Iron Man 3 (2011) - Extremis Arm Regrowth Concept

Originally in Iron Man 3 there would have been an elaborate sequence of Extremis limb regrowth during the battle. This was an early concept when the idea was still some kind of nanotech like in the comics. Ultimately it was considered a little too gory for an Iron Man movie, and the battle was so frenetic that there just wasn't the screen time to devote to this anyway.

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Severed arm, glowing with Extremis energy. Nikolas Coster-Waldau was still the front-runner for the role of Killian at the time.

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Reconstructed arm, glow showing internal structure.

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Stage 1 - Severed limb.

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Stage 2 - Bone and core muscle growth interlaced with nanotech structure.

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Stage 3 - Hand begins to form, surface musculature is filling in.

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Stage 4 - Musculature complete.

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Stage 5 - Underskin nano-mesh and skin begins to form.

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Stage 6 - Skin is forming over reconstructed arm.