Page 191 - Biodegradable Polyesters

7.3 Improving the Bioactivity of Electrospun Polyesters 169

that can be further functionalized. The EAPL method allows direct formation of
functional patterns into a biocompatible hydrogel.
What has recently begun to receive attention from a few research groups is
the possibility to combine the effects of UV radiation with electrospinning [111,
127–131]. Using this method, covalent cross-linking of polyesters, modified or
not with latent functional groups allows the formation of 3D scaffolds produced
by electrospinning. Although the first patent on electrospinning was issued nearly
80 years ago, it has recently undergone a revival in the production of biomaterial
scaffolds owing to its ability to produce porous 3D structures comprised of nano-
to microscale fibers. Many natural and synthetic polymers have been converted to
biomaterial scaffolds by electrospinning. Despite the difficulty of controlling the
process in terms of detail, it lends itself to the production of regular geometries in
sizes which are very useful for use as scaffolds. For instance, Yuan and colleagues
[130] have investigated the formation of electrospun scaffolds of polycarbonate
urethane (PCU) as a potential application in vascular tissue engineering because
their nanosized dimension can mimic the natural ECM. According to the authors,
PCUs have better biocompatibility than other synthetic polymers because of the
microphase-separated structure. However, these polymers are highly hydropho-
bic and PCUs usually tend to form thrombus when PCU biomedical devices are
in contact with blood for an extended period of time. To overcame this problem
and increase the hydrophilicity of the scaffold surface, poly(ethylene glycol)
methacrylate (PEGMA) was grafted onto the fiber surface using the surface-
initiated atom transfer radical polymerization (SI-ATRP) method. The SI-ATRP
method has been developed and used for surface modification for many years
and it is possible to obtain optimum conditions of grafting particular polymer
chains to control hydrophilicity by UV polymerization. The results obtained
by Yuan and colleagues showed that the scaffold morphology maintained the
original structure after the SI-ATRP UV polymerization step and the average
diameter of the fibers did not change significantly, although the roughness surface
increased. The PEGMA-modified scaffolds decreased the water contact angle
∘
∘
from 110 (untreated PCU) to about 70–80 , depending on the concentration of
PEGMA used. PEGMA-modified scaffolds also showed lower platelet adhesion,
thrombogenicity, and hemolysis than PCU scaffolds. Furthermore, the cytocom-
patibility of electrospun nanofibrous scaffolds was tested with human umbilical
vein endothelial cells (HUVECs). The results showed that the cells attached well
to the modified fibrous scaffolds. Finally, the prepared hemocompatible scaffolds
show potential application as artificial blood vessels.
A very interesting combination of electrospinning with simultaneous UV irra-
diation was reported by Theron and colleagues [128], who modified, cross-linked,
and carried out reactive electrospinning of a thermoplastic medical polyurethane
(PU) for vascular graft applications. Successfully induced cross-linking of modi-
fied pellethane was achieved after 20 min of UV irradiation. The apparatus con-
sisted of a custom-built high-voltage power supply (0–35 kV), an infusion pump
fitted with a 1 ml syringe containing a needle, and a rotating/translating mandrel.
An ultraviolet light source (315–400 nm) positioned 500 mm above the mandrel