Percolation Mechanism in Percolation Mechanism in BiotribologyBiotribology

Kyle JonesKyle JonesAME DepartmentAME Department

University of Notre DameUniversity of Notre DameAdvisor: Dr. SchmidAdvisor: Dr. Schmid

OutlineOutline

Background information on Background information on biotribologybiotribology

Motivation for researchMotivation for research Outline of current projects and Outline of current projects and

goalsgoals Areas for further researchAreas for further research

What is Tribology?What is Tribology?

Tribology is the study of friction, Tribology is the study of friction, lubrication, and wear. lubrication, and wear. (From the (From the Greek words tribos and logos.)Greek words tribos and logos.)

ImportanceImportance Lifespan of mechanical partsLifespan of mechanical parts Wear particles especially impact Wear particles especially impact

the usable lifespan of orthopaedic the usable lifespan of orthopaedic implants e.g. total hip replacementsimplants e.g. total hip replacements

Motivation for Motivation for BiotribologyBiotribology

Almost 200,000 new hip Almost 200,000 new hip replacements, and 40,000 replacements, and 40,000 revisions done in 2002 revisions done in 2002 (NHDS)(NHDS)

Premature failure has beenPremature failure has beenlinked to wear particles linked to wear particles causingcausingosteolysis and bone osteolysis and bone resorptionresorption

Many solution have been Many solution have been proposed: Metals and proposed: Metals and Ceramic heads/cups, Ceramic heads/cups, crosslinked cupscrosslinked cups

Most of these have the Most of these have the same problems, increasing same problems, increasing hardness decreases wear, hardness decreases wear, but also decreases fracture but also decreases fracture toughnesstoughness

Background on Background on LubricationLubrication

Three regimes of lubrication: full film Three regimes of lubrication: full film lubrication, mixed lubrication, and lubrication, mixed lubrication, and boundary lubrication.boundary lubrication.

2 2

avg

a b

h

R R

Boundary lubrication, surfaces contact, Boundary lubrication, surfaces contact,

high wear and frictionhigh wear and friction Mixed lubrication, some surface Mixed lubrication, some surface

contact, wear occurs at varying ratecontact, wear occurs at varying rate Full film lubrication, surfaces Full film lubrication, surfaces

completely separated, wear is essentially completely separated, wear is essentially zero.zero.

Percolation TheoryPercolation Theory

Inspiration from natural joints, cartilage is Inspiration from natural joints, cartilage is hydrophilic, but “percolates” fluid under pressurehydrophilic, but “percolates” fluid under pressure

Using percolation mechanisms, it is theorized Using percolation mechanisms, it is theorized that lubrication regime would be improvedthat lubrication regime would be improved

Stribeck curve shows regimes in actionStribeck curve shows regimes in action

Laser Textured Surfaces Laser Textured Surfaces (LTS)(LTS)

There has been a There has been a recent interest in the recent interest in the use of LTS to improve use of LTS to improve friction properties in friction properties in industryindustry Mechanical seals, Mechanical seals,

piston rings, etc.piston rings, etc. LTS is basically an array LTS is basically an array

of dimples, or craters of dimples, or craters formed by laser pulsesformed by laser pulses

They have been shown They have been shown to improve friction to improve friction properties significantly properties significantly in these applications in these applications (Etzion, Zhou, Wang, (Etzion, Zhou, Wang, etc.)etc.)

Published resultsPublished results

These results are These results are taken from a paper taken from a paper by Etsion, showing a by Etsion, showing a portion of a Stribeck portion of a Stribeck curve for curve for unidirectional slidingunidirectional sliding

Note transitions into Note transitions into full film region, full film region, marked by slow marked by slow increase in frictionincrease in friction

For orthopeadic For orthopeadic purposes, the purposes, the increase in friction is increase in friction is not so important as not so important as the decrease in the decrease in wearwear

Preliminary StepsPreliminary Steps

How to make How to make dimples? dimples? Laser parameters Laser parameters

must be correlated must be correlated to dimple to dimple morphologymorphology

Rim removalRim removal Grinding/PolishingGrinding/Polishing Chemical PolishingChemical Polishing Electro-chemical Electro-chemical

polishingpolishing

The next stepThe next step

Friction testsFriction tests Unidirectional, Unidirectional,

pin on flat pin on flat testingtesting

Use Hamrock-Use Hamrock-Dowson Dowson equations to equations to calculate calculate parameters to parameters to have have 21 2ˆ 128 0.131tan 1.6832H

.64 0.227.32 1 0.72exp 0.28H k U W

Goals for projectGoals for project

To show decrease in frictional To show decrease in frictional force when using LTSforce when using LTS

Show that increase in film Show that increase in film thickness causes regime of thickness causes regime of lubrication to change from lubrication to change from boundary to mixed lubrication boundary to mixed lubrication using LTSusing LTS

Create ovoid dimples and Create ovoid dimples and perform similar experimentsperform similar experiments

Hydrogels and 3-D woven Hydrogels and 3-D woven compositescomposites

To date there is no orthopaedic To date there is no orthopaedic technique to help technique to help youngyoung patients patients who have undergone who have undergone minescectimies or severe local minescectimies or severe local cartilage damagecartilage damage

This is due to lack of suitable This is due to lack of suitable replacement material for cartilagereplacement material for cartilage

Hydrogels mimic the percolation Hydrogels mimic the percolation behavior of cartilage, but have no behavior of cartilage, but have no load bearing capabilitiesload bearing capabilities

3-D woven structures3-D woven structures

Hydrogel fibers can be made, and can Hydrogel fibers can be made, and can be woven together with tougher be woven together with tougher materialsmaterials

Weave design allows for functional Weave design allows for functional gradations in fibersgradations in fibers

Functionally gradedFunctionally graded

Functionally grades structures allow a Functionally grades structures allow a continuous material to have different beneficial continuous material to have different beneficial properties as you advance through the thickness properties as you advance through the thickness directiondirection Different layers would use titanium, PE, PEEK and Different layers would use titanium, PE, PEEK and

PMMA, as well as selected hydrogels PMMA, as well as selected hydrogels Polymers have many variable performance based on Polymers have many variable performance based on

crystallinity, molecular weight, crosslinkingcrystallinity, molecular weight, crosslinking

ExperimentsExperiments

Creation of many different woven Creation of many different woven composites using different composites using different polymer reinforcements and polymer reinforcements and concetrationsconcetrations

Preliminary results taken from Preliminary results taken from friction tests in unidirectional friction tests in unidirectional sliding. Top performers to sliding. Top performers to undergo more rigorous testingundergo more rigorous testing

Major hurdlesMajor hurdles

Manufacturing processes are complex, but some Manufacturing processes are complex, but some companies say they can do itcompanies say they can do it

Brand new research, 3-D woven composites are Brand new research, 3-D woven composites are not well understood, especially failure not well understood, especially failure mechanismsmechanisms

No validated models for predicting the No validated models for predicting the mechanical properties and durability of 3-D mechanical properties and durability of 3-D woven compositeswoven composites Concurrent research team using non-linear elasticity Concurrent research team using non-linear elasticity

modelsmodels Optimization. There will be a balance of Optimization. There will be a balance of

percolation effects and strength. How thick percolation effects and strength. How thick must the hydrogel weave be? How thick must must the hydrogel weave be? How thick must transitional weaves be? How will polymer transitional weaves be? How will polymer chosen affect these parameters? Etc.chosen affect these parameters? Etc.

ConclusionsConclusions

No results or data at this time, so No results or data at this time, so there’s lots of work to be done!there’s lots of work to be done!