Biomimetic Artificial Bone Marrow Niches for the Scale Up of Hematopoietic Stem Cells

Hematopoietic stem cell (HSC) transplantation to treat haematological disorders is greatly restricted by poor cell availability. Ex vivo expansion of HSCs as a strategy to overcome this limitation has shown limited success so far, due to the loss of stem cell properties in culture. Therefore, engineering of culture platforms that mimic the physiological properties of the bone marrow (BM) in a scalable format is an important target to enable the translation of HSC therapies. Here, we report the design of biomimetic BM niches that enable the culture of HSCs in a scalable 3D platform. Beyond cellular and biochemical components (e.g., matrix and growth factors), an important element of the BM microenvironment is its architecture, dense in adipocytes, with relatively limited matrix and anisotropic mechanical properties. To capture this context, we propose the use of bioemulsions1,2 in which oil microdroplets and associated mechanical anisotropy recreate important architectural features of the hematopoietic niche. Mesenchymal stem cells (MSCs) grown at the surface of such bioemulsion remodelled this environment, assembling an interstitial matrix mimicking that of the BM microenvironment composition. In addition, MSCs secreted important factors underpinning the crosstalk between stromal cells and HSCs in the native environment. HSCs cultured in the resulting artificial BM niches maintained stemness whilst expanding significantly (> 33-fold compared to HSCs cultured in suspension) and enabling scale up of expansion in conical flask bioreactors, to produce 2M cells in a single batch. This platform therefore harnesses engineered BM microenvironments and the processability of bioemulsions and microdroplet technologies to produce HSCs in a scalable format, for application in cell-based therapies.