Figure 1. Controlling density and elastic modulus of hydrogel microposts.

(A) Strategy to control the presentation of matrix signals to cells. (i) Schematic illustration of cells in matrices with different degrees of packing between matrix signals while preserving the intrinsic mechanical properties of materials. (ii) A representative confocal image of a PEG-DA scaffold to enable cell adhesion only to posts (red). A 15 μm PEG-DA base layer without cRGD peptide (green) was made before fabricating posts. Cysteine-containing cRGD (0.8 mM) was crosslinked throughout the posts during printing. (B) Microscale control of spacing intervals during post printing (scale bar = 50 μm). Error bars in average vs. expected spacing are reported as standard error of the mean (SEM) of the measured distance interval; n = 18 per data point across 2 experiments. (C) Controlling elastic modulus of posts by varying concentrations of crosslinker (LAP), percent laser power and total dwell time. PEG-DA (25%) was used to fabricate all posts used in this study; n ≥ 5 posts per data point, each measured by AFM twice per post. Functional trend was fit to the two-parameter power series equation Y = a^.(1 + X)^b. (D) Standardization of post curvature by changes in laser focal height. (i) Z = −1.6 mm and Z = −0.8 mm focal heights were used to achieve regular post geometry between 20-kPa and 4-kPa posts, respectively. Cells attached predominantly to the linear region of the posts. Post curvatures were fitted to one-phase exponential association equation Y = Y₀ + (Y_max − Y₀)(1 − e ^−kx). (ii) Trends observed in 20-kPa and 4-kPa post half-widths based on fit equation. Post half-width corresponds to the Y_max of the exponential equation; n ≥ 10 posts per data point.