Scaffold Materials and Structures
M. Entezarian, Dick Smasal, Brad Heckendorf
Phillips Plastics Corporation
Methods for making porous structures
• Foaming
– Limited to polymeric materials
– Random pore structure
– weak
• Replication
– Copying geometry and features of precursor structure
– Porous metallic and ceramic materials possible
• Free-forming
– Geometry not limited
– Slow
• Molding
– Mass production
Macro reticulated porous ceramic process
A. Use reticulated foam
of Polyurethane or
Polyester, HA or TCP
powder, water, and a
binder
B. Coat the foam with
ceramic powder
C. Fire B, burn the
polymer scaffold and
sinter the ceramic
powders
Solid-free forming
A. Prepare
formulation
(Ceramic +
binders)
B. Construct
the designed
3D structure
C. Dry and fire
to produce the
desired
structure
Porous beads
A. Prepare
formulation
B. Make beads
and fire to
obtain porous
structure
C. use a pack of
beads for cell
growth
Macro reticulated porous ceramic process
(Through injection molding)
A. Mold porous
structures with
CIM feedstocks of
HA or TCP
B. Debind the
molded structure
C. Fire the structure
and produce an
ordered porous
structure
Replication Method
Raw Material-Reticulated Foam
Macro photograph
SEM micrograph
Raw Material
Ceramic Powder
•
Materials — any sinterable ceramic:
– Hydroxyapatite
– Tri-Calcium Phosphate
– Zirconia
– Alumina
Example Hydroxyapatite Powder
Manufacturing Process
•
Preparation of ceramic slip (like paint)
– disperse ceramic powder with:
• water
• polymeric binder
• dispersant
• additives
Manufacturing Process
•
•
•
Coat reticulated polymeric foam
– cell size of foam used to control ceramic foam cell size
Cut desired implant size
– 3D geometric features possible
Sinter ceramic foam
– burn out all organics — foam and slip additives
Manufacturing Process
“Green” coated foams ready for sintering
Manufacturing Process
• Sintering
– Temperatures of 1000° C to
1600° C
– Precursor foam and organics
removed
– Ceramic powder becomes
dense
Manufacturing Process
Sintered foam parts
Chemistry
• Hydroxyapatite (Ca5(PO4)6OH)
– Meets ASTM F1185 Standard Specification of Ceramic Hydroxyapatite
for Surgical Implants
• TriCalcium Phosphate (Ca3(PO4)2)
– Meets ASTM F1088 Standard Specification for Beta-TriCalcium
Phosphate for Surgical Implants
Structure
• Fully open and interconnected pores
• Structure independent of material
• Median pore size 264 µm
• Narrow and controlled pore size distribution
• 80% Porous (nominal)
Scanning Electron Micrograph of
Hydroxyapatite
Physical
• Hydroxyapatite
– Bulk Density 0.57 g/cc (±0.03)
– Porosity 81.1% (±1.01)
– Sintered (strut) Density 95%
– Crush Strength 1.89 MPa
(±0.19)
– Modulus 47.1 MPa
Physical
• TriCalcium Phosphate
– Bulk Density 0.51 g/cc (±0.05)
– Porosity 83.5% (±1.56)
– Sintered (strut) Density 93%
– Crush Strength 1.31 MPa
(±0.25)
– Modulus 39.9 MPa
IN VIVO EVALUATION OF BONE SUBSTITUTES IN A
RABBIT TIBIAL DEFECT MODEL
Hydroxyapatite
Start
6 Weeks
8 Weeks
Tricalcium phosphate
Start
6 Weeks
8 Weeks
Alumina
Start
6 Weeks
8 Weeks
Sintered Dense/Macro Porous Ceramics
•
•
•
•
Biocompatible
Bioresorbable
Maintain structural strength
Elicit minimal foreign body reaction
Study purpose:
To compare two injection molded sintered dense ceramics, HAP
and TCP,in a rabbit transcondylar femur model.
Histologic Results
• HAP – Well-defined smooth circumference
with thin layer of biofilm.
12 weeks
24 weeks
Histologic Results

TCP – Rough/irregular
circumference with bone
ingrowth into implant
12 weeks
24 weeks
MOPS Introduction
• Produce Porous Ordered
Structures of polymers,
metals, and ceramics through
Injection Molding
• 50% porosity
• Pore size of 0.020” for
polymeric materials
• Pore size of 0.016” for
metallic and ceramic
materials
Osteogenic Differentiations
Dan Collins, BioE Inc.
Chondrogenic Differentiation
TCP 7 days
TCP 14 days
Dan Collins, BioE Inc.
TCP 70 days
Crush Strength Comparison
Crush Stength (MPa)
Crush Strength Comparison
120
100
80
60
40
20
0
Ordered Porous Alumina
Reticulated Alumina
Structure
Materials molded in these structures
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•
•
•
•
•
•
•
•
Polyethylene
Polycarbonate
PEEK
PCL (bio-degradable)
PLA (bio-degradable)
Alumina
TCP
Stainless Steel (316L)
Titanium
Potential Applications
•
•
•
•
•
•
Implants
Drug delivery
Cell growth
Catalyst support
Filtration
Electrodes