CHEE 422 - Final
DEFINE: Syndiotactic Stereoisomerism
Pendant side groups are in alternating orientation
One common biomaterial application is the construction of an arterial graft, a device that replaces a section of an artery. An artery is a flexible blood vessel that withstands varying pressures and regulates the flow of blood. Arteries also provide a smooth interior surface to inhibit blood clotting within the vessel. (a) You need to design an arterial graft. List some advantages and disadvantages of each of the three major types of biomaterials. Which would you choose for this application? (b) What specific material characteristics need to be considered for the arterial graft application? (c) Would you use a natural or synthetic material for this application? What are the advantages and disadvantages of each?
(a) ADVANTAGES: Metal: Durable, Ductile Ceramic: Durable, Smooth, can withstand high Heat and Pressure Polymer: Flexible, Smooth DISADVANTAGES: Metal: Stiff, corrosive Ceramic: Brittle Polymer: Weak (b) durability, tendency to corrode, flexibility, and strength (c) Synthetic, these can be molded into essentially anything needed, and can provide superior strength and durability compared to natural materials. However, natural materials can have the advantage of being more biocompatible than synthetic materials in particular cases.
316 SS is an alloy containing about 70% iron with 30% other metals, usually chromium and nickel. Consider an alloy of about 70% iron, 18% chromium, 12% nickel. (a) Would the alloy be mechanically weaker or stronger than pure iron? Why? (b) Given the atomic radius of an Fe atom is 1.24A, the radius of a Cr atom is 1.25A, and the radius of Ni atom is 1.25A, will the Cr and Ni atoms in the lattice cause localized tensile or compressive strain? Why? (c) Name the type of defect created by the addition of C atoms
(a) Stronger, the addition of Cr and Ni causes additional localized strains in the lattice leading to a greater stress being required to deform the material (b) Compressive strain, the radius of both Cr and Ni are greater than that of Fe causing the Cr/Ni atom to push OUTWARD (c) Intersticial
What kind of lubricant graphite is: 1. Solid 2. Gaseous 3. Liquid 4. Semi liquid
1
Which one of the following is not a rationale for surface modification of biomaterials: 1. To change the mechanical properties of the bulk 2. To control protein adsorption 3. To influence cell adhesion/growth 4. To modify blood compatibility
1
How is chemical vapor deposition different from physical vapor deposition?
1.During CVD, chemical precursor breaks down the source material, while in PVD, deposition takes place by physical deposition. 2.CVD: High T, PVD: Low T. 3.CVD: Coating in gas form, which condenses as a thin film, PVD: Coating in solid form.
How does the rate of cooling affect the hardness of a metal: 1. Slow cooling-hard metal 2. Slow cooling-soft metal 3. Rapid cooling-soft metal 4. No effective change
2
Following strengthening mechanism applies to multi-phase materials: 1. Grain size reduction 2. Strain hardening 3. Solid state strengthening 4. None of the above
3
What type of wear occurs due to an interaction of surfaces due to adhesion of metals: 1. Adhesion wear 2. Abrasive wear 3. Fretting wear 4. Erosive wear
3
Composition of a metal affects: 1. Surface energy 2. Microstructure 3. Mechanical properties 4. All of them
4
A pure silicon chip consists of single crystal of silicon. Which of the following corrosion is least likely to occur? (a) Intergranular (b) Crevice (c) Stress (d) Pitting
A
Compressive and tensile strain results in the localization of ............ and ................ Impurity atoms, respectively: a) Smaller and larger b) Small only c) Large only d)Larger and smaller
A
External surface is in higher energy state because: (a) Coordination number of surface atoms not satisfied (b) Extensive compressive strain on surface atoms (c) Grain boundaries (d) Dislocations
A
High elastic modulus in materials arises from (a) high strength of bonds (b) Weak bonds (c) Combination of bonds (d) none
A
Higher dislocation density ____ yield strength of the metal. a) increases b) decreases c) doesn't affect d) can increase or decrease
A
In a tensile test, at the end of the elastic zone, the: (a) Tensile strain increases more quickly (b) Tensile strain decreases more quickly (c) Tensile strain increases in proportion to the stress (d) Tensile strain decreases in proportion to the stress (e) Tensile strain remains constant
A
Materials that show very small plastic range beyond elastic limit are called (a) brittle materials (b) elastomers (c) elastic (d) ductile material
A
Materials that show very small plastic range beyond elastic limit are called: (a) Brittle Materials (b) Elastomers (c) Elastic (d) ductile materials
A
Non specific protein adsorption is known as? a) Fouling b) Antifouling c) Grafting d) None of the above
A
Passivity is not reason for inertness of the following (a) Au (b) Al (c) Ti (d) Ni
A
Steel has a greater modulus of elasticity than rubber because under the same stress: (a) The strain in steel is less than in rubber (b) The strain in steel is more than rubber (c) Elongation in steel is more than rubber (d) None of the above
