Innovative Strategies for Tissue Engineering - Advances in Biomaterials Science and Biomedical Applications - page 305

achieving biomimetic tissues. Advances in microfabrication technologies have been exploited
by an increasing number of research groups. Often technologies from other engineering
disciplines have been translated and used in creating microfeatures in engineered scaffolds in
a controlled manner. These include photolithographic approach of the electrical engineering,
electrospinning tools of the textile industry, emulsification and fluid dynamics principles of
chemical engineering and rapid prototyping methods of mechanical engineering. The latter
will be covered in further detail in the next section [40].

Vacanti and coworkers pioneered the concept of engineering a vasculature using photolitho‐
graphic techniques (which use light, e.g. UV, to selectively remove parts of a thin film or the
bulk of a substrate), literally generating channels within biomaterials [43].

Electrospining techniques have also been considered and tested for tissue engineering
application, due to their potential of producing polymer fibers with nano to micrometer
diameter scale that are physically and topographically comparable to the collagen fibers,
commonly found in the natural ECM, as shown in Figure 5. It has been extensively employed
in tissue engineering strategies, including vascularization strategies [41].

Figure 5. Similarity between ultrastructure of natural collagen fibers (A) and electrospun biomaterials (B). Source: A -
author`s unpublished data; B - http://en.wikipedia.org/wiki/Electrospinning, accessed on September 2012.

Electrospun biomaterials must also be carefully fabricated, as even fiber diameter variation
results in different cell behavior, as observed in endothelial cells cultured on electrospun
poly(l-lactide-co-ε-caprolactone) with different fiber diameters. In contrast to cells cultured on
fibers of 0.3 or 1.2μm, cells cultured on 7μm presented lower cell adhesion, spreading and
proliferation [63].

Even though electrospining has presented promising results, it also suffers from some
limitations, such as poor cell invasion, as usually the electrospun biomaterials are highly
compacted, impeding cell migration towards the inner side of the scaffold. The search for
different solvents and electrospining conditions may solve this issue, promoting less fiber
compactation.