Biomedical Engineering Reference
In-Depth Information
by means of classical approaches. A more design-dependent method would be
attractive, and this can be attained by RP techniques.
9.2.3
Controlling the External and Internal Geometry
Solid freeform fabrication (SFF) is the general term covering all techniques that
produce objects through sequential delivery of energy and/or material. When rapid
fabrication of a prototype, a finished object or a tool is pursued, they are, respec-
tively, called rapid prototyping, rapid manufacturing (RM) and rapid tooling (RT)
[
129
]. By means of RP, an additive computer-controlled layer-by-layer process
generates a scaffold. 3D computer models shape the external design, and such
models can be designed either by CAD software or by modelling imaging data
(CT, MRI). On the other hand, the internal architecture is determined by the pro-
cessing of the CAD data into an STT file and subsequent slicing of the STT data
(generation of the machine parameters). This directly indicates one of the greatest
assets of RP: direct fabrication of scaffolds with a complex, patient-specific exter-
nal geometry [
16,
18,
64
] in combination with a precise control over the internal
architecture (limited by the resolution of the system). Other advantages comprise
high degree of interconnectivity, possibility to use heterogeneous materials, high
speed due to a high degree of automization and the limited number of process
steps, and a superior cost-efficiency [
2,
64
]. Both direct and indirect RP methods
exist. In the former case, the scaffold is directly processed from a biomaterial, and
in the latter case the scaffold is processed out of an RP mould. Worldwide more
than 30 different RP techniques are being applied in the most diverse industries
[
129
], and around 20 of them found applications in the biomedical field. This par-
ticular subject has been reviewed by several authors [
2,
129,
130
] . Despite the wide
diversity of RP technologies, only some of them seem to be compatible for the
processing of hydrogels. The next chapter describes the different RP scaffolding
techniques compatible with hydrogels.
9.3
Rapid Prototyping Hydrogels: Powerful Aid in Making
Scaffold-Based Tissue Engineering Work
A primary classification of the SFF techniques supporting biomedical applications
can be made hinged on the working principle: (1) laser-based, (2) nozzle-based and
(3) printer-based systems. Laser-based systems benefit from the photopolymeriza-
tion pathway as a basis to fabricate cross-linked polymeric TE scaffolds. The well-
known processing of (pre)polymers by dint of extrusion/dispension supports the
second category of RP systems. The last subclass works with powder beds and
deposition of a binder that fuses the particles, or direct deposition of material using
inkjet technology. An important characteristic feature of every technique will be its
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