Photocrosslinkable Materials for the Fabrication of Tissue-Engineered Constructs by Stereolithography - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 151

Fig. 4 Irradiation
phenomena
Conventional stereolithography has been successfully applied for the fabrica-
tion of tissue-engineered constructs using several natural and synthetic materials
[ 58 , 68 , 115 ]. However, the fabrication of porous 3D constructs with an intercon-
nected micro-architecture is limited by the resolution of the system [ 27 ]. Microstere-
olithography is a process that evolved from conventional stereolithography, allow-
ing the fabrication of complex 3D constructs with a micro-scale resolution of about
200 nm [ 27 , 55 , 71 ]. In this process, the laser beam is more precisely focused, reduc-
ing the spot size to a few micrometers in diameter, this way enhancing the resolution
of the system [ 13 , 56 ]. Today, there is a great interest in the use of 2PP processes
for the fabrication of various devices, such as microneedles, sensors and scaffolds
for different biological and biomedical applications [ 39 , 48 , 53 ]. These processes
are able to produce 3D structures with submicron resolution, enabling an ultra-fast
fabrication process at greater depth [ 8 ]. However, 2PP systems are very expensive,
operating with a single material type that prevents the fabrication of multimaterial
constructs [ 85 ]. These equipments usually employ a femtosecond titanium:sapphire
laser (short pulse width and high peak power) without photo-masks, operating at ap-
proximately 800 nm wavelength to induce the polymerization [ 53 , 74 , 82 ]. A great
variety of natural and synthetic photosensitive materials can be used for the 2PP
technique, like acrylate-based polymer, zirconium sol-gels, organically modified ce-
ramic materials, aliphatic polyesters and gelatin [ 52 , 74 , 79 , 105 ].
Despite these processes enable to produce complex 3D scaffolds with pre-defined
micro/nanoscale architectures, the major limitation of stereolithographic processes
for tissue engineering applications consists on the lack of available photocurable,
biocompatible and biodegradable materials.
3 Materials for Stereolithography
The first polymeric systems developed for stereolithography were based on low-
molecular weight polyacrylate or epoxy macromers, which present a rapid cure and