Mechanical Properties of Bone at the Sub-‐lamellar Level.
Abstract
Bone
is
a
complex
fibrous
biological
nanocomposite
material
optimized
to
avoid
catastrophic
failure
and
to
perform
a
variety
of
mechanical
functions,
most
notably
load
bearing.
The
fracture
behaviour
of
bone
is
expected
to
be
controlled
by
the
various
structural
features
present
across
the
many
existing
hierarchical
length
scales.
Micron
sized
bone
lamellae
present
the
simplest
composite
unit
in
bone
consisting
of
mineralized
collagen
fibrils
within
a
protein
matrix,
with
some
work
suggesting
that
this
length
scale
dominates
the
fracture
of
whole
bone.
However,
the
synergy
between
the
bone
components
even
at
these
relatively
small
length
scales
is
poorly
understood.
The
aim
of
this
work
is
to
therefore
examine
the
mechanical
properties
of
bone
at
length
scales
where
the
bone
material
itself
can
be
considered
as
a
composite
material.
To
achieve
this,
discrete
volumes
of
bone
corresponding
to
the
sub-‐lamellar
unit
were
mechanically
tested
using
an
in
situ
Atomic
Force
Microscope
(AFM)
while
monitoring
using
Scanning
Electron
Microscope
(SEM).
The
elastic
modulus
of
sub-‐lamellar
bone
units
mechanically
tested
by
the
AFM
in
a
bending
configuration
within
the
SEM
was
shown
to
be
similar
in
both
wet
and
SEM
vacuum
conditions,
indicating
that
the
SEM
vacuum
is
insufficiently
strong
to
drive
off
water
from
hydrated
bone
samples
at
lamellae
length
scales.
AFM-‐SEM
mechanical
testing
was
extended
to
determine
the
structural
effects
of
collagen
fibril
orientation
in
bone
sub-‐lamellar
units
on
both
elastic
modulus
and
fracture.
Final
experiments
examined
small
scale
mechanical
properties
of
osteoporotic
Mechanical
Properties
of
Bone
at
the
Sub-lamellar
Level
Queen
Mary
University
of
London
3
bone,
with
results
highlighting
how
osteoporosis
has
little
effect
on
the
strength
of
the
bone
material
but
lowers
the
elastic
modulus.
This
work
therefore
highlights
the
use
of
small
scale
mechanical
testing
using
AFM
and
SEM
to
determine
the
influence
of
structural
organization,
specifically
collagen
fibril
orientation,
and
compositional
changes
induced
by
osteoporosis
on
resultant
bone
material
behaviour.
Authors
Jimenez Palomar, InesCollections
- Theses [4490]