89-91 - Polskie Stowarzyszenie Biomateriałów

leads to an increased risk of bone fractures. Treatment for
osteoporosis must correspond with the causative agent and
with the state of the patient.
There is increasing demand for the evaluation of more
bone parameters, especially in the area of mechanical stress
distribution in the bone, so we have started to study the bone
mechanical properties to various types of testing and these
are three-point bending test, femoral neck fracture and finally
nanoindentation. The main benefit is that the mechanical
properties of healthy and treated bones can be compared,
and these findings can be confronted with medical tests.
materials and methods
The experiments were performed on 16 rats with an initial
body weight of 180-200g that were divided into two groups:
I – Alcohol administration, II – baseline control. Alcohol was
administered in dose of 15µg per day added to the water.
After four months of treatment, the animals were killed by
decapitation. The left femur was removed and cleaned of the
soft tissue and immediately frozen at a temperature of -20°C.
During 24 hours before testing the bones were hydrated in
the distilled water at the room temperature.
Biomechanical testing system MTS Mini Bionix 858.02
was used for the three-point bending test (see FIG.1). The
bone was placed on two supporting bars (2 mm in diameter)
with span 15mm and loaded by rounded bar from medial
side of the rat with the loading rate 5mm/min. The program,
written for the test control in TestWare software, controls
crosshead speed and measures important quantities such
as load, displacement and time. We calculated several
biomechanical parameters of bone that can be used to
characterize the bone integrity, such as the bending strength
σ max, flexural rigidity S and the work to failure U [1].
The second experiment was performed with Hysitron
TriboLab nanoindentation system (see FIG.2) at the Faculty
of Civil Engineering at CTU in Prague. It provides in-situ
scanning of topography (SPM) and piezo automation with
precision of the indent placement less than 1µm. The Berkovich
tip works in closed environment on active antivibrating
stage. Optic set up works with 1-10x zooming system with
the zoom 5x as the default value.
The specimens for this test were prepared from fractured
bones by three-point bending testing. Bone was set in a vertical
position to its section and casted in epoxy. After curing
the bone was cut into c. 1.5mm high cylindr by the precision
sectioning saw ISOMET LS and burnished.
Traditional trapezoidal shape of loading curve (15x10x15s;
F max=7mN) was used for the indentation. The automation
method was applied on each sample in two different zones.
Grid of 3x3 indents in load control regime was used.
fIg.1. Three-point bending
test. fIg.2. nanoindentation.
Experimental results
The elastic modulus E, determinated by three-point
bending test, was calculated from the force and displacement
of the loaders:
where S is the extrinsic stiffness, L is distance
between two supporting bars and I is the
cross-sectional moment of inertia around the axis of bending.
The most common method for analyzing nanoindentation
load-displacement data is that of Oliver and Pharr.
The effective modulus Eeff is derived from
where A is the projected contact area, β is 1.034 for
Berkovich indenter and S is the unloading stiffness.
The effective modulus is related to the specimen elastic
modulus through
where E and ν are indentation modulus and Poisson’s
ratio (0.3 for bone) for the specimen, and Ei and νi are the
same quantities for the indenter (1140GPa and 0.07) [2].
The experimental results are shown in TABLE 1.
Specimen
no.
TaBlE 1. values of the elastic modulus E and mean
elastic modulus E ± Sd.
Conclusion
Three-point bending
testing
E
[GPa]
1 4.66
Mean E
[GPa]
Nanoindentation testing
E eff
[GPa]
E
[GPa]
3.64 3.32
2 6.11 3.05 2.78
3 6.93 3.54 3.23
4 6.42 5.97 ± 3.41 3.11
5 6.19 0.49 26.90 24.53
6 6.36 3.54 3.23
7 5.50 3.32 3.03
8 5.23 3.37 3.07
9 5.86
3.29 3.00
10 7.30 3.30 3.01
11 5.32 3.08 2.81
12 6.21 5.86 ± 3.38 3.08
13 4.51 0.59 3.23 2.95
14 6.02 3.00 2.74
15 6.70 3.49 3.18
16 5.08 3.52 3.21
Mean
E
[GPa]
3.11 ±
0.16
3.00 ±
0.16
Alcohol administration lowers bone bending strength [1]
but for result values of the elastic modulus determinated by