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Biomaterials > Unit 1 > Flashcards

Unit 1 Flashcards

1
Q

What are two important aspects of identifying a biomaterial to be used in the human body?

A

Functional performance and biocompatibility.

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2
Q

What material is widley used as biomaterials for their strength and toughness?

A

Metal

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3
Q

Give 3 examples of metals used throughout the human body?

A

316L stainless steel, Titanium, Cobalt Chromium alloys

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4
Q

What is the most common type of medical grade stainless steel? Name 3 elements in this type of ss…

A

316L Stainless Steel

iron, chromium, nickel

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5
Q

State 3 physical properties of metals that make them attractive for their use as a metallic biomaterial?

A

Strength, usually good corrosion resistance, high melting point

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6
Q

What element increases the formation of carbon carbide (Cr23C6) in 316L Stainless stell?

A

Carbon

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7
Q

Name the overall classification of materials that could potential used as biomaterials.

A

Metals, Ceramics, Polymers, Composites

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8
Q

Which of these metallic biomaterials has the best corrosion resistance;

Cobalt alloys, Stainless steel, or pure Titanium?

A

Titanium

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9
Q

Why is pure gold not useable in dental applications? What is added to

it to make it a better dental biomaterial?

A

Pure Gold is too soft, It is enriched by platinum

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10
Q

Why is it advisable to reduce carbon content in medical grade stainless

steel material?

A

Reducing Carbon content in 316L stainless steel decreases corrosion in vivo by reducing carbide formation at grain boundaries of the metal. Carbide is unwanted because it hinders surface oxide formation.

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11
Q

What is the purpose in adding Tungsten or nickel to cobalt based

alloys?

A

Tungsten and nickel are added to cobalt based alloys to improve machinability and fabrication

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12
Q

State three reasons why amalgam is preferred as a dental biomaterial?

A

Soft application with quick hardening

endurable for ~8-10 years

inexpensive

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13
Q

. Metals are widely used as biomaterials due to their ________ & _______.

A

Strength and toughness

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14
Q

List four metallic implants materials and explain the composition

properties and potential applications for one of them.

A

Nitinol, Titanium, 316L stainless steel, cobalt chromium alloys.

Stainless steel: Made of mostly iron, some nickel, some chromium and a small amount of Carbon. Potential applications include bone scres.

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15
Q

What is biocompatibility?

A

Use of a material is a specific application in which it does not elicit a negative response to the biological environment.

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16
Q

What is Nitinol?

A

A shape memory alloy that can return to a predetermined shape when heated.

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17
Q

Name 3 types of medical devices?

A

Cardiac stents, Drug delivery systems, orthopedic bone screws

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18
Q

State two ways in which atoms of metals mix to form alloys.

A

(an alloys is a metal comprised of 2 or more elements)

Alloys mix by either substitution or interstitial atomic arrangement

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19
Q

Describe shape memory alloys?

A

Shape memory alloys are able to return to a predetermined shape once heated

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20
Q

What is the outer layer that protects a metal from corrosion?

A

Oxide layer

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21
Q

Although several types of stainless steel are available for implant use,in practice the most common is grade 2, _____ stainless steel. This

stainless steel alloy is composed predominantly ____, which makes up approximately 60-65%, plus addition of ____, makes up 17-20% of the

alloy. Additionally, approximately 12-14% of the alloy is comprised of _____. In order to reduce the possibility of in vivo corrosion, only trace

amounts less than 0.03% of _____ are found in the alloy.

A

316 L

iron

chromium

nickel

Carbon

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22
Q

Co-Cr-Mo alloys, ASTM F75 or ASTMF799 are mostly made up of Cobalt, comprising ______%. Also in the compound is approximately _____% of chromium and roughly ____% of molybdenum.

A

58-69

27-30

5-7

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23
Q

Define unit cell as it related to metallic crystal structure

A

smallest repetitive volume which contains the complete lattice pattern.

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24
Q

State and describe three types of imperfections / defects in the metallic crystal structure

A

vacancy (point defect): one atom is missing causing deformation around it.

Self interstitial (point defect): one extra atom between atomic sites causes distortion of plane

Dislocation (line defect): a slip between crystal planes, produces plastic deformation

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25
Q

State and describe two metal fabrication methods.

A

Extrusion: using a force to push material into a die to achieve a new shape.

