BIOMATERIALS AND MANUFACTURING METHODS FOR SCAFFOLD IN REGENERATIVE MEDICINE - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 35

polymer solution with appropriate concentration by rapid freezing.
Then the used solvent is removed by freeze-drying, resulting in a
porousstructureasaportionofthesolvent.Therearecollagenscaf-
folds with pores between 50 ∼ 150 μ m, collagen-glycosaminoglycan
blendscaffoldswithanaverageporesizebetween90 ∼ 120 μ m,and
chitosan scaffolds with a pore size from 1 m varied with

freezingconditions. 41 Also,scaffoldstructuresofsyntheticpolymers
suchasPLAorPLGAweresuccessfullymadewithover90%porosity
and 15

∼

250

μ

∼ μ

m size by this phase separation method. The freeze-
thaw technique induces phase separation between a solvent and a
hydrophilic monomer upon freezing, followed by the polymeriza-
tion of the hydrophilic monomer by means of ultraviolet irradiation
and removal of the solvent by thawing. This leads to the formation
of a macroporous hydrogel. A similar method is freeze-immersion
precipitation. A polymer solution is cooled, immersed in a nonsol-
vent,andthenvaporized,leadingtoaporousscaffoldstructure.Also,
the emulsion freeze-drying method is useful for the fabrication of
a porous structure, as shown in chapter 33. Mixtures of a polymer
solutionandanonsolventwerethoroughlysonicated,frozenquickly
in liquid nitrogen at -198 ◦ C, and then freeze-dried, resulting in a
spongestructure.Theadvantageofthesetechniquesistheloadingof
hydrophilic or hydrophobic bioactive molecules, whereas the disad-
vantages are a relatively small pore size and di culty in controlling
the precise pore structure. 1 , 5 , 14

250

1.3.1.6 Rapid prototyping

There are several rapid prototype methods for the scaffold appli-
cation, such as solid free form (SFF, chapters 25 and 31),
3D printing TM (3DP, chapter 29), selective laser printing (SLS,
chapter 45), selective laser ablation (SLA) and stereolithography
(STL), and 3D fiber deposition (3DF) such as fused deposition
modeling (FDM). These methods reveal to be the most promising
to satisfy many of the general requirements for scaffold biomate-
rials. Rapid prototype skills with highly sophisticated computer-
aided design (CAD)/computer-aided manufacturing (CAM) robotic
units can fabricate a fine-tunable porosity, pore size and shape,
and a completely interconnected pore network that might facilitate