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The Role of Metals in Prosthetic and Orthotic Technology

The Role of Metals in Prosthetic and Orthotic Technology. Ben Hertzberg. Introduction. Prosthesis: replaces part of the body Orthosis: augments part of the body Prosthesis includes: Artificial Limbs Prosthetic Eyes Replacement Joints Facial Prosthesis Artificial Hearts Neuroprosthetics.

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The Role of Metals in Prosthetic and Orthotic Technology

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  1. The Role of Metals in Prosthetic and Orthotic Technology Ben Hertzberg

  2. Introduction • Prosthesis: replaces part of the body • Orthosis: augments part of the body • Prosthesis includes: • Artificial Limbs • Prosthetic Eyes • Replacement Joints • Facial Prosthesis • Artificial Hearts • Neuroprosthetics

  3. Important Materials Characteristics • Strength • Stiffness • Fatigue Resistance • Density • Corrosion Resistance • Biocompatibility (more on that later) • Ease of Fabrication • Cost

  4. Chart of Materials Properties

  5. Special Requirements for Specific Technologies • Lower-body prostheses and orthoses will need to support huge amounts of weight • Also need good fatigue resistance • Other characteristics require more precise control • Precise control of elasticity • Low Density is Important

  6. Requirements for Implant Materials • Biocompatibility • Tissue-compatible • Corrosion-resistant • Similar elasticity to nearby tissue • Potential Problems: • Allergic reaction • Toxicity • Other immune system responses

  7. Facial Implants • Miniplates can be used to hold together fractured sections of skull • Biocompatibility is very important because of danger of immune response • Implant can be cemented, press-fitted, or affixed through impaction Facial Implant and X-Ray Picture of Subject

  8. Replacing Large Sections of Bone • Even greater tensile strength is required • Bone/metal interface is difficult • We must ensure there is effective load transfer between bone and implant

  9. Bone/Metal Interface • How do we get bone to grow to and connect with implant metal? • Interfacial loosening is leading cause of skeletal implant failure

  10. Problems With Bone/Metal Integration • Fibrosis – growth of fibrous connective tissue on surface of implant • Fibrosis can interfere with healing damage from implantation surgery • Immune system response • Abrasion of metal Comparison of Fibrosis in Ti Alloys Extracellular Titanium Debris

  11. Osseointegration • Connection between bone and implant • Important materials properties: • Frictional Coefficient • Bio-inert/-active components Progressive growth of bone near Ti implant

  12. Useful Materials: Titanium • Ti-6Al-4V is most common alloy used • High resistance to corrosion • Strong oxide layer that renews itself • More easily shaped and more malleable than steel • Strong general biocompatibility • Stiffness comparable to bone Microstructure of Ti-6Al-4V

  13. Biocompatibility of Titanium • Past evidence suggested that titanium might be dangerous • Causes fibrosis • Metal particles are abraded off • Immune system response detected • Studies show it is safe, however • This opens door for use of titanium in implants Extracellular Titanium Debris Pigmented Cellular Debris

  14. Osseointegration in titanium • TiAlV produces very little fibrous tissue – bone can grow normally • This can be enhanced by use of thin films Comparison of Fibrosis in Ti Alloys

  15. Metallic Thin Films & Osseointegration • Gold-thiol chemistry allows us to attach amino acids to implant surface that encourage bone growth • Using amino acid RGD produces significantly thicker bone shell around implant • Almost 40% greater interfacial shear strength Self-Assembled Monolayer on Gold Femur Cross-Section After Implant Removal

  16. Metallic Thin Films & Osseointegration – Part 2 • Titanium thin films such as Ti-Ca-P-C-O-(N) can also be used to encourage osseointegration • No additional immune response • Little frictional coefficient • Induces growth & serves as anchoring point for osteoblasts and epitheliocytes Dark Spectrum Micrograph of CaP thin film Microstructure of worn CaP thin film

  17. Useful Materials: Magnesium • Lightweight metal with mechanical properties similar to natural bone • Pure magnesium metal oxidizes quickly • This is beneficial because it allows the implant to degrade; however, it happens too rapidly • Mg + rare earths has dramatically reduced corrosion rate - up to 11 months • Subcutaneous gas pockets can be removed via syringe • No evidence suggests magnesium is toxic – high biocompatibility

  18. Magnesium & Osseointegration • Since Mg implants are designed to degrade, they need to be able to allow bone growth • Magnesium can enhance bone growth by itself – evidence is sketchy • Porous magnesium microstructures can enhance osseointegration • Porous magnesium has materials properties that are even closer to bone • Space-holding particles are typically used to produce porous microstructure SEM Micrograph of magnesium with porous microstructure

  19. Futuristic Technologies • Trabacular metal • 80% porous • Uses tantalum, which is highly biocompatible • Allows for high bone ingrowth • High soft tissue attachment

  20. Futuristic Technologies • Scientists have managed to create an prosthetic limb that connects directly to the brain, giving neural control over the limb’s movements & tactile senses

  21. References • http://www.corrosion-doctors.org/Implants/frconten.htm • http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12069513&query_hl=1&itool=pubmed_docsum • http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16077328&query_hl=5&itool=pubmed_docsum • http://www.lib.umich.edu/dentlib/Dental_tables/toc.html • http://www.ece.mcmaster.ca/~ibruce/courses/EE3BA3_presentation3.pdf • http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-ABY-MsSAYWW-UUW-U-AAVDBWBCWU-AAVVEUVBWU-DEAWCBZDY-ABY-U&_rdoc=1&_fmt=summary&_udi=B6TWB-4J2TSMW-1&_coverDate=05%2F31%2F2006&_cdi=5558&_orig=search&_st=13&_sort=d&view=c&_acct=C000022719&_version=1&_urlVersion=0&_userid=492137&md5=fec4c2772c67d9274dd8291a9bcf7f6d • http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-ABY-MsSAYWW-UUW-U-AAVDBWBCWU-AAVVEUVBWU-DEAWCBZDY-ABY-U&_rdoc=5&_fmt=summary&_udi=B6TWB-4HD8BC2-1&_coverDate=03%2F31%2F2006&_cdi=5558&_orig=search&_st=13&_sort=d&view=c&_acct=C000022719&_version=1&_urlVersion=0&_userid=492137&md5=be8025337f3cb22d93a3627b8efa1593 • http://www3.interscience.wiley.com/cgi-bin/fulltext/30001813/PDFSTART • http://www.zimmer.com/z/ctl/op/global/action/1/id/33/template/MP/navid/294 • http://www.nd.edu/~engineer/publications/signatures/2002/biomaterials.html • http://research.brown.edu/btp/technologies_detail.php?id=1115136426 • http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-D-MsSAYZW-UUW-U-AAVDBWBWAB-AAVVEUVUAB-DEAWVDEVU-D-U&_rdoc=1&_fmt=summary&_udi=B6TWB-3Y2F9B8-F&_coverDate=12%2F31%2F1999&_cdi=5558&_orig=search&_st=13&_sort=d&view=c&_acct=C000022719&_version=1&_urlVersion=0&_userid=492137&md5=aeb4d5b7c53f39972294683f1ca49979 • http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-AUUU-MsSAYZW-UUW-U-AAVDBWBWED-AAVVEUVUED-DEAWVEDUC-AWBA-U&_rdoc=1&_fmt=summary&_udi=B6TWB-4JG5FGW-1&_coverDate=07%2F31%2F2006&_cdi=5558&_orig=search&_st=13&_sort=d&view=c&_acct=C000022719&_version=1&_urlVersion=0&_userid=492137&md5=ba14ab48595fac51b45ce34304896e78

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