Design of a Three-Dimensional Composite Scaffold with Varied Engineered Micro-Architecture Matthew A Wettergreen, Mark D Timmer, Antonios G Mikos, Michael AK Liebschner 13 th GRIBOI March 14 th , 2003 Rice University Computational and Experimental Biomechanics Laboratory

Background Cellular environment infinitely complex Intricate consistently remodeled architecture Complicated nutrient requirements Mass of mechanical signals Complex environment leads to tissue function In vitro techniques attempt to approximate 3-D environment Fails to address many characteristics

Cellular environment infinitely complex

Intricate consistently remodeled architecture

Complicated nutrient requirements

Mass of mechanical signals

Complex environment leads to tissue function

In vitro techniques attempt to approximate 3-D environment

Fails to address many characteristics

Importance of 3-D environment Gene Regulation Shear flow modulates MMPs of endothelial cells Differentiation Concentration gradient in embryogenesis Mechanical forces influence function Shear flow modulates bone deposition Cell attachment and spreading ECM provides matrix for fibroblasts in wound healing

Gene Regulation

Shear flow modulates MMPs of endothelial cells

Differentiation

Concentration gradient in embryogenesis

Mechanical forces influence function

Shear flow modulates bone deposition

Cell attachment and spreading

ECM provides matrix for fibroblasts in wound healing

History of Cell Culture Chick embryo maintained in fluid, 1880 Aseptic Technique introduced, 1923, Carrel Demonstrated that cells were immortal in culture Media defined, 1950’s 3-D studies with gels proposed, 1972 Scaffolds with 3-D geometry, 1990’s Biomimetic scaffolds with true 3-D characteristics, ???

Chick embryo maintained in fluid, 1880

Aseptic Technique introduced, 1923, Carrel

Demonstrated that cells were immortal in culture

Media defined, 1950’s

3-D studies with gels proposed, 1972

Scaffolds with 3-D geometry, 1990’s

Biomimetic scaffolds with true 3-D characteristics, ???

Current State of Affairs 3-D scaffolds – extrusion of 2-D shape? Lacks complex architecture Current fabrication methods Salt leaching Gas elution Differences in regions of scaffold due to random action of porogen One trick pony May not result in permeability

3-D scaffolds – extrusion of 2-D shape?

Lacks complex architecture

Current fabrication methods

Salt leaching

Gas elution

Differences in regions of scaffold due to random action of porogen

One trick pony

Requirements Porosity similar to tissue Strength matching Sites for specific cell adhesion Surface topology Biomaterial tailored to region

Porosity similar to tissue

Strength matching

Sites for specific cell adhesion

Surface topology

Biomaterial tailored to region

Goal Porosity similar to tissue Strength matching Sites for specific cell adhesion Surface topology Biomaterial sufficient for desired region Build mold with varying architectures reflecting differences in tissue area

Porosity similar to tissue

Strength matching

Sites for specific cell adhesion

Surface topology

Biomaterial sufficient for desired region

Build mold with varying architectures reflecting differences in tissue area

Region of Study Temporal Mandibular Joint Disc Located on Mandibular condyle matching with the cranium Provide shock absorption for jaw movement TMJ Disorder may be due to dysfunction of disc Why analyze for this project (can be sectioned into 3 pieces)

Temporal Mandibular Joint Disc

Located on Mandibular condyle matching with the cranium

Provide shock absorption for jaw movement

TMJ Disorder may be due to dysfunction of disc

Why analyze for this project (can be sectioned into 3 pieces)

Methodology Remove TMJ Disc Scan Make CAD file Create architecture Build scaffold Inject scaffold with biomaterial Dissolve mold

Remove TMJ Disc

Scan

Make CAD file

Create architecture

Build scaffold

Inject scaffold with

biomaterial

Dissolve mold

Excision of TMJ Disc

Creation of TMJ Disc Positive CAD file of scanned disc Rapid Prototyped disc Excised Porcine disc μ CT slice of disc

Disc Generation Embedding of prototyped disc in Silicon Mold created Inject mold to obtain exact replica of TMJ Disc

Embedding of prototyped disc in Silicon

Mold created

Inject mold to obtain exact replica of TMJ Disc

Scaffold with Composite Materials Inject mold with biomaterials Clear mold allows usage of photocrosslinking Material Choice 1,3 Butanediene Poly (propylene fumarate) Diacrylate Poly (Ethylene Glycol) Diacrylate

Inject mold with biomaterials

Clear mold allows usage of photocrosslinking

Material Choice

1,3 Butanediene

Poly (propylene fumarate) Diacrylate

Poly (Ethylene Glycol) Diacrylate

Scaffold Generation Completed Scaffold with 1,3 Butane… & PPF-DA Blue light for crosslinking Inject material Crosslink material Inject 2 nd material

Scaffold Generation 2 Completed scaffold with PPF-DA/PEG-DA PEG-DA swells like Hydrogel Confined on sides due to PPF

Completed scaffold with

PPF-DA/PEG-DA

PEG-DA swells like Hydrogel

Confined on sides due to PPF

Complex Architecture Scaffold ( μ CT + FEA + CAD Method ) TMJ Disc is orthotropic Generate composite scaffold with differing architecture Begin with CAD file of disc following scanning and reconstruction Add engineered architecture that reflects mech. prop. 23.40 ± 6.5 Posterior Band .58 ± .39 Intermediate Zone 9.48 ± 3.32 Anterior Band Modulus (MPa) Location

TMJ Disc is orthotropic

Generate composite scaffold with differing architecture

Begin with CAD file of disc following scanning and reconstruction

Add engineered architecture that reflects mech. prop.

Creation Process (CAD Directions) Tedious, lengthy procedure Positive / Negative processing of shape Begin with global shape (scanned TMJ Disc) End with global shape with engineered micro-architecture

Tedious, lengthy procedure

Positive / Negative processing of shape

Begin with global shape (scanned TMJ Disc)

End with global shape with engineered micro-architecture

/3

Scaffold Creation Build mold of scaffold with RP One use mold due to interconnected pores

Build mold

of scaffold

with RP

Conclusions Combining μ CT and Rapid Prototyping methods, composite scaffolds can be created which contain intricate architecture Architecture may modulate apparent strength of scaffold as well as strength of location Process detailed may be used to design architecture for any tissue Results show first step towards creating fully engineered scaffold which mimics the three-dimensional environment

Combining μ CT and Rapid Prototyping methods, composite scaffolds can be created which contain intricate architecture

Architecture may modulate apparent strength of scaffold as well as strength of location

Process detailed may be used to design architecture for any tissue

Results show first step towards creating fully engineered scaffold which mimics the three-dimensional environment

Acknowledgements Musculoskeletal Laboratory Alex Almarza, Michael Detamore Computational and Experimental Biomechanics Laboratory Mikos Research Group Funding Source Texas ATP Grant

Musculoskeletal Laboratory

Alex Almarza, Michael Detamore

Computational and Experimental Biomechanics Laboratory

Mikos Research Group

Funding Source

Texas ATP Grant

Thank you