Page 106 - IJB-6-2

Scaffolds produced by combining porogen leaching and emulsion templating
2.2 PolyHIPE synthesis (45 × 45 × 6.2 mm), filled with approximately
12.5 mL of HIPE and placed under 100 W UV
For the continuous phase of the emulsion, the light (Omnicure S1500 with adjustable spot
monomer 2-ethylhexyl acrylate (26 g) was mixed with collimating adaptor, Excelitas Technologies), for
the crosslinker trimethylolpropane triacrylate (7 g). 180 s on both sides. With these dimensions and
The surfactant Hypermer B246-SO-(MV) was added exposure times the polyHIPEs were fully cured
at 10 wt% (3.3 g) relative to the total weight of the
acrylates (33 g) and mixed until dissolved. To create with no cavity left in the center of the monolith.
the emulsion, 2 g of this stock solution was taken and The polyHIPEs were removed from the mold
a photoinitiator (diphenyl (2,4,6-trimethylbenzoyl) and washed in acetone to remove any uncured
phosphine oxide/2-hydroxy-2-methylpropiophenone) monomer. To remove the alginate, polyHIPEs
was added at 5 wt% (0.1 g). This solution was were soaked in 0.2 M sodium citrate in diH O
2
continuously mixed at 350 rpm using a paddle stirrer for 2 h with sonication. The samples were then
(Pro40 scientific stirrer, SciQuip). While mixing, dried overnight under vacuum. A schematic of
diH O (diH O, 18 mL) was added dropwise to form the fabrication process is given in Figure 1. To
2
2
a 90 vol% W/O HIPE. Where alginate beads were produce cubes for cell culture the outer surfaces,
incorporated, beads were patted dry and weighed, including the top surface and polymer skin on the
then either 50 or 100 wt% relative to the total amount glass cured sides, were removed using a scalpel.
of emulsion was added to the HIPE (e.g. 100 wt% The remaining bulk polyHIPE was then cut into 5
means 4 g of beads were added to 4 g of HIPE). × 5 × 5 mm cubes.
The blend was then stirred for a further 2 min at To produce cylinders for mechanical testing,
350 rpm to homogenize the beads. Herein, these three the HIPE was polymerized in a 3 mL syringe
compositions will be referred to as “plain,” “50 wt%,” (internal diameter 8.2 mm). The cylinders were
and “100 wt%” polyHIPEs. This refers to the content washed using the same methods described above
of the alginate bead porogen in the HIPE. and then cut into 10 mm lengths. The surface skin
To polymerize the emulsion, it was poured into surrounding the outside of these cylinders was
a square, PTFE mold with a glass base and top retained to keep a constant volume of material.

Figure 1. Schematic detailing the alginate-leached polymerized high internal phase emulsions synthesis.
A 90% internal phase volume HIPE is synthesized by adding water to the continuous phase. Alginate
beads are produced by injecting an alginate solution to calcium chloride and sieving. Alginate beads are
then mixed into HIPEs at either 0, 50 or 100 wt% of the HIPE. Emulsions are then UV polymerized,
washed in acetone and the alginate dissolved using sodium citrate. Macropores within the bulk of the
polyHIPE left by alginate beads are clearly visible in the 50 and 100 wt% scaffolds.

102 International Journal of Bioprinting (2020)–Volume 6, Issue 2