Forging: hammering or stamping a metal into a specific shape

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26
Q

In an electrochemical redox reaction, loss of electrons is ____ and a gain of electrons is ____.

A

Oxidation.

Reduction

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27
Q

Describe the mechanism of metallic corrosion

A

The corroded state is desired since it is the lowest energy state (metals like to lose electrons). Metal atoms ionize, go into solution and combine with oxygen and metal flakes off.

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28
Q

. Define galvanic corrosion

A

two different metals exist in close proximity, one tends to oxidize while the other gains it’s electrons.

29
Q

What is corrosion?

A

Corrosion is an electro-chemical attack resulting in material degradation. It depends on many factors, but primarily oxidation/reduction reactions, and kinetic barriers.

30
Q

What are the two primary factors that drive metallic corrosion?

A

oxidation/reduction reactions and kinetic barriers.

31
Q

What substance is oxidized and which substance is reduced in the formation of rust?

A

Iron Is oxidized while oxygen is reduced in the formation of rust

32
Q

What is the main function of the oxide layer on the surface of a metal?

A

Protection: Resistance to corrosion

33
Q

State and describe three types of corrosion.

A
  1. Galvanic: 2 metals in close proximity, one oxidizes while one gains electrons
  2. Uniform corrosion: evenly distributed over entire corrosion region
  3. Selective leaching: one consituent of an alloy is preferentially removed, leaving behind an altered, weakened, residual structure
  4. Pitting corrosion: formation of pits and local thickness reduction due to higher concentration of ions is certain places
34
Q

Name and describe two basic reactions associated with corrosion.

A

Oxidation: reaction of metal with oxygen

Hydroxylation: Reaction of water under alkaline or oxidizing condition, yields a hydroxide or hydrated oxide

35
Q

How does galvanic corrosion occur?

A

metals are in an electrolytic environment. 2 metals are in close proximity, one loses electrons and is oxidized while the other gains those electrons. The metal being oxidized is corroding

36
Q

Which is the reducing agent and which is the oxidizing agent in the reaction below?

Cu(s) + 2Ag+(aq) –> Cu2+(aq) + 2Ag(s)

A

Reducing: silver

Oxidizing: copper

37
Q

In the galvanic series, which (gold, magnesium and titanium) is considered the most active metals in seawater?

A

magnesium

38
Q

Which type of corrosion occurs when two different metals/alloys are in close proximity in an electrolytic environment? A) Pitting Corrosion B) Crevice Corrosion C) Galvanic

Corrosion D) Intergranular Corrosion

A

Galvanic

39
Q

What is fretting corrosion?

A

Caused by relative motions (may be micromotions) in highly loaded devices

40
Q

What can one do to protect against corrosion?

A

Kinetic barriers such as coatings offer protection

41
Q

Describe uniform attack corrosion?

A

evenly distributed corrosion over entire corrosive region

42
Q

Explain deposit corrosion mechanism

A

moisture rich foreign substances of the environment adhere to metal surface causing the spot its covering to corrode because of lack of oxygen

43
Q

What is the difference between galvanic corrosion and fretting corrosion?

A

galvanic corrosion must be in an electrolytic environment where 2 metals exist, 1 losing and 1 gaining electrons. Fretting corrosion may deal with different metals, but it is due to micromotions of a load bearing material.

44
Q

Describe the possible effects of corrosion of medical devices

A

Ions lost due to corrosion may elicit a toxic reponse by the body and could be dangerous to the patient as well as may cause device failure.

45
Q

What are some of the advantages and disadvantages of the use of Magnesium for implantation?

A

Advantages: biodegradable, lightweight, close elastic modulus with human bone

Disadvantages: fast degredation rate before end of healing process, fast hydrogen evolution

46
Q

Describe the corrosion behavior of unprotected Mg alloys, and how does this behavior affect its potential as a biodegradable metal?

A

Unprotected magnesium alloys will degrade with hydrogen evolution. As magnesium dissolves it reacts with water and generate hydrogen bubbles which cause a pH increase

47
Q

State four potential applications for use of Mg alloys as a biodegradable metallic implant

A

bone screws, cardiac stents, bone wires, bone plates

48
Q

What are the ways to increase corrosion resistance for magnesium?

