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In-Depth Information
and BC [121]. Novel BC/PVA nanocomposites hydrogels mimicking aortic heart valve
leal et behavior were prepared by applying controlled strain to the nanocomposite sam-
ples, while undergoing low-temperature thermal cycling (optimal conditions: 15% PVA,
0.5 BC cycle 5, 75% initial tensile strain) [147]. h is technique allowed the control of the
anisotropy of PVA hydrogel and gives a good control of the mechanical properties of the
materials. In another study, layered BC/PVA nanocomposite hydrogels were prepared
by means of a physical method of freezing and thawing [148, 149]. h e tensile strength
and Young modulus of the nanocomposite gels reached 1.74 and 7.82 MPa, respectively,
when composed by 15 wt% of PVA and two layers of BC.
Poly(ethylene glycol), PEG, is another synthetic water soluble polymer with
unique properties and recognized applications in biotechnology and medicine. BC/
poly(ethylene glycol) biocompatible porous nanocomposites were prepared by immers-
ing a wet BC membrane in 1% PEG aqueous solution followed by freeze-drying [150].
h e thermal stability was improved from 263ºC to 293ºC, certainly due to the strong
interactions established between BC nanoi brils and PEG chains. h ough, as expected,
the tensile properties of the nanocomposite tended to decrease when compared to BC
since PEG can act as a plasticizer to the BC network. h ese scaf olds can be used for
wound dressing or tissue engineering scaf olds. BC/PEG nanocomposites have also
been obtained by adding PEG, with dif erent molecular weights, into
G. xylinum
cul-
ture [151]. In a distinct study, the impregnation of BC membranes with 0.5-2.5% w/v
diacetylglycerol in acetone/water provided BC/PEG nanocomposites with high hydro-
philicity, smother morphology and higher ductility [152]. Diacetylglycerol performs
also as a biodegradable and safe plasticizer for the BC membranes.
In an contrasting vein, BC networks were crosslinked via glyoxylation as a way to
improve the mechanical properties of BC membranes [153]. h e enhanced stress trans-
fer ei ciency within the BC networks was demonstrated by Raman spectroscopy and
was attributed to the covalent crosslinking induced by glyoxylation. h is constitutes a
quite simple strategy; however the use of glyoxal, that is a toxic reagent, could limit the
interest of this methodology.
2.3.3
BC/h
ermoplastic (and h
ermosetting) Nanocomposites
h e reinforcement of synthetic thermoplastic (and thermosetting matrices) with BC
nanoi brils has also been comprehensively investigated by several research groups
because of their high performance and simplicity of processing. However, in con-
trast to the excellent compatibility between BC and natural polymers, one of the main
problems faced by researchers in this i eld is the poor adhesion between intrinsically
polar BC nanoi bers and non-polar synthetic polymeric matrices. Several methodolo-
gies have been reported in literature targeting this limitation. Here some representa-
tive examples for BC-based nanocomposites processing and preparation with relevant
polymers as poly(lactic acid) (PLA), polyhydroxyalcanoates (PHAs), polycaprolactone,
acrylic polymers, among others are reviewed.
PLA is a biodegradable aliphatic polyester produced from D- and L-lactic acid, com-
monly obtained from fermentation of starch enriched products like sugar beet, corn
and wheat [154]. Over the past few years, a considerable number of studies dealing
with the reinforcement of PLA with BC have been reported in literature. One of the
