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Dhakshinamoorthy Sundaramurthi, Sakandar Rauf and Charlotte A. E. Hauser

4.3 Laser-assisted Bioprinting

Biological constructs developed using laser-assisted
bioprinting can yield resolution at a single cell per
droplet [21] . The tissue organization and cell population
can be easily controlled in laser-assisted bioprinting,
which makes it a potential technique to develop tissue
equivalents having similarities in both structure and
function of the native tissue [54] . This technique is ba-
sed on the principle of laser-induced forward transfer
which was initially used to print inorganic or organic
structures with micrometer scale resolution but now
successfully used to print bioinks such as DNA, cells,
[55]
and peptides . When compared to other bioprinting
Figure 4. Electrical heating thermal inkjet printer and acoustic
inkjet printer that uses piezoelectric material (Adopted from methods, laser-assisted bioprinting was not widely used
ref. [19,41] ). in earlier days, but it has been increasingly popular
nowadays for the fabrication of engineered tissues for
inkjet printers use acoustic radiation coupled with an regenerative medicine applications [56] . Laser-assisted
ultrasonic sound to pump out the ink [19] . In this me- bioprinting system consists of a pulsed laser beam (to
thod, the parameters of ultrasound such as amplitude, induce the transfer of bioink), a focusing system (to
time and pulse can be varied to control the rate and align and focus laser), an absorbing layer (ribbon- made
size of the ejected droplets [19] . Further, the desired ink of gold or platinum), and a substrate for the bioink
droplet size can be easily generated and monitored. In layer. During printing, the laser pulse is focused on the
this method, cells containing bioinks are not subjected ribbon layer that generates a high-pressure bubble
to pressure and heat, hence better cell viability [48] . In from the bioink layer which transfers the bioink onto
addition to this, nozzle-less print heads can be used to the substrate (Figure 5).
avoid exposing cells to shear stresses which may also The resolution of the laser-assisted bioprinting sys-
improve cell viability [49] . However, an important pro- tem depends on the laser energy, air gap between the
blem involved in this type of printing is the use of absorbing layer and substrate, nature of the substrate
15-25 kHz frequencies to eject ink, which causes cell surface, surface tension and viscosity of the bioink [57] .
membrane damage [50] . Also, it is hard to use bioinks It is a nozzle-free printing method, and hence clogging
with high viscosity [24] . of bioink/cells can be completely avoided. However,
In thermal inkjet printers, a pulsed pressure is gen-
erated to eject the ink by applying electrical heat to the
print head. Various reports have demonstrated that the
heating of the print head is localized and has no effect
on the stability of the bioinks or the cell viability after
printing [50,51] . The main advantages of thermal inkjet
printers are their low cost and enhanced print speed.
However, clogging, variable droplet sizes, less direc-
tionality and poor cell encapsulation are some of the
disadvantages of thermal inkjet printers. The resolu-
tion of the inkjet printers is in the range of 20–100 μm.
These printers can print the droplets of up to picolitre
volume to achieve higher resolution; however, the
time taken for printing can be longer depending on the
size of the droplet [20,52] . In the case of bioinks, picoli-
ter droplets are difficult to achieve due to the high Figure 5. Laser-assisted printers use an absorbing layer to
viscosity. Also, the mechanical integrity of the biolog- create laser pulse pressure that creates droplet ejection from the
ical constructs could be weak post-print [5,53] . bioink layer (Adopted from ref. [19,41] ).

International Journal of Bioprinting (2016)–Volume 2, Issue 2 13