BIOPRINTING FOR SKIN - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 281

FIGURE 13.2
Laser-assisted bioprinting: (a) schematic sketch of the laser-assisted bioprinting setup. (b) The laser pulse is focused
through the donor glass slide into the absorbing layer, which is evaporated immediately. Thereby, a vapor bubble is
generated. The subjacent hydrogel is accelerated by the expanding bubble. Although the bubble recollapses within
about 6 m s, the hydrogel moves on due to inertia and flows within a few hundred m s as a “jet” onto the donor slide,
where it remains as a droplet ( Unger et al., 2011 ). (c) The droplets can be precisely positioned. The diameter of the
droplets, each containing several cells, is about 80 m m, the distance between two droplets is 600 m m. The horizontal
lines in (b) are interference patterns resulting from the illumination of the process with coherent laser light.
there as a droplet ( Duocastella et al ., 2009 ; Unger, et al., 2011 ). By moving the glass slides and the
laser beam, any desired 2D pattern and layer-by-layer 3D pattern can be generated. Figure 13.2 shows
a printed pattern of droplets with several fibroblast cells. Fibroblasts labeled with Green Fluorescent
Protein (GFP) were embedded in a sol mixture of fibrinogen and hyaluronic acid and printed onto a
layer of fibrin with a spacing of 600 µm between droplets.
Often, the collector glass slide is coated with a hydrogel layer before printing to achieve a humid
environment for the cells and to cushion the impact. However, the cells survive the printing process also
without this hydrogel layer. Instead of the collector glass slide, other items can be put under the upper
glass slide to print onto or into (e.g. a scaffold) ( Ovsianikov et al., 2010 ).
The printed droplet volume can be controlled by the thickness and viscosity of the biomaterial
layer on the donor glass slide, the thickness of the absorption layer, the laser pulse energy ( Gruene
et al., 2011a ; Guillotin et al., 2010 ), and the focal spot size. The ratio between printed droplet volume
and laser pulse energy is nearly proportional in the relevant energy range at a constant viscosity and
layer thickness. In contrast, there is no simple dependency of the printed droplet volume on viscosity or