Biomedical Engineering Reference
In-Depth Information
sponses to the chitosan systems as stated above can complicate their applications to some
degree. The composite chitosan-collagen-soybean phosphatidylcholine film impregnated
with MMC-PLA-nanoparticles for treatment of hepatocellular carcinoma in mice has exhib‐
ited some special characteristics compared with pure chitosan delivery systems. In vivo, the
growth of the tumors were inhibited considerably and dose-dependently by the MMC-film
(P<0.05) with no any signs of vice reactions, such as inflammation, infection, and fibrous en‐
capsulation after 20d of implantation [16,146,147]. Thus a careful balance between the im‐
mune reaction and drug effectiveness is needed when a chitosan pertaining template is used
for biomedical applications.
10. Polyglycolide (PGA), Polylactide (PLA) and poly(Lactic-co-Glycolic
Acid) (PLGA)
Polyglycolide also named polyglycolic acid (PGA) is a biodegradable, thermoplastic poly‐
mer and the simplest linear, aliphatic polyester which contains the ester functional group in
it's main chain [148]. It can be prepared starting from glycolic acid by means of polyconden‐
sation or ring-opening polymerization. PGA has been known since 1954 as a tough fiber-
forming polymer. Owing to its hydrolytic instability, its use has initially been limited [149].
In vivo
, PGA initiates a marked host reaction around the implantations. This leads to the de‐
velopment of a foreign body response that comprises an initial acute inflammatory phase
and a subsequent chronic inflammatory phase. For example, when a synthetic PGA scaffold
seeding with adult-derived or somatic lung progenitor cells from mammalian lung tissue
was implanted in an immunocompetent host, a serious foreign body response totally altered
the integrity of the developing lung tissue [150].
Polylactic acid or polylactide (PLA) is another thermoplastic aliphatic polyester derived
from renewable resources, such as corn starch, tapioca products, and sugarcanes [30]. A
poly(L-lactide) (PLLA) coil stent has ever been implanted in pigs with no stent thrombosis
and late restenosis [151]. However, PLA, as well as PLLA, and poly(D,L-lactide) (PDLA), in‐
duces a strong inflammatory response when they are implanted in the body due to their
acidic products [152]. Aframian and coworkers implanted tubular PLLA, PGA coated with
PLLA (PGA/PLLA), or nothing (sham-operated controls) in Balb/c mice either beneath the
skin on the back, and found that inflammatory reactions were shorter and without epithe‐
lioid and giant cells in the sham-operated controls. Tissue responses to PLLA and PGA/
PLLA scaffolds are generally similar in areas subjacent to skin in the back and oral cavity.
Biodegradation proceeded more slowly with the PLLA tubules than with the PGA/PLLA tu‐
bules. No significant changes in clinical chemistry and hematology were seen due to the im‐
plantation of tubular scaffolds. [153]. It was reported that, after the PLLA segments were
swallowed
in vivo
by phagocytes, cell damage and cell death were obvious. The highest
numbers of necrotic cells were observed on day 2 [154]. These reactions can result in an un‐
expected risk for patients and have strongly limited in clinical applications of this kind of
biomaterials.
Search WWH ::
Custom Search