In this context, the ability to develop and utilize an in vitro model to account for the influences of bone marrow microenvironments is essential to elucidating the process involved in cell maturation, migration and function. The present work demonstrates that HSCs differentiating in Mks and hypoxia promote not only hMSC vitexicarpin differentiation towards the osteoblastic lineage, but also enhances fibrillar organization of type I collagen released from hOSTs, demonstrating for the first time that cellular and physical parameters are fundamental for both composition and structure of the osteoblastic niche. Importantly, by SHG-based imaging, an increase in type I collagen fibril deposition was Tectoridin observed when HSCs were added to the system under hypoxic conditions, with regularly ordered fibrils filling the well by the end of co-culture. These results clearly demonstrated that the combination of lower oxygen tension and HSCs formed a niche favorable to fibrillar type I collagen deposition. Thus, this environment constituted a quiescent site for HSCs for differentiation through the megakaryocytic lineage, but not to complete maturation and extension of proplatelets, even in the presence of growth factors. These results are consistent with a model in which the coexistence of hypoxia, HSCs and Mks promotes type I collagen deposition in the osteoblastic niche and thus restrains Mks from extending proplatelets and prevents the premature release of platelets. Moreover, this model demonstrated that PPF inhibition by type I collagen depended on its structural properties, as detected by SHG-based imaging. To support these findings, recent work has shown that Mk adhesion to collagen type IV, an ECM protein located around the marrow vessels, supports PPF. Overall, the mechanisms for the differential effects of collagen subtypes on PPF are still unknown, but preliminary evidence indicates that these differences may be ascribed to the distinctive structural properties of the collagens. The inhibitory effect of type I collagen on PPF is mediated by the interaction with integrin alpha2beta1.