organs, the combination of automation and flexibility in design
makes RP very suitable for the generation of personalized implants
[6–8]. Different processing techniques and methodologies have
been proposed to optimize final scaffold performances, but in the
last years, RP technologies have reached the best results in terms of
external shape and size, surface morphology, and internal architecture [9, 10]. Among all the RP techniques, stereolithography
(SLA) has become a valuable tool for the fabrication of biocompatible tissue engineering scaffolds, due to its ability to fabricate
precise internal architectures and external geometries, which
match those of human tissues [11, 12]. The working principle of
SLA is based on spatially controlled solidification of a liquid photopolymerizable resin through a computer-controlled laser beam or a
digital light projection [13]. While in most fabrication techniques
the smallest details are 50–200 μm in size, many commercially
available SLA setups can build objects that measure several cubic
centimeters at an accuracy of 20 μm [12, 14, 15]. Most of the
commercially available resins for SLA are based on low-molecularweight acrylate polymers that are generally glassy, rigid, and brittle
materials [16, 17]. The functionalization of resorbable polyesters,
such as poly(ethylene glycol) (PEG), polylactide (PLA), and poly
(ε-caprolactone) (PCL), with unsaturated groups and subsequent
ultraviolet (UV) crosslinking has been extensively studied to overcome this limitation [16–18]. However, the diffusion of unpolymerized methacrylates is one of the most important factors causing
irritation in tissues [19, 20]. To overcome these problems, here we
report the synthesis of a trifunctional photocrosslinkable vinylfumarate PCL for tissue engineering applications. Vinyl-poly-ε-caprolactone has been synthesized by ring opening polymerization (ROP) using an alcohol/methylaluminum diphenolate system
(AlMe(OR) 2 ) as a catalyst and 2-hydroxyethyl vinyl ether (HEVE)
as initiator [21, 22]. Subsequently the vinyl-terminated PCL was
reacted with fumaryl chloride in order to obtain a divinyl-fumarate
PCL (VPCLF). Networks were formed by UV irradiation (365 nm)
of VPCLF macromers using ethyl-2,4,6-trimethylbenzoylphenylphosphinate (Lucirin TPO-L) as a biocompatible initiator and
N-vinyl-2-pyrrolidone (NVP) as a crosslinking agent. In this way,
the VPCLF/NVP resin was used to realize porous scaffolds, based
on triply periodic minimal surface (TPMS) geometries, by SLA
technique.
2 Materials
The synthesis requires a standard glassware equipment for operation of air- and moisture-sensitive materials (Schlenk line, etc.). All
the materials involved in the synthesis of PCL and subsequent
reaction with fumaryl chloride should be anhydrous/dry and
56
Alfredo Ronca et al.
makes RP very suitable for the generation of personalized implants
[6–8]. Different processing techniques and methodologies have
been proposed to optimize final scaffold performances, but in the
last years, RP technologies have reached the best results in terms of
external shape and size, surface morphology, and internal architecture [9, 10]. Among all the RP techniques, stereolithography
(SLA) has become a valuable tool for the fabrication of biocompatible tissue engineering scaffolds, due to its ability to fabricate
precise internal architectures and external geometries, which
match those of human tissues [11, 12]. The working principle of
SLA is based on spatially controlled solidification of a liquid photopolymerizable resin through a computer-controlled laser beam or a
digital light projection [13]. While in most fabrication techniques
the smallest details are 50–200 μm in size, many commercially
available SLA setups can build objects that measure several cubic
centimeters at an accuracy of 20 μm [12, 14, 15]. Most of the
commercially available resins for SLA are based on low-molecularweight acrylate polymers that are generally glassy, rigid, and brittle
materials [16, 17]. The functionalization of resorbable polyesters,
such as poly(ethylene glycol) (PEG), polylactide (PLA), and poly
(ε-caprolactone) (PCL), with unsaturated groups and subsequent
ultraviolet (UV) crosslinking has been extensively studied to overcome this limitation [16–18]. However, the diffusion of unpolymerized methacrylates is one of the most important factors causing
irritation in tissues [19, 20]. To overcome these problems, here we
report the synthesis of a trifunctional photocrosslinkable vinylfumarate PCL for tissue engineering applications. Vinyl-poly-ε-caprolactone has been synthesized by ring opening polymerization (ROP) using an alcohol/methylaluminum diphenolate system
(AlMe(OR) 2 ) as a catalyst and 2-hydroxyethyl vinyl ether (HEVE)
as initiator [21, 22]. Subsequently the vinyl-terminated PCL was
reacted with fumaryl chloride in order to obtain a divinyl-fumarate
PCL (VPCLF). Networks were formed by UV irradiation (365 nm)
of VPCLF macromers using ethyl-2,4,6-trimethylbenzoylphenylphosphinate (Lucirin TPO-L) as a biocompatible initiator and
N-vinyl-2-pyrrolidone (NVP) as a crosslinking agent. In this way,
the VPCLF/NVP resin was used to realize porous scaffolds, based
on triply periodic minimal surface (TPMS) geometries, by SLA
technique.
2 Materials
The synthesis requires a standard glassware equipment for operation of air- and moisture-sensitive materials (Schlenk line, etc.). All
the materials involved in the synthesis of PCL and subsequent
reaction with fumaryl chloride should be anhydrous/dry and
56
Alfredo Ronca et al.