Characterization of porous scaffold materials for bone tissue engineering - Saartje Impens -

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Characterization of porous scaffold materials for
bone tissue engineering - Saartje Impens -
Micro-CT symposium 31/05/07
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GBE project

• 2 different aims
• Setting up a protocol for the healing of large
  and complex, but critical bone defects
• High throughput screening of different scaffolds
  ( porous structure)
• ? With the aid of micro-CT evaluation

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1. Healing of critical bone defects

Scaffold seeding and culturing with cells
Scaffold
Cells medium
Bioreactor
Patient own cells growth factors
Operation Room
Haeled bone defect
Bone defect
In vitro
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2. High throughput screening
input material coating growth factors
Optimize scaffold
Toxicity testing
Yes
Clinical approved scaffold
Not Ok
No
REJECT
Ok
If 2D plates are possible
Optimization possible?
Yes
2D plates
3D scaffold
No
µ-CT screening
Macrostructural Mechanical parameters
Fluid Flow
Macrostructural shortcoming
Further screening until clinical approvement
Not Ok
Yes
input cells
Ok
No
No perfusion perfusion possible
3D cell seeding
2D cell seeding
in vivo screening nude mice
3D cell culture
2D cell culture
No
output proliferation differentiation
Yes
time point analysis
No
Yes
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GBE strategy

• Multidisciplinary approach

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Micro-CT use

• Micro-CT based characterization of scaffolds
• Calculate structural parameters
• Calculate mechanical parameters with the aid of a
  FE-model
• Calculate fluid flow
• Evaluation of bone formation in explanted
  scaffold
• Replacement of histology?

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1. Scaffold characterization

• Important parameters for bone formation in Matlab
• Porosity ? As high as possible (100)
• Specific surface area ? As high as possible
• (Mentat) gt3,95mm-1 (Ding et
  al. based on bone)
• Pore size ? 100-800µm
• (PorousAnalyser)
• Permeability ? As high as possible
• (PoreNet) gt 10-8m2
  (Kohles et al. based on bone)
• Interconnectivity ? As high as possible (100)
• Mechanical parameters with FE-modeling (Mesh
  creation in Matlab)
• ? Expected load during walking is 1,2 x body
  weight
• Strength ? 100 under yield strength
• Stiffness ? 17-20 GPa (cortical bone)
• 10-1500MPa (trabecular bone)
• Stretch on surface ? (500-)1500-4000µstrain

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1. Scaffold characterization

• Scaffolds Reconstructed
  micro-CT FE-mesh
• Image

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1. Scaffold characterization

• Structural and biomechanical parameters

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Scaffold characterization

• Extra important parameter for the GBE project
• Fluid flow
• Nutrient Oxygen transport
• Wall shear stress
• May stimulate proliferation and differentiation
• i.e. May stimulate bone formation
• Ideally Computing Fluid Flow of micro-
• CT based models

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1. Scaffold characterization

• 2D Fluid flow on µCT based model

Inflow 1 ml/min
Scaffold Ø 6 mm, L 8 mm
Figures Tim van Cleynenbreugel
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1. Scaffold characterization

• 3D Fluid flow on CAD-based model

Figures Silvia Truscello
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1. Scaffold characterization

• Problems occur when meshing regular scaffolds
  produced by rapid prototyping

Blue ? Best Violet Pink Orange Red ? Worst
Manually remeshing
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2. Substitute for Histology

• Evaluation different scaffold materials
• Time consuming
• Embedding 2 weeks
• Sectioning
• 1 scaffold/day
• Labor intensive
• Staining
• 1 day
• Analysis
• 1 scaffold/day
• Labor intensive

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1. Scaffold characterization
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2. Substitute for Histology

• Polymer scaffolds

Binarized histological Section Interpolated
micro-CT image After registration
Green Overlap Blue only histology Red only
micro-CT
Histological image
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2. Substitute for Histology

• Distinguish between scaffold and bone by
  thresholding?
• ? Difficult, depends on scaffold
  material

Bone Scaffold Zone of bone ingrowth
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2. Substitute for Histology

• Micro-CT analysis
• Micro-CT Scanning
• Micro-CT scanning
  explant
• Positioning and subtrac-
  ting in Mimics to
  determine the amount
  of bone ingrowth

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2. Substitute for Histology

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Conclusion

• Micro-CT is a very useful tool for this type of
  research
• Scaffold parameters can be calculated
• Prior to implantation
• Non destructive
• Time consuming histology
• Can be replaced
• If necessary, histology can be performed after
  scanning
• If FE models and meshing problems are solved
• Fluid flow
• Wall shear stresses
• can be calculated

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Acknowledgement

• Special thanks goes to
• Jan Schrooten
• Tim van Cleynenbreugel
• Barbara Neirinck
• Silvia Truscello
• Greet Kerckhofs

-Thanks-
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-Thanks-