A method of forming an insoluble native collagen fiber additive, includes soaking the decellularized tissue powder, which includes collagen fibers, in acidic or basic, salt solution, enzymatically dissociating the insoluble collagen fibers, and isolating insoluble native collagen fibers from the solution. The isolated insoluble collagen fibers can be used in cell aggregates and/or tissue constructs to provide three dimensional cell growth and/or adhesion.