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406 E2 In Class

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eeverette's version from 2017-03-08 03:21

In-Class Review Questions

Question Answer
What is the structure of silicone?
How is silicone processed into medical grade tubing?Start with a carboxylic acid functionalized precursor instead of chlorinated precursor that can be toxic, Can also be made with acryl groups (double bonded C w/ COOH) subsitutuing for the methyl groups. These groups facilitate subsequent crosslinking. The polymer is typically mixed with a Pt catalyst and extruded into a tubular shape. The crosslinking reaction is triggered by heat
Why is it a bad idea to load an antibiotic into the silicone for a catheter?What goes in tends to come out easily --> uncontrolled release!, Adding the antibiotic can drastically affect the props of the polymer, You would need to use a solvent, and it is challenging to remove the residual solvent from the polymer --> could be toxic
Trying to deliver a small amt of antibiotic over a long time, do you want surface or bulk eroding polymer?SURFACE ERODING, because they display a constant release profile over time, as opposed to bulk eroding which exhibit a burst and taper release profile
Do you want polymer to be enzymatically or hydrolytically degrading?Hydrolytically degrading is preferred because every has the same amount of water in their body. Enzyme levels can vary from patient to patient, so you may not get consistent results for degradation
How to attach Ag to a polymer?Start w/ AgNO3, which dissociates in water, Modify the catheter to add a reducing agent (something negative like COO-). The Ag+ ions will be reduced by the reducing agent and bind to the surface of the polymer
How to tell how much Ag is on the surface of a polymer?Use energy dispersing x-rays in a SEM, must sputter coat with something other than Ag though. Can also use XPS, will get an Ag peak on the readout
How is UHMWPE synthesized?Ziegler-Natta polymerization, avoids branching by ensuring the monomer is added to the same point along the chain, no branching
What are the key steps/tests in characterizing UHMWPE for hip implant?Wear testing (high speed ball in cup), Compression testing (Instron), DSC (determine Tg, Tm), GPC (ensure there isn't low MW components), Size measurements (ensure the implant is always the same size), Surface characterization
What polymer would you choose as a hip implant cup if there was no UHMWPE?Low wear, low corrosion/pitting, Don't want fracture, Non-toxic; Crosslinked, biocompatible polymer
Explain why an artery exhibits a J-shaped stress-strain curveThe initial region is due to the elastin, which allows for large increases in strain at low stress. The upturn towards the end of the curve is due to the collagen fibrils aligning and crosslinks eventually engaging, which prevents further expansion even with increased stress
Describe the pros/cons of the following. How do they perform at low/high stress? A: stiff, low strain so there would be decreased blood flow at high pressure, surrounding artery could fail; B: lacks elasticity to mtch artery. improvement over A but not ideal; C: more elasticity, but may fail at high stress; D: Great elasticity at low stress, at high stress, expands like a balloon w/ respect to the artery
How to make matl perform better at high stress in vascular graft?blend with a stiff polymer to increase modulus at high stress OR reinforce with outer system to counter ballooning of graft
Problems you face after chemical modification of vascular graft?Toxicity, Thrombosis, Immune Response (long, short term), Degradation of Material over time, Allergic Response
Pros of tissue engineered arteryremodeling may produce better outcome, endothelial cells may prevent clotting, if matl is resorbed then there is no long term foreign body response
Cons of tissue engineering arteryTime, Cell Source, Functionality (how well it matches natural artery properties)
Gliadel wafer polymer ispolyanhydride
Anhydride linkage
PLA
PGA
PLGA
How is the gliadel wafer delivered to the tumor?Implanted directly in the cavity, put as many wafers as will fit
EpsilonRate of bond breaking / Rate of water diffusion
Is PLGA-b-PEO more likely to go by surface or bulk degradationBulk, PLGA already goes by bulk and PEO will only increase infiltration of water
Carbonate
Ester
Which degrades faster, carbonate or ester?Carbonate, the C is more electropositive because of the two adjacent O
Does PEG degrade?NO, nothing to degrade
PEG
Replacement for polyanhydride?Polycarbonate, it is hydrophobic and has a more cleavable linkage
How would you process the material for a gliadel wafer?Hot pressing
How would a polycarbonate mimic a polyanhydride wafer?Hydrophobic like the polyanhydride, still cleavable by hydrolysis so it can release drug
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