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International Journal of Bioprinting Development and characterization of AAMP for hydrogel bioink preparation

assessment of cell viability and proliferation ability post- 2.2. Preparation of alginate hydrogel for
mixing was conducted, as both measures are essential for characterization
the AAMP-mixed bioinks to be effectively used in tissue About 2.5% of sodium alginate (high molecular weight;
engineering. Together, the experimental and simulation Sigma-Aldrich, MO, USA) was first prepared in deionized
results provided instructive information on how to water with red food dye. About 6% of xanthan gum
achieve high-quality hydrogel bioink with homogeneity. (Sigma-Aldrich, MO, USA) solution was then prepared in
Beyond being a viable option in terms of its efficacy, deionized water separately with blue food dye and 2 mg/mL
our design with chassis size can be extended/reduced CaSO slurry (Sigma-Aldrich, MO, USA). The two separate
4
and movable stop sensors allow for a “one-size-fits-all solutions were then vortexed and left overnight to reach
approach”, in which the AAMP can accommodate various homogeneity. Then, the two solutions were centrifuged
syringe lengths and mixing volumes. For all these reasons, at 3000 rpm for 4 min to remove air bubble. A volume
we believe that the AAMP holds great promise in hydrogel of 1.5 mL of each of the solutions was then loaded into
bioprinting and tissue engineering. the 10-mL syringes, and mixed at 1:1 ratio using AAMP.
In the colorimetric test, 2.5% of sodium alginate and
2. Materials and methods 6% of Laponite (BYK, USA), or 20% polyethylene glycol
2.1. Design and set-up of the device dimethacrylate (PEGDMA; molecular weight = 1000) and
6% of xanthan gum were also used for mixing outcome
The AAMP is composed of a chassis, two pushing blocks, evaluation with red and blue dyes, respectively.
two holding blocks, a stepper motor (Nema 17) with a
TB6600 (Toshiba) driver and 24V power supply (Figure 1). 2.3. Rheological characterization
A 1/4”-20 lead screw is connected to the stepper motor for 2.5% of sodium alginate and 6% of xanthan gum solution
linear motion. All structural components were designed were prepared separately. Their viscosities were measured
in Solidworks and 3D printed (Dremel) with polylactic using flow ramp tests with an ARES-G2 rheometer (TA
acid (PLA). During operation, the holding blocks held the Instruments, DE, USA). For the flow ramp test, the shear rate
syringe barrels in place, while the pushing blocks, attached was gradually increased from 0 to 100 1/s, while the stress and
to the motor through a common lead screw, moved viscosity were recorded and plotted. Moreover, to study the
the syringe pistons back and forth, creating the cyclic effect of gelation on viscosity, the two solutions were mixed
pumping motion. The movement was programmed and thoroughly, and the viscosity of the mixture was continuously
controlled by an Arduino Uno. Both the TB6600 motor monitored for 10 min under a shear rate of 10 1/s.
controller and the 24 V power supply were specifically
chosen to allow for a speed sufficient for both adequate 2.4. Characterization of hydrogel mixing
mixing and overcoming the pressures inside the syringe. After mixing, the homogeneity of the hydrogel was
The baseline speed used in the following experiments, analyzed by colorimetry method. Our analysis includes
unless stated otherwise, is 3000 rpm. Added on either comparison of hydrogel with and without the alginate/Ca
2+
side of the chassis was proximity sensors (Gikfun MC-38 reaction, differing mixing cycles (5, 10, 20, 30, and 50) and
wired door sensor magnetic switches for Arduino) for differing speeds (750 rpm, 1500 rpm, and 3000 rpm) of
limiting the range of motion of the pushing blocks. A pair the same mixing cycles. The speeds of 750 rpm, 1500 rpm,
of 10-mL syringes (inner diameter 14.4 mm) was inserted and 3000 rpm correlate to theoretical linear speeds of
into the device and connected through a female-female 952.5 mm/min, 1905 mm/min, and 3180 mm/min. After
syringe connector (inner diameter 4.3 mm). While a mixing, the dye-containing gel mixture was extruded
volume of 10 mL was chosen, syringes of larger and and sandwiched between two glass sides separated by
smaller volumes can be loaded and inserted as well. SecureSeal™ imaging spacers. Pictures of the gel mixture

Figure 1. Top view of the automated dual-syringe mixing device with (a) device body, (b) syringe-syringe female connecter, (c) NEMA 17 motor,
(d) TB6600 motor controller, (e) Arduino Uno, and (f) 24V power supply.

Volume 9 Issue 4 (2023) 401 https://doi.org/10.18063/ijb.705