Biomedical Engineering Reference
In-Depth Information
Gas Foaming
Electrospinning
Salt Leaching
Figure 33.2.
Scanning electron micrographs of porous scaffolds fabri-
cated with (a) electrospinning,
1
(b) salt leaching,
3
and (c) gas foaming.
4
Reprinted with permission from Ref. 1; copyright 2006 Mary Ann Liebert,
Inc.; Ref. 3; copyright 2002 Wiley; Ref 4; copyright 2006 Elsevier.
may impede bone healing.
28
Recently, investigators have developed
highly cross-linked, degradable networks such as poly(propylene
fumarates) (PPFs) and polyanhydrides that can be formed
in situ
using either thermal or photoinitiated cross-linking.
30
−
33
Although
biodegradable and injectable, these materials lack the porosity nec-
essary to repair critical-size defects. In contrast,
in situ-
curing
hydrogels have su
cient mass transport properties but lack the
mechanical strength necessary for orthopedic applications. A scaf-
fold fabrication method that is injectable and porous, yet retains
high mechanical strength, would provide a significant improvement
over current methods.
Emulsion templating is a relatively new method for the produc-
tionofhigh-porosityscaffolds,whichinvolvesthetemplatepolymer-
izationofHIPEs.
34
Theseheterogeneousliquid-liquidemulsionsare
characterized by an internal, droplet phase volume fraction of at
least 0.74. This limiting value represents the hexagonal packing of
thesphericaldroplets.Increasingtheinternalphasevolumebeyond
this value results in deformation of the droplets into a polyhedral
shape.
35
When the external, continuous phase is composed of a
polymerizablemonomer,itmaybepolymerizedtoformarigid,high-
porosity foam (Fig. 33.3).
Researchers at Unilever Research Port Sunlight Laboratory
(Cheshire, UK) first coined the term “polyHIPEs” to describe
these polymeric foams.
34
,
36
Initially polyHIPE foams were primarily
closed-pore architectures with the internal aqueous phase trapped
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