Page 56 - IJB-3-1

Laser-assisted bioprinting at different wavelengths and pulse durations with a metal dynamic release layer: A parametric study

laser pulses) is not transferred into kinetical energy of It turns out that in combination with a metal DRL, a
the printing process. It is probably transferred into wide range of laser wavelengths and pulse durations
thermal energy, since significant thermal conduction can be applied and no optimal parameters really exist.
occurs within tens of nanoseconds [17] . Therefore, other laser parameters can be decisive such
A further important parameter for the printing pro- as pulse-to-pulse and long-term stability, compactness,
cess is the focusing geometry with the focal spot size or inexpensiveness. However, wavelengths and pulse
determining the relation between the laser pulse ener- durations outside the investigated range, especially
gy and intensity. Here, we investigated to what extent even longer pulse durations, might be less suitable for
the printing process is dependent on energy or inten- LaBP. Furthermore, if other absorption materials such
sity of the laser pulse. Therefore, the formation and as polymers are used, a significant effect of the ap-
velocity of the hydrogel jet were observed with the plied wavelength would be expected and UV lasers
stroboscopic imaging system; in general, a low jet are often preferred. Additionally, investigating the
velocity stands for low shear forces. It turns out that effect of the parameters laser pulse energy, focal spot
for low intensities above the threshold for printing at size, and the resulting pulse intensity also did not
about 0.7 J/cm², the jet velocity is dependent only on identify specific optimal parameters but a complex
laser pulse intensity and is independent on the focal dependence of droplet volume and jet velocities on
spot size (at least above 3000 µm²). With increasing focus geometry and pulse energy.
intensity the energy becomes a more relevant parame- In conclusion, this study does not identify the best
ter. Since the droplet volume increases with the laser
pulse energy, bigger droplets can be achieved without laser for LaBP, but demonstrates that a wide variety of
increasing shear forces. Therefore, the pulse energy lasers can be applied for LaBP with metal DRL.
has to be increased at constant intensity by increasing Conflict of Interest and Funding
the focal spot size.
The influence of the investigated laser parameters, No conflict of interest was reported by all authors. The
wavelength and pulse duration, on cell survival and authors acknowledge financial support from Deutsche
vitality has also been studied. As can be seen in Figure Forschungsgemeinschaft (DFG), the Cluster of Excel-
10, the cell survival rate is independent of the applied lence REBIRTH, and Lower Saxony project Biofabri-
wavelengths. This might be different if no absorption cation for NIFE.
layer is applied and wavelengths in the deep UV are
used. However, studies of other groups demonstrated References
high survival rates also with such wavelengths.
1. Palla-Papavlu A, Paraico I, Shaw-Stewart J, et al., 2011,
5. Conclusion Liposome micropatterning based on laser-induced for-
ward transfer. Applied Physics A, vol.102(3): 651–659.
The objective of this study was to investigate the ex- https://doi.org/10.1007/s00339-010-6114-1
istence of optimal laser parameters for the laser- 2. Schiele NR, Chrisey DB, and Corr DT, 2011, Gela-
assisted bioprinting technique and to identify these tin-based laser direct-write technique for the precise spa-
parameters if indicated. Since an optimum LaBP sys- tial patterning of cells. Tissue Engineering Part C:
tem should be equipped with a compact and relatively Methods, vol.17(3): 289–298.
inexpensive laser system, this study is limited to the https://doi.org/10.1089/ten.tec.2010.0442
parameter range of Q-switched solid state lasers with 3. Pirlo RK, Wu P, Liu J, et al., 2012, PLGA/hydrogel bi-
nanosecond and sub-nanosecond pulse durations. Na- opapers as a stackable substrate for printing HUVEC
nosecond lasers are also most commonly applied for networks via BioLP™. Biotechnology and Bioengineer-
laser-assisted bioprinting by other groups. In addition, ing, vol.109(1): 262–273.
some studies with femtosecond lasers have been pub- https://doi.org/10.1002/bit.23295
lished. However, there are no studies investigating the 4. Dinca V, Farsari M, Kafetzopoulos D, et al., 2008, Pat-
effect of the usually inalterable laser parameters terning parameters for biomolecules microarrays con-
wavelength and pulse duration on LaBP to an extent structed with nanosecond and femtosecond UV lasers.
that they could serve as a basis for a laser purchase Thin Solid Films, vol.516(18): 6504–6511.
decision. The present study should contribute to reme- https://doi.org/10.1016/j.tsf.2008.02.043
dy of this deficiency. 5. Othon CM, Wu X, Anders JJ, et al., 2008, Single-cell

52 International Journal of Bioprinting (2017)–Volume 3, Issue 1