A
The constant of proportionality in Hooke's Law is: (a) Modulus of Elasticity (b) Strain (c) Restoring force (d) Stress
A
The final point on the stere-strain graph is called (a) fracture point (b) Yield Point (c) Elastic Limit (d) Proportional Limit
A
The stress necessary to initiate yielding is: (a) Considerably greater than that necessary to continue it (b) Considerably lesser than that necessary to continue it (c) Greater than that necessary to stop it (d) Lesser than that necessary to stop it
A
Which of the following is the most stable state of metal? (a) Ore of metal (b) Pure metal (c) Corroded metal (d) Metal ion
A
Which of the following occurs in an ionic bond: (a) Oppositely charge ions attract (b) Two atoms share 2 electrons (c) Two atoms share more than 2 electrons (d) Like charged ions attract
A
Which of the following statements about polyethylene and polystyrene is correct: (a) PE has a lower Tg than PS (b) PE has a higher Tg than PS (c) Both have = Tg (d) None of the above
A
Which one of the following is related with a twin boundary? (a) Mirror image of atomic placement across the boundary (b) Similar crystal structure of metals forming the twin (c) Twinned alloy, untwin when heated (d) Twinning decreases the strength
A
DEFINE: Solid Solution
A mixture of two or more solids (solute and solvent) where the solids have similar diameter, crystal structure, and electronegativity
DEFINE: Grain Boundary
A region in the crystal lattice of higher atomic density that separates grains
Which one(s) of the below is/are used to add -NH2 and -OH groups: a) Plasma treatment b) Chemical vapor deposition c) Physical vapor deposition d) Self assembled monolayers
A, D
Process of corrosion is accelerated by?
Air and moisture Electrolytes in the water Metallic impurities
A solution of 2 or more metals is known as an ___________
Alloy
ASSERTION: Atactic polymers are much more difficult to crystallize REASON: Alternating placement of side groups prevents polymer chain packing in atactic polymers
Assertion is correct but reason is an incorrect statement
ASSERTION: Secondary bonds are weaker than primary bonds REASON: Secondary bonding does not require electron transfer or sharing
Assertion is correct, but the reason is wrong
Corrosion is a chemical reaction that involves: (a) The inside of the object changing from an element to a compound (b) The surface of the object changing from an element to a compound (c) Nothing happens (d) The surface of the object changes from one element into another element
B
During the formation of solid-state solution of Copper (Cu) and Nickel (Ni), the pre-dominant mechanism of inter-diffusion (considering similar atomic size of Cu and Ni) is: a) Interstitial Mechanism b) Substitutional Mechanism c) Can be either (a) or (b) d) None of the above
B
Impossible orbital among the following is: (a) 2p (b) 3f (c) 4d (d) 2s
B
In what physical state or states do IONIC substances conduct electricity: (a) Solid or dissolved in water (b) Liquid or dissolved in water (c) Solid or Liquid
B
Schottky defect is observed in crystals when (a) Some cations more from their lattice site to interstitial sites (b) Equal number of cation and anion is missing from the lattice (c) Some lattice sites are occupied by electron (d) Some impurity is present in the lattice
B
The solubility of solute in a solvent in a solid state is governed by substitutional solid solution rules. The solubility is more if: (a) Radii of solute are much smaller than that of solvent (b) Solute and solvent have a similar crystal structure (c) Solute has a low valency (d) All of the above
B
Toughness of metal with work hardening ___________ a) Increases b) Decreases c) Remains constant d) First increases and then decreases
B
Vitrification exploits the following property of glasses: a) Long range ordered structure b) Long range disordered structure c) High melting temperature d) Brittleness
B
Which of the following is a point defect in crystals? (a) Edge dislocation (b) Interstitial (c) Grain boundaries (d) Cracks
B
Which property decreases on strain hardening? a) Elastic modulus b) Percent elongation c) Yield strength d) Hardness
B
Which statement best describes why graphite is soft (a) Graphite is made up of only carbon atoms (b) it is layered (c) low melting point (d) None of the above
B
Which term is different from other options? a) Strain hardening b) Grain boundary refinement c) Cold working d) Work hardening
B
Why do atoms share electrons: (a) To become ions and attract each other (b) To attain noble gas electron configuration (c) to become more polar (d) To increase their atomic number
B
With decrease in temperature, hardness of material _____ and ductility ______ a) Increases, increases b) Increases, decreases c) Decreases, increases d) Decreases, decreases
B
With increasing concentration of plasticizer, the modulus of PVS (a) Increases (b) Decreases (c) Stays the same
B
You are examining a copolymer for its potential as a material for a vascular graft. You are trying to determine whether you want a high or low degree of crystallinity in the material. What type of structure for copolymers have a higher probability for crystallization?
