What’s wrong with this picture? The sugar polymers that make up the spheres in this image are designed to package and protect specially engineered cells that work to produce drugs and fight disease. While on-site, they must remain undetected by the body’s natural defense system. However, the reddish markers on the spheres’ surfaces indicate that immune cells (blue/green) have discovered these invaders and begun to block them off from the rest of the body. Further experiments with the spheres’ geometry and chemistry will lead to better invisibility cloaking and longer lasting protection for these cell-based factories.