Casey Steffen loves hemoglobin. “It’s such a wonderful, elegant transporter of oxygen,” says Steffen, who owns a company that produces 3-D animations on scientific topics.

A chance introduction to Michael Gulen, who makes action figures in his role as prototype development director at McFarlane Toys, led to a discussion of hemoglobin’s merits. Charmed by Steffen’s enthusiasm, Gulen agreed to mock up a hemoglobin toy. Of course, Steffen didn’t want to throw a cape on an amorphous blob, he wanted an accurate replica that was big enough to hold. That meant taking a digital model of the protein molecule—all 4,659 atoms—and blowing it up 18.5 million times.

Though Gulen routinely uses 3-D printing to prototype new products at McFarlane, this new challenge wasn’t easy, especially since they wanted the model to come apart so people could look inside. “When we broke the molecule down into 16 parts, most looked exactly the same,” Gulen says. And there was no indication that those parts would hold together.

But it worked, and there is now outside interest in the result: A big pharmaceutical company ordered 100 of the models, and a VC firm thinks it could be the next big children’s toy. Innocent plaything by day, bioresearch hero at night? Maybe it needs a cape after all.