(a) Compositions of Fractionated and Complete pECM. We found that there is ample basement membrane (BM) proteins including laminin, collagen (VI, XII, XIV and XV), fibronectin, BM-specific heparan sulfate proteoglycan in pECM which consist of more than 80% peptide fractions. Moreover, we quantified the peptides of ECM molecules and calculated the ratio of HMW over LMW pECM. We found that the amounts of placental BM proteins are at least two orders of magnitude higher in HMW pECM than that of LMW pECM. (b) Western Blot Results. SDS-page and positive immunostaining of collagen I, II serves as confirmation of the proteomics results. (c) Chromatogram of Solubilized pECM After Eluting Through a SEC Column. Samples were taken from the high molecular weight fractions (defined as HMW pECM, MW>158 kDa) and low molecular weight fractions (defined as LMW pECM, MW~1.35 kDa).