Page 189 - Biodegradable Polyesters

7.3 Improving the Bioactivity of Electrospun Polyesters 167

properties of porous collagen scaffolds without compromising their mechanical
integrity and biostability. The water contact measurements confirmed that
ozone perfusion could improve the surface wettability of chemically cross-linked
collagen scaffolds. As a result, water and phosphate buffered saline (PBS) solution
could wet the collagen fibrils and diffuse into the structure of the scaffolds, which
led to enhanced water and PBS solution intake capability.

7.3.1.4 Ultraviolet Radiation
Surface functionalization of polymeric materials by using polychromatic or
monochromatic electromagnetic radiation is a relatively new field of research,
in particular when monochromatic radiation is used as a tool to introduce new
surface functionalities [97]. UV-light treatment of polymer surfaces provides
similar effects with other techniques, such as plasma treatment, modifying their
hydrophilicity, chemical properties on the surfaces, and so on [98, 99]. The use
of UV light for surface treatment is a classic application of this methodology for
surface modification. However, there are significant differences, advantages, and
disadvantages of UV treatments compared with plasma modification techniques.
Plasma treatments are generally limited to surfaces but photochemical reactions
can be surface-limited or can take place deep inside the bulk, depending on the
UV absorption coefficient at the specific UV wavelength. In this sense, UV-light
treatments have similarities with UV/O treatments where the bulk region of
3
the scaffold can be also modified. Plasma can treat wide surface areas, while
UV treatment can process wide areas as well as very small spots. Lithographic
processes are particularly suited for the construction of minute structures and
the technology is a very well known process used in the fabrication of the
actual integrated circuits. Classic LIGA (initially, an acronym for “Lithografie
und Galvanik”), based on X-ray deep-etch lithography, is characterized by very
small lateral dimensions and side walls with a roughness of less than 50 nm. UV
lithography is a less complex and less expensive alternative to X-ray technology,
which is able to meet less demanding specifications [100–102].
Another important difference is the power-intensity control. Controlling
plasma intensity is generally limited although with some methods such as
magnetic field confinement, it can be enhanced locally. In UV-photo treatment,
continuous wave (CW) UV lamps with a moderate light intensity to very high
power output of a pulsed laser can be used. In general, UV processes do not
require costly equipment and offer the advantage of patterned surface mod-
ification through the use of lithographic techniques. In the last decade, new
applications of UV surface functionalization have been published, combining
reactive gas or vapor atmospheres with simultaneous UV irradiation of the
polymer [99, 103–107]. A simple photochemical reactor used for UV-assisted
modification of polymer surfaces is shown in Figure 7.3.
Owing to the properties of UV radiation for the easy generation of radical
species on the polymer surface and in the bulk (photo-cross-linking), UV lithog-
raphy has begun to be used in several tissue engineering applications, such as
lithographic microfabrication of biocompatible polymers for tissue engineering,