Matrix composition and stiffness jointly modulate EMT in dECM‐ALG hydrogels. A) Relative mRNA FN1 expression by MCF10A cells cultured in ALG or dECM‐ALG hydrogels, with and without TGF‐β1 (data normalized to GAPDH, n = 4 individual experiments). B‐i) Relative mRNA expression of EMT‐related markers by MCF10A cells cultured in adECM‐ALG (red bars) compared to ndECM‐ALG hydrogel (blue line) (data normalized to GAPD, n = 6 individual experiments). B‐ii) Representative immunofluorescence images of dECM‐ALG hydrogels stained for FN (magenta, M‐marker). Scale bar: 10 µm. C) Viscoelastic properties of cell‐laden soft and stiff dECM‐ALG hydrogels after 1 day of culture (G’ and G”: elastic and viscous components of the shear moduli, respectively). Data are presented as mean ± standard deviation (n = 3 individual experiments). D) Relative mRNA expression of EMT‐related markers of cells cultured in stiff (dark red bars) versus soft adECM‐ALG hydrogels (red line) (data normalized to GAPDH, n = 6 individual experiments). E) CSLM images of mammary acini stained for E‐cad (red) and DAPI (blue). Scale bar: 10 µm. Statistical significance: *p < 0.05, **p < 0.01, ***p < 0.001.