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
