For B i was sthinking enzymatic or oxidative, I was not sure For A i was thinkin

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For B i was sthinking enzymatic or oxidative, I was not sure

For A i was thinking something about the crystal structure or degredation rate, but was not sure either

2. Dr. Aggie works for a large medical device company that makes Implantable Cardioverter Defibrillators (ICD). You have had a 2% failure rate of these devices due to electrical dysfunction caused by externalization of the lead wires. Upon examination, the externalization is caused by abrasion of your insulating polymer (shown in light blue below). a) Your colleague suggests that the silicone insulation should be replaced with a poly(ether urethane) with a 50X increase in abrasion resistance. Name one other design criteria that you would consider about the polyurethane for this application. b) Given that abrasion resistance goes down with degradation, your colleague runs a series of accelerated degradation tests in the lab. He asks you which mechanism you think would be the most likely: hydrolytic, enzymatic or oxidative so that he can test that one first. Which one do you tell him?

Explanation / Answer

A) insulation and packaging materials on implantable electronic devices must be biocompatible. Silicon rubber insulation on electronic circuit immersed in saline has been shown to breakdown in electrical field of about 10^5 V/m. This place a constraint on the distance between electrical contact pads on integrated sensors. silicon has low tear and tensile strength and high cofficient of friction. This property make silicon vulnerable to abrasion in vivo whereas polyurethane has more tear and tensile strength means high abrasion resistance. Polyurethane has more lubricating property along with low friction characterstic that make it more suitable than silicon insulation.

B) polyurethane encapsulants susceptible to metal induced oxidation ( a subsequent free radical chain reaction degradation ) by certain metal under aniodic potential. So, oxidation mechanism associated with degradation.

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