In bone tissue engineering,stem cell-scaffold constructs play an important role in bone regeneration.Desirable biomimetic scaffolds which can facilitate the committed differentiation of stem cells into osteoblasts at high efficiency in the absence of inducing media are essentially useful for the application in bone tissue engineering.Among a variety of polymers,poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV),a microbial polyester,with biodegradable,nonantigenic,and biocompatible properties,is attracting more and more attention in tissue engineering.Hydroxyapatite,similar to the mineral component of natural bone,is known to be osteoconductive,nontoxic,and noninflammatory.In this study,we have investigated the potency of spontaneous osteogenic differentiation of bone marrow-derived mesenchymal stem cells(MSCs)on PHBV nanofibrous scaffolds loaded with hydroxyapatite nanoparticles using electrospinning technique,and studied the underlying mechanisms as well.By tests of cell morphology and cytoskeleton,as well as specific marker gene expression,we found that MSCs culturing on above nanofibrous scaffolds could efficiently differentiate into osteoblasts in the absence of inducing media.Moreover,we examined the activity of several signaling pathways involved in osteoblast differentiation including Wnt/β-catenin,BMP-Smad and MAPK(ERK1/2 and p38)pathways.This study uncovers the regulatory mechanisms of MSCs differentiation into osteoblasts stimulated by biomimetic nanofibrous scaffolds,which will help understand bone tissue repair for therapeutic applications and optimize the biomaterial scaffolds.