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Collagen sponges fabricated via lyophilization of a 0.6 wt./vol.% solution of plant-derived human (A–C) or bovine collagen (D–F) in 0.5 M acetic acid. Casting frames were frozen in −20°C air [slow; (A, D)], −80°C air [medium; (B, E), or −80°C ethanol [rapid; (C, F). Scale bar=200 μm.
