Page 192 - Biodegradable Polyesters

170 7 Electrospun Scaffolds of Biodegradable Polyesters: Manufacturing and Biomedical Application

was used in the reactive electrospinning of the modified PU. The prepared cross-
linked materials may be useful in applications such as vascular grafts where a
repetitive and relatively low stress is encountered.
Fabrication of PU/PEGMA cross-linked hybrid scaffolds by in situ UV pho-
topolymerization was also recently reported by Wang and colleagues [129].
Similar to the work of Theron and colleagues [128], cross-linked electrospun
PU/PEGMA hybrid nanofibers were fabricated by a reactive electrospinning
′
process with N, N -methylenebisacrylamide as cross-linker and benzophenone as
photoinitiator. The photoinduced polymerization and cross-linking reaction took
place simultaneously during the electrospinning process. Combining the fiber
fabrication process with photochemical reactions enabled the polymerization
and cross-linking of hydrophilic materials while they were produced in the
nanofibrous form. It was observed that the pure PU scaffold had the highest con-
tact angle values at (118.8 ± 7.8) degrees among all the scaffolds and the contact
angle values decreased with the increased content of PEGMA. When the weight
ratio of PEGMA increased up to 50 wt%, the contact angle decreased to about
(20.2 ± 2.3) degrees, revealing that the PEGMA changed the hydrophobicity of
PU/PEGMA scaffolds. Finally, HUVECs were cultured onto the cross-linked
PU/PEGMA scaffolds. The cells attached, survived, and proliferated significantly
better compared with the PU scaffold, confirming the advantages offered by the
cross-linked PU/PEGMA hybrid scaffolds in providing appropriate mechanical
properties combining with good cytocompatibility.

7.3.1.5 Functionalization of Polyester Electrospun Scaffolds with Bioactive Molecules
Onestrategytoachieve better controlofcellularresponseisthrough the
attachment of biomolecules onto the polyester scaffold surface. A large number
of bioactive molecules have been used to functionalize these biomaterials.
The functionalization of scaffolds with ECM constituents provides them with
greater analogy with the native cellular microenvironment, making them more
desirable features for biomedical applications [132]. Fibronectin and laminin
are two proteins present in ECM, which have been extensively used for scaffold
bioactivation. These proteins contain varying numbers of binding domains
for cells or constituents of the matrix, providing greater cell adhesion and
proliferation [133]. Another approach is the use of specific sequences of proteins
responsible for the anchorage of cell receptors in the ECM components. Polyester
bioactivation with specific adhesion-promoting peptides can efficiently increase
the interaction selectivity of the scaffolds with the cells. These peptides activate
certain signaling pathways leading to cell adhesion and promote better spreading
and proliferation on the structure [134]. RGD (arginine–glycine–aspartic acid)
tripeptide has been extensively used for bioactivation of polyesters [135]. It
is found in fibronectin and in other components of ECM such as laminin,
vitronectin, and type I and IV collagen and it stimulates the adhesion of the cells
to these proteins. SIKVAV (serine–isoleucine–lysine–valine–alanine–valine), a
laminin sequence, and GEFYFDLRLKGDK, a collagen fragment, are other motifs
used to treat polyester scaffolds [134, 136, 137]. More examples of motifs used