Regional and sustained dual-release of growth factors from biomimetic tri-layered scaffolds for the repair of large-scale osteochondral defects

Mesenchymal stem cells (MSCs) are considered to be important cell sources for tissue regeneration. Growth factors (GFs) are key mediators of MSCs chondrogenesis and osteogenesis in the enhancement of osteochondral repair. However, uncontrolled delivery and release of these bioactive factors may reduce their bioavailability and lead to off-target side effects. In this study, tri-layered scaffolds, based on the chondrocyte extracellular matrix, nano-hydroxyapatite and silk fibroin were prepared by imitating the structural layers of the osteochondral unit. Particularly, tri-layered scaffolds were functioned for the local and sustained release of transforming growth factor-β3 to the chondral layer and bone morphogenetic protein-2 to the bony layer. In conjunction with engrafted human umbilical cord mesenchymal stem cells (hUCMSCs), osteochondral regeneration was enhanced. In vitro experiments indicated that scaffolds supported hUCMSCs proliferation, vitality and adhesion, and facilitated hUCMSCs lineage differentiation toward chondrocytes or osteoblasts, dependent on stimulation by sustained GFs release, at chondral layer or bony layer, respectively. Furthermore, evaluation of osteochondral repair in vivo after 8- and 16-weeks post-implantation indicated that the tri-layered scaffolds with sustained release function and hUCMSC delivery significantly accelerated the repair of large-size osteochondral defects, compared with other scaffolds. In summary, our studies showed that tri-layered scaffolds with the biomimetic structure of osteochondral unit, with sustained GFs release and seeded with hUCMSCs were more conducive to osteochondral regeneration, providing new materials and strategies for tissue engineering for the repair large-scale osteochondral defects.