Em 906 electron microscope

Samples were fixed immediately with 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer (both Serva) for 30 min at RT and stored at 4 °C. Postfixation was performed with 1% osmium tetroxide (Electron Microscopy Sciences) and 0.8% potassium ferrocyanide II (Roth) in 0.1 Mol/L cacodylate buffer for 1.5 h followed by the dehydration of the samples in a graded ethanol series and the embedding of the samples in Epon resin (Roth). Finally, ultrathin sections with a thickness of 70 nm were stained with uranyl acetate and lead citrate. Samples were examined using a Zeiss EM 906 electron microscope at 80-kV acceleration voltage (Carl Zeiss).

Matrigel‐coated beads covered with cells were harvested, rinsed with PBS and fixed with 2.5% glutaraldehyde (Serva, Heidelberg, Germany) in 0.1 M sodium cacodylate buffer (Serva, Heidelberg, Germany) for 30 min at RT and stored at 4°C. The samples were postfixed with 1% osmium tetroxide (Electron Microscopy Sciences, Hatfield, USA) and 0.8% potassium ferrocyanide II (Roth, Karlsruhe, Germany) in 0.1 M cacodylate buffer for 1.5 h and embedded in agarose overnight. After cutting the agarose in smaller blocks, the samples were dehydrated in a graded ethanol series and transferred to Epon resin (Roth, Karlsruhe, Germany). Finally, ultrathin sections of the samples (70nm) were stained with uranyl acetate, and lead citrate. The examination was carried out with a Zeiss EM 906 electron microscope at 80kV acceleration voltage (Carl Zeiss, Oberkochen, Germany).