According to an aspect of the disclosure, a treatment method may include treating a wall of a portion of a gastrointestinal tract of a patient. Treating the wall may include positioning one or more injection units adjacent to the wall. Treating the wall may also include affecting at least one of movement of gastrointestinal tract contents through the gastrointestinal tract and absorption of gastrointestinal tract contents by the gastrointestinal tract, by injecting material into the wall using the one or more injection units. Injecting the material may include injecting the material between layers forming at least a portion of the wall.