Expression of MMP2 and Ki-67 were observed by immunofluorescence. Explants were fixed with 4% paraformaldehyde (PFA; Carl Roth, Karlsruhe, Germany) on ice, incubated in PFA:PEM (1:1) for 5 minutes and PFA:Borat (1:1) for 10 minutes, and washed with PBS. Afterward, explants were treated with Triton X-100 (5 minutes), NaBH4 (10 minutes), and washed in PBS twice following 1 hour in Immunoblock (Carl Roth). Staining was performed with primary antibodies for MMP-2 (Santa Cruz Biotechnology, Inc., Heidelberg, Germany) and Ki-67 (Abcam, Cambridge, United Kingdom) at 4°C over night. Explants were washed with PBS three times and stained with Phalloidin Atto-488 (Sigma), Hoechst (Sigma), and Alexa-fluor-647 donkey-α-goat (Invitrogen, Darmstadt, Germany), following wash steps with PBS and aqua dest. Explants were removed from rings and covered with Fluoromount G (EBioScience, San Diego, CA, USA) under cover slips. Fluorescence microscopy was performed at Axio Imager microscope 2 (Carl Zeiss); images were taken with Axio-cam MRc5 and processed with Zen 2012 (Carl Zeiss).