A sustained release of BMP2 in urine-derived stem cells enhances the osteogenic differentiation and the potential of bone regeneration.

Cell-based tissue engineering is one of the optimistic approaches to replace current treatments for bone defects. Urine-derived stem cells (USCs) are obtained non-invasively and become one of the promising seed cells for bone regeneration. An injectable BMP2-releasing chitosan microspheres/type I collagen hydrogel (BMP2-CSM/Col I hydrogel) was fabricated. USCs proliferated in a time-dependent fashion, spread with good extension and interconnected with each other in different hydrogels both for 2D and 3D models. BMP2 was released in a sustained mode for more than 28 days. Sustained-released BMP2 increased the ALP activities and mineral depositions of USCs in 2D culture, and enhanced the expression of osteogenic genes and proteins in 3D culture. In vivo , the mixture of USCs and BMP2-CSM/Col I hydrogels effectively enhanced bone regeneration, and the ratio of new bone volume to total bone volume was 38% after 8 weeks of implantation. Our results suggested that BMP2-CSM/Col I hydrogels promoted osteogenic differentiation of USCs in 2D and 3D culture in vitro and USCs provided a promising cell source for bone tissue engineering in vivo . As such, USCs-seeded hydrogel scaffolds are regarded as an alternative approach in the repair of bone defects.