MicroCT symposium 310507 Characterization of porous scaffold materials

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

GBE project • 2 different aims: 1. Setting up a protocol for the healing of large and complex, but critical bone defects 2. High throughput screening of different scaffolds (= porous structure) With the aid of micro-CT evaluation

1. Healing of critical bone defects Scaffold seeding and culturing with cells Cells + medium Bioreactor Bone Patient own + growth defect cells factors Operation Haeled bone Room defect In vitro

2. High throughput screening input = material + coating + growth factors Optimize scaffold Toxicity testing Yes Not Ok If 2 D plates are possible REJECT Clinical approved scaffold No Ok 2 D plates Optimization possible? 3 D scaffold Yes No Macrostructural & µ-CT screening Mechanical parameters Fluid Flow Macrostructural shortcoming Further screening until clinical approvement Not Ok Yes input = cells Ok 2 D cell seeding 3 D cell seeding 2 D cell culture 3 D cell culture time point analysis No No perfusion possible in vivo screening nude mice output = proliferation differentiation No Yes

GBE strategy • Multidisciplinary approach

Micro-CT use 1. Micro-CT based characterization of scaffolds – – – Calculate structural parameters Calculate mechanical parameters with the aid of a FE-model Calculate fluid flow 2. Evaluation of bone formation in explanted scaffold – Replacement of histology?

1. Scaffold characterization • Important parameters for bone formation in Matlab – Porosity – Specific surface area (Mentat) – Pore size As high as possible (100%) As high as possible >3, 95 mm-1 (Ding et al. based on bone) 100 -800µm (Porous. Analyser) – Permeability (Pore. Net) – Interconnectivity As high as possible > 10 -8 m 2 (Kohles et al. based on bone) 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 – Stiffness – Stretch on surface 100% under yield strength 17 -20 GPa (cortical bone) 10 -1500 MPa (trabecular bone) (500 -)1500 -4000µstrain

1. Scaffold characterization Scaffolds Reconstructed micro-CT Image FE-mesh

1. Scaffold characterization • Structural and biomechanical parameters

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

1. Scaffold characterization • 2 D Fluid flow on µCT based model Inflow: 1 ml/min Scaffold: Ø 6 mm, L 8 mm Figures: Tim van Cleynenbreugel

1. Scaffold characterization • 3 D Fluid flow on CAD-based model Figures: Silvia Truscello

1. Scaffold characterization • Problems occur when meshing regular scaffolds produced by rapid prototyping Blue Best Violet Pink Orange Red Worst Manually remeshing

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 *

1. Scaffold characterization

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

2. Substitute for Histology • Distinguish between scaffold and bone by thresholding? Bone Scaffold Zone of bone ingrowth Difficult, depends on scaffold material

2. Substitute for Histology • Micro-CT analysis – Micro-CT Scanning – Micro-CT scanning explant – Positioning and subtracting in Mimics to determine the amount of bone ingrowth

2. Substitute for Histology

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

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

-Thanks-