THE POWER OF CAD/CAM LASER BIOPRINTING AT THE SINGLE-CELL LEVEL: EVOLUTION OF PRINTING - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 79

optically-transparent “ribbon” disks, biopolymer-coated receiving substrates, beam delivery optics, and
imaging and pulsed laser system, but contain variations in ribbon processing and laser wavelength for
optimal laser-material interaction ( Figure 4.1 ). Auxiliary components include in situ imaging devices,
laser beam energy meters, and up to three computer-controlled stages. A complete survey of laser-
assisted printing systems is provided by Phamduy et al. (2010) . Two specific system schemes, AFA-LIFT
and MAPLE-DW, are highlighted here.
The laser-transparent disks, termed “print ribbons,” are analogous to ink ribbons historically uti-
lized in typewriters. By analogy, ribbons are loaded on one side with ink, as the optically transparent
print ribbon disks are coated on one side with cells. Cells either adhere to a biopolymer coating on
the disk ribbon or are suspended in a sacrificial matrix layer, such as cell culture media or low vis-
cosity biopolymer (e.g. hydrogel). In AFA-LIFT, there may be an additional metallic layer between
the ribbon surface and cell-embedded medium. This sacrificial layer acts as an absorption medium
intended to reduce the effects of laser radiation on cells and facilitate the conversion of light energy to
mechanical energy. In systems with UV or near-UV lasers this is a laser-absorbing biopolymer layer.
However, in high-power (longer wavelengths with longer pulse widths) laser systems, this layer is often
metallic, gold, or titanium. Potential cytotoxic effects exist from volatilization of the sacrificial metal
layer, which leads to potential nanoparticulate inclusion during droplet ejection ( Smausz et al., 2006 ;
Lewinski et al., 2008 ). In addition, the metal layer blocks visualization of cells on the ribbon.
MAPLE-DW positions the print ribbon on planar motorized stages in conjunction with a coordi-
nated imaging system, which allows researchers to traverse the ribbon and select individual cells for
printing in real time. For single-cell transfer applications, print ribbons must have enough intercellular
spatial separation so that only one cell is situated within the transfer area. The ability to visually target
individual cells by way of coordinated imaging and a low cell density on print ribbon removes the
element of volumetric probability, reducing droplet-to-droplet variation.
FIGURE 4.1
General schematic for laser-assisted bioprinting.