Effects of Mechanical Conditioning on Cardiac Fibroblast Tissue Constructs

1
Effects of Mechanical Conditioning on Cardiac
Fibroblast Tissue Constructs

• J.J. Wille1, E.L. Elson2, and R.J. Okamoto1,3
• Washington University in St. Louis
• 1 Dept. of Biomedical Engineering
• 2 Dept. of Biochemistry and Molecular Biophysics
• 3 Dept. of Mechanical Engineering
• October 15, 2004

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WHY CARDIAC FIBROBLASTS?
WHY MECHANICAL CONDITIONING?

• Application of unaxial cyclic stretch
  (conditioning) during incubation of cardiac
  tissue constructs appears to improve their
  morphology and function.

Cardiac fibroblast are one of two main cell types
of cardiac tissue. They are responsible for ECM
production and remodeling.
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Fabrication
a
c
b
Collagen Solution

Chicken Embryonic Cardiac Fibroblasts
Standard Solution 106 cells/ml 1 mg/ml collagen
e
f
d
Incubation in a humidified environment at 5 CO2
and 37oC
Incubated in DMEM supplemented with 10 FBS
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THE TESTER
Computer for data acquisition and motor control
Isometric force transducer
Actual Sample at Day 8
Heated tissue bath
Micrometer
Stepper motor
Enlarged view
Side view
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MAGNITUDE EFFECT
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MAGNITUDE EFFECT
MAGNITUDE EFFECT
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FREQUENCY EFFECT
8
CytoD Effects at Different Magnitudes
Start of cyclic stretch
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COMPONENT FORCES
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SUMMARY OF SHORT-TERMMECHANICAL CONDITIONING

• After an initial period of a few hours, cyclic
  strain magnitudes higher than 5-10 do not lead
  to higher applied forces during conditioning
• The frequency of conditioning has little effect
  on the applied forces in the range of frequencies
  studied
• The decrease in total force (cell matrix)
  during conditioning at higher magnitudes suggest
  that cells may be accommodating, i.e. actively
  changing the properties of the tissue to maintain
  a desired level of cell deformation
• This accommodation results in shifting the matrix
  force to higher strains while spreading out the
  cell force over the larger strain
• Short-term conditioning doesnt lead to higher
  per cell forces

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LONG TERMMECHANICAL CONDITIONING

• Identical samples to short-term conditioning
• Static incubation for 2 days
• Continuous mechanical conditioning for the
  following 6 days

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LONG TERM CONDITIONING
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Component Forces at 15 Stretch Magnitude in the
presence of 10 serum
Component Forces at 5 Stretch Magnitude in the
presence of 10 serum
Component Forces at 10 Stretch Magnitude in the
presence of 10 serum
9.19 MC
Static
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LONG TERM CONDITIONING
Mechanical Conditioning at 0.25 Hz
Mechanical Conditioning at 0.25 Hz
Mechanical Conditioning at 1.47 Hz
Mechanical Conditioning at 1.47 Hz
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LONG TERMMECHANICAL CONDITIONING

• Sample compaction is quicker under static
  incubation but ultimate compaction after 8 days
  is similar
• Cell number increases 2-3 fold up to day 8 with
  little influence due to mechanical conditioning
• Serum-free conditioning results
• Stops compaction
• Causes a 50 reduction in cell number
• Significantly lower tissue forces
• Most of the tissue force is matrix instead of
  cells

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LONG-TERM CONDITIONING CONCLUSIONS

• Long-term conditioning leads to similar
  phenomenon of accommodation
• At low strains the tissue force is due mostly to
  the cellular component while at higher strains
  the matrix begins to contribute more of the
  tissue force
• At a low conditioning frequency there doesnt
  appear to be an effect on the properties of the
  tissue at higher strains.
• At a higher conditioning frequency there appears
  to be an effect over static controls.
• This indicates that the tissues may be much more
  sensitive to the mechanical signals and respond
  only to narrow set of conditions.

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Acknowledgements

• Whitaker Foundation
• Members of the Elson Lab

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QUESTIONS?