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International Journal of Bioprinting Vector-based G-code generation for biofabrication

pattern for both the laser cutting and the FDM process can be drawn as only one continuous path and printed as such.
be the same illustration. This approach eliminates the need For example, a simple meandering pattern in Figure 5A,
for separate design phases in different programs. such as the one used for assaying ink/printing properties,

Another scenario where regular FDM slicers struggle or even complicated shapes such as the outline of a heart
is when processing objects such as grid structures or in Figure 5B, can be produced. Splitting the illustration
lattices with small strut diameters, which are best printed into several paths also enables toggling of the extrusion in
as a continuous pattern. In contrast, traditional slicers between these, turning it off and on again when desired,
require the printhead to jump between segments and start as shown in Figure 5C. The toggling of the extrusion
extrusion multiple times per layer, leading to poor bed depends on the machine that is used but can usually be
adhesion, reduced print quality, stringing, and weaker done by either adding/removing the E command to each
scaffold strength, as shown on the sliced version of a grid G1 where it should extrude, or adding the pressure on/
in Figure S3B, Supporting Information. Using the drawing off commands, which are often machine-specified with a
method, these codes can easily be generated, not only for pressure quantity. Shapes can also be stacked into several
simple grid structures, as shown in Figure 4B, but also for layer constructs or used conveniently for multimaterial
more complex shapes, as demonstrated in Figure 4C. printing approaches with more than one extruder as in
Figure 5D and a detailed rundown shown in Figure S4,
The ability to surpass the limitations of conventional Supporting Information. Therefore, for instance, having
slicers is also crucial for freeform printing techniques, the ability to use different colors for each path/printhead
such as the one demonstrated with polyoxazolines, where makes the whole process and patterns more comprehensive
28
pathfinding and complex 3D structures are too difficult for
traditional layer-by-layer FDM slicers to process, resulting and intuitive. The swapping of the printhead can then just
in incorrect prints. In this case, we used the method to be added in the code before the corresponding paths are
print structures initially drawn in the X–Y plane, with the followed and vice versa for swapping back to the original
Y-coordinate replaced by Z, to create a 3D structure in the printhead. For maintaining the correct positioning, the
X–Z plane, as shown in Figure 4D. This principle can also simplest way is to have the start point of each printhead
be applied to scaffold segments, enabling the printing of kept the same and then drawing a path to the point at
lattices that are flexible in the X, Y, and Z directions, as which the extrusion should start. Another alternative is to
demonstrated in Figure 4E. Similarly, a progressive increase accommodate for the difference in printhead position and
in Z height can be added to code segments, provided the just continue with the second printhead at the position the
desired height range and the start and end of each segment previous one left of.
are defined, typically for the entire subroutine or path The ability to draw the paths freely also allows for the
section. This approach allows for the programming and creation of custom infill patterns, which can mimic the
printing of shapes like spirals and arches, as shown in alignment of collagen fibers or muscle fibers in tissues, such as
Figure 4F. in the example of the heart shown in Figure 5E. By controlling
3.4. G-code conversion used for the start and stop of extrusion, adjusting printhead movements,
extrusion-based bioprinting and customizing the infill and other paths, complex prints can
One aspect of extrusion-based additive manufacturing be generated quickly—prints that would otherwise be very
is the processing of liquid materials such as silicon, time-consuming to create. An example of this is the institute
elastomers, or hydrogels such as bioinks, which are applied logo with infill and dual-material extrusion shown in Figure
in the field of bioprinting. 29,30 5F. In general, the method allows for the effortless tracing and
printing of even complex shapes. With full control over the
3.4.1. 2D bioprinting shapes printing paths, tissue alignment in the direction of printing
In the field of biofabrication using biomaterial inks or can be optimized, such as by incorporating fibers as guiding
bioinks, different aqueous-based scaffolds are produced structures for cells. 33,34 as demonstratively shown with fibers
with the aim of inhabiting them with cells. 31,32 These aligned in Figure 5G.
range from simple 2.5D shapes meant to primarily assess
printability of the ink or cell survival, to more complex 3.4.2. 3D bioprinting
8,33
grids or actual organ or tissue-shaped structures intended 3D bioprinting enables the generation of several-layer
as drug testing alternatives or tissue replacements. Simple constructs, with the working principle remaining the same
structures consisting of one layer or only a few layers can as previously described. An increase in the Z direction is
be drawn in Adobe Illustrator and assembled as shown in added between each layer. The advantage over conventional
the previous sections. Some desired printing patterns can slicers in these applications lies in the full control over

Volume 11 Issue 4 (2024) 218 doi: 10.36922/ijb.6239