Liquefied Microcapsules Compartmentalizing Macrophages and Umbilical Cord-Derived Cells for Bone Tissue Engineering

Extraordinary capabilities underlie the potential use of immune cells, particularly macrophages, in bone tissue engineering. Indeed, the depletion of macrophages during bone repair often culminates in disease scenarios. Inspired by the native dynamics between immune and skeletal systems, this work proposes a straightforward in vitro method to bioengineer biomimetic bone niches using biological waste. For that, liquefied and semipermeable reservoirs generated by electrohydrodynamic atomization and layer-by-layer techniques are developed to coculture umbilical cord-derived human cells, namely monocyte-derived macrophages, mesenchymal-derived stromal cells (MSCs), and human umbilical vein endothelial cells (HUVECs). Poly(ε-caprolactone) microparticles are also added to the liquefied core to act as cell carriers. The fabricated microcapsules grant the successful development of viable microtissues, ensuring the high diffusion of bioactive factors. Interestingly, macrophages within the bioengineered microcapsules increase the release of osteocalcin, osteoprotegerin, and vascular endothelial growth factor. The cytokines profile variation indicates macrophages' polarization into a prohealing phenotype. Altogether, the incorporation of macrophages within the fabricated microcapsules allows to recreate an appropriate bone microenvironment for developing new bone mineralized microtissues. The proposed bioencapsulation protocol is a powerful self-regulated system, which might find great applicability in bone tissue engineering based on bottom-up approaches or disease modeling.