In Chapter 15, go to the final room where there is a store and save point. Then, go back down the corridor and enter the room with the two power nodes, a Ruby Semiconductor and some other items. Collect all of the items and return to the save point. Save the game, the reload it. Go back to the locked Node room and the items will be there again. Collect them again and repeat this as desired. You can also do this in chapters 6 & 7.