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Biomaterials Lecture 4&5 Material Classes

Biomaterials Lecture 4&5 Material Classes -...

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Metallic biomaterials Primary Application: 1. Traditional devices such as hip and knee prostheses 2. Newer devices such as cardiovascular stents Fundamental requirements: mechanical integrity and biocompatibilit y
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Metallic materials: commonly used in biomedical applications Metal Cobalt-chromium alloys Gold and platinum Silver-tin-copper alloys Stainless steel Titanium alloys What is significant about the materials in this list?
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Metallic biomaterials Basic properties: 1. Crystalline 2. Non-directional bonding-allow for many crystal structures Defined by the unit cell Metals have a variety of crystal structures depending on temperature, processing, and alloying 3. Three major metallic material crystal structures:
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Metallic biomaterials Defects in crystal structures: 1. Crystal structures are not perfect 2. Defects can be good or bad 3. Many types of defects but we will focus on point defects
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Metallic biomaterials Alloy: metal, composing of a mixture of elements. Preparation: melting, sintering of powder mixtures, diffusion of alloying element into base metal, plasma/vapor deposition of elements Single or a multi-phase alloy structure Phase: uniform part of an alloy, with a certain chemical composition and structure- separated by phase boundaries Solid solution: phase where 2 or more elements are completely soluble Two types of solid solutions? Addition of impurities-Solid Solutions
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Metallic biomaterials Solid solution: phase where 2 or more elements are completely soluble: Substitution or Interstitial Addition of impurities-Solid Solutions What happens with excess solute element? Hume-Rothery rules?
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Metallic biomaterials Addition of impurities-Solid Solutions Alloys are used to impart: strength, corrosion resistance, or improved electrical properties Examples: Interstitial alloys: steels (carbon and iron)- stainless steel orthopedic implants Substitutional alloys: cobalt-chromium alloys- orthopedic implants
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Metallic biomaterials Addition of impurities-Solid Solutions Alloys are used to impart: strength, corrosion resistance, or improved electrical properties Interstitial alloys: steels (carbon and iron): one of the most common is 316L stainless steel 1. Designation “L” means low carbon steel ~ 0.030% C by weight 2. Composition: Fe (60-65%), Cr (17-20%), and Nickel (12-14%) + minor amounts of other additives 3. Alloying for microstructure, both surface and bulk 4. Role of Cr: form a surface oxide “corrosion resistance”. Downside? 5. Why add Ni? 6. Why low C? What happens above 0.03%? Cr 2 O 3 and Cr 23 C 6
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Metallic biomaterials Addition of impurities-Solid Solutions Substitutional alloys: cobalt-based alloys- used in orthopedic implants. Two groups, four main types: 1. F75 and F799 (Co-Cr-Mo) : basically same composition. What’s the difference? Processing.
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