2.4 3D printing of A-SA-Gel hydrogel scaffolds
To fabricate the A-SA-Gel hydrogel scaffolds, an in-house built
extrusion-based 3D printing system was employed. The schematic
representation of the material preparation and printing process is shown
in Figure 1A. The system and solution parameters were optimized prior to
3D printing. Briefly, the printing system was designed with a computer
controlled automated X–Y–Z stage, a receiving platform, a nozzle
mounting block, a printer head (syringe needle), and a pneumatic
(pressured-air) system, which consist of compressor, air tube, and
control valve. The syringe needle was directly connected with the
pneumatic system through air tubes. The pneumatic controller provided
air pressure for extruding hydrogel material. The receiving platform was
mounted in the X-Y plane that was capable of printing with high
precision; the syringe needle mounted to a solo motorized linear Z-axis,
and it can be controlled to move up and down. The prepared A-SA-Gel
hydrogel was gently added to a 50 ml syringe, and a 22G needle was used
for extrusion printing.
In order to print a grid-structured scaffold, as a model scaffolding
system, having the size 20 ×20 × 5 mm (L×W×H), and the following
parameters were used. The interval of parallel-arranged filaments within
the grid structure was kept 0.6 ± 0.1 mm in each layer, and adjacent
layers were perpendicularly stacked to construct the porous structure.
During the printing process, the prepared A-SA-Gel hydrogel was extruded
from the syringe needle to generate continuous filament at room
temperature, and the extruded filaments deposited layer-by-layer to form
the grid-structured A-SA-Gel hydrogel. A stable air pressure value of
2.8 ± 0.1 Psi was applied to extrude hydrogel. After printing, the
hydrogel was crosslinked with CaCl2 solution (4%, w/v),
followed by oven-dried for 3 h at 37 °C.
In addition, a thick scaffold
structure (10(L)×10(W)×10(H) mm), blood vessel structure (12mm in
diameter, 15mm in height), the abbreviations of Shanghai University
(SHU) and Vellore Institute of Technology (VIT), and human ear models
were also printed under the optimal conditions, in order to further
evaluate the 3D printability and self-standing ability of the A-SA-Gel
hydrogel, in terms of various shapes, sizes and structures.