After 72 hours in contact with USPIO NPs, pure or composite collagen hydrogels were fixed with PFA (4% w/v), then dehydrated with ethanol, butanol and embedded in paraffin. Five micrometer transverse sections were performed using a manual microtome (Stiassnie, France). Sections were stained with Prussian blue 5% potassium ferrocyanide in water (Sigma) for 15 min, then with Prussian blue 5% potassium ferrocyanide in hydrochloric acid (5% w/v) (Sigma-Aldrich) for 15 min and counterstained with hematoxyline (Sigma) for 5 min. Then, samples were rinsed with dH 2 O and dehydrated again using ethanol and toluene.
Last, sections were mounted between glass and coverslip using the Eukitt mounting medium. Samples were observed at magnification X600 with a Nikon Eclipse E600 POL and pictures taken with a Nikon DS-Ri1 camera
Last, sections were mounted between glass and coverslip using the Eukitt mounting medium. Samples were observed at magnification X600 with a Nikon Eclipse E600 POL and pictures taken with a Nikon DS-Ri1 camera