BIOPRINTING FOR SKIN - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 288

FIGURE 13.6 Printed skin constructs implanted in the dorsal skin fold chamber in nude mice.
Printed skin constructs were inserted into full-thickness skin wounds in the dorsal skin of nude mice and fill the
wounds completely after implantation (left). After 11 days, the constructs are connected to the surrounding host
tissue (right). Reprint from Michael et al. (2013b) .
The printed keratinocytes formed a dense stratified tissue, similar to normal epidermis. In some
samples, even a corneal layer could be observed ( Figure 13.7 ). The printed keratinocytes did not
exhibit a complete differentiation, though, but a beginning one could be found ( Figure 13.8 ). Since
the experiments lasted only 11 days and complete differentiation require about 3 weeks, these results
are not unexpected.
Formation of adherens junctions and later tissue/epithelium was confirmed by detection of
e-cadherin throughout the whole epithelium ( Figure 13.9 ). Despite the similarity to normal mouse
skin, the epidermis developed by the printed keratinocytes was less thick and had no rete ridges. While
not optimal for the mechanical stability of the skin, the results looks promising, though, since they
represents the first and successful step toward tissue engineering of skin by laser-assisted bioprinting.
Thicker epithelium may be printed in the future, including rete ridges.
In contrast to the keratinocytes, only part of the printed fibroblasts remained on top of the Matri-
derm™, while a large fraction migrated into it. The fibroblasts and keratinocytes together formed a
multilayered tissue ( Figure 13.7 ). This is very satisfactory, since an organotypic structure of the skin
construct is essential for a future application.
Small blood vessels growing into the Matriderm™ from the depth of the wound bed and the wound
edges could be found ( Figures 13.7 and 13.10 ). They were directed toward the printed cells, which may
be explained by cytokine expression (e.g. vascular endothelium growth factor or VEGF) of the cells
( Ballaun et al., 1995 ). In control experiments without cells, no vascularization of the constructs at all
could be found ( Michael et al., 2013a ). This strengthens the conclusion that the printed cells induced
blood vessel formation.
13.3.4.7 Ink-jet-based In Situ Bioprinted Skin
Instead of printing skin and implanting it afterwards, Binder (2011) used a commercial ink-jet printer
to print skin cells directly into wounds in situ . He combined the printer with a laser scanning system
to measure the wound size and calculate a wound surface model. Then the ink-jet printer, mounted on