Page 179 - Biodegradable Polyesters

7.2 Preparation of Polyesters for the Electrospinning Method 157

hydrophilicity, roughness, crystallinity, conductivity, lubricity, and cross-linking.
Therefore, in order to improve the biocompatibility of polyesters, polymer or
scaffold modifications are employed. Surface treatments of polyesters after
electrospinning have been extensively used and this transforms these inexpensive
materials into highly valuable finished products. In recent years, many advances
have been made in developing surface treatments to alter the chemical and
physical properties of polymer surfaces without affecting their excellent bulk
properties. In particular, the past two decades have seen the rapid development
of new strategies for the design of polymer functional surfaces.
Physical and chemical modifications to increase electrospun polyester
hydrophilicity and surface scaffold functionalization with ECM proteins, pep-
tides, or other bioactive molecules are some examples of posttreatments in use
[16]. Another strategy to improve the biocompatibility of the scaffolds is to
combine the polyester with a natural polymer or other natural biomolecule to
conduct the electrospinning process [17, 18].
This chapter concerns the recent progress in the use of polyester polymers to
produce electrospun scaffolds for medical regenerative applications, with empha-
sis on the processing of the polyesters for electrospinning, their applications, and
the improvement of their biological performance.

7.2
Preparation of Polyesters for the Electrospinning Method

In order to conduct the electrospinning process, the polyester must be in liquid
form and it can be used as a polymer solution or molten polymer. To prepare a
polymeric solution, the solid polymer is firstly dissolved in an adequate solvent or
cosolvent mixture. Meanwhile, for the melt-electrospinning, the polymer is placed
inside an electrospinning apparatus reservoir, which is maintained at a constant
heat and remains in the molten state until it is submitted to the electrospinning
process [19, 20]. A great advantage of melt-electrospinning is the absence of an
organic solvent in the produced scaffold. In addition, melt-electrospinning can
be less expensive than polymers dissolved in solution. Many solvents used in a
polymer solution are costly and this is often the major part of the cost factor asso-
ciated with the electrospinning process [21]. However, molten polymers exhibit a
dense entanglement network of their chains and can have much higher viscosity
than polymer solutions, generally resulting in fibers with diameters outside the
nanometer range, from just a few micrometers up to 10 μm [19, 22, 23]. There-
fore, polyester solutions are more frequently used than melt-polyesters to produce
biomedical scaffolds.
Intrinsic properties of polyester, such as its molecular weight and parameters
of the polymeric solution, such as concentration, viscosity, and conductivity have
significant influence on the electrospinning process and the characteristics of
the formed fibers [8]. The electrospinning method requires a minimum concen-
tration of polymers for the formation of fibers. The polymer solution must have