Biomedical Engineering Reference
In-Depth Information
construct a porous scaffold structure [90]. In this case, the fiber diameter
and the distance between the fibers are adjusted to meet the requirements of
the scaffold porosity. The structural and mechanical properties of the scaf-
folds are significantly influenced by their pore size. These parameters also
greatly influence the functionality of the engineered tissue by influencing cell
growth, differentiation, and tissue organization [18, 91]. Ma et al. have used
thermally induced phase separation followed by subsequent sublimation to
create highly porous three-dimensional scaffolds for bone tissue engineer-
ing [18]. In this approach, the morphology and size of pores can be varied
by changing the solvent, polymer concentration, and phase separation tem-
perature. This method has also been used to create macroporous scaffolds
with pore diameter which are amenable to osteoblastic cells and bone tissue
growth [18].
Another important criteria in using any biomaterials as a tissue engin-
eeringscaffoldfororganreplacementisthatthescaffoldshouldbeableto
assume the anatomical shape and structure of the targeted tissue or organ.
For example, tube-shaped scaffolds are used to engineer tubular tissues like
arteries [92]. Cao et al. have engineered a three-dimensional elastic carti-
lage graft by seeding chondrocytes onto a prefabricated (ear shape) PLGA
scaffold, where the scaffold directed the ultimate shape of the neocartilage tis-
sue [93]. Shastri et al. have used a different approach based on a hydrocarbon-
templating process to create three-dimensional PLA scaffolds with specific
shapes to regenerate tissues with pre-defined shapes [85].
Most of the solid scaffolds discussed above are hydrophobic and are pro-
cessed under severe conditions, which make further modifications such as
incorporation of biochemical and biophysical functions a serious challenge.
They also need to be prefabricated and are therefore not ideal for irregularly
shaped defects. Furthermore, these scaffolds need to be surgically implanted
through invasive surgical procedures [93]. To this end, viscoelastic hydrogels
have been employed as alternative scaffolding materials because of the many
advantages they offer over hydrophobic polymer networks as discussed in the
following sections.
4
Hydrogel Scaffolds
Hydrogels are three-dimensional networks of hydrophilic polymers which
have the ability to imbibe a large quantity of water and biological fluids. The
network is formed through either chemical crosslinking (covalent and ionic)
or physical crosslinking (entanglements, crystallites, and hydrogen bonds) as
shown in Fig. 3. The elastic network holds the solvent inside the matrix by
osmotic forces, while the liquid prevents the polymer network from collaps-
ing into a compact mass. The combination of these two parameters, namely,
