Effects of bioreactors and biomaterials on bone-marrow mesenchymal stem cells proliferation and differentiations for tissue engineering applications

Bone marrow and Adipose tissue are now recognized as an important source of postnatal mesenchymal stem cells (MSCs) for regenerative medicine applications. Here we described several applications of tissue engineering in enhancing proliferation and differentiation of MSC towards osteoblasts to reduce the gap between the process of bone formation in vitro and the subsequent graft of bone substitutes in vivo. These techniques include: three-dimensional organic or inorganic scaffolds and the bioreactors, that improve the static culturing cell methods by regulate the homogenous tissue growth. In particular we demonstrated that the combination of 3D-nanostructured biomaterials and bioreactors, such as mechanical vibration and electromagnetic stimulation, improves the amount of cell adhesion, osteoblastic differentiation and bone matrix deposition to engineer bone for clinical use. We used high frequency vibration (HFV) to accelerate MSC differentiation and pulsed electromagnetic field (PEMF) to induce differentiation of bone marrow MSCs (BM-MSCs) and adipose-tissue MSCs (ASCs). Among the biomaterials considered to produce the 3D scaffolds, pectin hydrogels resulted particularly suitable as injectable cell carriers. Macrogels with different rheological properties and microspheres were produced with different degree of crosslinking. The injectability of the gels cross-linked with different salts (CaCl2, CaCO3, ZnCl2 and FeCl3) through different needle size was tested by texture analysis and rheological characterization. The rheological parameters confirmed that pectin gels behave as soft-gels with mechanical properties similar to soft tissues. Such properties may provide minimally invasive implantation and the ability to fill a desired shape. The tight control over the gelation kinetics allows loading cells or drugs in the hydrogels before injection. The obtained results support the idea that pectin gels can recreate adequate microenvironments for cell delivery. All these models represent a good starting point to engineer bone constructs for potential clinical use in regenerative medicine.