Biomedical Engineering Reference
In-Depth Information
Medical imaging
CT, MRI, etc.
3-D solid model creation in CAD
Pro / engineer (PTC)
SFF system computer
Generation of slice data, etc.
SFF fabrication
SLS, FDM, etc.
Post-processing
Finishing and cleaning
FIGURE 1.7
Flowchart of the typical rapid prototyping (RP) process [160].
1.4.1.3.2 Fused Deposition Modeling
FDM employs the concept of melt extrusion to deposit a parallel series of material rods that forms a
material layer. In FDM, fi lament material stock (generally thermoplastic) is fed and melted inside a
heated liquefi er head before being extruded through a nozzle with a small orifi ce.
Indirect fabrication methods involving FDM have been applied for producing porous bioc-
eramic implants. In this method, FDM was employed to fabricate wax molds containing the nega-
tive profi les of the desired scaffold microstructure. Ceramic scaffolds were then cast from the mold
through a lost mold technique [193,194].
1.4.1.3.3 Selective Laser Sintering
SLS employs a CO 2 laser beam to selectively sinter polymer, ceramic, or polymer-ceramic com-
posite powders to form material layers. The laser beam is directed onto the powder bed by a high
precision laser scanning system. The fusion of material layers that are stacked on top of one another
replicates the object's height [202,203].
1.4.1.4
Comparison of Fabrication Techniques for Ceramic or Glass Scaffolds
Table 1.11 lists the porosity, pore size, and mechanical properties of several porous ceramics pro-
duced by different techniques. Figure 1.8 shows typical pore structures produced by different tech-
niques. Comparing the pore structures of ceramic scaffolds shown in Figure 1.8 with the structure
of cancellous bone, it is evident that the pore morphology produced by the replication technique is
the most similar one, containing completely interconnecting pores and solid material forming only
the struts. The ceramic foams synthesized by gelcasting and sol-gel techniques come next in terms
of structural similarity to cancellous bone, however, it is expected that these foams exhibit lower
pore interconnectivity than foams made by the replication method.
The advantages of replication method over other ceramic foaming techniques are summarized
in Table 1.12. In brief, the replication technique meets all criteria posed on the fabrication process of
tissue-engineering scaffolds: suitable for commercialization, reproducible, cost-effective, safe, and
capable of producing irregular or complex shapes. Contemporary authors consider the replication
technique as the optimal technique for production of novel bioactive glass-ceramic scaffolds for
bone tissue engineering [204].
 
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