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(T/F) When hardening metals, the grain size hardening increases with the grain size because the barrier for any dislocations becomes more robust
False. Smaller grain size –> more barriers for dislocations
(T/F) One main disadvantage with titanium for bio-implant use, is their proneness to fatigue failure
False. Cobalt-chromium is prone to fatigue, Titanium has poor friction properties
Poly(ethelene terephthalate) is less susceptible to hydrolysis than poly(tetrafluoroethylene) because of the chemical moieties along the backbone (i.e ester groups)
False.
In ceramics, with decreased temperature, the surface to mass ratio decreases
False.
Poly(methyl methacryalate) (PMMA) is a thermoplastic.
True.
Generally, ceramics have a very high Young’s modulus as well as hardness and, exhibit a high melting point and density.
False. The atoms are small so they have a low density.
Hydroxyapatite is an example of a bioactive ceramic that specifically is used for heavy load bone implants
False.
PGA is considered a crystalline polymer.
True. Crystalline polymers have regions of regular and neat packing, like crystals.
Mixing the two isotactic PLLA and PDLA, decreases the tensile strength over time compared to PLLA and PDLA alone.
False.
When a material is deformed, all bonds break simultaneously
False.
Metals are brittle
False. Metals are tough and have high tensile strength.
Silicon in the fcc structure has directional bonds
False. FCC comes from non directional bonding.
Body-centered cubic crystal structure shows a higher packing density than the hexagonal close-packed crystal structure.
False. Close-packed=high density
The diamond structure is typical for directional bonds.
True.
Generally, ionic bonds are displaying a higher heat of vaporization than metallic bonds.
True. More energy is required to break the bonds.
The green body formation is a step in the ceramic fabrication process.
True. It is when the powder is compacted/shaped
With decreased temperature, the surface to mass ratio in ceramics increases.
True. Grains are packed more tightly in higher temperatures
Hydroxyapatite is a resorbable ceramic type
False.
The permeability of a hydrogel increases with increased swelling of the gel.
True.
Hydrogels are commonly used for loading of hydrophobic drug substances
False. Hydrogels have a poor loading capacity
Stress shielding is a positive characteristic referring to how well a material withstands chemical degradation.
False. Stress shielding is when bone around an implant gets weaker due to an implant taking on the pressure and stress the bone normally has.
Ceramics have a good high temperature stability
True.
Metals are brittle
False.
Metallic bonding is directional
False. Electrons can be found in any direction from a given atom
The ionic bonds in MgO have a lower heat of vaporization than the covalent bonds present in a diamond.
False. Ionic bonds are stronger than covalent bonds
The bonding orbital in sigma bonds show rotational symmetry
True. They are just balls
Silicon in the FCC structure is a semi-conductor
False.
Metals can form the HCP structure
True. They are close-packed structures and a result of non-directional (i.e metallic) bonding
Diamond structure is a more densly packed structure than BCC
False. Diamond structure is 34% while BCC is 68%
A rubbery-like polymer (elastomers) is weak, but highly extensible
True. Low youngs modulus but high failure strain.
In an isotactic polymer, the R group is randomly located in or behind the polymer backbone.
False. In an isotactic polymer all R groups are on one specific side
An elastomere has high flexibility and low crystallinity
True. Crystallinity prevents stretching
Elastomers are usually thermoplasts
False. They are usually thermosets
The two most common synthesis methods for polymers are condensation and hydrolysis
False
One characterization method that determines Tg and Tm is differential scanning microscopy
False. Its called differential scanning calorimetry. Another method is “dynamic mechanical analysis”
The chemical compostition of polymers is usually determined via Auger electron spectroscopy
False. NMR or IR that is used for bulk and XPS/ESCA is used for surface.
The “PDI” describes the degree of polymerization of a specific polymer
False. Its depicted as “DP”
One main degradation rate determinant of polymers is susceptibility of the polymer backbone to hydrolytic cleavage. (L17)
True. Polymers that undergo hydrolytic cleavage are preferred as medical implants due to predictable degradation, compared to enzymatically degradable implants.
PGA erodes faster than the PLA but a 50:50 mixture of the two degrades the fastests
True.
Degradation rate increases with high surface area to volume ratio
True.
Degradation rate decreases with compactness of the material
True.
