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EVALUATION OF A NOVEL
TECHNIQUE TO MAP THE
BIOMECHANICAL PROPERTIES OF
ENTIRE ARTICULAR SURFACES
USING INDENTATION
S. Sim1, 2, E. Quenneville2, M. Garon2, C.D. Hoemann1, M. Hurtig3 and M.D. Buschmann1
1. Biomedical & Chemical Engineering, Ecole Polytechnique de Montreal, Montreal, QC, Canada
2. Biomomentum Inc., Laval, Qc, Canada
3. Comparative Orthopaedic Research Laboratory, Department of Clinical Studies, University of Guelph, Guelph, Ontario, Canada
ICRS 2013
Purpose • Mechanical testing of articular cartilage is a useful outcome measure in studies of
cartilage degeneration and cartilage repair.
• Mechanical testing can be done in different experimental configurations:
Indentation Compression
Shear Torsion Tension
Bending
Practical Advantages
of Indentation
• Cartilage need not be harvested
from the articular surface
• Minimal disruption of the articular surface
• Maintains the mechanical environment of the cartilage layer and its
interaction with the subchondral bone
• Testing multiple sites
Indentation requires the compression axis
aligned perpendicular to the articular surface.
Mathematical models are more complex in
indentation with a spherical indenter.
Picture from: http://www.kneeclinic.info/
Articular surface
Tide mark
Calcified cartilage Subchondral bone
Cancellous bone
However
Methods
Thickness
is missing
• Automated Perpendicular Indentation:
spherical indenter for a new automated indentation technique
multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force
3-axis mechanical tester – uses 3 displacement components to provide
a perpendicular displacement based on the surface orientation
Contact coordinates (x,y,z)
of predefined positions and 4
surrounding positions
Surface orientation
(θz)
Normal
force/displacement vs
time
Methods
Thickness
is missing
• Automated Perpendicular Indentation:
spherical indenter for a new automated indentation technique
multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force
3-axis mechanical tester – uses 3 displacement components to provide
a perpendicular displacement based on the surface orientation
Contact coordinates (x,y,z)
of predefined positions and 4
surrounding positions
Surface orientation
(θz)
Normal
force/displacement vs
time
Methods
Thickness
is missing
• Automated Perpendicular Indentation:
spherical indenter for a new automated indentation technique
multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force
3-axis mechanical tester – uses 3 displacement components to provide
a perpendicular displacement based on the surface orientation
Contact coordinates (x,y,z)
of predefined positions and 4
surrounding positions
Surface orientation
(θz)
Normal
force/displacement vs
time
Methods
Thickness
is missing
• Automated Perpendicular Indentation:
spherical indenter for a new automated indentation technique
multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force
3-axis mechanical tester – uses 3 displacement components to provide
a perpendicular displacement based on the surface orientation
Contact coordinates (x,y,z)
of predefined positions and 4
surrounding positions
Surface orientation
(θz)
Normal
force/displacement vs
time
Methods
Thickness
is missing
• Automated Perpendicular Indentation:
spherical indenter for a new automated indentation technique
multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force
3-axis mechanical tester – uses 3 displacement components to provide
a perpendicular displacement based on the surface orientation
Contact coordinates (x,y,z)
of predefined positions and 4
surrounding positions
Surface orientation
(θz)
Normal
force/displacement vs
time
Methods
• Thickness measurement:
Technique adapted from Jurvelin et al., 1995
Position of the
cartilage surface Position of the
subchondral bone
Vertical
force/displacement vs
time
Thickness can
be obtained
Methods
• Thickness measurement:
Technique adapted from Jurvelin et al., 1995
Position of the
cartilage surface Position of the
subchondral bone
Vertical
force/displacement vs
time
Thickness can
be obtained
Analysis – Thickness
Vertical
Distance
Thickness = vertical distance x cosine (surface orientation)
Surface orientation
Cartilage
surface Subchondral
bone
Analysis – Automated Indentation
Instantaneous Modulus
(MPa)
Elastic Model
in Indentation
(Hayes, 1972)
Using the known
thickness
No
rmal
Fo
rce
(N
)
Spherical
indenter
Intradermal Bever
Needle
from Precision Glide
Camera
from Point Grey
Research
Radius of 0.5 mm Needle size of 26G 3/8” FMVU USB 2.0
Methods
Mach-1 v500css
from
Biomomentum Inc.
Multiaxial mechanical
tester
Device Equipment
Methods
• Mechanically-Controlled Surface Mapping
sample
camera
picture (1280x960 pixels)
position grid superimposed
converted in units of length (mm)
MACH-1
Methods • Samples:
Ovine Murine
current use in articular
cartilage repair studies
use in many disease and
developmental studies
Male Male
100-140 lbs 0.08 lbs
4-5 y.o Mature
No indications of joint pathology
Visually normal tibial plateau and femoral condyles were collected from
closed stifle joints
Pictures from: http://www.123rf.com/
Small dimensions
To reveal the high
spatial resolution and
sensitivity of this novel
technique
Results
≈ 150 measurements/articular surface
≈ 1 minute per indentation
≈ 30 seconds per thickness
3
D
S
U
R
F
A
C
E
Verifier le
graphique Fmax
vs. Angle pour voir
corriger
compliance ou
non
Discussion Works with any type of articular
cartilage as thin as murine.
Thickness obtained are in line with those
reported in the literature (Stockwell et al., 1971;
Frisbie et al., 2006).
Results can also be fit with poroelastic models,
e.g. the fibril-reinforced poroelastic model where
the permeability, the matrix modulus and fibril
modulus can be extracted.
≠ Aggregate Modulus: a measure of
stiffness of the tissue at equilibrium
when all flow fluid has ceased.
Discussion • Possible applications:
• Characterization of articular surfaces in cartilage
repair studies
• Monitoring of cartilage degeneration
• Monitoring of the mechanical properties in
knockout mice knee joints
• Characterization of bone, skin or
different materials for implants
Pictures from: http://www.genome.gov/
Conclusions
• This novel indentation mapping technique allows
to highlight the spatial variation over the entire
surface.
• A promising tool for studies that need to
characterize mechanical properties of the
articular surface.
Acknowledgement
• Funding provided by National Sciences and
Engineering Research Council (NSERC),
the Fonds du recherche du Québec -
Nature et technologies (FRQ-NT) and
Biomomentum Inc.
Questions