Bionics
These allow an Imperial Guard character who has suffered a crippling injury to return to service but they do not improve his abilities in any way.
However, there is a chance that an attack will damage a bionic part rather than doing any real harm. To represent this, if a model with bionics is killed, instead of removing it place it on its side. Roll a D6 at the start of the next turn: on a roll of 6 the model is stood back up with 1 wound but on any other roll it is removed as a casualty.