Biomedical Engineering Reference
In-Depth Information
the prosthesis and the bone. Finite element models (FEM) combined with
a mathematical description of adaptive bone remodelling suggest high
performances of composite prostheses in terms of mechanical stability and
tissue conservation (Van Rietbergen
et al
., 1993; mihalko
et al
., 1992; Kuiper
and Huiskes, 1997; Apicella
et al
., 1994; Peluso
et al
., 1994).
Based on the rapid prototyping, silicon mould and filament winding
technology, a replica of a human mandible has been obtained. the spongy
bone is simulated by using poly(methylmethacrylate) (PMMA) bone
cement. the cortex of the mandible has been replicated by using a glass
fibre reinforcement. The orientation of the windings are chosen according
to the osteons' orientation of a human mandible, mainly oriented at 45° in
the ramous and at 0° in the mandible arch (De Santis
et al
., 2004, 2005,
2007b).
early examples of composite biomimetic design are also well documented
for dense connective tissues, ligaments and intervertebral disc. Hydrogel
consisting of poly(hydroxyethylmethacrylate) PHEMA and poly(caprolactone)
PCL reinforced with PET fibres was used to mimic the intervertebral disc.
Using a filament winding machine, samples with a softer and more hydrophilic
inner part (i.e. nucleus) and a harder and less hydrophilic outer part (i.e.
annulus) were made. By varying the composition of the hydrogel matrix, the
winding angle and the quantity of PET (polyethylenetelephthalate) fibres, it
has been possible to modulate the hydrophilicity and the mechanical properties
of intervertebral disc prosthesis (ambrosio
et al
., 1996, 1998a, 1998b).
Composite structures based on a polyurethane matrix (HydroThaneTM)
reinforced with PET fibres were designed and realised by filament winding
in order to model the morphology and mechanical properties of natural
ligaments and to reproduce the typical J-shaped stress-strain curve, displayed
by natural tendons and ligaments (De Santis
et al
., 2004). By using a PEI
matrix reinforced with carbon fibres through filament winding technology,
a composite cage has also been developed (manto
et al
., 2005).
9.5 Biodegradable composites
Currently, much research work has been addressed to the production of
bioresorbable surgical devices for hard tissue repair. in fact they avoid the
employment of surgical operations for their removal, reducing the pain of
the patients and the total cost of the treatment with a significant advantage
in terms of life quality of the patients (Daniels
et al
., 1990).
traditionally, metals such as stainless steel, titanium and Co/Cr alloys
were commonly used for fracture fixation. Although they provide the right
strength and rigidity to align and control bone motion during healing, they
are much stiffer than bone (
E
m
= 100-200 GPa and
E
b
= 6-20 GPa) carrying
the majority of the load. as result of the large difference in stiffness between
