A biomatrix was a biological characteristic of a lifeform.
In 2371, Ensign Harry Kim detected some kind of highly coherent energy pulses in the dark matter nebula which included a biomatrix. (VOY: "Cathexis")
The Vidiian chief surgeon Sulan used the genotron to separate the Klingon DNA from B'Elanna Torres and created a completely separated biomatrix. (VOY: "Faces")
In 2381, Ensign Sam Rutherford accidentally inhaled vapors from an alien frog skull that altered his biomatrix, afflicting him with full molecular engorgement. (LD: "The Spy Humongous")