(A) MCF10AT cells in printed HELP bioinks retain high viability immediately after printing and after 3 days in culture as tested by a Live/Dead cytotoxicity assay (n = 3 to 4, means ± SD). (B) Representative images of MCF10AT cells in printed HELP bioinks, which form noninvasive spheroids after 6 days in culture. (C) Schematic of the recombinant ELP component of HELP, which can be engineered to contain a non–cell-interactive scrambled RDG sequence instead of the integrin-binding RGD sequence. Alternating regions of HELP-RGD (green, fluorescent microspheres) and HELP-RDG (gray, fluorescent microspheres) can be printed together to form a cohesive structure. Scale bar, 2 mm. (D) Printed MCF10AT cells treated with TGF-β are significantly less circular in printed HELP-RGD regions compared to that in HELP-RDG regions (N = 3 replicate printed structures, n = 92 to 448 cells per printed region, median ± interquartile range, two-tailed Mann-Whitney test, ****P < 0.0001). (E) Printed structures containing both MCF10AT cells (green, dyed with CellTracker Green) and cancer-associated fibroblasts (CAFs; red, dyed with CellTracker Red) maintain their spatial patterning in the support bath (before release), after release from the support bath (after release), and after 6 days in coculture. Scale bars, 2 mm.