Biomedical Engineering Reference
In-Depth Information
7.3.1 PEG-PPG Block Copolymers as in situ -Forming
Hydrogel Scaffolds
Triblock copolymers (poly[ethylene oxide]-b-poly[propylene oxide]
-b-poly[ethylene oxide], PEO-PPO-PEO), known as Pluronics R
(BASF) or Poloxamer (ICI), are initially commercialized nonionic
surfactants. In the past few decades, Pluronics perhaps is the most
intensively investigated thermo-response polymer for biomedical
application. 35
PEG and PPG blocks exhibit hydrophilic and hydrophobic prop-
erties, respectively. By adjusting the composition, aqueous solu-
tionsofcommercialPluronicsorPoloxamerseriescanexhibitphase
transitions from sol-to-gel at physiological temperature. 36 , 37 These
block copolymer solutions became gel-faster at body temperature,
but the gels formed are mechanically weak and have limited sta-
bility and short residence times, resulting in relatively rapid ero-
sion of the gels at the injection site. In addition, block copolymers
are nonbiodegradable polymers. To circumvent the drawbacks of
common Pluronic gels, multiblock Pluronic copolymers via linking
biodegradable carbonate, ester, disulfide, urea, or urethane bonds
were designed and synthesized. 38 - 40
Despite these disadvantages, Pluronics have been tried in tis-
sue engineering as in situ -forming hydrogels. Matthew et al .inves-
tigated the effect of mammalian cell culture medium compared to
pure water on the gelation properties of Pluronics. There is no dif-
ferenceinthethermodynamicsofgelformationbetweencellculture
medium and pure water. 41
Pluronics represent a bio-inert environment attributed by the
hydrophilicity and flexibility of PEO chains. 42 It was shown that a
Pluronic gel can be a good substrate for hematopoietic stem cells,
supporting their culture and preservation more than conventional
tissue culture dishes. 43 , 44 Maheu et al . have studied the effect of
Pluronics on osteoblast viability and phenotype maintenance in
vitro . When supplemented with osteoactive factors, a Pluronic gel
couldbeusedasacellcarrierwithoutalteringosteoblastphenotype
for bone tissue engineering. 45 A Pluronic gel was also reported as a
scaffold for osteoblastic differentiation of rabbit mesenchymal stem
cells. 46 Toincreaseclinicaldemandforadiposetissue,aPluronicgel
 
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