Deposition of sulfated proteoglycan in D21 constructs. Inner and outer MFC were cultured on collagen scaffolds under normal (21%) or low (3%) oxygen tension for 21 days. 5 μm paraffin-embedded sections were stained with Safranin-O and counterstained with fast green. Images captured from constructs seeded with inner and outer MFC cultured under normal (21% O2, top row) or low oxygen tension (3% O2, bottom row). Scale bar 100 μm. Asterisk represents scaffold collagen fiber and surrounding area where fibers have been replaced by ECM synthesized de novo.