Biomedical Engineering Reference
In-Depth Information
TABLE 4.1
A Comparison of Well-Known Microfabrication Methods, Their Resolution, and Limits
(References Are Given in the Text)
RTM Ratio
(cm
2
/min)
Resolution
(
μ
m)
Technique
Materials Used
Cells Used
Limits
Low (
<
1)
Membrane
lamination
Bioerodable polymers
(PLA, PLGA, etc.),
bioceramics
1000
Osteoblasts
Structures not really
porous, low resolution
3-D printing
Bioerodable polymers
(PLA, PLGA, etc.),
hydroxyapatite
Medium
(about 1)
300
Various types
Presence of polymeric
grains and of excess
solvent
<
400
Laser sintering
Calcium phosphates,
polymers (PLA,
PLGA, etc.)
Medium to
high
Osteoblasts
Presence of polymeric
grains and of excess
solvent
Photopolymerization
Photopolymeric
resins
0.5 (medium)
250
Osteoblasts
Use of photo-sensitive
polymers and initiators,
which may be toxic
Fused deposition
modeling
Bioerodable polymers
(PLA, PLGA, etc.)
7 (very high)
200
Various types
Limited to nonthermolabile
materials. Layered
structure is very evident
Sacrifi cial molds—
multiphase ink-jet
printing
Bioerodable polymers
(PLA, PLGA, etc.),
collagen
0.1 (low)
300
Various types
Complex to realize, build
materials limited, low
fi delity
Pressure-assisted
microsyringe
Bioerodable polymers
(PLA, PLGA, etc.),
gels (alginate)
1 (medium)
5-10
Neurons,
endothelial
cells,
fi broblasts,
hepatocytes,
muscle
Highly water soluble
materials cannot be used.
Extrusion head is very
small
Organ printing
Cells and
thermoreversible
gels
Medium
(about 1)
100
Hepatocytes
Limited range of gels
available
Bioplotter
Gels and polymers
Medium
50
Various types
Gels have low fi delity
hybrid materials with different chemical and mechanical properties should result in major improve-
ments in this fi eld.
These materials are either used in powder or solid form, as in the case of laser sintering, 3-DP,
or FDM or as solutions as with the PAM or photopolymerization. Obviously different materials
are suited to different methods, and some methods are limited to a very narrow range of polymers,
particularly in the case of photopolymerization and ink-jet organ printing. Table 4.1 lists some of
the different materials employed in RP for tissue engineering.
4.4 RESOLUTION AND RESOLUTION/TIME
OF MANUFACTURE RATIO AND GEOMETRY
Table 4.1 clearly shows that RP methods have a wide range of resolutions ranging from 5 to 1000 µm.
Prior to discussing the issue of cell response to spatial patterns or geometry and topography, it is neces-
sary to defi ne these terms in the context of this chapter. We defi ne geometry as the 2-D or 3-D spatial
organization of cells, referring to spatial dimensions over fi ve times greater than that of the cell. Topog-
raphy, on the other hand, can be defi ned as surface features and relief with dimensions of the order
