Biomedical Engineering Reference
In-Depth Information
For musculoskeletal tissue engineering, scaffolds made out of silkworm
silk have been widely used to tissue engineer anterior cruciate ligaments,
bone, and cartilage [228-230]. Unlike many other scaffolds, silk scaffolds
facilitate cell attachment and cell spreading without further modifica-
tions [231]. Recent studies using matrices made out of silk demonstrates that
human MSCs (hMSC) adhere to them [230, 232]. Silk is known for its slow
degradation kinetics and possesses biocompatible properties comparable to
that of PGA and collagen [231]. The proteolytic degradation rate is mainly
dependent upon the environmental conditions. Particularly, silk degrades
completely within two years in vivo [231].
From the ongoing discussion it is clear that using natural polymers as tis-
sue engineering scaffolds offer a wide range of advantages such as biological
signaling, cell adhesion, cell responsive degradation and re-modeling. How-
ever, these materials lack adequate mechanical properties which compromise
their utilization as unique scaffold materials. Another major concern of using
natural materials is the possibility of immuno-rejection, and can also transfer
various viruses even though proper screening and purification can overcome
these limitations. To this end, various synthetic polymers have been specific-
ally developed for tissue engineering scaffolds.
Synthetic Hydrogels
Recent years have witnessed a surge of interest in using synthetic hy-
drogels in tissue engineering approaches, and the most appealing factor
about them is that their properties such as hydrophilic-hydrophobic bal-
ance, mechanical and structural properties, degradation profile, etc. can
be molecularly tailored. Poly(ethylene oxide) (PEO), poly(ethylene glycol
diacrylate) (PEGDA), poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA),
poly(acrylamidomtheyl propane sulfonic acid) (PAMPS), poly(hydroxyl ethyl
methacrylate) (PHEMA), and poly(propylene fumerate-co-ethylene glycol)
(see Fig. 5) are just a few examples of synthetic polymers used to create hy-
drogels and have found applications as tissue engineering scaffolds.
Poly(ethylene oxide) (PEO) : PEO and its oligomer poly (ethylene gly-
col) (PEG) are widely used in various biomedical applications because of
their biocompatibility, hydrophilicity, and resistance to protein adhesion and
cell adhesion [123, 233]. It has been reported that PEG-modified proteins
exhibit decreased immunogenicity and antigenicity at an increased circu-
lation time in the body [234]. PEGDA with a molecular weight less than
20 000 Da can be dissolved in body fluid and can be eliminated from the
body via excretion through the kidneys [233]. The resistance of PEG to pro-
tein adhesions has been widely used to create nonfouling surfaces, where
PEG chains are immobilized onto the surface by covalent bonding or ad-
sorption [9, 235]. The biocompatibility and hydrophilicity of PEG has been
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