BLOOD VESSEL REGENERATION - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 158

FIGURE 7.7 Laser Assisted Bioprinting.
A typical setup for laser-assisted bioprinting is shown in the illustration. (A) The excitation source is focused on a
point on the glass slide containing the hydrogel with cells embedded. (B) An air bubble forms from the excitation of
the substrate. (C) The air bubble then can lead to a stream formation that propels the cells + matrix toward the build
area. (D) The build area is positioned micrometers to millimeters away to serve as a collection slide for the droplets
produced from the rapid expansion of the radiation-absorbing layer. In the case of blood vessel regeneration, this
technique has a few drawbacks in regards to the mechanical strength of the printed structure, but it excels in regards
to spatial resolution as well as the ability to exchange the donor plate with another with a separate matrix and
cellular composition. As such, it can print heterogeneous scaffolds that have the potential for use in the creation of
vasculature as well as microvasculature. This sort of additive manufacturing has been used to generate cell based
scaffolds to mimic the native vasculature.
to the printing process can be cultured normally and trypsinized to remove them from their culturing
environment. Upon resuspension in a compatible hydrogel (collagen, alginate, fibrin, etc.), the hydrogel
is mounted on a glass slide with or without a coating of a laser radiation absorbing layer. This glass
slide is then positioned parallel to a collection slide several hundred micrometers to a few millimeters
away. The basic principle of this printing process is that an excitation source is focused on a small point
above the desired deposition location. The focused light causes the local expansion of gases (through the
evaporation of either the laser radiation absorbing layer or the hydrogel directly) which then provides
the kinetic energy required to push the hydrogel beneath the focal point toward the collection slide. The
exposure time/intensity of the laser can adjust the volume ejected from hydrogel, and as such, volumes
can be adjusted on the order of picoliters, allowing for very rigorous control of the ejected volume and cell
seeding density of the printed construct. The spatial resolution of this technique also has some unique
advantages due to the ability to precisely control the focal point of excitation, controlling the ejection of
hydrogel loaded with cells from the source plate towards the collection plate.
Additionally, the properties of the ejected material can be tailored to the application at hand.
Depending on the viscosity of the source hydrogel, either a droplet or a stream can be formed upon
excitation by the light source. This in turn can help control the shape of the patterns deposited on
the collection plate. In the case of vascular regeneration, this technique has a unique advantage be-
cause multiple source plates with different cell types embedded in different hydrogels can be used to
build the vascular implant. The ECs could be deposited along an inner ring with smooth muscle cells
surrounding the outside and based upon the implant location, the diameter of the scaffold and the