Introduction - Microsurgery: Advances, Simulations, and Applications - page 33

inside a scaffold by using hydrosoluble particles. In previous studies,
salt or sugar particles have been commonly used as porogens. This
method has following absolute advantages compared with other
techniques:
i. The size of porogens can be controlled easily by using sieves.
ii. Porogens can be packed in complex 3D structure, thereby
ensuring 3D porous scaffolds with arbitrary shape.
iii. Porogens such as salt and sugar do not dissolve in general
organic solvents and can be removed by water easily.
Salt particles are most commonly used in the fabrication of
porous scaffold. Lee et al. reported an artiicial skin by using salt
leaching method in gelatin scaffolds [82]. Murphy et al. reported a
salt fusion method to enhance the pore connectivity inside a scaffold
[83]. They used heat and humidity of CO 2 incubator to fuse adjacent
salt particles. Subsequently, Gao et al. applied this salt fusion
method to tubular scaffolds [84]. Elastic biodegradable polymer of
PGS was cast on a fused salt template by using a cylindrical mold.
Heijkants et al. combined salt leaching and freeze drying methods
to achieve hybrid structure of macropores and micropores [85]. Wu
et al. developed an ear-shaped scaffold by packing salt particles and
polymer in an ear-shaped mold [86].
Similarly, sugar particles have been used as porogens. Lee et al.
packed sucrose particles to a complex mold designed by CAD [87].
After the molding of PLGA and the removal of sucrose particles,
patterned indented surface was generated. Wei et al. proposed a
unique method to enhance pore connectivity by using -fructose
spheres as porogens and achieved ordered and well-connected
pores inside PLLA scaffolds [88]. Ice microparticles [89] or parafin
spheres [90] have been used as porogens too. In the case of porogen
leaching method, the average diameter of pores and porosity can
be truly controlled by the size of porogens and the weight ratio of
polymer/porogens, respectively. Therefore, this method has been
widely used in scaffold fabrication
1.3.4.3 Three-dimensional printing
Three-dimensional (3D) printing is a mass production method of
scaffold fabrication. Therrihault et al. developed 3D microvascular
networks by direct-write assembly of fugitive inks [91]. After printing
wax in the shape of jungle gym, they cast epoxy resin on the wax and