Photocrosslinkable Materials for the Fabrication of Tissue-Engineered Constructs by Stereolithography - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 155

Stereolithography has also been used to produce scaffolds for the delivery of
growth factors. Lee et al. [ 56 ] produced 3D scaffolds containing bone morpho-
genetic protein-2 (BMP-2)-loaded poly(DL-lactic-coglycolic acid) (PLGA) micro-
spheres (Fig. 7 ), by the polymerization of a suspension consisting of a PPF/DEF
photopolymer and microspheres. In this work, scaffolds were also produced through
a conventional process (particulate leaching/gas foaming) to evaluate the influence
of the fabrication process on the scaffold performance. Results showed that scaf-
folds, produced by microstereolithography, provide a better environment for cell
proliferation and differentiation. To evaluate the in vivo bone formation, scaffolds
were implanted into a rat cranial defect. After 11 weeks of implantation, it was pos-
sible to observe a significant bone formation on the defect treated using the BMP-
2-loaded scaffold, produced by microstereolithography (Fig. 7 ).
Thermoplastic aliphatic polyesters, such as PCL, poly(lactic acid) (PLA) and
poly(glycolic acid) (PGA), represent another class of synthetic polymers extensively
applied for the fabrication of tissue engineering scaffolds through stereolithography.
The large number of existing aliphatic polyesters offers the possibility to prepare
structures with distinct properties. For example, lactide-based precursors have been
used to fabricate hard and rigid structures for both orthopedic and bone tissue appli-
cations, while the copolyester precursors are employed for the fabrication of flexible
and elastomeric structures suitable for soft-tissue applications [ 92 ].
PCL is a biodegradable, biocompatible and semi-crystalline polymer FDA ap-
proved for various applications, such as sutures, wound dressings and stents
[ 28 , 83 , 99 ]. This material presents a low melting point and its degradation kinetics,
physical and mechanical properties can be easily adjusted by different approaches,
including the (i) manipulation of the polymer molecular weight, (ii) the copolymer
ratio, (iii) the blending with other polymers, and (iv) the incorporation of labile
bonds into the backbone [ 35 , 87 ].
Elomaa et al. [ 35 ] synthesized three-armed PCL oligomers by ring-opening poly-
merization of ε -caprolactone monomers. The photocrosslinkable PCL-based resin
was end-functionalized with methacrylic anhydride, and subsequently employed to
produce 3D porous scaffolds trough a mask stereolithographic system. The pro-
duced scaffolds exhibited porosity of 70.5 %, pore size in the range of 400-500 µm,
and a high interconnectivity between pores without material shrinkage. NIH3T3
fibroblasts, cultured on photocrosslinked PCL networks, can be easily attached pre-
senting uniform spreading.
Two-photon polymerization has been explored to produce scaffolds using PCL-
based polymers. Claeyssens et al. [ 31 ] fabricated 3D structures composed of the
biodegradable triblock copolymer poly( ε -caprolactone-co-trimethylenecarbonate)-
b-poly(ethylene glycol)-b-poly( ε -caprolactoneco-trimethylenecarbonate), using
4 , 4 -bis(diethylamino) benzophenone as the photoinitiator. Constructs with differ-
ent geometries were prepared with a resolution of 4 µm (Fig. 8 ). Fibroblasts, cul-
tured onto spin-coated thin films after photopolymerization, remained viable and
showed comparable cell attachment and division regarding cells cultured on glass
surfaces (control), which indicates that the developed material do not affect cell pro-
liferation. In a similar work, Koskela et al. [ 53 ] used the 2PP technique to produce