A major obstacle in defining the exact role of extracellular matrix (ECM) in stem cell niches is the lack of suitable in vitro methods that recapitulate complex ECM microenvironments. Here we describe a methodology that permits reliable anchorage of native cell-secreted ECM to culture carriers. We validated our approach by fabricating two types of human bone marrow-specific ECM substrates that were robust enough to support human mesenchymal stem cells (MSCs) and hematopoietic stem and progenitor cells in vitro. We characterized the molecular composition, structural features and nanomechanical properties of the MSC-derived ECM preparations and demonstrated their ability to support expansion and differentiation of bone marrow stem cells. Our methodology enables the deciphering and modulation of native-like multicomponent ECMs of tissue-resident stem cells and will therefore prepare the ground for a more rational design of engineered stem cell niches.

research has revealed that, together with the provision of morphogens and the presentation of adhesion ligands, [ 2 ] the mechanical characteristics of extracellular matrices have a decisive infl uence on cell fate, provoking the development of materials with effective physical properties. [ 3 ] This interplay of biomolecular and biophysical signals thus defi nes an obvious, but until now unmet, need for a new generation of biomaterials that can be selectively and independently tuned for biomolecular properties and physical material parameters. A conceptual basis to address this need is currently missing. As such, we have developed a rational design approach relying on mean fi eld concepts to guide the design of biofunctional matrices. Considering the decisive role of electrostatic interactions in functional assemblies of living matter we selected a system that allows for a far-reaching modulation of structure-determining forces: crosslinking a hydrophilic and fl exible, multi-armed polymer (with four-armed, amino-terminated poly(ethylene glycol) (starPEG) as an example system known for its anti-adhesive characteristics towards proteins, [ 4 ] with a multifunctional, highly charged crosslinker (such as heparin (HEP) or a similarly charged glycosaminoglycan), which can function as a multivalent binding site capable of complexing a plethora of important bioactive molecules. [ 5 ] We explored whether and how the combination of the particular gel components permits varying the physical and biomolecular characteristics of the swollen materials independently.Based on the successful experimental verifi cation of the theoretical predictions and the functionalization of starPEG-heparin gels with adhesive ligand peptides (such as the integrinbinding arginine-glycine-aspartic acid sequence (RGD))) and morphogens (vascular endothelial growth factor (VEGF), bone morphogenetic protein-2 (BMP-2)) through covalent and noncovalent conjugation schemes we were able to illustrate the resulting options for two selected example systems: studying the interplay of matrix elasticity and growth factor presentation in inducing the pro-angiogenic state of human endothelial cells and promoting osteogenic differentiation of human mesenchymal stem cells we identifi ed effective combinations of matrix parameters and demonstrated exciting options for the fully matrix controlled direction of the cells, i.e., removed the Using Mean Field Theory to Guide Biofunctional Materials DesignCell-instructive characteristics of extracellular matrices (ECM) resulting from a subtle balance of biomolecular and biophysical signals must be recapitulated in engineered biomaterials to facilitate regenerative therapies. However, no material explored so far allows the independent tuning of the involved molecular and physical cues due to the inherent correlation between biopolymer concentration and material properties. Addressing the resulting challenge, a rational design strategy for ECM-inspired biohybrid hydrogels based on multi-armed poly(ethylene glycol) and he...

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