In a dramatic demonstration of the first-ever method for grafting synthetic materials onto minuscule bits of biological tissue, scientists have stenciled the word hair—in 3-D block letters—on a single human hair. “You can actually make any three-dimensional object you’d like,” says John Fourkas, a chemist at Boston College, who developed the technique along with colleagues at Boston College and Boston University. More important, the technique leaves the underlying tissue unharmed, prefiguring a day when doctors might build miniature sensors directly onto the skin of their patients, or biologists might use microscopic tweezers to capture and study individual cells.
The secret, Fourkas explains, is building the 3-D structures from a special chemical resin, similar to the composite fillings used by dentists, that hardens under low-energy laser light. After bathing the hair in the resin, a computer-guided laser traces out the desired pattern under a microscope, selectively hardening only the areas where the beam strikes. The resin is so sensitive to light, and the beam so tightly focused, that the hair remains intact. “You might imagine that you would end up burning the hair, but this isn’t what happens,” says Fourkas. Furthermore, the laser beam is so precise that it can create parts just a few millionths of an inch wide. Fourkas is now experimenting with ways to fabricate tiny electrical motors or machines using a similar technique.