metals and alloys exam 1

Question 1

what are applications of metals and alloys in biomaterials

Answer 1

bone and joint replacements, dental implants, cardiovascular devices, surgical instruments

Question 2

what does metallic bonding consist of

Answer 2

positive ions surrounded by a sea of electrons

Question 3

what are the four types of crystal structures atoms are packed into

Answer 3

primitive, body centered (equal in the middle), side centered (2 atoms - one on top, one on bottom), face centered (atoms on all faces)

Question 4

what is polycrystalline

Answer 4

made of many single crystals (grains) - most metals are

Question 5

what is an alloy

Answer 5

comprised of two or more elements (at least one metallic) for easier processing and/or controlled physiochemical properties

Question 6

what are the classifications of alloys

Answer 6

ferrous: steel (Fe + C, Cr, Ni, Mo, etc.)
non-ferrous: titanium alloys (Ti + Ni, V, Al, etc.) or cobalt alloys (Co + Cr, Mo, Ni, etc.)

Question 7

what are the types of metallic crystal defects

Answer 7

point defects, line defects/dislocations, grain boundaries, macroscopic defects

Question 8

what are the four types of point defects

Answer 8

• substitutional impurity (replaced by another element - might be necessary)
• vacancy (element is gone)
• self-interstitial (in place it shouldn’t be)
  impurity interstitial

Question 9

what are the steps for fabricating a metallic implant

Answer 9

mineral deposits -> metallic raw material in bulk form -> stock shapes -> preliminary implant device -> final implant device -> market

Question 10

why do metallic implants fail

Answer 10

fatigue, wear, corrosion

Question 11

what is fatigue

Answer 11

sudden and catastrophic failure in structures due to dynamic and fluctuating stresses (stress levels lower than yield strength)
concern for dental and joint implants

Question 12

what is wear

Answer 12

loss of material due to contact and relative movement
concern for joint prostheses (load-bearing)

Question 13

what are wear particles

Answer 13

something that immune system tries to get rid of that then causes side effects, such as osteolysis (destruction of bony tissue)

Question 14

what is corrosion

Answer 14

deterioration of materials by chemical or electrochemical reaction with the environment
i.e. oxidation reaction at anode or reduction reaction at cathode

Question 15

what are common stainless steel elements

Answer 15

316Ls (low carbon) - chromium, nickel, molybdeum - need cold work to increase strength

Question 16

what are desirable microstructure of 316L SS

Answer 16

single phase austenite (non-magnetic), no free ferritic phase (magnetic) or carbide phase, <100 um uniform grain size

Question 17

what are the properties of 316L

Answer 17

good biocompatibility
high strength
easy processing
good corrosion resistance
possible allergy to Ni and heavy metal toxicity (minimized by alloying)

Question 18

why are titanium alloys the metal of choice for load bearing implants

Answer 18

can reduce corrosion, excellent biocompatibility, high strength and low modulus for reduced stress shielding, osseointegration

Question 19

what is the microstructure of titanium

Answer 19

commercially pure Ti - single phase

Ti-6Al-4V - two phases (alpha (more Ti, less V), beta (more V, less Ti) body centered cube)

Question 20

what is osseointegration

Answer 20

direct structural and functional connection between ordered, live bone, and the surface of a load carrying implant - doesn’t need connective tissue

Question 21

what does stress shielding do

Answer 21

change the force (stress) distribution on the neighboring bone - weak and leads to pain and implant loosening

weight loaded leads to dense skeleton

Question 22

what is Nitinol

Answer 22

Nickel Titanium Naval Ordnance Laboratory, 1962
Ni-Ti alloy which were developed to overcome the deficiencies of pure metals for fabricating medical devices

Question 23

what are thermal and elastic shape recovery

Answer 23

thermal = shape memory (thermal memory - goes back to original w heat)
elastic = super/pseudo elasticity (mechanical memory - goes back to original once force is gone)

Question 24

what are types of cobalt alloy implants

Answer 24

Co-Cr-Mo
Co-Cr-W-Ni
Co-Ni-Cr-Mo-Ti

Question 25

what is the process of processing cobalt alloys

Answer 25

pattern tree, shell-making, investment casting, casting

Question 26

what are the properties of cobalt alloys

Answer 26

good biocompatibility, high yield and fatigue strength, excellent wear resistance, good corrosion resistance

Question 27

what are applications of liquid metals and examples

Answer 27

EGaIn, GeInSn (alloys)
-stretchable/wearable electronics
- microfluidic devices
- reconfigurable devices
- electronic and medical cooling