M.Sc. Anna Schöser

Hematopoietic stem cells (HSCs) receive a combination of biochemical and biomechanical signals within the bone marrow that guide their differentiation process. These include soluble factor signaling with cytokines, cellular confinement in the stem cell niche, and contact-dependent receptor–ligand interactions with stromal cells. Recreating this complex microenvironment in vitro is a principal engineering challenge for regenerative therapies and tissue engineering. While cytokines can be easily supplemented in vitro, and several systems for confined HSC culture have been developed, integrating receptor-based intercellular interactions found in stem cell niches has only been achieved with quantitatively undefined heterotypic co-cultures. We report here the development of microwell-based systems that integrate synthetic cells to mimic receptor–ligand interactions within hematopoietic niches. The synthetic cells are based on droplet-supported lipid bilayers (dsLBs) with cytomimetic stiffness and present Notch receptor ligands on a laterally mobile lipid membrane. We show the system's applicability to individually tune the three signaling axes: soluble factors, confinement, and intercellular interactions for HSC differentiation. Introducing synthetic cells as an alternative to coculture and feeder cells opens the possibility to engineer precisely defined HSC niches with adjustable biochemical and biomechanical properties.

Approaches in tissue engineering, organoid culture, and organs-on-chip have propelled the development of increasingly sophisticated in vitro models of human tissues. However, as they are formed from natural cells, it is challenging to control their molecular composition and biophysical properties, increasing variability and limiting their robustness. To overcome these limitations, we introduce a self-assembly strategy for synthetic cells that enables the formation of millimeter-sized synthetic constructs based on single synthetic cells. Specifically, we functionalize the lipid membrane of synthetic cells with cholesterol-tagged single-stranded DNA aptamers, which drive programmable intercellular adhesion through sequence-specific hybridization. This allows individual synthetic cells to interconnect into higher order 3D constructs. By varying aptamer complementarity, internal architecture with spatially distinct functional zones and tuneable mechanical properties can be encoded. Most importantly, the DNA-driven self-assembly operates directly in cell culture medium, is compatible with high-throughput microwell formats enabling scalable screening workflows and is reversible by DNA displacement. To demonstrate the biological functionality of these synthetic tissues, we incorporate T cell-stimulatory antibodies into spatially segregated tissue regions. This design mimics lymph node organization and supports infiltration of natural primary human T cells, which subsequently expand within the synthetic tissue. Together, these results establish a route to tissue-scale matrices built from synthetic cell collectives and represent a critical step toward functionally integrating living and non-living matter.