Endogenous Osteocyte-Osteoclast Signaling Enables Growth Factor-Free Bone Remodeling, Drug Response, and Cancer Invasion in a Nanoscale Calcified Bone-on-a-Chip Model.

Bone homeostasis depends on spatially orchestrated interactions among osteoclasts, osteoblasts, and osteocytes that are embedded within a unique extracellular matrix that is mineralized on the nanoscale to define the structure and function of bone. Reconstructing these interactions to enable autonomous cell differentiation and tissue remodeling has remained a significant challenge towards mimicking adequate bone physiology in-vitro. Here, we present an engineered model that spatially defines the paracrine communication of heterogeneous cell populations within bone tissue that support the rapid maturation of primary osteoblasts into osteocytes, the differentiation of macrophages into osteoclasts, and calcified tissue resorption within a mineralized cell-laden bone-like tissue. We demonstrate that nanoscale mineralization of cell-laden collagen hydrogels on-a-chip enhances osteoblast to osteocyte differentiation, whereas osteocytes in the matrix accelerate osteoclastogenesis and remodeling in a spatially defined manner without the need for exogenous growth factors. Osteocyte-dependent osteoclastogenesis on-a-chip outperformed conventional stimulation with RANKL and M-CSF, reproduced the clinical response of anti-resorptive drugs, and mimicked established tumor-bone interactions observed in invasive oral cancer. By replicating essential aspects of bone composition and function, this system provides a robust, self-regulated microphysiologic model to investigate bone remodeling, cancer-bone crosstalk, and therapeutic interventions.