Block and Alternating copolymers have a greater probability for crystallization.
ASSERTION: Crosslinked polymers degrade faster REASON: Crosslinked polymers will have fewer primary and secondary interactions holding the material together, hence degrades faster
Both statements are WRONG and reason does not support assertion NOTE: Crosslinked polymers degrade slower b/c the have MORE primary and secondary interactions
ASSERTION: External surface is in higher energy state REASON: Coordination number of surface atoms is not satisfied
Both statements are correct and reason DOES explain assertion
ASSERTION: Transition through Tg to Tc leaves to highly ordered crystalline state REASON: Polymer chain energy and motion increases through Tg to Tc
Both statements are correct and reason DOES explain assertion
ASSERTION: Twin boundary occurs when there is a mirror image of atomic placement across the boundary REASON: Crystal Structure is same both inside and outside of the twin
Both statements are correct but reason does NOT explain assertion
ASSERTION: Hydrolysable polymers have low molecular weight and less cross link points REASON: Chain entanglements restricts the influx of water molecules
Both statements are correct, reason does not explain assertion
ASSERTION: ceramics are generally more stable than metals in physiological environments REASON: water molecules can dissolve ionic compounds
Both statements are correct, reason does not explain assertion
ASSERTION: hydrophilic polymers will swell in the physiological environment REASON: water molecules in polymer chains reduces the GTT
Both statements are correct, reason does not explain assertion
ASSERTION: a biopolymer with Tg = 50 degC will be difficult to hydrolyze under physiological conditions REASON: rubbery state of a polymer encourages water penetration
Both statements are correct, reason does not explain assertion NOTE: Glassy state is rigid and makes it difficult to absorb water
ASSERTION: A biopolymer with Tg = 50degC will be easier to hydrolase under physiological conditions REASON: Glassy state of a polymer encourages water penetration
Both statements are incorrect
Anisotropic materials are materials with (a) Different properties in all directions (b) Same properties in all directions (c) Different properties at different location (d) Same properties at different location
C
Atactic polystyrene (tg = 160degC) quenched from 120degC to room temp: (a) is a rubbery material (b) crystallizes (c) is a glassy material
C
High density polyethylene cooled slowly from 160 degC to room temperature (a) is still amorphous (b) crystallizes (c) is a mixture where some regions are rubbery and some are glassy
C
Hydrogen bonding occurs in molecules when: (a) A hydrogen atom forms a covalent bond with one other atom (b) A H atom forms covalent bond with more than one atom (c) A H atom bonded to small electronegative atom is attracted by an electron pair on an electronegative atom on an adjacent molecule (d) A H atom forms an ionic bond with one other atom
C
Imperfections most likely to be present in an alloy single crystal include all of the following except: (a) dislocation (b) vacancies (c) Grain boundaries (d) pores
C
Passivity is due to: (a) higher EMF (b) Lower EMF (c) Oxide film
C
Polyethylene and polypropylene (in the melt) will (a) Form hydrogen bonds with one another (b) Interact strongly due to polar forces (c) Only interact weakly
C
Sodium and chlorine react together to form the compound sodium chloride. How are sodium and chlorine held together in this compound? (a) Na and Cl share electrons and are held together by their attraction for the shared pair of electrons (b) Na and Cl join together to form molecules (c) Positive Na ions and negative chloride ions form a crystal lattice
C
The chemical Formaldehyde has a chemical formula of CH2O. The carbon atoms needs and can share 4 electrons. The oxygen atom needs and can share 2 electrons. The hydrogen atoms need and can share 1 electron. State the structure that is true for this bond. (a) The oxygen atom has a single bond with the carbon atom, and the hydrogen atoms have a double bond with the Carbon atom. (b) The hydrogen atoms each have a double bond with the Oxygen atom, and the Oxygen atom has a single bond with the Carbon atom. (c) The carbon bond has a single bond with both hydrogen atoms, and a double bond with the oxygen atom. (d) The carbon atom has a single bond with they Oxygen atom, and the Hydrogen atoms have a single bond with the Oxygen atom.
