The Picrosirius Red Stain Kit (24901, Polysciences, Warrington, PA, USA) was used to stain collagen in the scaffold inserts. The insert was rinsed with DDI water then soaked in 0.5 mL of Solution B (Picrosirius Red F3BA stain) for 60 minutes. The insert was then rinsed with Solution C (0.1 N HCl) for 1 minute, twice, followed by rinsing in DDI water and then in 70% ethanol for 60 s. The stained inserts were then imaged or placed in a plate reader (SpectraMax i3x, Molecular Devices, San Jose, CA, USA) with the wellscanning mode to detect PSR fluorescence signals (560 nm excitation, 650 nm emission).