Studies On Osteogenic Differentiation Of Human Embryonic Stem Cells Directed By Biomineralized Porous Hydrogels

Human embryonic stem cells (hESCs), with distinguished pluripotency and unlimited ability for proliferation, hold great promise to treat various diseases and tissue loss in regenerative medicine as an ideal cell source. Methods for inducing differentiation of stem cells into functioning cells include the transgene technology, cell co-culturing and exogenous cytokines etc. To the best knowledge of the authors, this is the first demonstration that the terminal differentiation of hESCs can be achieved solely through synthetic matrices without the use of culture medium supplemented with differentiation inducing chemicals and/or growth factors.A highly interconnective porous hydrogel (PEG-co-A6ACA) based on poly (ethylene glycol) containing N-acryloyl-6-aminocaproic acid moieties has been developed via micro sphere templating. This hydrogel was explored as an organic molecular template to induce the mineralization of calcium phosphate nanocrystallites on its surface. When hESCs were seeded into this hydrogel matrices and cultured in the absence of any osteogenic inducing supplement, the mineralized matrices exhibited a good micro-environment for osteogenic differentiation of hESCs as evidenced by the remarkable up-regulation of osteogenic gene and protein expression. On contrast, no osteogenic differentiation was observed in hESCs-laden non-mineralized matrices. When implanted subcutaneously in vivo, the hESCs-laden mineralized materials contributed to ectopic bone formation without teratoma formation. In a striking contrast the hESCs transplanted in vivo using non-mineralized matrices underwent adipogenic fate. This in vivo study proved the excellent osteoinductive ability of the mineralized hydrogel matrices. Furthermore, the ectopic bone formation created by different cell types were studied in details. The results found that the essential process during ectopic bone tissue development by either hESCs or hMSCs was through the endochondral ossification.The approach that utilize tissue specific cell-matrix interactions to control stem cell fate could be a powerful tool in regenerative medicine. Biomimetic materials such as the mineralized porous hydrogel employed in this study can be used to deliver stem cells, where the matrices would not only act as a structural support but would also direct their differentiation into targeted cells. Therefore, the findings that the matrix-based cues alone can direct osteogenic differentiation of stem cells represent a significant advancement in the field of biomaterials, stem cell engineering, regenerative medicine, and bone tissue engineering.