EMULSION TEMPLATING - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 674

polystyrene (PS) network, a significant amount of PCL diol was
removedduringpurificationofthepolyHIPE.Initialcellculturestud-
iesindicatedthatthesemi-IPNmonolithssupportthegrownanddif-
ferentiation of mouseskeletal cells.
33.4.3 Fully Degradable: Fumarate-Based PolyHIPEs
Although several studies have examined semidegradable polyHIPEs
based on styrene or MMA copolymer systems, Christenson et al .
reported the first fully biodegradable polyHIPE based on fumarate
macromers. 37 PPF is an unsaturated polyester that biodegrades via
esterhydrolysisintothebiocompatiblecompoundsfumaricacidand
propylene glycol. 52 When reacted with the cross-linker propylene
fumarate diacrylate (PFDA), this system forms a highly cross-linked
network that imparts mechanical strength su cient for its use in
bone tissue engineering scaffolds. Previous studies with fumarate-
based scaffolds have demonstrated its biocompatibility, biodegrad-
ability, and osteoconductivity. 52 − 54
Similar to previous polyester-based polyHIPEs, toluene was uti-
lized as a diluent to reduce the viscosity of the organic phase to
enable HIPE formation. A range of polyHIPE scaffolds of different
pore sizes and morphologies were generated by varying the dilu-
ent concentration (40%-60 wt%), cross-linker concentration (25-
75wt%),andmacromermolecularweight( M n = 800-1000g/mol).
Although some formulations resulted in macroporous monoliths
(pore diameter > 500 μ m), the majority of the polyHIPEs studied
were rigid, microporous monoliths with average pore diameters in
the range of 10-300 μ m. Gravimetric analysis confirmed the poros-
ity of the microporous monoliths as 80%-89% with most scaffolds
above 84%. PolyHIPEs with pores greater than 50 μ m had a closed-
pore morphology, whereas scaffolds with pores smaller than 50 μ m
had an open-pore morphology (Fig. 33.7).
These two morphologies were attributed to differences in film
thickness between the droplets at the gel point. It was concluded
thatthesmallerdropletsizeresultedinareductionoffilmthickness
below the threshold value that results in interconnect formation.
Unlike the vinyl-terminated PCL and PLA systems, the fumarate-
based HIPEs generated rigid, microcellular foams without the