Biomedical Engineering Reference
In-Depth Information
Thread
Rollers
Heater
FDM
head
x
y -axis
Noozle
z- axis
Platform
FIGURE 4.5
Schematic representation of fused deposition modeling.
it is heated to near fusion. The semimolten extrudate is driven through a needle having a diameter
of 1.27 mm onto a substrate mounted on a platform, and solid objects are built string-by-string as
the platform moves down (Figure 4.5). The FDM-fabricated structures have a lateral resolution of
a few hundred microns [13]. Several improvements to the FDM system have been reported by the
NUS group, in particular, the extrusion head has been modifi ed to enable incorporation of particles
or granules rather than fi laments and hence renamed as precision extrusion deposition and precision
extrusion manufacturing (PED and PEM) [2].
The main limitation of this technique is its resolution since many cell types are smaller than
50 µm. Small scaffolds are diffi cult to produce because previous layers may melt during heating,
whereas larger structures tend to split or peel along layers due to insuffi cient bonding. Furthermore,
because the extrusion is forced by a heating system, this method cannot be used with thermolabile
materials. On the other hand, it has the highest RTM ratio of all RP methods because the postpro-
cessing phase is practically nonexistent as there are no intervening layers or binders and solvents to
remove as with most other techniques.
4.5.3 O RGAN P RINTING
Mironov et al. [14] developed an ink-jet printer that can print gels, single cells, and cell aggregates.
This method, which is known as organ printing, relies on the use of a thermosensitive gel to gener-
ate sequential layers for cell printing. This nontoxic biodegradable gel is a liquid below 20°C and
solidifi es above 32°C. Living cells are sprayed onto the solidifi ed thin layers of the thermoreversible
gel, which also serves as printing paper. The printers used are old commercial printers adapted by
washing out the ink cartridges and refi lling them with cell suspensions. The software that controls
 
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