They are about 200 nanometers across, or less than one-hundredth the width of a human hair, allowing them to hang out in the body without triggering any immune response. To build the microworms, researchers used a chemical vapor deposition method, which involves coating materials by vaporizing a material and letting it float onto a surface. In this case, researchers coated an aluminum oxide layer that contains tiny pores. Then the coated material was dissolved away, an MIT news release explains. This leaves a series of hollow tubes in the pores' place, which can be filled and capped at either end.