Biomedical Engineering Reference
In-Depth Information
5.4.2.2 StarchNanocomposites
The starch molecule has two important functional groups, the -OH groups
that are susceptible to substitution reactions, and the C-O-C groups where
chain breakage starts. By reaction of its -OH groups, chemical modifi ca-
tion of starch can be performed, leading to materials with various prop-
erties, and can be used as scaffolds for hard tissue engineering [17, 109,
110]. Biodegradable starch-based polymers have recently been proposed
as having great potential for several applications in the biomedical fi eld,
such as bone replacement implants, bone cements, drug delivery systems,
and tissue engineering scaffolds [111]. The development of new process-
ing techniques and the reinforcement with various (nano) fi llers has
resulted in materials with mechanical properties matching those of bone
[110]. Mendes and coworkers [18] described an extensive biocompatibility
evaluation (
in vitro
and
in vivo
) of biodegradable starch-based materials
aimed at orthopaedic applications as temporary bone replacement/fi xa-
tion implants. For that purpose, they studied a polymer starch/ethylene
vinyl alcohol blend (SEVA) and a composite of SEVA reinforced with HAp
particles (Table 5.2). As a result of their investigation it was found that
SEVA and SEVA/HAp materials did not show relevant toxicity in both
short- and long-term
in vitro
testing. Furthermore, when implanted, these
materials induced a satisfactory tissue response.
The biocompatibility of two different blends of corn-starch, SEVA and
starch/ cellulose acetate (SCA), and their respective composites with
HAp, was studied by Marques
et al.
[110]. Authors found that both types
of starch-based polymers exhibit a cytocompatibility that might allow for
their use as biomaterials. Furthermore, SEVA blends were found to be less
cytotoxic for the tested cell line, although cells adhere better to SCA sur-
face. Considering the overall behavior of SEVA, SCA and their composites
with HAp, it can be expected that their cytocompatibility will allow their
use, in the near future, in bone replacement/fi xation and/or tissue engi-
neering scaffolding applications.
5.4.2.3 CelluloseNanocomposites
Cellulose is another type of polysaccharide produced from plants, biosyn-
thesized by different types of microorganisms, enzymatic
in vitro
synthe-
sis, and chemosynthesis from glucose derivatives. Cellulose is a very high
molecular weight polymer with very highly crystalline and is infusible
and insoluble in all but the most aggressive, hydrogen-bond-breaking sol-
vents such as N-methylmorpholine-N-oxide.
Bacterial cellulose (BC)/HAp nanocomposites were examined by Wan
et al.
[111]. The most striking features of BC are its high mechanical strength
and modulus, as well as its biodegradability. Compared with other natural
biodegradable polymers, BC presents much better mechanical properties,
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