Introduction - Microsurgery: Advances, Simulations, and Applications - page 34

removed wax by heat. They also reported improvement of fabrication
materials [92]. Vozzi et al. reported a microsyringe deposition
method controlled by a computer, a stepping motor and a pressure
regulator [93]. They printed a PLGA mesh-like ordered structure by
controlled positioning of a syringe needle. Sakai et al. developed a
biodegradable scaffold with ordered and 3D microchannels [94].
They have been developing scaffolds with microvascular networks
as a liver substitute
Additionally, some groups are printing cells with scaffold
materials. This method is called “bioprinting” or “organ printing.” Tan
et al. developed a strategy for layer-by-layer microluidic patterning
of living cells and biopolymer matrix [95]. Mironov et al. proposed
organ printing method [96]. Similarly to Tan's group, they developed
a cell printer that can print gels, single cells, and cell aggregates. The
combination of an engineering approach with the developmental
biology concept of embryonic tissue luidity enables the creation of
a new rapid prototyping 3D organ printing technology, which will
dramatically accelerate and optimize tissue and organ assembly.
1.3.4.4 So lithography
Soft lithography, a set of techniques for microfabrication, is
based on printing and molding using elastomeric stamps with
the patterns of interest in bas-relief [97]. The technology was
established by Whitesides' group in the 1990s. As a technique
for fabricating microstructures for biological applications, soft
lithography overcomes many of shortcomings of photolithography.
In the ield of tissue engineering, soft lithography has been used
mostly for vascular channel inside scaffolds. Originally PDMS has
been used as a soft material for 3D microvascular structure [98].
Biodegradable polymers have been also applied in soft-lithography-
based tissue engineering. Borenstein et al. and King et al. developed
biodegradable microchannel by casting PLGA thermoplastic on a
PDMS mold with vascular coniguration [99-100]. To overcome the
brittleness of previous biodegradable polymers, Wang et al. reported
PGS, as tough and elastic biodegradable polymer [101]. By using PGS
in soft lithography, Fidkowski et al. developed an endothelialized
microvasculature inside PGS [102]. Bettinger et al. extended this
PGS microvasculature sheet to 3D microluidic scaffold by piling it
up [103]. They cultured hepatocytes in the microchannel to mimic
liver structure.