Hydrogels Containing Gradients in Vascular Density Reveal Dose‐Dependent Role of Angiocrine Cues on Stem Cell Behavior

Abstract

Biomaterials that replicate patterns of microenvironmental signals from the stem cell niche offer the potential to refine platforms to regulate stem cell behavior. While significant emphasis has been placed on understanding the effects of biophysical and biochemical cues on stem cell fate, vascularderived or angiocrine cues offer an important alternative signaling axis for biomaterial-based stem cell platforms. Elucidating dose-dependent relationships between angiocrine cues and stem cell fate are largely intractable in animal models and 2D cell cultures. In this study, microfluidic mixing devices are leveraged to generate 3D hydrogels containing lateral gradients in vascular density alongside murine hematopoietic stem cells (HSCs). Regional differences in vascular density can be generated via embossed gradients in cell, matrix, or growth factor density. HSCs co-cultured alongside vascular gradients reveal spatial patterns of HSC phenotype in response to angiocrine signals. Notably, decreased Akt signaling in high vessel density regions led to increased expansion of lineage-positive hematopoietic cells. This approach offers a combinatorial tool to rapidly screen a continuum of microenvironments with varying vascular, biophysical, and biochemical cues to reveal the influence of local angiocrine signals on HSC fate.

Perivascular Stromal Cells Instruct Glioblastoma Invasion, Proliferation, and Therapeutic Response within an Engineered Brain Perivascular Niche Model

“…[ 13a ] The role of MMP9 in matrix remodeling suggests future studies to probe for biochemical and biophysical changes to the hydrogel microenvironment that may also facilitate tumor cell invasion. Based on our secretomic analysis and by using microfluidic invasion models we have previously described, [ 13 , 44 ] ongoing work is studying the individual and combined role of these specific soluble proteins on proinvasive response of the GBM cells within our model, as well as identifying the cell types that are secreting these proteins. These findings suggest that a complex perivascular niche model assembled from brain‐derived endothelial cells along with pericytes and astrocytes not only replicates structural elements of the brain perivascular microenvironment but also expresses soluble factors consistent with the GBM tumor microenvironment known to enhance GBM cell invasion.…”

Engineered Tissue Models to Replicate Dynamic Interactions within the Hematopoietic Stem Cell Niche

“…B) Current in vitro culture approaches lead to a non‐uniform clonal expansion, producing an enlarged subset of HSCs that does not represent the in vivo HSC pool. C) Biomaterial cultures are well suited to probing features of an in vitro niche that bias HSC potential: single‐cell cultures in microdroplet environments probe the heterogeneous response of HSCs to specific factors, [ 127a ] gradients of factors and material properties identify combinations and synergies among extrinsic cues, [ 130 ] and spatial and temporal presentation of multiple factors at specific time points. [ 131 ]…”

“…Response surface mapping (RSM) is a subset of design of experiment methodology that has historically been used in the chemical engineering and materials science field to identify initial inputs that lead to a desired output (e.g., dopant concentrations leading to increased toughness, biodiesel production). [124] Such a system can be applied to design of hematopoietic culture, in which [127a] gradients of factors and material properties identify combinations and synergies among extrinsic cues, [130] and spatial and temporal presentation of multiple factors at specific time points. [131] a subset of a large number of combinations, e.g., modulus, cytokine concentration, is used to infer optimal combinations that lead to a hematopoietic response.…”