Microenvironments play complex roles during tissue development and altered environments can contribute to disease progression. Mammary epithelial cells (MECs) respond to mechanical and chemical signals within three-dimensional environments to produce diverse tissue architectures, ranging from polarized, spherical structures (acini) to disorganized, malignant phenotypes. We are investigating the interplay between matrix rigidity and extracellular molecule composition on MEC tissue development. We employ synthetic hydrogels composed of poly(ethylene glycol)-acrylate (PEG) interspersed with natural extracellular molecules to controllably present these cues. By varying the concentration of the PEG backbone, shear moduli of the matricies are achieved over four orders of magnitude (~ 10 to 10,000 Pa). ECM compositions are varied by blending different amounts of laminin and collagen IV into uncross-linked hydrogel solutions. MCF-10A cells are overlaid on the PEG hydrogels, or Matrigel as a positive control for acini formation, and cultured over a period of 20 days. Structures are imaged for morphology, polarity, and proliferation, with acinar-like structures characterized further by size, number, and presence of lumen. Sixty micrometer polarized acini containing hollow lumens form on hydrogels of low shear moduli (60 Pa) and a laminin:collagen IV weight ratio matching that of Matrigel (2:1), but lumens fill and tissue becomes less organized upon increases in shear modulus or variations of laminin and collagen IV composition. We also compare the effects of PEG-based matrices on normal MECs to the cancerous cell line MCF-7. PEG-based hydrogels provide model systems to investigate how mechanical and chemical cues contribute to MEC tissue formation.

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