M. Entezarian, Dick Smasal, Brad Heckendorf Phillips Plastics Corporation Scaffold Materials and Structures

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 (Ca 5 (PO 4 ) 6 OH) –Meets ASTM F1185 Standard Specification of Ceramic Hydroxyapatite for Surgical Implants TriCalcium Phosphate (Ca 3 (PO4) 2 ) –Meets ASTM F1088 Standard Specification for Beta-TriCalcium Phosphate for Surgical Implants

Structure Scanning Electron Micrograph of Hydroxyapatite Fully open and interconnected pores Structure independent of material Median pore size 264 µm Narrow and controlled pore size distribution 80% Porous (nominal)

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 Start8 Weeks6 Weeks

Tricalcium phosphate Start 8 Weeks 6 Weeks

Alumina 6 Weeks8 WeeksStart

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 weeks24 weeks

Histologic Results TCP – Rough/irregular circumference with bone ingrowth into implant TCP – Rough/irregular circumference with bone ingrowth into implant 12 weeks24 weeks

TCP 12 weeks24 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 TCP 70 days Dan Collins, BioE Inc.

Crush Strength Comparison

Materials molded in these structures 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