Explanation of the function of a PLA-based 3D printer (also consider the coordinate system (
CS) in images
a and
b). Flexible PLA filament of an even diameter (
F), typically sold on a roll and mounted on a spool (
S), is routed to the extruder (
E) of the 3D printer via a sheath (
Fs). The extruder typically contains a cold end (
cE) and a hot end (
hE). In the cold end, there is a motor (
M) to pull the unheated and thus still solid filament to feed it into the hot end. The filament will lose its stiffness when melted so it can only be successfully transported by the motor as long as it is still solid. The hot end contains parts to generate, control and transmit heat (
H) that and only there, aims to melt the PLA, which then is extruded through a nozzle (
N). At this exact location (
L), the liquid PLA is added to what is under the nozzle which is located immediately above L in any well calibrated 3D-printer. When the print process is started, the first layers of PLA will be placed directly onto the build plate (
P), which is later lowered (and thus moved in the direction of −
Z), so the model (
T) is built incrementally. Subsequently, more PLA layers will be added onto the top surface of the model as it is being built (see also Fig.
3, images
a–
c). A new layer can only be added once the previously deposited PLA has sufficiently cooled and hardened. Therefore, if one prints too fast, warping may occur. To reach across the area of the build plate, the extruder is moved along rails (
R) in the directions of
X and
Y. Images
a and
b are symbolic images to illustrate the technical function of our PLA-based 3D printer. Images
c and
d show our 3D printer that was also used to print the model shown in Fig.
3. That device had been initially set up with dual ABS extruders, but then was modified with an experimental PLA extruder (
E). Images
e and
f expose the inner details of our experimental extruder (
E) after we had removed the fan used for temperature control to take these photographs