BLOOD VESSEL REGENERATION - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 153

One application that has seen some use in tissue engineering is the generation of artificial heart
valves and conduits. Research groups have developed models based upon X-ray computed tomography
and magnetic resonance imaging scans to determine the portions that need to be replaced to treat the
patients' conditions. The 3D models were then printed layer-by-layer with stereolithography out of poly-
4-hydroxybutyrate and polyhydroxyoctanoate, both of which allow for the generation of a biocompati-
ble implant. For the replacement conduits and the trileaflet valves, these printed models were then tested
in perfusion bioreactors ( Sodian et al., 2002; Sodian et al., 2005 ). The application of stereolithography to
the printing of biocompatible polymers for vascular regeneration has the promise of providing a method
that can construct intricate implants that can have multiple components within one printed model.
7.1.6 FUSED DEPOSITION MODELING
Fused deposition modeling (FDM) has been around for several years in tissue engineering applications
( Zein et al., 2002; Hutmacher et al., 2001 ). However, it has recently seen an increase in usage in both
industrial as well as personal applications. In fact, systems based on the RepRap open source 3D printer
have been utilized for tissue engineering applications ( Miller et al., 2012 ).
In these systems, a material such as a thermoplastic or a glass is feed from a source coil into a heated
extruder ( Figure 7.4 ). The material is then deposited layer-by-layer and the scaffold is created in this
stepwise fashion. The rate of extrusion, diameter of the nozzle head, temperature of the nozzle, and the
speed of the nozzle head all influence the diameter of the deposited filament. Typically, as the speed of
the nozzle increases for a given extrusion rate and nozzle size, the diameter of the fiber decreases. This
can be used to tailor the size of the deposited filament such that it is smaller than the diameter of the
extrusion nozzle. Furthermore, based upon the temperature of the extrusion process, it is possible to
control the adhesion of the extruded filament to previously deposited layers. This allows for the creation
of interconnected filaments that are deposited according to the 3D design.
FIGURE 7.4 Fused Deposition Modeling.
This illustration shows how the extruded filament is deposited creating an interconnected 3D scaffold. (A) A
scaffold is deposited in the desired pattern. (B) The scaffold is coated with a biocompatible polymer to protect it
from the ECM/ hydrogel laden with cells that is (C) deposited around the scaffolding. (D) The scaffolding is then
dissolved by the perfusion of water through the scaffold. Endothelial cells are injected into the interconnected
network and line the walls forming vasculature/microvasculature.