Biomedical Engineering Reference
In-Depth Information
Microfabrication techniques
2-D
3-D RP
Photolithograpy,
soft lithography,
and its derivatives
PS3D (pseudo 3-D),
layer-by-layer
Sacrificial molds
Liquid or fluid dispensing
Printing head and powders
PAM and its derivatives
FDM
Organ printing
Laser sintering
Photopolymerization via stereolithography
3-D printing
Membrane lamination
FIGURE 4.2
Classifi cation of RP methods.
We will use the classifi cation suggested by Yeong et al. [2], which subdivides RP methods into PS3D
solution or fl uid-based systems and printing head and powder-based fabrication, in addition a third class
is added, which is based on the use of sacrifi cial molds. Pressure-assisted microsyringe (PAM), ink-jet
organ printing, and fused deposition modeling (FDM) are some of the processes that use solutions. RP
methods such as 3-D printing (3-DP) and laser sintering fall into the second class of fabrication, which
relies on the use of a printing head emitting a binder such as light, heat, or a solvent.
4.3 MATERIALS USED FOR TISSUE ENGINEERING SCAFFOLDS
One of the most critical aspects of tissue engineering is the choice of biomaterial. Typically bio-
materials fall into two main categories: biological polymers and synthetic polymers. Biological
polymers are rarely used in RP because of their delicate nature; they denature easily, are diffi cult
to sterilize, and often do not possess adequate mechanical properties to allow the creation of free-
standing porous 3-D structures. However, some reports using collagen containing RP scaffolds
have been published. In particular, Sachlos et al. [3] have used reconstituted collagen composites,
which were poured in the rapid-prototyped sacrifi cial molds. Biological hydrogels such as gelatin
and alginate have also been employed, despite the fact that their fl oppiness makes them diffi cult
to manage and assemble, and in general the resolutions obtained are low [4,5]. Synthetic polymers
are, however, the preferred material for most systems. The most commonly used synthetic polymers
for the realization of 3-D scaffolds for tissue engineering are the polyesters—polylactide (PLA),
lactide/glycolide co polymers (PLGA), and polycaprolactone (PCL). Often synthetic polymers are
incapable of supporting an adequate degree of cell adhesion and must be surface treated or modi-
fi ed with appropriate ligands. These synthetic polymers, also perform poorly in mechanical terms,
being too compliant for bone tissue but too rigid for soft tissue. It is therefore becoming increasingly
common to use composites or blends, and hydroxyapatite is very often used to render synthetic poly-
mers more rigid for bone engineering applications [6]. The positive trend toward the employment of
