findings will enable further study of bone health and regeneration, and could provide insight into dynamic processes driving bone homeostasis and fragility disorders.

Nonlinear microscopy for the evaluation of bone health and regeneration

ACS Fall 2020 Virtual Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.