metals and alloys exam 1 Flashcards
what are applications of metals and alloys in biomaterials
bone and joint replacements, dental implants, cardiovascular devices, surgical instruments
what does metallic bonding consist of
positive ions surrounded by a sea of electrons
what are the four types of crystal structures atoms are packed into
primitive, body centered (equal in the middle), side centered (2 atoms - one on top, one on bottom), face centered (atoms on all faces)
what is polycrystalline
made of many single crystals (grains) - most metals are
what is an alloy
comprised of two or more elements (at least one metallic) for easier processing and/or controlled physiochemical properties
what are the classifications of alloys
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.)
what are the types of metallic crystal defects
point defects, line defects/dislocations, grain boundaries, macroscopic defects
what are the four types of point defects
- substitutional impurity (replaced by another element - might be necessary)
- vacancy (element is gone)
- self-interstitial (in place it shouldn’t be)
impurity interstitial
what are the steps for fabricating a metallic implant
mineral deposits -> metallic raw material in bulk form -> stock shapes -> preliminary implant device -> final implant device -> market
why do metallic implants fail
fatigue, wear, corrosion
what is fatigue
sudden and catastrophic failure in structures due to dynamic and fluctuating stresses (stress levels lower than yield strength)
concern for dental and joint implants
what is wear
loss of material due to contact and relative movement
concern for joint prostheses (load-bearing)
what are wear particles
something that immune system tries to get rid of that then causes side effects, such as osteolysis (destruction of bony tissue)
what is corrosion
deterioration of materials by chemical or electrochemical reaction with the environment
i.e. oxidation reaction at anode or reduction reaction at cathode
what are common stainless steel elements
316Ls (low carbon) - chromium, nickel, molybdeum - need cold work to increase strength
what are desirable microstructure of 316L SS
single phase austenite (non-magnetic), no free ferritic phase (magnetic) or carbide phase, <100 um uniform grain size
what are the properties of 316L
good biocompatibility
high strength
easy processing
good corrosion resistance
possible allergy to Ni and heavy metal toxicity (minimized by alloying)
why are titanium alloys the metal of choice for load bearing implants
can reduce corrosion, excellent biocompatibility, high strength and low modulus for reduced stress shielding, osseointegration
what is the microstructure of titanium
commercially pure Ti - single phase
Ti-6Al-4V - two phases (alpha (more Ti, less V), beta (more V, less Ti) body centered cube)
what is osseointegration
direct structural and functional connection between ordered, live bone, and the surface of a load carrying implant - doesn’t need connective tissue
what does stress shielding do
change the force (stress) distribution on the neighboring bone - weak and leads to pain and implant loosening
weight loaded leads to dense skeleton
what is Nitinol
Nickel Titanium Naval Ordnance Laboratory, 1962
Ni-Ti alloy which were developed to overcome the deficiencies of pure metals for fabricating medical devices
what are thermal and elastic shape recovery
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)
what are types of cobalt alloy implants
Co-Cr-Mo
Co-Cr-W-Ni
Co-Ni-Cr-Mo-Ti
