Biomedical Engineering Reference
In-Depth Information
Alkoxides: TEOS and TEP
Prepare a sol from the alkoxides and
Ca(NO
3
)
2
in deionized water solvent
Add
Catalysis (HNO
3
) to
speed up hydrolysis
Add
Surfactant for foaming,
catalyst (HF) for gelation
Foam the sol by vigorous agitation
When the gelation of the foamed sol is
nearly completed, cast the gel in molds
Age, dry, and sinter the gel
Glass foam
FIGURE 1.6
Flowchart of the production of bioactive glass foams using sol-gel technology.
of a surfactant and catalysts [188-190]. Therefore, after sol hydrolysis, the surfactant (e.g., Teepol,
a detergent containing a low-concentration mixture of anionic and nonionic surfactants), water
(improves foamability of surfactant), and the catalyst for polycondensation (e.g., HF) are added by
vigorous agitation. A fl owchart of the process is given in Figure 1.6. Porosity of the foam scaffolds
is infl uenced by the foaming temperature, water content, and catalyst content. Sol-gel derived bio-
active glass foams [191,192] and gelcast hydroxyapatite scaffolds [181,183] have shown favorable
results in both
in vitro
and
in vivo
tests for bone regeneration.
1.4.1.3
Solid Free-Form Techniques
SFF techniques, also known as RP, are computer-controlled fabrication processes. They can rapidly
produce highly complex 3-D objects using data generated by computer-aided design (CAD) systems.
In a typical case, an image of a bone defect in a patient can be taken, which is used to develop a
3-D CAD model. The computer can then reduce the model to slices or layers. The 3-D objects are
constructed layer-by-layer using RP techniques such as fused deposition modeling (FDM), selective
laser sintering (SLS), 3-D printing (3-DP), or stereolithography [160]. Calcium phosphate scaffolds
have been produced using the FDM process [193,194], SLS, 3-DP processes [160], stereolithogra-
phy [195,196], and RP combined with replication technique [197]. The typical process chain for all
SFF techniques is presented in Figure 1.7.
To date, only a small number of SFF techniques, such as 3-DP, FDM, and SLS, have been
adopted for tissue-engineering scaffolds. The following paragraphs give brief descriptions of the
principles on which these three techniques are based. Comprehensive technical details can be found
in previous detailed reviews [160,198-201].
1.4.1.3.1
Three-Dimensional Printing
Three-dimensional printing employs ink-jet printing technology for processing materials from pow-
ders. Therefore, this technique is a combination of SFF and powder sintering. During fabrication, a
printer head is used to print a liquid binder onto thin layers of powder following the object's profi le
being generated by the system computer. The subsequent stacking and printing layer recreates the
full structure of the desired object.
