Orthopaedics Flashcards
Orthopaedic biomaterial wishlist
withstand cyclic loading high strength ductility fracture toughness corrosion resistance the usual
Most common orthopaedic biomaterials
Metals - Ti alloy, Co-Cr-Mo alloy, stainless steel
Polymers - PMMA, UHMWPE
Ceramics - alumina, zirconia
Polymers in Orthopaedics
Articulating surfaces
First Teflon but creep, then UHMWPE
polymer debris of UHMWPE against Co-Cr alloys
solve by xlinking with gamma radiation, but lose tensile strength
PMMA for bone cement
Ceramics in Orthopaedics
Superior wear resistance than m-m or m-p
resistance to oxidation
need small grain size for high stiffness and low friction
Clinical concerns of materials in Orthopaedics
wear
corrosion
local tissue effects of wear and corosion
remote and systemic effects of wear and corosion
3 wear processes
1 - abrasion (harder surface plows softer)
2 - adhesion (softer smeared onto harder surface, film)
3 - fatigue (loading/unloading forms cracks)
Wear rate
wearing in period - high wear rate
over time rate decreases to become linearly dependent on contraction force and sliding distance
Corrosion variables
geometric metallurgical mechanics solution mechanical loading
Passivating oxide films
formation of passive films to prevent oxidation
consist of metal oxides
form spontaneously
must be compact, cover entire surface, withstand mechanical stressing and abrasion
Local tissue effects of wear and corrosion
osteolysis from release of: - pro and anti inflam cytokines - bone resportion factors - RANKL fibrous encapsulation and FBR to debris
Remote and systemic effects of wear and corrosion
Wear debris release chemically active metal ions
can bind to protein and transported -> metal toxicity
dermatitis, hypersensitivity, carcinogenesis
wear particles found in lymph nodes
Polyethylene preventative strategies
reduce size of femoral head
reduce manufacturing defects
improve surface finish
eliminate PE altogether -> m-m c-c new interest
Metal preventative strategies
nitriding decrease wear in Ti
polish to be smooth
matching moduli or CSAs -> improved load transfer to bone
2 factors of corrosion
thermodynamic driving forces which cause corrosion (ox/red)
kinetic barrier to corrosion
5 structural characteristics of passivating oxide films
very thin semiconductor characteristics ratio of oxide specific volume needle or dome shape morphology can be abraded or fractured (from micromotion or stresses)
