Biomedical Engineering Reference
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Fig. 3 Distribution of phenotypes (yellow fibrous tissue; red cartilage) in an idealised model of a
fracture callus subjected to cyclic bending. Vector plots show predicted collagen fibre orientation
in the region of interest when collagen alignment was regulated by stress (left) or deformation
(right). The predicted orientations of collagen fibres [
81
] were comparable to those observed
experimentally [
25
]. Colour version available online
results in the formation of cartilage as opposed to bone tissue. These neoarthroses
exhibited preferred fibre angles consistent with those seen in articular cartilage.
Hayward and Morgan [
43
] further demonstrated that the patterns of tissue
differentiation observed experimentally could be predicted using the mechanore-
gulation theory of Prendergast et al. [
91
], providing further evidence to suggest
that both strain and fluid flow are key regulators of tissue differentiation. Nagel and
Kelly [
81
] extended the mechanoregulation model of Prendergast et al. [
91
], as
implemented by Lacroix et al. [
68
], to include a biphasic fibre reinforced consti-
tutive model for soft tissues, where the organisation of the fibre network is
regulated by the mechanical environment. Collagen fibres where assumed to align
between the principal directions of various stress and deformation measures and
depending on the local maximum principal values occurring during a bending
cycle. By simulating the effect of bending on bone defect repair, the predicted
patterns of differentiation and collagen fibre orientations in the repair tissue could
be compared to those observed experimentally [
25
]. It was demonstrated that
mechanoregulation
models
can
be
used
to
successfully
predict
both
tissue
differentiation and organisation during skeletal tissue regeneration (Fig.
3
).
3.4 Variability in Tissue Differentiation
A high degree of variability is observed in the outcome of tissue engineering as
well as in vivo experiments. In the context of tissue differentiation models, this
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