BIOPRINTING FOR SKIN - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 274

FIGURE 13.1
The image shows the skin with its specific and complex 3D structure. It consists of several layers: the epidermis,
which is tightly connected to the dermis via the basement membrane, the dermis, and the hypodermis. Specific cell
types and organs are present in the different layers, exhibiting specific functions.
solarium). Also, the hair can send optical signals with social, cultural, psychological, or political con-
tent, depending on its form, color, presence, or absence ( Michael, 2013c ).
13.1.1.2 Structure
The skin is composed of four layers, namely, the epidermis, the basement membrane, the dermis, and
the hypodermis. All of these structures, except the basement membrane, contain various specialized
cell types and serve different purposes ( Figure 13.1).
13.2 EPIDERMIS
The epidermis is the uppermost skin layer and consists of a multilayered stratified squamous
epithelium formed by keratinocytes. Depending on its location, the epidermis is normally about
0.05 mm thick, but may reach several millimeters at the palms and the sole of the feet ( Michael,
2013c ). Throughout life the epidermis regenerates continuously, having a turnover rate of about
30-56 days. It is composed of four layers: the basal layer, the spinous layer, the granular layer, and
the cornified layer (from inside to outside). In the basal layer, epidermal stem cells are responsible
for the regenerative capacity of the skin. These cells are highly proliferative, are characterized by
cytokeratin 5 and 14 expression, and comprise interfollicular stem cells, hair follicle stem cells,