3D PRINTING AND NANOMANUFACTURING - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 39

FIGURE 2.11
SEM images of the dipentaerythritol pentaacrylate (DPPA) mold after imprinting (a and b) and the imprinted
PEGDA structures (c and d) ( Zhang and Chen, 2011 ).
complex 3D structures encapsulated with cells ( Soman et al. , 2013 ) ( Figure 2.8 ). Live cell-captured
scaffold was fabricated with PEGDA using commercialized apparatus ( Lin et al. , 2012 ).
Femtosecond lasers are usually utilized to achieve 2PP for the fabrication of complex 3D struc-
tures with very high resolution ( < 100 nm) and fidelity. Various types of hydrogels are employed in
the 2PP lithography. In the work of Zhang and his colleagues, PEGDA was patterned by a Ti:sapphire
femtosecond laser into multiple forms of 3D structures, such as woodpile ( Figure 2.9 ) and microdot
array with various feature sizes ( Figure 2.10 ) ( Zhang and Chen, 2011 ). These structures can further
be used as a mold for the nano-imprinting of other hydrogels ( Figure 2.11 ) ( Zhang and Chen, 2011 ).
Methacrylamide-modified gelatin was utilized to create 3D scaffold ( Ovsianikov et al. , 2011a, 2011b ).
A kind of natural hydrogel, collagen, and fibrinogen was dissolved in distilled water and printed layer
by layer to construct 3D scaffolds ( Gebinoga et al. , 2013 ).
2.3.3 PHOTOCURABLE POLYESTERS
Photocurable resin (PPF/DEF) was polymerized using a stereolithography system ( Lee et al. , 2007 ). PPF
is an unsaturated linear polyester that has carbon-carbon double bond cross-linking ( Peter et al. , 1998 ).
It is degradable by simple hydrolysis of the ester bonds and its product is nontoxic ( He et al. , 2001 ).
Poly (propylene fumarate) is mixed with diethyl fumarate (DEF) and bisacrylphosphrine oxide (BAPO)
as solvent and photoinitiator, respectively. The glass transition temperature and viscosity of PPF and