While most cells are studied on 2-dimensional tissue culture plastic or glass that is appropriate for epithelium and endothelium, most mesenchymal cells generally function within a 3-dimensional solid tissue environment in the body. And while collagen gels are often used for “3D” studies of cells, the fibrous nature of such matrices means these systems are essentially 1D with ill-characterized elasticities. Interest has also rapidly grown in defining and creating niches for mesenchymal stem cells because it is increasingly believed that the microenvironment contributes or controls self-renewal and differentiation. Our past work has focused on characterizing and controlling the cell-scale micro-stiffness of various hydrogels by altering the concentrations of polymer and crosslinker, and then measuring the gel's elasticity with AFM. The elasticity of these hydrogels has proven to be a key insoluble cue in 2D for mesenchymal stem cells (MSCs), profoundly affecting cytoskeletal organization and eventually differentiation. The results suggest that the elasticity of scaffolds used in tissue engineering might also need to be fine tuned for cell engraftment and for suitable restoration of tissue function. Toward this end as well as a more basic understanding of elasticity effects in 2D versus 3D, we have engineered hydrogels by various methods, one of which involves creating a network of collagen-caoted microchannels for cells to crawl into; the cells within are thus exposed to a 3D matrix of tunable stiffness. MSCs not only crawl into the microchannels and seem to fill the lumen, but they also clearly adhere and appear to assemble cytoskeletal stress fibers. Engineering 3D microenvironments that can be tuned for stiffness should thus provide more appropriate means for studying cells because the mesenchymal cells can engage receptors over their entire surface rather than being polarized top-to-bottom like epithelial cells.