Biomedical Engineering Reference
In-Depth Information
Cell type I
Cell type II
Gel
FIGURE 4.6
A representation of the organ printing concept.
the viscosity, electrical resistances, and temperature of the printing fl uids has been reprogrammed
and the feed systems altered. As defi ned by Mironov et al. [14], organ printing includes the many
different printer designs and components of the deposition process, for example, jet-based cell print-
ers, cell dispensors or bioplotters, the different types of 3-D hydrogels, and varying cell types. The
concept is schematized in Figure 4.6.
With this method the resolution is about 100 µm, and in fact several cell aggregates are formed
within the drops. Due to the use of an ink-jet head, cells may be damaged during spraying due to
the high shear stress by the piezoelectric actuator, and obviously the choice of materials is also
restricted to a narrow range of biocompatible thermoreversible hydrogels.
4.6 PRINTING HEAD AND POWDER-BASED MICROFABRICATION
In this section, we include all the techniques where the polymeric powders or liquids are placed on
the x - y plane of the system, and the working head (laser, ink-jet head, etc.) realizes microstructures in
which the resolution is a function of the grain dimensions or of the printing head beam or drop size.
4.6.1 M EMBRANE L AMINATION
Membrane lamination consists of the realization of membranes having a thickness between 500 and
2000 µm. They are then cut by a laser beam or scissors in the form of predetermined, 2-D shapes.
Once the basic elements are ready, the structure is assembled layer-by-layer using microcontrolled
and microactuated system controlled by CAD/CAM software. Lamination is obtained by wetting an
absorbent material such as paper, cloth, or a sponge with an organic solvent. Light pressure is applied
to the exposed surface of each membrane for a suffi cient amount of time to wet each surface. The
resulting bilayer-laminated structure is gently compressed to ensure suffi cient adhesion between the
wet surfaces of the fi rst and the second membranes. This procedure is repeated with the bilayer or
resulting multilayer-laminated structure until the desired 3-D shape is obtained. The fi nal laminated
structure is dried to ensure complete solvent evaporation [15]. Since the resolution of this method is
insuffi cient for most tissue engineering applications, it has been replaced by more precise techniques.
 
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