"The challenge is how to make it artistically appealing for tattoo artists," says Mathiowitz. "They are not going to use something that's just safer, but something they like the look of. There's a lot of art and science involved."

Mathiowitz and Anderson found an ideal candidate in the polymer polymethyl methacrylate, or PMMA--a transparent plastic originally used as an alternative to glass that has been shown to be nontoxic in human tissue. PMMA is now used in contact lenses and heart valves, as well as in cosmetic surgery to smooth wrinkles and scars. Mathiowitz designed tiny, nano-sized PMMA beads to house Anderson's biodegradable pigments. Researchers found that these microencapsulated inks held up for months in animal studies.

The final challenge was to modify the inks so that they're easily removable with one laser treatment. Traditionally, to remove a single tattoo, a dermatologist matches a laser's wavelength to a specific color in a tattoo. Black is the easiest to target, since it can absorb all wavelengths. The laser breaks the pigment into smaller particles, which are then absorbed by the body's immune system. Since artists use a wide range of pigments and sometimes mix their own, it's difficult to exactly match a laser to a given color, which is why multiple treatments are often needed to fully erase a tattoo.

To get around this problem, Anderson inserted a tiny "energy-absorbing target" into each microcapsule--a substance that looks black. The target is small enough that it doesn't affect the ink's appearance but big enough to react to laser light, so that the bead ruptures and releases the pigments.

"They're basically taking the individualization out of it," says Ranella Hirsch, president elect of the American Society of Cosmetic Dermatology and Aesthetic Surgery. "And the simplicity and beauty of this is in standardizing the ink."

Anderson has formed a company, Freedom-2, to commercialize the inks, and he hopes to bring the first generation of microencapsulated inks to market in the next year. He adds that the design opens up possibilities for a whole range of specially timed tattoos. "You could sit around and think of all kind of things, like a time-limited tattoo, one that would last three years and then disappear, or tattoos that only appear at night."