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66 Cards in this Set
- Front
- Back
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What are Polymers?
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High molecular weight long chain molecules made from a simple repeating unit
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What is a Monomer?
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Starting material for polymerization
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What is a Polymer?
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Finished compound
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What is the Polydispersity Index (PDI)?
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It is a measure of breadth of molecular weight
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A PDI of 1 indicates what?
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That Mw=Mn, that is, all molecules have equal length
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Synthetic polymers have a PDI between what two numbers?
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1.5 < PDI < 5
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What is the formula for the PDI?
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Mw/Mn
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At best, what PDI can be attained?
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1.1 usually
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What are 4 common Polymers?
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1. Polyethylene
2. Polyvinyl Chloride 3. Polypropylene 4. Polystyrene |
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In Polyvinyl Chloride, the H atom is replaced with what?
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Cl!
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In Polypropylene, the H atom is replaced with what?
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CH3
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In Polystyrene, the H atom is replaced with what?
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C6H6
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What are Thermoplastics?
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Polymers that melt on heating and solidify when cooling
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What are some examples of Thermoplastics?
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PE, PP, PVC, and PS!
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What are Thermosets?
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Polymers that melt on 1st heating and "cure". Doesn't melt afterwards, instead degrades = burns!
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What are Elastomers?
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Polymers with very large elastic deformations when loaded (and recovered) up to 900% elongation!
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What is the skin made of that is a natural polymer?
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Collagen!
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What are 6 types of molecular order a polymer can have?
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1. Homopolymer
2. Alternating Co-Polymer 3. Co-Polymer 4. Random 5. Block 6. Graft |
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Side branches of a graft order polymer tend to do what?
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Tend to make the polymer harder and stronger
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What is Syndiotactic?
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Asymmetric carbons have alternate configuration
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What is Isotactic?
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All asymmetrical carbons have the same configuration
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What is Heterotactic or Atactic?
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Asymmetrical carbons have statistical variation of configuration. RANDOM!
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What are the three types of molecular structures polymers can have?
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1. Linear
2. Branched 3. Network or Crosslinked |
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What is a Linear Polymer?
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A long, straight, flexible chain with VDW or hydrogen bonding
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Crosslinked Polymers occur during when?
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During synthesis!
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What are the 2 states of Polymers?
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1. Semi-crystalline
2. Amorphous |
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Amorphous polymers are like what?
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Noodles! Cuz they're randomly packed.
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What is the Glass Transition Temperature?
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Temperature at which polymer changes from brittle, glassy solid to rubberlike
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The melting point is only related to what structure?
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Crystalline structure!
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What is required to allow motion?
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Free volume!
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If the molecular weight of polystyrene is 4000, what is the Glass transition temperature? 30000?
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40 C!
100 C! |
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Below the glass transition temperature, polymers are what?
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brittle and glasslike!
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As you increase load, decrease temperature, or increase crystallinity, what happens to the polymer?
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Becomes more and more brittle!
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Of Amorphous and Semi-Crystalline, which degrades faster? Why?
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Amorphous degrades faster because it is not as closely packed!
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What are 4 benefits of Biodegradable Implants?
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1. Prevent "stress shielding"
2. Act as scaffolds for neo-tissue growth 3. Act as drug delivery systems 4. No long term complications |
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Once implanted, a biodegradable device should be able to what two things?
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1. Maintain mechanical properties until no longer needed
2. leave no trace |
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What is the prevailing mechanism for polymer degradation in the body?
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Chemical hydrolysis of the hydrolytically unstable backbone
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What is the Degradation Pathway for PGA?
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PGA -> Glycolic Acid -> Excreted in the urine OR -> Glycine -> Serine -> Pyruvic Acid -> Trycarboxylic Acid Cycle -----> H2O + CO2
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What is the Degradation Pathway for PLA?
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PLA -> Lactic Acid -> Pyruvic Acid -> Trycarboxylic Acid Cycle ----> H2O + CO2
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What are the two types of Degradation?
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Surface degradation or erosion and Bulk degradation
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Degradation depends on what two factors?
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1. Rate of water penetration
2. Rate of transformation of polymer into water soluble form or size |
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Of PLA and PGA, which degrades faster?
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PLA!
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Copolymers degrade depending on what?
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Ratio!
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What ratio degrade faster than either PGA or PLA?
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50:50
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What is PMMA?
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A self-curing grouting agent used for total joint arthroplasty, spinal fixation and filler for pathological fixation
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What are the two components of PMMA?
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1. Solid Powder
2. Liquid |
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What is the liquid component of PMMA?
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It is a colorless, flammable, acrid smelling monomer
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What are the overall requirements of using PMMA?
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1. Adequate working time
2. Short setting time 3. Good fixation 4. Heat given off should be minimal 5. Sterilizable |
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When using PMMA, too high a temperature increases what?
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Tissue damage and porosity which results in lower mechanical properties
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When using PMMA, more monomer increases what?
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Increases the amount of heat produced, setting time, and amount of free monomer available to tissue
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When using PMMA, incomplete penetration can lead to what?
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Lead to microscopic de-lamination and micro-fractures
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Collagen is what kind of helix?
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Triple Helix!
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What is Type I Collagen?
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Bone, skin, and tendons
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What is Type II Collagen?
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Cartilage
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What is Type III Collagen?
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Major constituent of blood vessels
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What is Type IV Collagen?
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Constituent of basement membrane
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What is Chitosan?
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Collagen from shell fish
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UHMWPE is produced by what kind of techniques?
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Low pressure polymerization techniques
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TRUE OR FALSE: The molecular weight of UHMWPE is greater than 3x10^6 daltons?
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TRUE!
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What are 4 characteristics of UHMWPE?
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1. Good machinability
2. Difficult to injection mold 3. Can be extruded or compression molded 4. Limited solubility in xylene and benzene |
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With limiting Extraneous Materials, a 400 cm^2 sample should not have more than how many particles of extraneous material?
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100 particles
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With limiting Extraneous Materials, particles should be less than how many micrometers?
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300 micrometers!
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With limiting Extraneous Materials, density should between what two densities?
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0.93 - 0.94 g/cm^3
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What is the common technique of sterilization?
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Gamma radiation!
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Radiation causes the formation of what?
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Free radicals
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Sterilization in air or oxygen causes what?
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Causes oxidation which results in significant increase in wear
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