Biomedical Engineering Reference
In-Depth Information
3Dprintingfabrication,athinlayerofpowderisfirstspreadoverthe
buildingplatformandthentheinkjetprintheadprintsordepositsa
bindersolutionontothepowderbed.Manybiodegradablepolymers
inthefinepowderformcanbeprocessedinto3Dscaffoldsusingthe
3D printing technique. For synthetic poly(
α
-hydroxy esters) such as
poly(
L
-lactic acid) (PLLA), poly(lactic-
co
-glycolic acid) (PLGA), and
PCL,anorganicsolventsuchaschloroformisusedasthebinder.
36
,
37
Theparticulate-leachingtechniquehasalsobeencombinedwiththe
3D printing technique to create porous scaffolds using a PLGA mix-
ture with NaCl particles.
38
Using an organic solvent as the binder
could cause problems for cell incorporation in the 3D printing
process. Therefore, a starch-based biomaterial composed of corn-
starch, dextran, and gelatin was used for scaffold construction via
3D printing withwater being the binder.
39
LDM uses a computer-controlled nozzle to extrude a polymer
solution in a layer-by-layer manner, and each layer of the deposited
material is frozen on the platform. After the frozen objects are
formed by the LDM system, they are freeze-dried in a freeze dryer
to remove the solvent.
40
The scaffolds thus formed have both con-
trolled micro- and macrostructures. Xu
et al.
used polyurethane
(PU),anelastomer,tofabricatecomplexvascularsystemsviaLDM.
41
An LDM system with two nozzles was later designed in order to
extrude two types of biomaterials with different properties.
42
With
this improved LDM system, a double-layer PU-collagen nerve con-
duit was produced for peripheral nerve regeneration. The hollow
tubesachievedtheoptimalporosityof75%andporesizesof15-25
μ
mfortheexternalPUlayerthroughtheadjustmentofpolymercon-
centrations and orientation offilaments in the innercollagen layer.
TPP is based on the simultaneous absorption of two photons
which induce chemical reactions between starter molecules and
monomers within a transparent matrix.
26
An ultrashort pulse laser
is needed to provide the high intensity, and the current capability of
the TPP technique allows the generation of 3D porous structures at
a resolution down to 100 nm.
43
As an established member of the RP family, SLS employs a CO
2
laser to selectively sinter thin layers of powdered polymers or their
composites,formingsolid3Dobjects.Theschematicdiagramforthe
operation of a commercial SLS machine isshown in Fig. 45.2.
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