Biomedical Engineering Reference
In-Depth Information
powder is removed and the remaining structure is stabilized, in most cases
by sintering, which results in a ceramic body possessing high crystallinity
and mechanical stability (Seitz et al. 2005; Khalyfa et al. 2007). Using this
technique, scaffolds with designed pore parameters have been successfully
fabricated. However, there are still some disadvantages such as difficulty
removing the unbound powder, especially from small pore structures.
As an alternative strategy, 3D extrusion approaches of CaP pastes and
slurries have been developed. Miranda and coworkers have used so-called
ceramic inks, highly concentrated, water-based suspensions of β-tricalcium
phosphate or HA powder, which are dispensed through a moving deposi-
tion nozzle in an oil bath to build a ceramic scaffold (Miranda et al. 2006,
2007, 2008; Franco et al. 2010). This process, introduced in the literature as
“robocasting” or “direct write assembly,” is very similar to the technique of
3D plotting. After building, the scaffolds are dried and sintered at high tem-
perature resulting in ceramic bodies. However, the second sintering hinders
loading of drugs, growth factors, and living cells in the CaP pastes.
4.1.4 Rapid Prototyping-Based Tissue Engineering
There are three strategies to engineer tissues, tissue substitutes, or even
organs by using RP technologies (Figure 4.1). According to the first, the scaf-
fold is fabricated by processing an adequate biomaterial into 3D porous scaf-
folds with a predesigned outer and inner structure. In principle, each RP
method described earlier can be used if it is suitable for the respective mate-
rial. After fabrication, the scaffold can be modified to improve its proper-
ties. Subsequently, living cells (e.g., stem cells) are seeded and cultured on
the sterilized scaffolds
in vitro
and the construct finally is implanted
in vivo
.
The main advantage of this strategy is the nearly unlimited feasibility to
modify the scaffolds, because living cells are added only after scaffold fab-
rication is completed. For example, biomaterials and scaffolds can be modi-
fied by introducing active groups or improving mechanical properties under
chemical reaction and heat treatment during processing and postprocessing.
However, the disadvantage of this strategy is that cell seeding is relatively
uncontrolled and often associated with a low seeding efficiency and inho-
mogeneous cell distribution. Although a number of upgraded cell seeding
Tailorable
scaffold
+ Cells
Biomaterials
3D scaffolds
Tissue
Biomaterials,
cells, biofactors
Rapid
prototyping
3D cell-matrix-
constructs
Multicell
arrangement
Functional
complex tissues
Cell mass
ECM
Organ printing
FIGURE 4.1
Strategies of rapid prototyping-based tissue engineering.
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