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International Journal of Bioprinting In situ 3D bioprinter for skin wound healing

process. It also provides the ability to manually control the 3.4. Fidelity
printer. To assess the print quality, a test grid was printed. The
With the help of SprutCAM software, a trajectory for the resulting structure was photographed using a Nikon
plane is generated based on a 3D model of the defect. Thus, SMZ18 binocular microscope (Nikon, Japan). An image of
we set the main printing parameters, such as the thickness the intended trajectory was superimposed on the resulting
of the filament, the printing speed, and the filling method. photo (Figure 6A). Then, the number of pixels that is
When the user presses the command to start printing, the outside the expected trajectory was calculated. Fidelity was
program sends a message to the robot controller about calculated as the ratio of the error to the entire area of the
the start of printing, and the robot controller responds by trajectory. For the developed system, the fidelity was 93%.
sending points characterizing the printing surface. The
program decrypts the file with the trajectory and is saved 3.5. Collagen contraction
as an array, while all lines are divided into short ones with We studied the contraction of collagen and collagen + platelet
a length of 1 mm. Then, according to the loaded points, the lysate gels by HF cells. As shown in Figure 7, the addition of
trajectory is cut along the border. Then, the equations of the platelet lysate increased the contraction of collagen gels. To
surface are calculated from the points, and the trajectory quantitate gel contraction, the images of gels were obtained
is projected onto the resulting surface. Thus, an array of at 48 h, and the area of the gel was calculated and expressed
lines is obtained, which is already transmitted to the robot as a percentage of the original area.
controller. After that, the program starts working in the To assess the effect of platelet lysate on the spreading
link mode between the robot controller and the printer of HUVEC and HUVEC + HF spheroids, a 3D migration
controller. The program sends messages about the supply assay in a collagen and collagen + platelet lysate gels was
of material from the robot controller to the controller of performed. As shown in Figures 8A and 9A-C,E, the
the printing device.
addition of platelet lysate dramatically improved the
3.3. In situ bioprinting process migration of HUVEC spheroids and changed the spreading
pattern of HUVEC + HF spheroids.
The robotic system consisted of collaborative robot KUKA
LBR iiwa 14 R820 with controller (“KUKA Systems For HUVEC spheroids, the spreading area increased
GmbH,” Germany), custom-designed extrusion 3D by 2.3 times in collagen + platelet lysate gel and only by
bioprinting device (3D Bioprinting Solutions, Russia), and 1.2 times in collagen gel (Figure 8B). Despite the fact that
software SprutCAM (“SPRUT Technology,” Russia). Three- the total area of spreading of HUVEC + HF spheroids
layer collagen meshes with living cells and PL were created in the two types of gels was comparable, the density of
according to the 3D CAM. The experimental setup also migrated cells was higher in the collagen + platelet lysate
included the sensors for detecting respiratory movements gel (Figure 9D).
and correcting the bioprinting path. 3.6. Adhesiometric analysis
The printed patches (meshes with 0.6 mm pores) for The level of adhesion of bioprinter hydrogel to non-injured
skin wounds were produced following pre-calculated 3D and injured cadaveric human skin has been estimated
models. The robotic-assisted system spent several minutes using commercial adhesion tester and high level of
to determine the pattern of movement and to perform adhesion has been demonstrated. The level of estimated
bioprinting. The sensors with feedback allowed bioprinting adhesion of bioprinted hydrogel to injured rat cadaveric
of complex structures without significant deviations from skin was higher (Figure 4C). There were also no statistically
the digital model and damages to the subcutaneous tissues significant differences in the level of adhesion between the
due to animals’ breathing movements. two types of hydrogel used in this study as bioinks.

The in vivo experiments also demonstrated evident
biocompatibility and healing potencies of complex bioinks. 3.7. The composition of bioink determines the
In all animals, the defects healed within 4 weeks – that intensity and complexity of regeneration processes
is, wound contraction, matured re-epithelialization, After applying the tissue-engineered composition to the
and restoration of the hairs could be observed without area of the skin defect using a collaborative bioprinter, the
any signs of inflammation or rejection (Figure 5E-H). wound was closed with a surgical dressing and left under
Thus, the complex composition of bioinks allowed for dynamic observation for 4 weeks. At the end of this period,
complex 3D bioprinting without affecting its viscosity and the animals were sacrificed, and after that, histological
polymerization and provided an excellent wound healing preparations were prepared for subsequent microscopic
effect. analysis. In the experiment, two types of bioink were used,

Volume 9 Issue 2 (2023) 386 https://doi.org/10.18063/ijb.v9i2.675