Lecture 13 Flashcards
advantages of biometals?
- high strength
- high ductility
- sustains tensile and bending loads
- easy to fabricate
- easy to strengthen
- easy to sterilize
- conductive (pace makers)
- made in high volumes
- good fatigue strength
disadvantages of biometals?
- corrosion and toxic products
- inertness does not allow tissue stabilization
what are the grades of stainless steels?
SS 316LVM (low carbon vacuum melt) –> bone screws and plates
SS 304 (pacemakers)
SS416, 420, and 302 (surgical tools)
what are SS 316LVM properties?
- austenitic
- nonmagnetic
- least corrosion resistant biometal
- rarely fails (high strength)
- short term toxicity is low
advantages of SS 316LVM
- cheap
- easy to machine
- readily available
- good strength
- acceptable corrosion resistance
- surgeons can shape some at operation
disadvantages of SS 316LVM7
- high susceptibility to localized corrosion (pitting and crevice)
- susc. to wear corrosion
- variability of properties from different melts
- tends to pit up tool metal via transfer
- corrosion resistance depends on high surface polish
- limited lifetime in body
- high conc. of ions in surrounding tissue
what is the corrosion resistance of SS 316LVM influenced by?
- work hardening makes it more susc. to corrosion
- high inclusion content
- cracks
- poor surface finish
- large grain size
- high residual stresses
- irregular bending by surgeon
- fatigue
how does tissue reaction occur with SS 316 LVM?
the corrosion products are generally tolerated but wear particles can cause inflamm, esp in joints;
Cr is rapdily excreted
Ni is quite allergenic
what composes Cr-Co alloys?
Co plus %25 Cr
properties of Cr-Co alloys?
high yield stress
high corrosion resistance
low wear rate
high strength
what are Co-Cr alloys mainly used for
femur heads (hip implants), inramedullary rods
how biocompatible are Co-Cr alloys?
Co is toxic but in high doses (increased heart size = failure)
-Co powder causes sarcoma in rats
advantages of Tivanium (Ti6Al4V) & alloys?
- best corrosion resistance
- elastic mod. close to that of bone
- promotes osteointegration
- ductile and workable
- may help in fighting infx??
disadv. of tivanium & alloys?
- diffiult to manufacture bc v reactive (burns in air)
- poor wear resistance
- very high coeff. of friction
- poor machinability
what is tantalum used for?
wires, staples, and bone plates
adv of tantalum?
high ductility
disadv of tantalum?
can cause granuloma
may not do well depending on pH, O2, and under stress
study slide 18
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