The tissue rectifier was a stubby, tubular device of Sontaran design, which they used to heal their wounds.
On Earth, Commander Churl offered to use his tissue rectifier to heal Lieutenant Stavv's wounded leg. Stavv declined, preferring to carry the scars as a badge of honour and bravery and a reminder of being beaten. The tissue rectifier was later used to restore a blind girl's sight. Stavv was exposed as a Rutan in in disguise. Churl explained that a real Sontaran would only carry wounds as a mark of victory in battle. Other wounds would be healed in preparation for the next battle. (PROSE: Blind Terror)