A wound dressing for vacuum therapy comprising: a cover configured for placement over the wound to maintain a reduced pressure over the wound and adapted for communication with a source of vacuum, and a screen structure for placement between the cover and the wound, wherein the screen structure is adapted to remove or inactivate undesirable components from the wound environment and/or to concentrate desirable components present in the wound environment. Also provided are kits for the assembly of such wound dressings, and systems comprising the wound dressings in combination with a source of vacuum.