3D BIOPRINTING TECHNIQUES - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 65

and matrix-assisted pulsed laser evaporation direct writing (MAPLEDW) ( Barron et al., 2004; Patz
et al., 2006 ). The AFA-LIFT and BioLP are bioprinting versions of the laser-induced forward trans-
fer (LIFT) technique which was originally developed for the direct writing of metal features using a
high-energy pulsed laser to deposit a metal film on an optically transparent substrate and has also been
employed for direct writing of biomolecules ( Duocastella et al., 2007 ). In AFA-LIFT and BioLP, a
high-powered pulsed laser is used to vaporize and deposit the bioink onto the substrate. To protect cells
from direct exposure to the high-energy laser beam, a sacrificial metal or metal oxide (e.g. Au, Ag,
Ti, and TiO 2 ) thin film ( ∼ 100 nm) is included at the interface between the target plate and the bioink.
The rapid thermal expansion of this interfacial layer due to the high-energy laser pulse propels a small
volume of bioink onto the substrate, but with minimal heating of the bioink to prevent cell damage.
The BioLP process also utilizes computer-controlled motorized stages and a CCD camera to visualize
and focus the laser. Unlike AFA-LIFT and BioLP, the MAPLE-DW process uses a low-power pulsed
laser and an interfacial layer of a sacrificial hydrogel such as Matrigel ® instead of a metal thin film to
accomplish cell transfer. This interfacial layer that acts as an attachment layer for the cells also absorbs
the laser energy to prevent it from affecting them. Similar to BioLP, computer-controlled manipulation
of the stages coupled with a CCD camera allows for selective cell patterning. Laser-guided direct writ-
ing (LGDW) is another commonly used LAB process, but unlike other LAB processes, it does not use
a pulsed laser or a print ribbon ( Nahmias et al., 2005 ). Instead, the optical energy of a weakly focused
continuous laser is directly used to target and manipulate individual cells from liquid cell suspension
onto the substrate. Several parameters related to the laser source, bioink, substrate, interfacial ribbon
layer, among others, affect the resolution and performance of LAB processes, and have been described
by ( Guillemot et al., 2010 ).
MAPLEDW was one of the first processes used to successfully demonstrate the feasibility of laser-
based printing of mammalian cells. Bu et al. (2001) first demonstrated the patterning of Chinese ham-
ster ovary (CHO) cells using the process. Later, Ringeisen et al. (2004) and Barron et al. (2005) printed
mouse carcinoma cells (P19), human osteosarcoma (MG-63), and rat cardiac cells with the same pro-
cess with viability greater than 95%. Recently, ( Schiele et al., 2010 ) have used the MAPLEDW to
create viable patterns of human dermal fibroblasts, mouse C2C12 myoblasts, bovine pulmonary artery
endothelial (BPAEC), breast cancer (MCF-7), and rat neural stem cells. The AFA-LIFT and BioLP
processes have also been successfully used to print various cell types including human osteosarcoma
(MG-63), rat Schwann and astroglial and pig lens epithelial cells, BAEC, human umbilical vein en-
dothelial cells (HUVECs), and human umbilical vascular smooth muscle cells (HUVSMC). Invalid
source specified. Schiele et al. (2010b) have recently provided a thorough topical review of LAB pro-
cesses and their applications.
3.3.4 SOLENOID VALVE-BASED PRINTING
Microdispensing using solenoid valves has seen applications in depositing solder and adhesives onto
electronic boards, deposition of optical and electrical polymers, and deposition of biomolecules such
as DNA, proteins, and diagnostic reagents. The system has shown itself capable of printing live
biological cells for dermal repair, printing mesenchymal stem cells onto tissue well plates, and print-
ing of constructs within a controlled environment. A complete system consists of a fluid reservoir, a
solenoid-based dispensing device with droplet volumes ranging from 5 pl to 1 nl droplet quantities,
heating elements to control the nozzle head temperature, connections to the pneumatic controller, and