Aeroponics, by definition, doesn't use grow media, unless you're adding support for a taller plant. Since aeroponics focuses on maximizing oxygen supply to the roots, and roots tangled up in grow media blocks not only oxygen but nutrient solution from penetrating the root mass, the preference is to simply have roots hanging freely.
In reality, some aeroponic growers do use net cups filled with grow media when support for larger plants is necessary. The media itself doesn't contribute any nutritional value to your plant, so materials like marbles or Styrofoam chunks could be used just as well, if you wanted. If you do plan to reuse grow media, be sure to sterilize it thoroughly between uses to avoid spreading disease.
