Rational Design of Artificial Cellular Niches for Tissue Engineering - Tissue Engineering: Computer Modeling, Biofabrication and Cell Behavior - page 136

produce tailor-maid structures with relatively thick polymeric fibers. The diameter
of these fibers ranges from several dozens to hundreds of microns. These techniques
are based on a computer controlled micro-extruder that dispenses a fluid polymer
following a predefined path that solidify once it has been deposited [ 65 ]. Another
standard method used for manufacturing fibrous scaffolds is electrospinning. This
technique is used to produce randomly placed nanometric fibers. The process starts
when a polymeric solution is placed into a syringe, and a high voltage is applied
between the syringe needle and a collector plate. As the solution exits from the nee-
dle, the electric field accelerates the jet and shrinks its diameter down to nanome-
ters [ 66 ].
4.1.1 Additive Manufacturing
The manufacture of scaffolds using additive manufacturing starts with the design
of the microstructure in a CAD environment. Modeling complex microstructures
created by this method is not always an easy task. A straightforward way to model
scaffolds produced with additive-manufacturing-based approaches consists of using
the same computational information that has been created to print the scaffold as an
input to generate a virtual scaffold [ 67 ].
In some cases, it may be interesting to model the manufacturing process itself,
directly generating in silico digital volumes with a certain disposition of the fibers
so that the virtual scaffold matches the microstructure produced experimentally by
other researchers [ 68 ]. Also, it might be practical to use data from computer to-
mography imaging of real scaffolds as input for the generation of scaffolds in silico
[ 69 ]. The generation of those digitalized 3D microstructures could be used to mea-
sure or predict some physical and mechanical properties of the scaffold related to its
microstructure, or even for degradation studies.
4.1.2 Electrospinning
Modeling the generation of scaffolds by electrospinning is definitely more challeng-
ing than by rapid prototyping. Scaffolds produced by electrospinning are fibrous
polymer-based materials where the arrangement of fibers and their diameters are dif-
ficult to predict. Many parameters, such as polymer/solvent ratio, molecular weight
of the polymer, viscosity, surface tension, conductivity, applied voltage, flow rate,
needle-collector distance, among others, have an impact on the final geometry of the
scaffold [ 70 ]. In the following lines, a method to model electrospun microstructures
in a very realistic fashion will be presented. As an example obtained applying this
method, Fig. 4 left shows a real electrospun microstructure and Fig. 4 right shows a
modeled scaffold generated for degradation studies.
If studies are going to be performed in very small regions of the scaffold, it is
possible to presume that fibers have a constant diameter, are locally straight and
randomly oriented in different layers. Using these assumptions, some authors have