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Orthopedic Polymer Applications

Orthopedic Polymer Applications. Elizabeth Doolittle, Jonathan Lopatin, Kihwan Kim, Kelsey Nurmi. Orthopedic Applications. Bone Plates, Composite PEEK Bone Cement, PMMA Joint Replacements, UHMWPE Joint Lubrication, MPC . C C Composite Bone Plates.

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Orthopedic Polymer Applications

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  1. Orthopedic Polymer Applications Elizabeth Doolittle, Jonathan Lopatin, Kihwan Kim, Kelsey Nurmi

  2. Orthopedic Applications • Bone Plates, Composite PEEK • Bone Cement, PMMA • Joint Replacements, UHMWPE • Joint Lubrication, MPC

  3. C C Composite Bone Plates • Used to hold bones together so they can heal properly. • Currently made from Stainless Steel • Stainless Steel is effective, but has drawbacks Okran, ISM. "Pinned Ankle Facture, X-Ray." Photograph. Science Photo Library. Web, 4/15/2012

  4. Issues With Stainless Steel • Stainless steel is much stiffer than bone • With holes for bone screws, plates only flex at holes, not evenly • Holes and different properties between bone and Stainless lead to compromises in healing.

  5. Stress Shielding • Steel carries most of the Load • Carrying stress improves bone growth • Steel plates need to be rather stiff so as not to brake at holes.

  6. Composite Bone Plates • Less stiff than Stainless Steel, more bonelike • Similar impact resistance • Lighter weight • Carbon Fiber weave can be arranged so that minimal stress concentrations occur around screw holes. • More customizable properties

  7. Materials • Carbon fiber weaves are the fiber of choice • Poly Ether Ether Ketone or PEEK is polymer of choice • High Biocompatibility and High Properties • Epoxy and other thermosets not used because of fear of BPA and other reactants

  8. PEEK • Engineering Thermo-Plastic • Incredibly high material properties • Very inert and biocompatible • Expensive • High temperature stability Ramakrishna, S., Mayer, J., Wintermantel, E., & Leong, K. W. (2001). Biomedical applications of polymer-composite materials: a review. Composites Science and Technology, 61, 1189-122 Solvay Plastics, "KetaSpire® polyetheretherketone (PEEK) " http://www.solvayplastics.com/sites/solvayplastics/EN/specialty_polymers/Spire_Ultra_Polymers/Pages/KetaSpire.aspx, 4/15/12

  9. Carbon Fiber • Weaves with lower angles between fibers used • Weaves allow no loss in properties around holes • Composite allows stress strain curve similar to bone • Holds bone in place but allows bone to carry some load to improve outcome

  10. Downsides • Doctors need to develop ways to take advantage of benefits • Potential interactions between materials and body. • Still relies on screwing into bone. • Still needs to be removed.

  11. Future • Biodegradable plastics considered • Could dissolve as needed • Could be stiff at start and become more flexible over time. • PLA, PGA • Better control of bone plate properties with fiber manipulation.

  12. PMMA Bone Cement • Poly Methyl Methacrylate • Also called Acrylic Cement Bellare, A. (2007). Orthopedic Bone Cement. Callaghan, J. J., Rosenburg, A. G., & Rubash, H. E. (Eds.), The Adult Hip Vol.1 (pp. 144-154). Philedelphia, PA: Lippincott Williams & Wilkins.

  13. Background • Discovered in 1877 • In mid 1930s first Bone Cement formed • 1940s, PMMA first used as Bone Cement. • Practice by Sir John Charnley still used currently

  14. Main function • Fixate the Total Joint Replacement • Act as a Load Transfer Bridge

  15. Properties of PMMA • High Tensile Strength • High Modulus • High Stiffness Ramakrishna, S., Mayer, J., Wintermantel, E., & Leong, K. W. (2001). Biomedical applications of polymer-composite materials: a review. Composites Science and Technology, 61, 1189-1224 Bellare, A. (2007). Orthopedic Bone Cement. Callaghan, J. J., Rosenburg, A. G., & Rubash, H. E. (Eds.), The Adult Hip Vol.1 (pp. 144-154). Philedelphia, PA: Lippincott Williams & Wilkins.

  16. Properties of PMMA • Creep Deformation • Does not experience Plastic Deformation • Self Polymerize • Minimal Adhesive Properties • Biocompatibility

  17. Market price • Market Price of PMMA Bone Cement • Antibiotic Bone Cement Price 4x more than Non Antibiotic Bone Cement. Mendenhall Associates, Inc. (2010). 2010 Bone Cement update. Orthopedic Network News, 21, 20-21.

  18. Fabrication of Bone cement • Powder Component: pre-polymerized PMMA, • Liquid Component: MMA monomer Bellare, A. (2007). Orthopedic Bone Cement. Callaghan, J. J., Rosenburg, A. G., & Rubash, H. E. (Eds.), The Adult Hip Vol.1 (pp. 144-154). Philedelphia, PA: Lippincott Williams & Wilkins.

  19. Fabrication of Bone Cement • Free radical polymerization • 4 step periods: • Mixing • Waiting • Working • Hardening

  20. Problems with bone cement • Low Fatigue Strength and Fracture Toughness due to High Stiffness. • Wearing of Bone Cement • Temperature Increase During Polymerization • Volume Loss

  21. Solution and Future Development • Fiber Reinforcement • Addition of Bioactive Fillers • Replacement of Radiopaque Agent • Addition of Rubber Particles • Improvement of Fracture Toughness by adding 1.0 wt% Nano-sized Titania Fibers Khaled, S. M. Z., Charpentier, P. A., & Rizkalla, A. S. (2011). Physical and Mechanical Properties of PMMA Bone Cement reinforced with Nano-sized Titania Fibers. Journal of Biomaterials Applications, 25, 515-537

  22. Joint Replacements • Ultra High Molecular Weight Polyethylene • (-CH2-CH2-)n Steven M. Kurtz UHMWPE Biomaterials Handbook: Ultra High Molecular Weight Polyethylene in Total Joint Replacement and Medical Devices. Amsterdam: Elsevier/Academic, 2009.

  23. "Active ArticulationTM E1® Dual Mobility Hip System." Biomet : Orthopedics, Sports Medicine, Biologics, Craniomaxillofacial, Dental. Biomet. Barad, Justin. "DePuy Receives PMA for AOX Antioxidant Polyethylene." Medgadget. 14 Dec. 2011. Bearing Surface Used in combination with metal or ceramic

  24. Material Requirements • Biocompatibility • Compatible with Metal Bearing Surfaces • High E and TS • Ductility

  25. Fabrication • Polymerization • Processing

  26. Failure Mechanism • Cyclic Loading • Debris • Implant Loosening

  27. Future Development • Known Failure Mechanism • Improve Life Expectancy

  28. Joint Lubrication MPC:2-methacryloyloxyethyl phosphorylcholine • Hip and Knee Replacements • Chains of MPC Fluid Motion

  29. Best Option • Polystyrene & Toluene • Polyelectrolytes in Water • Hyaluronic Acid

  30. Material Requirements • Biocompatibility • Low Friction • High Strength

  31. Fabrication • Radical polymerization • PMB and CLPE additions

  32. Other Uses • Artificial hearts • Drug delivery devices

  33. Conclusion • Different applications • Questions?

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