Fig. 4

Constructs with the multi-layered skin cells and collagen were printed by an extrusion printer via layer-by-layer [36, 37]. a Fibroblasts were printed in the 2nd collagen layer, and six layers of collagen were printed over the fibroblasts. Keratinocytes were printed in the 8th layer of collagen and two layers of collagen were used to cover the keratinocytes layer. b The printed skin structure contains eight collagen layers. These include six collagen layers alternating with three layers of fibroblast layers and two collagen layers separating the stacked fibroblast layers from keratinocytes