Why are there tiny blue lines in the sterile gauze of Steady Medical Brand? Everybody help me.

The name of gauze is developing gauze, and there is a small blue thread in the gauze. This is the function of X-ray developing line. It is to use gauze during the operation to prevent gauze from staying in the body, and then take X-rays, which can be seen to prevent gauze from staying in the body and causing medical accidents.