Needle-punched Three-Dimensional Nonwoven Wound Dressings with Density Gradient from Biocompatible Calcium Alginate Fiber

Three-dimensional calcium alginate fiber (CAF) dressings with density gradients were fabricated by the needle-punching process. As a skin substitute, the dressings under wet conditions showed "skin-like" performance. The interconnected pores enabled the dressings to absorb more wound exudates. CAFs arranged vertically and the density gradients along thickness direction altered the diffusion and distribution of wound exudates in the dressings and prevented the wound exudates from infiltrating back to the wound surface, which kept the wound in excellent healing conditions. The changes in performance and structure of the dressings during wound healing were investigated. After absorbing the wound exudates, in the presence of Na+ ions, the Ca2+ ions in CAFs were exchanged and parts of CAFs turned into sodium alginate (SA) gels. The CAFs residues and SA gels composed the gelled dressings with a special composite structure, which displayed unique performance, especially the tensile process and the stereoscopic structure. The ion-exchange reaction was influenced by the H+ and OH- ions in wound exudates, affecting the properties of the gelled dressings. An in vitro cell culture assay indicated that the Ca2+ ions released from the dressings promoted cell growth and proliferation. The density gradient structure had a significant effect on the spread of cells on the dressings.