Extracellular matrix rigidity influences morphological differentiation of neuroblastoma cells. (A) Phase contrast and fluorescence images of cell nuclei (DAPI) and actin (phalloidin) of SK-N-DZ neuroblastoma cells cultured on 0.1 kPa versus 1000 kPa collagen-coated polyacrylamide (PA) gels with or without exposure to 1 μM 13-cis RA for three days. Scalebar = 50 μm. (B) Average neurite length of SK-N-DZ neuroblastoma cell clusters cultured on collagen-coated PA gels of varying rigidities with and without exposure to 1 μM 13-cis RA. Populations within brackets are statistically indistinguishable from each other but statistically distinguishable from populations in the other brackets (p < 0.01 for all significant comparisons). Each population represents >100 cell clusters. 90th percentile, 75th percentile, median, 25th percentile, and 10th percentile values are represented by the top whisker, top line, middle line, bottom line, bottom whisker, respectively, of each bar.