A

Surface coatings

Different alloy combinations

49
Q

Describe two coating strategies to control behavior of bagnesium

A
  1. Layer by layer assembly: Does not affect magnesium corrosion process, customizable thickness, uses alternating charge chains,
  2. Self assembled monolayers: A spontaneous process in which nanoscale layers of molecules are adsorbed on a substrate secondary to bonding between surface and molecular head groups. Doesn’t affect magnesium corrosion properties. Layer expands/contracts uniformly with metal, can be loaded with multiple drugs, drug release rate is tunable.
50
Q

What are the 2 types of hydrocarbons that monomers can be classified as? Which is more susceptible to polymerize and why?

A

Saturated v. Unsaturated Hydrocarbons.

Unsaturated hydrocarbons are more susceptible to polymerize because they are more reactive and can grow further

51
Q

List and briefly describe the classification of polymer?

A

Polymers are classified by being Thermoplastic, thermoset, composite, or an elastomer/rubber

Thermoplastic: long chains with limited-no cross linking, behave like plastic and can be melted and remolded.

Thermoset: highly cross linked, usually brittle, decompose when heated and can’t be reshaped

Elastomers and rubbers: light cross linkage, large amount of elastic deformation possible without plastic deformation

52
Q

Schematically describe each of the copolymer chain structures (block, graft, alternating,)

A

A copolymer is two or more monomers polymerized together, arrangements are random, alternating, block, and graft.

random: polymer A & B are in random variation along a chain

block: A & B are in alternating large sections

alternating: A&B alternate every other time

Graft: chains of B are grafted onto A

53
Q

What is a saturated hydrocarbon?

A

One in which all Carbons make 4 single bonds

54
Q

State and schematically describe the three steps in free radical / chain polymerization

A

A free radical combines with a monomer to form an initiator. The initiator propagates with a group, this process must begin with the initiator. Termination happens when disproportionation occurs, combination occurs, or the supply of monomers runs out. (Multiple chains can be growing simultaneously)

55
Q

What are the three possible chain tacticity found in polymeric chains?

A

Tacticity is stereoregularity of chains. There are

Isotactic: R groups are on the same side of chain

Syndiotactic: R groups alternate sides

Atactic: R groups are random

56
Q

What are the ways to quantify polymeric chain size?

A

Degree of polymerization

chain length

molecular weight of chain

end-to-end distance

57
Q

What are the different covalent chain configurations? List in order of increasing streng

A

Linear

Branched

Crosslinked

network

(increasing strength direction)

58
Q

What is the distinction between a saturated and unsaturated hydrocarbon

A

Each carbon is bonded to 4 other atoms in hydrocarbons but is not in unsaturated hydrocarbons( unsaturated can have multiple bonds)

59
Q

What is thermoplastic polymer? Give an example.

A

One that has little to no cross linkage, can be melted then remolded and recycled.

60
Q

What is thermoset polymer? Give an example.

A

One that has high cross linkage, usually brittle. when heated it deforms and cannot be recycled

61
Q

What are elastomers and rubbers?

A

Have rare cross linkage, can go through deformation and then go back to original form( with a limit)

62
Q

What are the different kinds of copolymers? Draw pictures to illustrate the various types.

A

alternating, block, graft, random

63
Q

What are some examples of polymer additives?

A

fillers like silica gel

stabilizers like UV protectants

colorants like dye

flame retardants

64
Q

Name different processing methods of plastics

A

thermoplastic: can be reversibly cooled and recyceld. heat till soft then shape then cool
thermoset: when heated it forms a network, degrades and does not melt.

65
Q

What is a polydispersity index (PDI)?

A

Molecular weight to molecular number average ratio.

PDI=1 indicates all molecules have equal length and are monodispersed.

PDI=1 is possible for natural proteins where synthetic polymers need P above 1.5 and < 5.

66
Q

What is a thermoset polymer?

A

polymer that has high cross chains. brittle usually. cannot be recycled. if heated it degrades.

67
Q

State the difference between cis and trans isomers in a polymeric chain.

A

cis: bulky groups on same side of chain
trans: bulky groups on oposite sides of chain.

68
Q

Define polymer crystallinity. Describe how a polymer crystal forms.

A

Chains of polymers can be very long, so they fold on themselves. polymers don’t usually have 100% crystallinity, usually there are regions of high crystinlinity and then amorphous regions.

crystalline regions grow with controlled annealing.

speherulites are fast lamellar, layered structure growth, inbetween are amorphous regions.

Biomaterials (4 decks)

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