Biomedical Engineering Reference
In-Depth Information
then heated to just below the glass transition temperature. A pow-
erful infrared laser is then directed at the powder material, and it
heats the powder to just above the glass transition temperature,
sintering the particles together. The laser fuses the particles in a
pattern dictated by an inputted computer drawing. Once a layer is
completed, the powder bed is lowered one-layer thickness and the
laser begins to fuse a new layer. The fusing of a new layer results
in the bonding of the particles of the new layer to the previously
completed layer. The powder that remains provides structural sup-
port and is removed after the scaffold is complete. Like 3DP, prob-
lems are encountered with removing unused powder from highly
porous scaffolds. Techniques such as air pressure, solvents, and
vibration are utilized in addition to traditional brushing to aid in
removing the powder.
15
,
20
,
21
,
60
SLS can be used with a fairly large
range of materials, and many common polymers and ceramics used
for bone tissue engineering applications have been successfully uti-
lized in scaffolds produced by SLS, including PCL, polyetherether-
ketone, HA, poly(vinyl alcohol) (PVA) , PLA, Nylon-6, and PLGA
(Table 25.3).
6
,
18
,
61
-
70
Scaffolds made from PCL, a readily available,
bioresorbable polymer used in bone tissue engineering, were suc-
cessfully fabricated into 3D scaffolds and shown to have mechanical
propertiessimilartotrabecularbone.Despitethestrongmechanical
properties of this scaffold its minimum feature size was 1.75 mm, a
lower resolution than what is optimal for bone tissue engineering
scaffolds. The SLS-fabricated scaffold feature size is dictated by the
particle size as it is in 3DP. Also like 3DP, overall porosity of the fab-
ricated scaffolds is reduced by unremoved polymer particles from
the pores.
6
Though improved techniques may lead to a smaller pore
size and increased removal of loose powder, the pore size is limited
Table25.3. ScaffoldsmanufacturedusingSLSandusedforbone
tissue engineering purposes.
Scaffold material
Properties
References
PCL
Bioresorbable, maintain mechanical strength
6, 63, 66
Nylon
Does not biodegrade, biocompatible
68
PLGA and HA
Osteoconductive, biodegradable
61, 66
PVA and HA
Biodegradable
64, 66, 72
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