Page 84 - IJB-6-3

LIFT hydrogel printing: A defined route for highly controlled process
2.1 Laser printing setup
The experimental setup used a pulsed fiber laser
YLPM-1-4x200-20-20 (NTO “IRE-Polus,”
Russia) with a wavelength of 1064 nm, with an
approximate Gaussian intensity profile in the
beam (M <1.3). Laser radiation was focused
2
on an absorbing layer of the ribbon using a
LscanH-10-1064 galvo scanning head (AtekoTM,
Russia) with a F-theta SL-1064-110-160 lens
(Ronar-Smith, Singapore) with a focal length of
160 mm. The system (Figure 3) formed a laser
spot with diameter of 30 μm positioning it with
an accuracy of several microns in the X-Y plane.
The range of laser energies in the experiments
ranged from 7 to 35 μJ with a pulse duration of
8 ns.
The glass slides, the donor (ribbon) and acceptor,
were mounted on the precision optical translators
with the distance of 0.5 – 2 mm and were placed
in the working plane parallel to the lens. Using a
Figure 2. The main input parameters of the
experiments and the scheme for evaluating the
results.
80 International Journal of Bioprinting (2020)–Volume 6, Issue 3
galvo scanning system, laser radiation was moved
along the surface of the donor ribbon according to
a predetermined pattern.
2.2 Ribbon preparation
For all printing presented experiments, 1-mm
thick glass slides (25 × 75 mm) were purified by
sequential exposure to isopropanol, deionized
water, and acetone in an ultrasonic treatment for
30 s for each liquid, followed by purging with
purified air. The slides were coated with a 50-nm
thick gold layer by magnetron sputtering. The
thickness of the deposited layers was controlled
by a microinterferometer (Lomo Mii4, AO
Lomo, Russia). A hydrogel layer 200 ± 20 μm
thick was applied to the absorbing layer using
blade-coater.
Importantly, we used a gel layer of relatively
large thickness based on the following. The use
of hydrogel layers with a thickness of more than
100 μm allows (1) a significant reduction of the
effect of drying-induced hydrogel layer thickness
change of the ribbon; (2) avoidance from strong
shock stresses associated with the action of shock
waves and a reduction of dynamic stresses during
transfer ; (3) minimization of the negative effect
[34]
of high temperature and nanoparticles produced
by the absorbing layer [13,32,44] ; and (4) an increase
in system performance and the ability to transfer
quite large objects, for example, cell spheroids.
2.3 Hydrogel viscosity and evaporation
determination
For the experiments, the hydrogels were obtained
by dissolving the powder of methylcellulose
(Sigma-Aldrich – M0262), hyaluronic acid
sodium salt (Contipro - HySilk), and sodium
alginate (Sigma-Aldrich – А-2033) in deionized
water overnight with mass concentrations of 1%,
2%, and 1%, respectively.
The viscosity of the studied hydrogels was
measured using a Kyoto Electronics Manufacturing
EMS-1000 electromagnetically spinning
viscometer. The measurements were carried out in
the temperature range of 20 – 37°C, with exposure
at each temperature point for 5 min. The drying