Transcript Slide 0

Orthopaedic Biomechanics
Role of collagen IX in the integrity of cartilage
collagen network
Sami Musa, Daniel Florea, Jacques Huyghe, Keita Ito
Orthopaedic Biomechanics Group; Eindhoven University of Technology
Uwe Hansen and Peter Bruckner
Dept. Physiol. Chem. & Pathobiochem; Muenster University
Cartilage collagen fibrils
consist mainly of collagen II, XI
interface
and IX. Collagen IX, which is a fibril associated collagen,
resides on the surface of the fibril. It is considered to
enhance the mechanical property of the fibril network.
Mutation of this collagen are associated with premature
disc degeneration.
Results
MSD measurements:: beads displacement amplitudes
averaged over selected time windows, as function of time.
10
Col_IX=0%
1
0.01
0.1
1
10
100
Col_IX=36%
0.1
MSD [um]
Background
S.L.M. van Loon, S. Musa, J.M. Huyghe
Col_IX=70%
0.01
Col_IX=100%
0.001
0.0001
Time [s]
MSD as function of time for different collagen IX content.
Research Objective
The aim of this research is to study the role of collagen IX in
the mechanical integrity of cartilage collagen network. We
have measured shear moduli of collagen networks as a
function of collagen IX content.
Storage and loss measurements: Shear moduli as function
of frequency for different collagen IX ratios.
10
Col_IX=100%
Materials and Methods
We have conducted micro-rheology experiments using
multi-particle tracking method to measure the viscoelastic
properties of the collagen network such as mean squared
displacement (MSD) and storage and loss (G’ and G”) as
function of collagen IX.
Beads in collagen network; real and schematic.
Four samples of collagen network consisting of collagen II,
XI and varying content of collagen IX were prepared as the
following.
1.Each sample has 0.5mg/ml collagen mixture
concentration. They differ in collagen IX ratio being 100%
71% 36% and 0% compared to physiological condition.
2.Probes of 1 um radius polystyrene beads (0.008%) were
added to the collagen mixture.
/ Department of Biomedical Engineering
G'[Pa]
0.01
10
1
1
0.1
1
0.1
Col_IX=71%
10
100
0.01
0.1
Col_IX=100%
G"[Pa]
Schematic illustration of cartilage fibril.
1. Beads displacements get more restricted as concentration
of collagen IX increases.
2. At 100% collagen IX concentration MSD is constant at
larger time windows indicating very limited movements.
1
10
100
0.1
Col_IX=71%
0.01
0.01
Col_IX=36%
Col_IX=36%
0.001
0.001
Col_IX=0%
Col_IX=0%
0.0001
Frequency [Hz]
0.0001
Fequency [Hz]
Storage G’ and loss G” response of the collagen mixture.
1. Values of G’ and G’’ clearly depend on collagen IX
concentrations.
2. G’ for the sample with 100% of collagen IX shows a flat
dependence on frequency indicating dominant solid
behavior.
3. For sample with 0% collagen IX the G’ increase as
function of frequency indicating viscous behavior.
4. Slope of G” varies a function collagen IX content
indicating increase in dissipation as collagen IX content
decreases.
Conclusion and future work
Shear moduli of collagen network have been determined
using multi-particle tracking. The results show that collagen
IX indeed plays a role in the mechanical property of
cartilage fibril network.