Enhanced Differentiation of Human Embryonic Stem Cells on Extracellular Matrix-Containing Osteomimetic Scaffolds for Bone Tissue Engineering

Current methods of treating critical size bone defects include autografts and allografts, however, both present major limitations including donor-site morbidity, risk of disease transmission, and immune rejection. Tissue engineering provides a promising alternative to circumvent these shortcomings through the use of autologous cells, three-dimensional scaffolds, and growth factors. We investigated the development of a scaffold with native bone extracellular matrix (ECM) components for directing the osteogenic differentiation of human embryonic stem cells (hESCs). Toward this goal, a microsphere-sintering technique was used to fabricate poly(lactic-co-glycolic acid) (PLGA) scaffolds with optimum mechanical and structural properties. Human osteoblasts (hOBs) were seeded on these scaffolds to deposit bone ECM for 14 days. This was followed by a decellularization step leaving the mineralized matrix intact. Characterization of the decellularized PLGA scaffolds confirmed the deposition of calcium, collagen II, and alkaline phosphatase by osteoblasts. hESCs were seeded on the osteomimetic substrates in the presence of osteogenic growth medium, and osteogenicity was determined according to calcium content, osteocalcin expression, and bone marker gene regulation. Cell proliferation studies showed a constant increase in number for hESCs seeded on both PLGA and ECM-coated PLGA scaffolds. Calcium deposition by hESCs was significantly higher on the osteomimetic scaffolds compared with the control groups. Consistently, immunofluorescence staining demonstrated an increased expression of osteocalcin in hESCs seeded on ECM-coated osteomimetic PLGA scaffolds. Gene expression analysis of RUNX2 and osteocalcin further confirmed osteogenic differentiation of hESCs at the highest expression level on osteomimetic PLGA. These results together demonstrate the potential of PLGA scaffolds with native bone ECM components to direct osteogenic differentiation of hESCs and induce bone formation.