Simultaneous three-dimensional visualization of mineralized and soft skeletal tissues by a novel microCT contrast agent with polyoxometalate structure

Biological tissues have a complex and heterogeneous 3D structure, which is only partially revealed by standard histomorphometry in 2D. We here present a novel chemical compound for contrast-enhanced microfocus computed tomography (CE-CT), a Hafnium-based Wells-Dawson polyoxometalate (Hf-POM), which allows simultaneous 3D visualization of mineralized and non-mineralized skeletal tissues, such as mineralized bone and bone marrow vasculature and adipocytes. We validated the novel contrast agent, which has a neutral pH in solution, by detailed comparison with (immuno)histology on murine long bones as blueprint, and showed that Hf-POM-based CE-CT can be used for virtual 3D histology. Furthermore, we quantified the 3D structure of the different skeletal tissues, as well as their spatial relation to each other, during aging and diet-induced obesity. We discovered, based on a single CE-CT dataset per sample, clear differences between the groups in bone structure, vascular network organization, characteristics of the adipose tissue and proximity of the different tissues to each other. These findings highlight the complementarity and added value of Hf-POM-based CE-CT compared to standard histomorphometry. As this novel technology provides a detailed 3D simultaneous representation of the structural organization of mineralized bone and bone marrow vasculature and adipose tissue, it will enable to improve insight in the interactions between these three tissues in several bone pathologies and to evaluate the in vivo performance of biomaterials for skeletal regeneration.