Page 190 - Biodegradable Polyesters

168 7 Electrospun Scaffolds of Biodegradable Polyesters: Manufacturing and Biomedical Application

Gas out
Gas in

hν

Polymer sample

Quartz window

Figure 7.3 Photochemical reactor used for UV-assisted functionalization of polymer films in
the presence of a gas-reactive atmosphere.

cross-linked hybrid scaffolds, photo-cross-linking of electrospun biodegradable
polyester scaffolds without the use of photoinitiators, UV laser lithography for the
fabrication of 3D microstructured tissue scaffolds, and many more [108–125]. For
example, Chen and colleagues applied a microfabrication process, the UV-LIGA
method, to generate an array of microneedles with a similar projective structure
and size as those of the mouse duodenal villi. They used a commonly used
epoxy-based negative photoresist (SU-8) and applied UV-light (UV) lithography
to generate microprojective structures from the SU-8 photoresist. The SU-8
was then replaced with degradable poly(lactic acid), PLA for cell seeding and
proliferation of the intestinal epithelial cells. The integration of UV lithography,
molding, hot embossing, and solvent erosion enabled the design and synthesis
of a tissue-culture PLA villus array with smooth tip curvature and higher cell
population.
In a recent study, Gu and Tang [126] reported a new patterning technique,
termed enzyme-assisted photolithography (EAPL), to simultaneously achieve
topographical and chemical patterning of hydrogels. They used as substrate a
widely used biocompatible polyethylene glycol (PEG) to obtain arbitrary patterns
of biological molecules and intact cells on integrated PEG hydrogel substrates.
The overall design of the EAPL approach was simple and inspired by the general
photolithography techniques used for microelectronic fabrication. A two-step
process parallel to that of fabricating via positive photoresist is employed to create
patterns on the hydrogel surface. The hydrogel is first UV-irradiated through a
designed photo mask; cross-linkers localized at the exposed portions are then
decaged and the native protease recognition sequences are revealed. The hydrogel
is then treated with an aqueous solution containing the protease to specifically
digest the decaged cross-linkers and remove the hydrogel with precision only in
the regions that have been exposed to UV radiation. Owing to the inability of
the protease to proteolyze the caged peptides, the regions of the hydrogels that
have been UV protected by the mask remain intact. Additionally, proteolysis of
the peptide bonds generates free nucleophilic amine groups at the patterned area