Biomedical Engineering Reference
In-Depth Information
Fig. 2.5
Scaffolds can be processed with different methods into different structures.
a
Sintered
HAp.
b
Fibre bonded meshes of starch-polycaprolactone.
c
Methacrylated gellan gum hydrogel.
d
Freeze-dried chitosan
Scaffolds can be manufactured with various methods. Figure
2.5
presents some
examples of scaffolds that were processed with different methods into different struc-
tures. Figure
2.5
a-d present, respectively, a macroporous HAp scaffold produced by
sintering [
75
], a starch-polycaprolactone mesh produced by fibre bonding [
76
], a
methacrylated gellan gum hydrogel obtained by ionic cross-linking [
74
], and a chi-
tosan sponge obtained by freeze-drying [
59
].
Rapid prototyping (RP) is an interesting group of non-conventional scaffold man-
ufacturing techniques. With RP, a physical construct can be created layer-by-layer
using a computer-aided design data [
77
-
79
]. One of the RP techniques is 3D plotting
[
80
], which is a melt-dissolution deposition based technique. In 3D plotting, liquids
or hydrogels can be dispensed into a liquid medium through a nozzle that moves
on the horizontal plane to build a layer, then the next layers will be created on top
of the previous layer by the movement of the nozzle on the vertical plane [
77
]. For
the first time, Landers et al. [
81
] processed hydrogels into a scaffold with defined
pore-size and shape with this technique. RP techniques bring several advantages.
It is possible to produce scaffolds with customized structural design based on the
computer-aided design data and this will make it possible to produce patient-specific
scaffolds [
78
]. The advantage of customized design is that it gives the opportunity to
produce scaffolds with desired porosity and pore size. It is also possible to change
the plotting parameters to control the architecture and mechanical properties [
82
].
These parameters include nozzle size, speed of nozzle arm, speed of extrusion, and
distance between the strands [
81
]. Furthermore, when a computerized manufactur-
ing technique is used, minimum manpower is required and thus, higher throughput
manufacturing is possible [
78
]. Another advantage is the possibility of including the
cells and growth factors into the biomaterial before the scaffold is manufactured [
81
].
Growth factors
represent a large number of polypeptides that have a specific
effect on the activities of cells by transmitting signals [
83
,
84
]. They can bind to the
specific receptors found on the surface or inside the target cells. The effect could
be inhibition or stimulation of differentiation, proliferation, adhesion, migration and
