Publication: Procesado por técnicas coloidales y caracterización de materiales polímero/Mg para aplicaciones en la industria biomédica
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Publication date
2018-09
Defense date
2018-10-29
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Tutors
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Abstract
During recent years, PLA / Mg composite materials have emerged as new bioabsorbable
biomaterials for osteosynthesis applications. It has been proposed that the incorporation
of Mg particles into a matrix based on a biodegradable polymer can address, on the one
hand, the lack of bioactivity and the low mechanical properties of the polymers and, on
the other, the high rate of degradation or corrosion of Mg and its alloys. Many methods
for the preparation of polymer/bioinorganic material have been reported, some typical
examples are extrusion mixing, compression molding and solvent casting. The
manufacture challenge of these materials is to achieve a particle homogeneous
dispersion in the final PLA structure.
This work reports on a novel processing route that is based on a colloidal mixture of Mg
powder and PLA aimed to prevent the drawbacks associated to the polymer degradation
during the mixing step of conventional thermoplastic routes and increase the maximum
load achieved (10% by mass) during conventional routes. To fulfill this requirement it
was necessary to improve the PLA-Mg interaction, as well as to increase the dispersion
of the Mg in the final mixture through the surface modification of particles. Mg was
modified by the adsorption of two different stabilizers, a surfactant (CTAB) and a
polyelectrolyte (PEI). The dispersed and chemically stable suspension of modified Mg
particles was mixed with the PLA solution in THF, and was used as feedstock material
to obtain tapes, by tape casting, and granules, by drying the mixture under reduced
pressure conditions. Besides, these granules were used as feedstock for further
manufacturing of bulk cylinders by compression moulding and 3D printing scaffolds by
Fused Deposition Moulding (FDM).
The results show that, in the tapes, particle surface modification is directly associated
with good load dispersion through interactions between groups present in the PLA and
in the stabilizers either by the formation of hydrogen bonds or by ionic and electrostatic
interactions. In the case of granules and compression moulding cylinders it is observed
a covalent bond between PEI and PLA, which is produced by the temperature applied
during processing.
Mechanical behaviour was evaluated in terms of nanoindentation, mechanodynamics
and tensile properties for tapes, and compression for compression moulding cylinders.
In the case of tapes, a Mg reinforcement effect in the matrix is observed at the proximity
of the particles. Young’s module and strength improve in tapes with up to 10 wt.% of
Mg. At higher particle content, tensile mechanical improvement could not be verified
due to fragilization of the materials. The thermopressed composites present a more
evident improvement in the mechanical properties under compression with respect to
the neat polymer, observing an increase of 10% in the elastic modulus for composites
with 30 wt.% of Mg.
Regarding in vitro behavior, degradation and viability tests were carried out to verify
that the new processing defined does not affect the biocompatibility and viability of
PLA/Mg composites. The hydrogen release test shows that no material exceeds the
amount tolerable by the human body, although the release is not proportional to the
load, which is associated with a process of autocatalytic degradation. In the case of
tapes, materials processed with modified Mg particles with PEI release less hydrogen
than those modified with CTAB. Concerning biological tests, it is proved that the
released components during the degradation of the composite do not produce
cytotoxicity at the cellular level with fibroblastic cells (MEF) or stromal cells (ST-2).
Finally, the direct tests carried out on the composite tapes allow concluding that for all
the materials, except for the sample with 50 wt.% Mg, there is a significant increase in
cell viability in comparison with the polymer matrix.
Description
Mención Internacional en el título de doctor
Keywords
Materiales compuestos PLA/Mg, Polímeros biodegradables, Biomateriales, Procesado coloidal, Técnicas coloidales, Osteosíntesis, PLA/Mg composites, Biodegradable composite materials, Biocomposites, Osteosynthesis