Exploring the Future of Hydrogels in Rapid Prototyping: A Review on Current Trends and Limitations - Biologically Responsive Biomaterials for Tissue Engineering - page 215

Table 9.3 Classi fi cation of inkjet printers

Electromechanical (piezo-actuated and electrostatic actuated)

Drop-on-demand Electrothermal (thermal actuated)

Electrostatic vacuum

Inkjet printers

Electro-field controlled inkjet
Hertz continous inkjet (mutual charged droplet repulsion type)

Continuous ejection

lowing topics should be addressed: optimal scaffold design, bioactivity of the
scaffold as well as the issues of cell seeding and encapsulation possibilities. So,
future development will need to focus on the engineering of new materials, the scaf-
fold design and the input of cell biologists. Keeping this in mind, rapid prototyping
still remains a promising technique as a methodical interface between tissue and
engineering.

9.3.3 Printer-Based Systems

9.3.3.1 Working Principle and Recent Trends of Printer-Based Systems

In literature, “printing” is often used as a general term for both the construction of a
scaffold or to indicate printer-based systems. To differentiate between both, we
define the latter as manufacturing techniques that implement inkjet technology.
Inkjet printers can be divided in drop-on-demand or continuous ejection types. In
drop-on-demand systems, electrical signals are used to control the ejection of an
individual droplet. In continuous-drop systems, ink emerges continuously from a
nozzle under pressure. The jet then breaks up into a train of droplets whose direction
is controlled by electrical signals [ 217 ]. Both drop-on-demand and continuous-jet
systems can be operated with droplets ranging in size from 15 to several hundred
microns [ 217 ] .
Many commercial (adapted) printers fall in the former category, and will only
eject ink when receiving a demand signal from the computer. Table 9.3 classi fi es the
existing inkjet printers (modified from Nakamura et al. [ 218 ] ). Like the nozzle-
based systems, building a construct occurs in an additional computer-controlled
layer-by-layer sequence with deposition of material.
3DP™. Prof. Sachs from the Massachusetts Institute of Technology (MIT)
introduced the 3D Printing™ technology [ 219 ]. It is an example of a solid-
phase RP technology. 3D Printing can be used to fabricate parts in a wide vari-
ety of materials, including ceramic, metal, metal-ceramic composite and
polymeric materials. 3D printing is the only of the solid-phase RP techniques
compatible with hydrogel manufacturing. A scheme of a typical 3DP™ set-up
is given in Fig. 9.7 . The technique employs conventional inkjet technology. The