Biomedical Engineering Reference
In-Depth Information
Pluronics, forms thermoreversible hydrogels in aqueous environments and
has been used in various biomedical applications including tissue engineer-
ing scaffolds [237]. Our laboratory uses PEGDA scaffolds for cartilage engin-
eering where photopolymerization of PEGDA is used to encapsulate chon-
drocytes, MSCs, and ES (Hwang et al, 2005, personal communication) [22,
24]. Our findings indicate that PEGDA serves as an efficient scaffold for
anchorage-independent cells such as chondrocytes and also helps in tissue
formation. Recently, our laboratory has also started exploring the possibil-
ity of using PEGDA hydrogel for guided regeneration of damaged cartilage
(Casio et al, 2005, personal communication). We use micro-drilling to achieve
migration of MSCs from the bone marrow to the defect site. Here, we hypoth-
esize that the hydrogel will provide an adequate niche for the migrated MSCs
to produce hyaline cartilage over fibrous cartilage. The nonadhesive nature
of PEGDA hydrogels prevents the cells from adhering onto an unmodified
scaffold. Hence, researchers have incorporated various peptides to impart ad-
hesive properties to PEGDA [238]. Another major concern about the use of
PEGDA is their nondegradable nature, which has been circumvented through
the introduction of various degradable groups onto the polymer, although
some degradation is observed when the material is in contact with cells or
implanted [239, 240].
Poly(vinyl alcohol)
: PVA is a hydrophilic polymer and is generally prepared
from poly(vinyl acetate) by hydrolysis, alcoholysis, or aminolysis [241]. PVA-
based hydrogels have previously been used in various drug delivery devices
such as artificial pancreas because of their biocompatibility [242]. Physical
crosslinking of PVA can be achieved by repeated freeze-thawing of aqueous
PVA solutions [243, 244]. The crystallites formed during the freeze-thawing
process are responsible for creating the network [110]. The resulting network
is stable and highly elastic at room temperature [245]. However, at higher
temperature the crystallites melt, lose their stability, and dissolve in the solu-
tion. PVA can also be crosslinked chemically by using bi-functional crosslink-
ing agents such as glutaraldehyde [104]. Boeckel et al. have used hydrogen
bonds between PVA and amino acids to create novel cell-interactive hydro-
gels [9, 246]. Polyvinyl alcohol has also been modified with methacrylate
groups to form photocrosslinkable polymers [133]. Unlike other hydrogels,
PVA-based hydrogels possess good mechanical properties. Their mechanical
properties have motivated many researchers to create PVA-based biomaterials
for various biomedical applications such as artery, knee cartilage, and inter-
vertebral disc replacements [245, 247-252]. Salubria is one such PVA-based
biomaterial developed for artery and cartilage replacement.
Poly (fumerates)
: Biomaterials based on poly(propylene fumerate) (PPF)
have been extensively used for orthopedic application such as injectable bone
cement [253]. Unlike PEGDA and pluronics, fumerate-containing polymers are
biodegradable since the ester link in the polymers can be cleaved hydrolyt-
ically. PPF is hydrophobic, and in order to synthesize hydrogels, it has been
