Percolation Mechanism in Biotribology Kyle Jones AME Department University of Notre Dame Advisor: Dr. Schmid

Outline Background information on biotribology Background information on biotribology Motivation for research Motivation for research Outline of current projects and goals Outline of current projects and goals Areas for further research Areas for further research

What is Tribology? Tribology is the study of friction, lubrication, and wear. (From the Greek words tribos and logos.) Tribology is the study of friction, lubrication, and wear. (From the Greek words tribos and logos.) Importance Importance Lifespan of mechanical parts Lifespan of mechanical parts Wear particles especially impact the usable lifespan of orthopaedic implants e.g. total hip replacements Wear particles especially impact the usable lifespan of orthopaedic implants e.g. total hip replacements

Motivation for Biotribology Almost 200,000 new hip replacements, and 40,000 revisions done in 2002 (NHDS) Almost 200,000 new hip replacements, and 40,000 revisions done in 2002 (NHDS) Premature failure has been linked to wear particles causing osteolysis and bone resorption Premature failure has been linked to wear particles causing osteolysis and bone resorption Many solution have been proposed: Metals and Ceramic heads/cups, crosslinked cups Many solution have been proposed: Metals and Ceramic heads/cups, crosslinked cups Most of these have the same problems, increasing hardness decreases wear, but also decreases fracture toughness Most of these have the same problems, increasing hardness decreases wear, but also decreases fracture toughness

Background on Lubrication Three regimes of lubrication: full film lubrication, mixed lubrication, and boundary lubrication. Three regimes of lubrication: full film lubrication, mixed lubrication, and boundary lubrication.  Boundary lubrication, surfaces contact, high wear and friction  Boundary lubrication, surfaces contact, high wear and friction  Mixed lubrication, some surface contact, wear occurs at varying rate  Mixed lubrication, some surface contact, wear occurs at varying rate  Full film lubrication, surfaces completely separated, wear is essentially zero.  Full film lubrication, surfaces completely separated, wear is essentially zero.

Percolation Theory Inspiration from natural joints, cartilage is hydrophilic, but “percolates” fluid under pressure Inspiration from natural joints, cartilage is hydrophilic, but “percolates” fluid under pressure Using percolation mechanisms, it is theorized that lubrication regime would be improved Using percolation mechanisms, it is theorized that lubrication regime would be improved Stribeck curve shows regimes in action Stribeck curve shows regimes in action

Laser Textured Surfaces (LTS) There has been a recent interest in the use of LTS to improve friction properties in industry There has been a recent interest in the use of LTS to improve friction properties in industry Mechanical seals, piston rings, etc. Mechanical seals, piston rings, etc. LTS is basically an array of dimples, or craters formed by laser pulses LTS is basically an array of dimples, or craters formed by laser pulses They have been shown to improve friction properties significantly in these applications (Etzion, Zhou, Wang, etc.) They have been shown to improve friction properties significantly in these applications (Etzion, Zhou, Wang, etc.)

Published results These results are taken from a paper by Etsion, showing a portion of a Stribeck curve for unidirectional sliding Note transitions into full film region, marked by slow increase in friction For orthopeadic purposes, the increase in friction is not so important as the decrease in wear

Preliminary Steps How to make dimples? How to make dimples? Laser parameters must be correlated to dimple morphology Laser parameters must be correlated to dimple morphology Rim removal Rim removal Grinding/Polishing Grinding/Polishing Chemical Polishing Chemical Polishing Electro-chemical polishing Electro-chemical polishing

The next step Friction tests Unidirectional, pin on flat testing Use Hamrock- Dowson equations to calculate parameters to have 

Goals for project To show decrease in frictional force when using LTS To show decrease in frictional force when using LTS Show that increase in film thickness causes regime of lubrication to change from boundary to mixed lubrication using LTS Show that increase in film thickness causes regime of lubrication to change from boundary to mixed lubrication using LTS Create ovoid dimples and perform similar experiments Create ovoid dimples and perform similar experiments

Hydrogels and 3-D woven composites To date there is no orthopaedic technique to help young patients who have undergone minescectimies or severe local cartilage damage To date there is no orthopaedic technique to help young patients who have undergone minescectimies or severe local cartilage damage This is due to lack of suitable replacement material for cartilage This is due to lack of suitable replacement material for cartilage Hydrogels mimic the percolation behavior of cartilage, but have no load bearing capabilities Hydrogels mimic the percolation behavior of cartilage, but have no load bearing capabilities

3-D woven structures Hydrogel fibers can be made, and can be woven together with tougher materials Weave design allows for functional gradations in fibers

Functionally graded Functionally grades structures allow a continuous material to have different beneficial properties as you advance through the thickness direction Functionally grades structures allow a continuous material to have different beneficial properties as you advance through the thickness direction Different layers would use titanium, PE, PEEK and PMMA, as well as selected hydrogels Different layers would use titanium, PE, PEEK and PMMA, as well as selected hydrogels Polymers have many variable performance based on crystallinity, molecular weight, crosslinking Polymers have many variable performance based on crystallinity, molecular weight, crosslinking

Experiments Creation of many different woven composites using different polymer reinforcements and concetrations Creation of many different woven composites using different polymer reinforcements and concetrations Preliminary results taken from friction tests in unidirectional sliding. Top performers to undergo more rigorous testing Preliminary results taken from friction tests in unidirectional sliding. Top performers to undergo more rigorous testing

Major hurdles Manufacturing processes are complex, but some companies say they can do it Manufacturing processes are complex, but some companies say they can do it Brand new research, 3-D woven composites are not well understood, especially failure mechanisms Brand new research, 3-D woven composites are not well understood, especially failure mechanisms No validated models for predicting the mechanical properties and durability of 3-D woven composites No validated models for predicting the mechanical properties and durability of 3-D woven composites Concurrent research team using non-linear elasticity models Concurrent research team using non-linear elasticity models Optimization. There will be a balance of percolation effects and strength. How thick must the hydrogel weave be? How thick must transitional weaves be? How will polymer chosen affect these parameters? Etc. Optimization. There will be a balance of percolation effects and strength. How thick must the hydrogel weave be? How thick must transitional weaves be? How will polymer chosen affect these parameters? Etc.

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