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

demarcations for collapsible code segments but is defined Information. It is helpful for each layer to start and
using ;EBSTART:extrusion factor (where the extrusion end at the same point to ensure consistent alignment.
factor, which is the amount of extrusion per mm, must Additionally, different layer structures can be intermixed
be calculated by the user as it varies between machines) to create more complex scaffold shapes. The method’s
and ends with ;EBSTOP. This means that the segment and advantages become more apparent when dealing with
amount of extrusion therein can be defined/adapted this more complex grid structures that are challenging to write
way. Similarly, when wanting to add segments where the manually, such as intersections at 45° that should meet
Z gradually increases per segment, such as for diagonally at the center of a box, as shown in Figure 2B. One key
ascending lines or spirals, the Z-increase per segment benefit is that the geometries are visible before printing,
is defined with ;ZBSTART:total height increase in mm allowing for a clearer preview of the result. The repetition
and ends with ;ZBSTOP. Both of these commands can of layers and the combination of different patterns can
alternatively be added by using the “Add extrusion block” be visualized beforehand, facilitating the generation of
or “Add height block” functions in the EDSTAG, whereby more intricate shapes, such as hexagon-like patterns with
the extrusion factor and Z height can be input directly in a single box layer crossing through them, as shown in
the designated fields in the program. In both cases, either Figure 2C. Furthermore, the shapes can be easily scaled
by importing the code with the designated Z- and E-block or transformed in the vector drawing software, making it
commands, or doing it locally in EDSTAG, the EDSTAG simple to adjust the design as needed.
can then automatically calculate the extrusion (E) and
Z height values for these blocks based on the extrusion 3.2.2. Complex melt-electrowritten shapes
factor or height of the interval, by clicking the “Calculate The major advantages of the drawing method become
extrusions” and “Calculate heights” buttons, as illustrated especially evident when working with more complex
in Figure 1F. shapes. MEW is not only capable of producing fine grids
but also larger, more intricate scaffolds using thicker
This method of generating codes is intuitive, and fibers—tasks that are otherwise difficult to program
because it is based on relative G-code blocks, it is easy manually. Combining this with a vector drawing program
to adapt the code for use on different devices, as also offers additional benefits, such as the ability to draw
demonstrated by the variety of different machines used the code over an image to scale, as demonstrated with a
herein shown in Figure S1, Supporting Information. This cornea membrane reinforcement printed, as shown in
flexibility is particularly beneficial for machines that Figure 3A. Furthermore, the software allows for easy
interpret non-G1 commands differently or cannot process adaptation and transformation of the drawn shape
anything beyond simple movement codes. The drawing and into different configurations, such as changing a round
subroutine approach significantly simplifies the horizontal structure into a square, as shown in Figure 3B.
transfer of codes between various biofabrication devices,
compared to complex programmed and parametric codes. The drawing method is particularly advantageous for
Moreover, it enhances the convergence capabilities of creating non-repetitive shapes or those with paths that are
different fabrication methods and machines. difficult to conceptualize and therefore hard to code using
conventional methods. For instance, the spiral pattern
3.2. Application and practical examples for use with loops in Figure 3C exemplifies a complex design that
in MEW would be challenging to program through other means.
Additionally, hand-drawn patterns can be seamlessly
3.2.1. Melt-electrowritten grids converted into code using this approach, as demonstrated
In biofabrication, many substrates are composed of melt- with the rose design in Figure 3D. This type of pattern
electrowritten meshes with various geometries, such as would be impossible to generate using parametric or
boxes, triangles, and other variations of these shapes. 10,27
For simpler cases, it is common to manually write the function-based programming and can only be created by
coordinates or create parametric, adaptable designs. tracing or transferring individual points.
However, the drawing approach presented in this paper Another versatile feature of the method is its ability
can also be conveniently applied to these tasks. A single to convert text into an outline and connect the paths
layer of the repetitive grid structure can be drawn, with accordingly to form a printable design, as shown in
the paths connected into a continuous pattern, defined Figure 3E. More complicated shapes, like the wolf design
as a subroutine, and repeated for each layer as needed. in Figure 3F, can be broken down into multiple paths, with
Commands such as pressure or speed changes can also be distinct pauses or varying speed settings for each path,
integrated between separate layers or within sections of a offering more control over the parameters and improving
layer, as demonstrated in Figures 2A and S2, Supporting print quality. The method also benefits from Illustrator’s

Volume 11 Issue 4 (2024) 214 doi: 10.36922/ijb.6239