For the development of the human-based tissue engineering devices proposed in the REBORN project, cells, and extracellular matrices have been isolated from perinatal tissues. In this context, mesenchymal stem cells (MSCs) have been isolated from the Wharton jelly of the umbilical cord, as a reliable alternative source of the bone marrow MSCs. Additionally, endothelial cells were isolated from the same tissue and used as a substitute for the outgrowth endothelial cells obtained from the peripheral blood. Such as the umbilical cord, the placenta is a widely available clinical waste obtained from a non-invasive procedure, that exhibits very interesting biochemical features for tissue engineering purposes. Therefore, the whole placenta and the individual amniotic and chorionic membranes were isolated, decellularized, enzymatically digested, and solubilized in order to be chemically modified. Of note, tissues from multiple donors were pooled to minimize the lot-to-lot variability and ensure high reproducible experiments. Diverse protein-targeting chemical groups were conjugated with these human-derived materials through cross-reactive chemical modifications using clickable and photoresponsive moieties, rendering high cell-friendly and viscoelastic hydrogels whose biochemical and mechanical properties perfectly match diverse tissues’ features. These innovative human-derived biomaterials were used to fabricate liquified pockets in which a robust PC protein shell was formed employing processing technologies based on an emulsion technique, including electrodynamic atomization and microfluidics. Leveraging the potential of these liquified pockets to confine biological materials in a semi-closed soft environment, we have been working on the development of a new generation of protein MicroBlocks with customizable size, shape, topography, and stiffness, to promote cell attachment and self-assembly, while mediating cell fate in a controllable way. Different in vitro assays demonstrated the successful encapsulation of cells and MicroBlocks in a liquified biofactory. We also incorporated magnetic nanoparticles into the MicroBlocks to regulate cell differentiation in a dynamic pseudo-3D environment controlled by a magnetic field, in which the biophysical stimulation improved the robustness of the microtissues and their osteogenic differentiation over the static culture. Interestingly, we were able to create an autonomous homeostatic bone microcompartment by encapsulating osteoblast- and osteoclast-like cells. Envisioning the fabrication of more complex 3D structures for bone remodeling, different bottom-up strategies are being studied, including unconventional 3D bioprinting and robot arm-mediated liquified pockets assembly. The results achieved so far under the scope of the REBORN project provide great indications of the potential of the developed hydrogel biomaterials and derivative microstructures to more efficiently direct stem cell differentiation towards a relevant 3D bone tissue construct.
