Biomedical Engineering Reference
In-Depth Information
Figure 33.3.
Schematic of the polyHIPE process.
within the cellular structure. In 1982, Unilever scientists gener-
ated open-pore polyHIPEs using low-hydrophile-lipophile-balance
(HLB) surfactants with the styrene-divinylbenzene system.
34
The
open-pore structure facilitated the rapid removal of the aqueous
dispersed phase and resulted in low-density foams of less than
0.1 g/cm
3
.
37
A wide range of porosities (75%-99%), pore sizes (5-
100
μ
m), and closed- or open-pore morphologies can be achieved
by varying the HIPE composition.
34
,
35
,
37
−
43
The windows between
poresformwhenthethinfilmseparatingdropletsopensduetopoly-
mer shrinkage during polymerization. Thus, the open- or closed-
pore morphology is related to the thickness of this film and the
amount of polymer shrinkage.
37
Such materials have been inves-
tigated for a variety of uses, including solid-phase synthesis and
catalyst supports, aerosol filters, and substrates for porous Ni
electrodes.
34
,
35
,
39
,
40
,
44
Anattractivecharacteristicofthesenewpolymericfoamsfortis-
sueengineeringisthehighlevelofcontroloverthestructuralarchi-
tecture.Experimentalparametersmaybecontrolledbyvaryingsuch
factors as composition, mixing speed, and temperature to generate
either open- or closed-cell polyHIPE foams(Fig. 33.4).
Porosity (75%-99%) and pore size (5-100
μ
m) can also be tai-
lored by tuning the HIPE composition.
34
,
37
,
42
−
44
Furthermore, prior
to polymerization, the HIPE has a whipped-cream or mayonnaise
consistency that is well within the viscosity range of injection. The
homogeneous and spherical pores of the polyHIPE also eliminate
stress concentrators that can limit mechanical properties as in salt-
leached scaffolds.
45
Overall, the combination of injectability, high
porosity,andsuperiormechanicalpropertiesmakepolyHIPEsexcel-
lent candidates for tissue engineeringscaffolds.
36
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