C
Time dependent permanent deformation is called (a) Plastic deformation (b) Elastic Deformation (c) Creep (d) Inelastic Deformation
C
Toughness of a material is equal to area under_________ part of the strep-strain curve (a) Elastic (b) Plastic (c) Both (d) none
C
Which property deteriorates on strain hardening? a) Hardness b) Ultimate Tensile Strength c) Ductility d) Yield strength
C
Why are metals good conductors of electricity: (a) They contain ions that are free to move (b) They contain atoms that are free to move (c) They contain electrons that are free to move
C
Select the description(s) that correctly define biocompatibility: (a) The ability to heal an injured or diseased organ or tissue (b) The capacity to encourage damaged tissue to regenerate (c) Therapeutic performance (d) No harm to the host body
C, D
What happens to corrosion rate as pH decreases?
Corrosion rate increases
What is pitting corrosion? Where are pits usually initiated? Describe electromechanical mechanism for the growth of a pit in a SS implant immersed in an aerated sodium chloride solution
Corrosion that leads to "pits" (similar to pores), these grow in the direction of gravity and begin on the surface. The metal ions react with chloride ions, forming a hydroxide and hydrogen chloride. This lowers the pH of the material and increases the rate of corrosion
Solid A is very hard, electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it? (ex. Ionic, Covalent, Metallic)
Covalent
Corrosion that involves the stagnation of solution is known as ________ corrosion
Crevise
Annealing improves (A) Grain size (B) Mechanical properties (C) Electrical properties (D) All of above
D
Autoclaving does not involve the following: a) High temperature b) High pressure c) Moist air d) Dry air mixed with steam
D
Biodegredation will be more for a polymer with: (a) More molecular weights and high crystallinity (b) Low molecular weights and high crystallinity (c) More molecular weights and less crystallinity (d) Low molecular weights and less crystallinity
D
Figure out the off point in the following (a) Proportional limit (b) Elastic limit (c) Yield Point (d) Fracture Point
D
If the radius of a wire stretched by a load is doubled, then it's young's modulus will be: (a) doubled (b) halved (c) increase by 4x (d) Remains unaffected
D
One of the characteristic property of thermoplastic polymeric materials (a) High temperature stability (b) High mechanical strength (c) High elongation (d) Low hardness
D
Select the off statement about functionality of a monomer: (a) Allows a polymer to polymerize (b) Minimum value required is 2 (c) Can give rise to cross-linked and/or network polymers (d) Improves crystallinity of a polymer
D
Shape of street-strain curve for a material depends on (a) strain (b) Strain rate (c) Temperature (d) All
D
The advantage of radiation grafting is that: a) Can be performed at low T b) Can be used to graft hydrophilic and hydrophobic polymers c) Can be used to synthesize copolymers d) All of the above
D
What is/are the type of attraction between water molecule in ice: (a) Dipole-Dipole interactions (b) Electrostatic interaction between charged atoms (c) Hydrogen bonds (d) All of the Above
D
Which of the following polymers would you expect to have the best barrier properties: (a) atactic polystyrene (b) A random ethylene/propylene copolymer (50/50) composition (c) low density polyethylene (d) high density polyethylene
D
Which of the following statements about water is INCORRECT? (a) Water molecules contain a covalent bond (b) Water has weak forces between bonds (c) Water has a low melting point (d) Water molecules contain H+ and OH- ions
D
Which one of the following is the objective of biomaterial's surface modification? a) To promote fouling b) To promote bacterial adhesion c) To promote thrombogenecity d) To enhance corrosion resistance
D
Graphite cannot be classified as (a) Conducting solid (b) network solid (c) Covalent Solid (d) Ionic Solid
D (b/c electrons can not go b/w layers)
Which statement is not true about carbon nanotubes: (a) Tubular allotrope of carbon (b) Wrapped hexagonal graphite sheets (c) diameter ranges from 2-100 nm (d) high volume to surface ratio
D (should be surface to vol ratio)
(T/F) Atomic number changes during the conversion of an atom to cation or anion
False
(T/F) Biomaterials do not exist naturally
False
(T/F) Grain boundary is a location of higher atomic density
False
(T/F) Since ceramics are non-metallic in nature, they are covalently bonded only
False
(T/F) Strength of a thermoplastic polymer can be increased by removal of a highly polar atom on the main carbon chain
False
(T/F) The melting point of a polyester (thermosetting polymer) is 200 degC
False
(T/F) A pore is a two-dimensional defect
False (3-D)
(T/F) In the molecule of H2 the single bond is polar covalent
False (not polar)
(T/F) Since ceramics are non-metallic in nature, they are only covalently bonded
False (polymers are covalently bonded)
(T/F) Strength of a thermoplastic polymer can be increased by removal of a highly polar atom from the main carbon chain
False (would decrease strength)
(T/F) Graphite possess electrical conductivity in the direction perpendicular to the graphene sheets
False, electrons can not move between sheets
Describe the structure of grain boundaries. Why are grain boundaries favorable sites for corrosion and the growth of precipitates?
