Biomedical Engineering Reference
In-Depth Information
are not resorbable (glass, carbon, aramides) in a continuous or chopped fibre
form. the easy processability caused by thermal stability at high temperature
combined with the use of economical and versatile processes (i.e. injection
moulding) rapidly enabled the market to be captured in the last decade for
devices (i.e. pins, screws, wires, plates) for fracture fixation applications.
in general, partially resorbable composites comprising copolymers of
methylmethacrylate and N-vinyl-pyrrolidone reinforced with polyamide fibres
showed quite good mechanical properties (i.e. bending modulus 3-20 GPa)
(belykh
et al
., 1981). However, the long-term effect of bio-inert, biostable or
slowly degradable fibres is not well documented in living tissue and recent
studies have demonstrated the presence of an acute or chronic inflammatory
reaction in some cases under specific conditions with the detection of a thin
encapsulating membrane of mature connective tissues around the implant
region.
in this context, totally degradable reinforced composites may represent
the main goal in the design of new fixation materials because of the drastic
decay of long-term problems induced after their digestion by living tissues
(ambrosio
et al
., 2001). More specifically, an interesting strategy may be the
development of composite scaffolds composed of polymers with different
degradation rates. the capability to control composite morphology by the
selection of materials with well-known degradation kinetics, certainly offer
a significant opportunity to guide tissue formation within the composite after
their implant. to date, several approaches are investigating the ability to
overcome these limitations even if the most promising strategy provides the
development of composites with either dicarboxylic acid or an organic polymer
(Pal
et al
., 1995). Manifold processes such as pultrusion and compression
moulding are more complicated and less economical than other techniques,
limiting their application in highly advanced technologies. instead, improved
mechanical properties with constrained costs may be obtained by filament
winding technologies (Dauner
et al
., 1998).
in this direction, ambrosio and co-workers proposed a composite structure
obtained by merging a Hydrotane matrix with continuous fibres of PLA
and PGA helically wound by filament winding technique in order to design
porous and non-porous tubular constructs (Fig. 9.3a). The approach consists
of applying the composite theory to design composite biodegradable systems
able to mimic the structural organization and performance of living tissue
(ambrosio
et al
., 2001). Continuous fibres are preliminarily preimpregnated
into a Hydrotane/DMAC (dimethylacetammide) solution and then helically
wound on the polyethylene (PE) hoses with the desired outer diameter. After
winding, once removed from the machine, the composite is inserted in an
ethyl alcohol bath to remove the solvent. Finally, the Pe hose was removed to
obtain three-dimensional (3D) composite constructs with a tubular shape.
Similarly, fibre reinforced composite scaffolds may be fabricated by the
