1. Define each term and give the example of an application which uses the following:
a. Biocompatible material
b. Biodegradable material
c. Biomimetic
2. An electronic chip is to be implanted in the body. During in vitro (in the lab) testing it is observed that the chip will dissolve over time if exposed to liquid with similar pH to extracellular liquid found in the body. To avoid this, you coat the chip with a polymer layer. This prevents dissolution in vitro but when implanted in the body (in vivo) the chip still dissolves. Give three reasons why the protective coating might fail in vivo but not in vitro.
3. You have two bags of polymer. Bag A has 10 kgs of polymer with weight average molecular weight of 336.6 kg and Bag B has 20kg of polymer with weight average molecular weight 392.7kg. Bag A has a polydispersity of 1.2 and Bag B has a polydispersity of 1.4.
a. What is the number average molecular weight of each bag?
b. If the polymer is polyethylene (mer = C2H4) what average polymerization (chain length) by weight for each bag?
c. If you combine the two bags what is the weight average and numerical average molecular weight of the mixture?
4. What are three modifications to a polymer that can make it transparent? How will these modifications affect the mechanical properties of the polymer?
5. Given the properties in the table below
Yield Strength Ultimate Strength Young’s Modulus Length of 10 cm
(MPa) (MPa) (GPa) specimen at fracture
Bone 80 100 20 10.1
Cartilage 50 70 2 10.7
Alumina 120 90 300 10.003
a. Plot the engineering stress-strain curves for the 3 materials. You can assume the materials behave linearly when they plastically deform.
b. Which material is the strongest?
c. Which material is the stiffest?
d. Which material is the toughest?
e. If you impose a 1% strain what happen to the three materials
f. After removing the 1% strain is there any permanent deformation in any of the materials? If so how much? Will any of the material properties in the table change? If so what is the new property?