ECM is the physicochemical support for the cells living in the tissue microenvironment. it is important to know the protein contents within the ECM that are critical for extra- and intracellular signaling, cell growth, migration, cell-cell/ECM interactions. The ECM gel derived from the Engelbreth-Holm-Swarm murine sarcoma (commonly known as Matrigel or lrECM) purchased from the Sigma Aldrich in the liquid concentration of 8-12 mg/ml (Lot # 064M4075V) was used for the LC-MS/MS analysis and to prepare the 3D scaffolds used for downstream experiments. The Matrigel mass spectrometry data will be used to compare with those of the decellularized mice mammary tissue ECM/DBT-TMS.