Biomedical Engineering Reference
In-Depth Information
scaffolds.
19
After injection of the hybrid structure of chondrocyte
cells and biodegradable hydrogels, hydrogels degraded
in vivo
,and
then neocartilage tissueremains.
Also, copolymers of PEO and poly(propylene oxide) (PPO), such
as PPO-PEO-PPO or PEO-PPO-PEO block copolymers, are the basis
for Pluronics
R
and Tetronics
R
. Pluronics
R
forms a thermosensi-
tive gel by the shrinking of hydrophobic segments of the copolymer
PPO.
1
Thephysicochemicalpropertyofhydrogelscanbevariedwith
the composition and structure of the ratio of PPO and PEO. Some of
themhavebeenapprovedbytheFDAandtheEnvironmentalProtec-
tionAgency(EPA)fortheapplicationsinfoodadditives,pharmaceu-
ticalingredients, andagricultural products. Althoughthepolymer is
notdegradedbythebody,thegelsdissolveslowly,andthenthepoly-
meriseventuallycleared. Thesepolymershavebeenappliedforthe
treatmentofskinburnsandproteindelivery.Theseinjectablehydro-
gels have advantages such as no surgical operation, easy pore size
manipulation, and no need for the fabrication process of complex
shapes.
1.2.3.5 Polyvinylalcohol
PVA is a hydrogel resulting in the containing of water content,
especially similar to that of cartilage. It is relatively biocompatible,
swelling to hold a large amount of water, is easily sterilized, and
is easily fabricated and molded into desired shapes. It has reactive
pendant alcohol groups that are available for modification such
as chemical cross-linking, physical cross-linking, or incorporation
of an acrylate group resulting in the improvement of mechani-
cal properties. Changing the ratio of PVA and water, the molecu-
lar weight of PVA, and the quantity and duration of freeze/thaw
cycles can control the physical properties of PVA hydrogels. PVA
has been applied to cartilage regeneration due to similar mechan-
ical properties, breast augmentation, diaphragm replacement, and
bonereplacement.
20
Oneofthesignificantdrawbacksisitisnotfully
biodegradable because of the lack of labile bonds within the poly-
mer backbone. So, it is recommended that low-molecular-weight
PVA around 15,000 g/mole, which can be penetrated through the
kidney, mightbeapplied to the tissueengineering scaffolds.
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