To finish it, here the exam questions of todays test:
Also, if you`ve been there today and can think of something I forgot to mention, please tell me and I´ll spread the word
1) Describe the term „Biocompatibility“.
2) Describe Biofuntionality +ONE example.
load by hip implant, drug delivery, …
3) What is a hydrogel? TWO applications. Characteristics?
hydrophilic, contact lenses, intraocular lenses, wound dressing, soft, water as dispersion medium, matrix character,…
4) Describe steam steri. & sterilisation by irradiation. One advantage, one disadvantage for each.
Steam: high temp and high pressure. Adv.: mass sterilisation; Dis.:not for thermal sensitive materials (so use metals only)
Irrad.: electron, x-ray, gamma. penetration depth? Adv.: Produce less heat- can be useed for those which you can´t use steam for. Dis.: may induce ionization, penetration depth,…
5) Describe the carrier system.
Drug carrier system with two repeating bound chains: both have spacers, one is degradable !, the other one is not degradable., but has the rezeptor on it. This allows the carrier system do find the prefered tissue side, attach and place the drug, once the spacer degrade.
6) Draw+ describe in words the bone ingrow for a degradable biomaterial.
(Curve that exponentially falls down for the degradable material, at the same time the bone builds up, aka expon. growth of this curve)
This is due to Wolff´s law: Once a bone feels more stress (because the implant degrades and can´t bear the full stress anymore), the bone will build up, to tackle the new load. So you want your implant to degrade slow enough for the bone to follow. (2 weeks shifted cycle?)
7) What is stress shielding?
Is it the same as Wolff´s law? You have to look it up, I don´t know. But it says quite the same: If you consider an metal implant taking away all the stress from the implant side, this side says: Ok, I don´t need to be so strong anymore, so let´s resorb! Then the implant may get loose, more stress at the surrounding again and you will soon get additiona fractures next to the implant. Therefore aim for homo-elasticity (=matching the implant sides mechanical properties)
You got two pictures of bones. One with fancy lines, one where you see the cut section of a bone. What should this tell you?
The fancy lines should show anisotropy and the cross section that there is a spongy bone and a compact bone. The spongy- compact- bone system results in an lightly weighted, but high stress bearing material, which is hard to match with other materials.
The two arrows which are also scatched- I would assume they should show a tensile force and a compression force, which togehter result in a bending moment for the bone.
9) Name the four degradation mechanism of polymers and describe them.
This one you find in the summaries. The polymer dissolution is physical, the other three are chemically drifen. Read it and remember it. This often came for the tests
10) Picture of hip and femur: name the components.
(femur, neck of femur, head of femur, hip, and what was the name of the hole in which the head fits?
11) Materials, design, shape of acept. cups?
Al2O3, ZrO2, PE-UHMW; just the cup, then the stem or also as three body system with three body friction. Shape: With plates, porous, with screws…
12) Counter chamber for the cell number: How does it work?
I can´t remember this one, as I was to lazy to look it up before the test. Damn, again those things you don´t look up. Anyway, should be something about the voltage difference I guess. Better you won´t make the same mistake. So let´s look it up before…
13) What is creep resistance?
Define creep first. What is creep? Under stress the material starts to stretch while the normal surface is getting smaller and smaller. The force needed for this is constant. Look at the stress strain curve for metals. There you can also find some creepy stuff quite after you passed the plastic region.
14) What is a copolymer?
Good question. As far as I can remember there are several monomers at the beginning of the prozess, in comparision with the other polymer group. Maybe it would be good to write a little more about it at the exam…
Guess that was it. If you are fast, there is enough time. It was a seven pages exam, with two questions each side, so there´s plenty of place to answer them.
Good luck with that one and your next exams as well!
best wishes,
Manuel