Photocrosslinkable Materials for the Fabrication of Tissue-Engineered Constructs by Stereolithography - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 166

Fig. 19 ( a ) Poly(HEMA) scaffolds containing 2 wt % initiator. ( b ) Poly(HEMA) scaffolds con-
taining 1 wt % initiator

fibres, projection and focal lenses irradiate a UV-DMD and a IR-DMD. A dichroic
mirror captures the images projected on both DMDs (1024

768 pixels, 14 mm
in size), combining them into a single image that is transferred to the liquid poly-
mer. The equipment also includes a multi-vat system enabling the fabrication of
multi-material constructs. The vertical displacement of the platform is secured by
a positioner uniaxial MYCOSIS ® Translation Stage VT-80. This positioner allows
vertical increments of 1 µm, at a speed ranging between 0.001 and 20 mm / s.
STLG intends to solve some of the major limitations of conventional stere-
olithography, such as efficiency, speed and accuracy. Its main advantages over other
stereolithographic processes are [ 10 ] as follows:
•

×

a more efficient generation of radicals due to the combination of multiple light
effects;

• use of small concentrations of the two types of initiator (UV and near-IR initia-

tors), enabling the radiation to penetrate deeper into the polymer;

• a more localized curing reaction, improving the accuracy of the produced models;

• the system has more tunability. Three subsystems can be considered. Subsys-

tem A : uses UV radiation to solidify a photopolymer containing a certain amount
of UV initiator. Subsystem B : uses IR radiation to solidify a photopolymer con-
taining a certain amount of IR initiator. Subsystem C : uses both UV and IR ra-
diation to solidify a photopolymer incorporating a certain amount of UV and IR
initiators.
The STLG process has been used to produce highly reinforced polymeric systems
with metallic and ceramic constructs, PVA and polyHEMA scaffolds (Fig. 19 )[ 33 ].
The effect of light intensity, photo-initiator concentration, metallic/ceramic powder
concentration and powder particle size has been investigated.
Stereolithography has also been used for the direct fabrication of ceramic scaf-
folds, where the ceramic particles are dispersed on the photocurable polymer and
subsequently polymerized. Upon polymerization, the polymer (binder material) is
removed using an appropriated thermal or dissolution treatment, and the ceramic
particles sintered in order to confer the final properties to the construct [ 20 , 82 ].