Page 182 - Biodegradable Polyesters

160 7 Electrospun Scaffolds of Biodegradable Polyesters: Manufacturing and Biomedical Application

7.3
Improving the Bioactivity of Electrospun Polyesters

Polyesters are widely employed to produce electrospun scaffolds. These polymers
exhibit appropriate characteristics for tissue engineering application, such as
biocompatibility and low cost. In addition, it has already been shown that
polyester electrospun scaffolds are capable of supporting the development of
different types of cells, such as mesenchymal stem cells (MSCs), endothelial
cells, schwann cells, fibroblasts, keratinocytes, chondrocytes, and osteoblasts
[38–44]. Furthermore, polyester fibers have been researched for the regeneration
of a variety of tissue, such as skin, bone, cartilage, spinal cord, vessels, and
peripheral nerve [30, 36, 45–50]. Despite successful use in various areas of
tissue engineering, electrospun polyesters display poor biological properties.
These polymers do not exhibit active cell sites or functional groups along their
backbone and are generally quite hydrophobic. Therefore, several strategies have
been employed to increase the surface functionality of polyester fibers [15, 51,
52]. Some of these strategies are functionalization with hydrophilic groups by
chemical modification or physical treatments and the coating of surface scaffolds
with proteins, peptides, or other bioactive molecules. Some techniques have
been shown to improve the biological properties of the scaffolds produced with
polyester polymers [14]. These treatments are able to introduce functionalities
in polymeric materials, enhancing the cell function on these materials and
favoring tissue formation [15]. Some surface modification techniques for appli-
cation in tissue engineering electrospun polyester scaffolds are presented in the
following.

7.3.1
Surface Modification Techniques

7.3.1.1 Wet Chemical Surface Modification
In this classical approach, a material is treated with liquid reagents to generate
reactive functional groups on the surface. The methodology does not require
specialized equipment and thus can be conducted in most laboratories. It is
also more capable of penetrating porous three-dimensional substrates than
plasma and other energy-source surface modification techniques [53]. The wet
chemical method also allows for in situ surface functionalization of microfluidic
devices. For example, cyanuric chloride was used as a coupling molecule between
hydroxyl groups on the surface of an epoxy resin and polyamines [54]. Thus,
two polyamines, diethylenetriamine and branched polyethylenimine, were
successfully coupled to the surface via chemical modification. The chemical
surface treatment method is often used in surface functionalization of polymeric
materials. For example, a recent interesting application of TiO self-cleaning
2
coatings on polycarbonate (PC) substrates was reported [55]. A chemical surface
treatment method was used to create hydrophilic groups on the PC surface. TiO
2
was then deposited via wet coating, using an anatase sol of TiO nanoparticles of
2