Biomedical Engineering Reference
In-Depth Information
gene expression, and the tailorable degradation rate make bioactive glasses promising scaffold
materials over others, and so they could be the material of choice as the inorganic component of
composite scaffolds. Although bioactive glasses are brittle with low fracture toughness (Table 1.4),
they can be used in combination with polymers to form composite materials. The ability to couple
mechanical strength with tailorable biodegradability makes 45S5 Bioglass-derived glass-ceramics
advantageous over calcium phosphates (including hydroxyapatite), as well as other bioactive glasses
and related glass-ceramics.
Between the two types of polymers, the bulk degradable type is more promising than the
surface-erosive group, considering that being replaced by new bone tissue is one of the important
criteria of an ideal scaffold material (Table 1.1). Finally, it is obvious that composites can be consid-
ered ideal scaffolding materials for bone tissue engineering if fabrication processes suitable for the
production of 3-D structures of the required size and shape and amenable to commercialization are
further developed and optimised.
1.4
FABRICATION OF TISSUE-ENGINEERING SCAFFOLDS
1.4.1 F
ABRICATION
OF
I
NORGANIC
S
CAFFOLDS
Porous ceramics can be produced by a variety of different processes [2,159], which may be classi-
fi ed into two main categories: (1) manual-based processing techniques and (2) computer-controlled
fabrication processes, such as solid free-form (SFF) technology, which is also commonly known as
rapid prototyping (RP) [160]. Most manual-based processing techniques can further be divided into
two groups: conventional powder-forming processes and sol-gel techniques [161].
1.4.1.1 Powder-Forming Processes
A fl owchart that is common to all powder-forming processes is shown in Figure 1.2, and the differ-
ent steps involved in these processes are discussed in this section.
1.4.1.1.1
Preparation of Slurries
Slurry is a suspension of ceramic particles in a suitable liquid (e.g., water or ethanol) used to prepare
green bodies. The inherent mechanism of pore formation in a powder compact is illustrated in
Figure 1.3. Attractive forces that consist of hydrogen bonds, van der Waals forces, Coulomb's forces,
and physical friction between particles cause agglomeration of particles. Addition of fi llers to the
Start with a ceramic powder
Additives
(e.g., porogen, binder)
Add
Prepare slurry from the powder
Form a green body from the slurry
Heat treatment of the green body
to sinter the ceramic structure
Porous ceramic
FIGURE 1.2
Flowchart of the powder-sintering method to produce porous ceramic scaffolds.