Grain boundaries have a different structure from the grains themselves, and are in a higher energy state. This leads to the promotion of corrosion
Explain why is H2 a gas at room temperature while H2O is a liquid
H2 only has one covalent bond, while H2O has both covalent and hydrogen bonding. This results in a higher B.P. because the bonds are harder to break apart in water
DEFINE: Plasticizer
Increases the space b/w polymer chains
A biomaterial company has produced several metallic hip implants that have a fatigue strength of 20,000 psi. These implants prematurely failed during high bending loads. Design a process by which the remaining implants can be salvaged by improving their mechanical properties?
Mechanical strength can be improved by strain hardening or by making an alloy. Another method could be grain size refinement or recrystallization.
Element X has 2 valence electrons, Element X is:
Metal
____________ are the class of materials with the highest thermal and electrical conductivity
Metals
Explain why many metallic materials exhibit strain hardening? Does a strain hardening mechanism depend on grain size? Does it depend on dislocation density?
Metals do not require the charge balance requirement, so strengthening by strain hardening is obvious for metals. Strain hardening is dependent on grain size, smaller grains with higher grain boundary area can prevent dislocation motion, thereby strengthening the mater. As strain hardening increases, so does dislocation density.
A researcher has created a biodegradable polymeric scaffold that degrades through surface erosion mechanism. Long term cell adhesion is detrimental for this application. However, it was found that cells will not attach with this substrate. The researcher is considering covalent attachment of peptide sequence using photo-grafting. Will you support the idea? Why or why not? Would bulk modification with the peptide sequence be a more or less appropriate method of modification for the intended result?
No, ultimately the material will still degrade leaving the non cell friendly surface exposed. Bulk modification would be a better method of modification.
Someone in your company has developed a material that closely matches the native mechanical properties of bone, and would be an ideal femoral stem of a hip joint prosthesis. Unfortunately, the material is cytotoxic. Another engineer in the company has developed a coating that can be applied to the material, sealing the cytotoxic material away from the body. Is this a viable option?
Not necessarily. Delamination of the coating may affect long term use.
You are considering two different surface modification techniques (Plasma Discharge and self-assembled monolayers) to control protein adsorption to the interior surface of a drug delivery nanoparticle. Which method would be better suited for this particular application? Why?
SAM technique can be effectively used on nanoparticles
__________ materials have the ability to sense and respond to external stimuli
Smart materials
You are given a relatively hydrophobic material with hydrophilic polyethylene glycol (PEG) chains covalently attached to its surface. What do you expect to be the effect of PEG attachment on protein adsorption to the material surface?
Steric hindrance from PEG chains will restrict protein adsorption
Corrosion is a chemical reaction that involves
The surface of the object changing from an element to a compound
(T/F) Corrosion involves the loss of material
True
(T/F) Corrosion is a combination of chemical and physical properties
True
(T/F) Corrosion is an oxidation reaction
True
(T/F) Due to corrosion, useful properties of metals such as malleability, ductility, and electrical conductivity are lost
True
(T/F) Ions tend to have the same electronic configuration as noble gases
True
(T/F) The glass transition temperature of a polymer can be changed using a plasticizer
True
(T/F) Plastics and ceramics are immune to many forms of corrosion because they are not good conductors of electricity
True, they have no free electrons and can not be oxidized
You have designed a bone plate that is manufactured via rolling under cold working conditions, and tests show good biocompatibility results for the device. The Manufacturing Department has put in a request to change the processing method to rolling under hot working conditions, in an effort to reduce the total manufacturing cost. Since the material from which the device is fabricated will not change, do you need to rerun the biocompatibility tests? Why or why not?
YES. Processing techniques changes surface properties
Waters high boiling point can be explained by __________ bonding
hydrogen bonding
_____________ have a characteristic size smaller than 100 nm
nanoparticles/nanomaterials