An apparatus and method in which the apparatus includes a first electrospinning device configured to electrospin first fibers of a first substance, a second electrospinning device configured to electrospin second fibers of a second substance such that first and second fibers combine in a mat formation region, and a biasing device configured to bias the first electrospinning device with a first electric polarity and to bias the second electrospinning device with a second electric polarity of opposite polarity to the first electric polarity to promote attraction and coalescence between the first and second fibers. The method electrospins under the first electric polarity first fibers from the first substance, electrospins under the second electric polarity fibers from the second substance, and coalesces the first and second fibers to form the fiber mat.