DP-1 Milestone 3 - Materials Selection (Liner)

Structure

Polyether-ether-ketone (PEEK)

Polymer

Semi-crystalline

Covalent

-Stiff aromatic polymer backbone

-Thermally stable

-Resistant to hydrolysis

Silicon nitride

Ceramic

Crystalline

Covalent

-Si3N4

-Covalent bonding between metallic silicon and gaseous nitrogen

Alumina

Ceramic

Most naturally occurring form of alumina is corundum, oxygen atoms form slightly distorted hexagonal packing in the lattice structure.

Ionic Bonding

The strong ionic bonds between alumina molecules promotes desired properties further examined.

alpha alumina has shown shrinkage in microstructural characterization, this could be good as more alumina could be used for Diane Chambers, further supporting her frailer bones.

Porous Titanium

Metal

Crystalline Structure with hexagonal pattern at ambient temperature and pressure.

Metallic Bonds, bonds between valence electrons and nucleus is relatively weak so outer electrons leave individual atoms and become apart of an “electron cloud”. Valence electrons have considerable mobility and give metallic properties.

Porous Titanium has uniform, bimodal, gradient honeycomb and closed-pore structures. Pores lead to reduced weight and relatively high mechanical strength.

Isotropic

Cobalt-Chromium

Metal

1-1 cobalt and chromium bonded together

Metallic intramolecular & dipole intermolecular

UHMWPE (Polyethylene)

Polymer plastic

Non-branching polymer, composed of mainly carbon & hydrogen atoms arranged in a semi-crystalline structure

Covalent intramolecular & LDF’s intermolecular

Zirconia toughened alumina (ZTA)

Ceramic

The zirconia particles change their crystal structure from a tetragonal to a monoclinic structure, causing a volume expansion that compresses the surrounding crack in the alumina matrix

Covalent bonding

high strength, fracture toughness, elasticity, hardness, and wear resistance

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Properties

Polyether-ether-ketone (PEEK)

3.6 GPA

90-100 MPa

-High strength, toughness, and stiffness

-Good resistance to wear and dynamic fatigue

-Outstanding corrosion resistance

-High compatibility due to resistance to both organic and aqueous environments

Silicon nitride

280-290 GPA

68-172 MPa

-Strong and hard

6.1 MPa.m1/2

-High strength and fracture toughness

-More resistant to micro crack propagation than alumina

-Outstanding wear resistance

-Resists corrosion

-Extremely biocompatible

Zirconia toughened alumina (ZTA)

360 GPA

390 MPA

-Wear resistant

-very difficult to corrode

Alumina

370 GPa

240 MPa

3.3-5 MPa.m^1/2, ductile

Good, excellent wear resistance due to high strength and hardness which are determined by the strong ionic bonding between the atoms.

High corrosion resistance in many strong acids and organic acids

biocompatible

Alumina ceramics rely on good tribological properties, meaning favourable frictional behaviours, hardness, high wear resistance, good compression but weak resistance to tensile strength but weak. mechanical resistance. Using alumina decreases fracture occurrence and is highly resistant to wear.

UHMWPE

(Thermoplastic polyethylene)

1258 Mpa

45.8MPA

5.16 MPa-m1/2

- Abrasion, wear and impact resistant

-corrosion resistance

Very high

Cobalt-Chromium

210 GPa

1130 to 1900 MPa

Low ductility but high compressive strength

0.005mm/year with metals & 0.17mm/year with PE

High resistance

Very high

Porous Titanium

2.67 – 18 GPa

94 – 468 MPa

Ductile

Relatively poor wear resistance

Very reactive metal that shows high corrosion resistance. When in contact with oxygen, it forms a thin layer of titanium dioxide protecting the underlying layers.

Biocompatible

Porous titanium is a compromise between mechanical strength and adequate pore size for tissue ingrowth. Resistant to corrosion. When placed over the polyethylene liner it is expected to reduce the wear and increase the longevity. This is beneficial for Diane Chambers as it reduces the likelihood of complications with her implant.

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Processing

Zirconia toughened alumina (ZTA)

High corrosion resistance already

UHMWPE

(Thermoplastic polyethylene)

Very high corrosion resistance already

Polyether-ether-ketone (PEEK)

-use hydroxyapatite or Ti dioxide coatings to enhance bone growth

-outstanding corrosion resistance

Silicon Nitride

-can be coated with SiO2

SiO2 nanoparticles can be used in drug delivery systems

-SiO2 coating prevents corrosion

Cobalt Chromium

-Zirconium / titanium-coatings improve integration with the bon

Very high corrosion resistance already

Alumina

-Can be sprayed with titanium nitride (TiN) coatings via vapour deposition to femoral heads and acetabular liners. This coating has sufficient hardness and therefore may resist abrasion and reduce overall wear. Can also act as a diffusion barrier against metal ion release.

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Proposed Material: UHMWPE (Thermoplastic polyethylene)

Explain why you selected this material based on the structure, properties, and processing:

· High corrosion resistance

· High chemical resistance

· Very low friction

· Can survive exposure to body fluids

· Can survive exposure to body fluids (e.g. resistant to degradation from lipid exposure)

· Abrasion, wear, and impact resistant

· Very biocompatible

· Low toxicity

· Doesn’t need any specific coating to increase any properties

Comment on why the material selected makes the most sense for your patient

· Patient has osteoporosis, but liner does not come in contact with the bone, so materials that benefit bone growth or osteointegration may be focused on in other components (acetabular cup & femoral stem)

· Patient has rheumatoid arthritis; thus, the liner must not have much wear debris and should be highly biocompatible to not trigger or further complicate her immune responses

· Least expensive bearing, suitable for a patient who has other financial demands, such as her 3 children.

· UHMWPE has a long life (patient is only 63)