Bioactive Self‐Regulated Liquified Microcompartments to Bioengineer Bone‐Like Microtissues

Designing a microenvironment that drives autonomous stromal cell differentiation toward osteogenesis while recapitulating the complexity of bone tissue remains challenging. In the current study, bone‐like microtissues are created using electrohydrodynamic atomization to form two distinct liquefied microcapsules (mCAPs): i) hydroxypyridinone (HOPO)‐modified gelatin (GH mCAPs, 7.5% w/v), and ii) HOPO‐modified gelatin and dopamine‐modified gelatin (GH+GD mCAPs, 7.5%+1.5% w/v). The ability of HOPO to coordinate with iron ions at physiological pH allows the formation of a semipermeable micro‐hydrogel shell. In turn, the dopamine affinity for calcium ions sets a bioactive milieu for bone‐like microtissues. After 21 days post encapsulation, GH and GH+GD mCAPs potentiate autonomous osteogenic differentiation of mesenchymal stem cells accompanied by collagen type‐I gene upregulation, increased alkaline phosphatase (ALP) expression, and formation of mineralized extracellular matrix. However, the GH+GD mCAPs show higher levels of osteogenic markers starting on day 14, translating into a more advanced and organized mineralized matrix. The GH+GD system also shows upregulation of the receptor activator of nuclear factor kappa‐B ligand (RANK‐L) gene, enabling the autonomous osteoclastic differentiation of monocytes. These catechol‐based mCAPs offer a promising approach to designing multifunctional and autonomous bone‐like microtissues to study in vitro bone‐related processes at the cell‐tissue interface, angiogenesis, and osteoclastogenesis.