The samples were then submerged in EPON812:acetone(1:1) for 30 min and EPON812 for 1 h. After that, the samples were polymerized for 48 h at 60 °C and followed by 24 h at 30 CThin sections were prepared on a diamond knife in a LKB Ultra microtome(BROMMA, Sweden) and deposited on a collodion-coated Formvargrids. Ultrathin sections were stained in uranyl acetate and lead citrate and viewed using a transmission electron microscopy