ABSTRACT Clinical transplantation of hematopoietic stem cells (HSCs) has been used to treat a broad range of hematologic, immune, genetic, and neoplastic diseases. A major obstacle for this treatment is the limited availability of HSCs. In vitro expansion of HSCs can solve the issue by generating quality-controlled, off-the-shelf HSC products. However, to date, it remains difficult to expand, or even maintain HSCs in vitro. Here, we propose to create micro-engineered artificial stromal cells that offer the spatial presentation of stromal factors necessary for HSC maintenance and expansion. Our central hypothesis is that spatial presentation of HSC niche signals by stromal cells is critical for HSC maintenance and expansion. We will develop biomimicry ?artificial stromal cell? platforms with more realistic in vivo features of HSC niches, with mouse HSCs as a model. We will carry out our study by a) evaluating the spatial organization of membrane-bound signals and its impact on HSC maintenance and expansion at subcellular and cellular levels, and b) evaluating the maintenance and expansion of HSCs on a microparticle-based platform of artificial stromal cells. The proposed study will provide novel insights and concepts into the signaling dynamics of HSC with its stromal microenvironment. Our long term goal is to translate our findings to human HSCs and their large-scale production to meet the demand of clinical bone marrow transplantations. The knowledge developed here can also be extended to a broad range of tissue and organ systems with stem cell-stromal cell interactions.