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Some Aspects of Skin Tribology : Friction Blister

Some Aspects of Skin Tribology : Friction Blister. Holly Sibley MEng Supervisor: Dr. Georges Limbert University of Southampton. Main Functions of Skin. Barrier functions as the skin straddles both the external and internal environments. Main Functions Cont.

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Some Aspects of Skin Tribology : Friction Blister

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  1. Some Aspects of Skin Tribology: Friction Blister Holly Sibley MEng Supervisor: Dr. Georges Limbert University of Southampton

  2. Main Functions of Skin Barrier functions as the skin straddles both the external and internal environments

  3. Main Functions Cont. What happens when the skin is broken? • Self-regeneration! • Allows the skin to remain an effective barrier • Deep skin wounds close spontaneously by • Epitheliasation • Wound contraction • Scar synthesis • Skin is one of the body’s main sensory interfaces • It contains many of the peripheral endings of the sensory nerve system

  4. Secondary Functions of Skin • Protection against UV damage • Production of Vitamin D3 • Production of pheromones

  5. Variability of Skin • Location • Age • Ethnicity • Hydration levels http://3.bp.blogspot.com/_kqkBbz54MBo/Skvc2XeY-4I/AAAAAAAAABk/nxpZYBcwYgk/s400/right+forearm.JPG (Accesseed 09/04/10) http://camelsnose.files.wordpress.com/2009/01/hand-left-500px.png (Accesseed 09/04/10) https://www.storesonlinepro.com/files/1862656/uploaded/baby%20face.jpg (Accesseed 09/04/10) http://www.tribuneindia.com/2005/20051017/ldh6.jpg (Accesseed 09/04/10)

  6. Multilayered Material

  7. Structure of Skin Cells at the Stratum Basale layer replicate by mitosis and end at the keratinised Stratum Corneum. http://wpcontent.answers.com/wikipedia/commons/thumb/2/20/Skinlayers.png/250px-Skinlayers.png (Accessed 24/03/10)

  8. Structures within skin Nerves Sweat Gland Hair Follicle Sweat Glands and Hair Follices Blood Vessels and Lymphatics http://www.relata.info/ (Accessed 25/03/10)

  9. Dermatological Problems Melanoma BCC Allergies Acne Cancer Cuts SCC Dermatological Problems Eczema Emergency Dermatology Infections Psoriasis Infestations Fungal Viral Blisters Blisters

  10. Blisters • There are different types of blisters and each ‘splits’ the skin at a different histological level PemphigoidBullosa Pemphigus Vulgaris http://www.bing.com/health/static/articles/mayo/1BCC967C5563FFF0270561FAAAFA8E5F.jpg (Accessed 10/04/10) http://meded.ucsd.edu/clinicalimg/skin_pemphigus2.jpg (accessed 10/04/10)

  11. Importance of Understanding Blisters • Create a model that accurately predicts blister formation • Ascertain the effect each variable has on the system • Use the results to further knowledge in aiding blister prevention

  12. Friction Blisters • ‘Split’ occurs in the Stratum Spinosum • These blisters occur after frictional forces are applied to the skin • Self healing BUT... • Friction blisters can have a disastrous effect with the sports and military world http://feet.thefuntimesguide.com/images/blogs/bad-foot-blister-on-heel-by-Lady-Weaxzezz.jpg (Accessed 21/04/10)

  13. Questions to Answer • What are the main variable in promoting the formation of friction blisters? • If a force and repetition creates a blister, would doubling the force and halving the repetitions make the same blister? • What is the respective influence of hydrostatic and shear forces within blister formation? • How can this work improve blister prevention?

  14. Assumptions • Linear • Poroelastic • Isotropic • Simplified fluid flow in the skin • Blood flow and lymphatics • Boundary conditions As the model progresses these assumptions can be slowly modified to become more accurate.

  15. Poroelastic Model Porous Structure Fluid Fluid Infiltrated Porous Structure • Look at the cube of skin as a whole • Response of the fluid can be described by Darcy’s Law • Response of the solid can be demonstrated by the poroelasticty equations

  16. Poroelastic Model Fluid conservation Eqn: Solid conservation Eqn: Darcy’s Law:

  17. Poroelastic Model Strain: Poroelastic Response: Force Balance Equation:

  18. Which Value to Use?

  19. COMSOL Model 50 N/m2 Free Atmospheric Pressure 1000 MPa 0.085mm Inward Flux: 0.01 mm/s Zero Flux/ Symmetry Zero Flux/ Symmetry 1.150mm 5 MPa Free Free Inward Flux: 0.01 mm/s 1.750mm 0.025 MPa Fixed Zero Flux/ Symmetry 10mm

  20. COMSOL Results Surface: First Principal Stress [Pa] Arrow: Velocity Field Deformation: Displacement

  21. COMSOL Results Surface: First Principal Strain Arrow: Velocity Field Deformation: Displacement

  22. COMSOL Results Surface: Pressure [Pa] Arrow: Velocity Field Deformation: Displacement

  23. COMSOL Results Surface: Velocity Field [m/s] Deformation: Displacement

  24. Limitations with the Model • Deciding on realistic boundary conditions for the COMSOL model • Value of the flux • Meshing...needing to use 1D element – not necessarily a necessity to model the stratum corneum.

  25. General Difficulties in Modelling Skin • Age and location of the skin • Issues in obtaining the values for the model: • Young’s modulus: How do you find this in living tissue? • Other mechanical values

  26. Future Work • Refine the model • Obtain more realistic boundary conditions for fluid flow • Add other properties beyond poroelasticity • Take the model to the next stage: ‘The split’ • Verification of the model through experimental work

  27. Other Applications of Skin Tribology • Dr. Georges Limbert, ‘Multi-layer finite element model of skin’ presentation • http://missinglink.ucsf.edu/lm/DermatologyGlossary/img/Dermatology%20Glossary/Glossary%20Clinical%20Images/Eczema_Nummular-L.jpg (Accessed 19/04/10) • http://www.enaturalhealth.com/blog/wp-content/uploads/2009/12/tips-to-improve-psoriasis1.jpg (Accessed 19/04/10) • http://www.holytrinitytn.org/images/shaving_face.jpg (Accessed 19/04/10) • http://www.bioinf.uni-sb.de/DN/Projects/Skin%20Penetration/Skin%20Penetration/skin_logo.png (Accessed 19/04/10) • http://content.answers.com/main/content/img/elsevier/dental/f0329-01.jpg (Accessed 19/04/10) • http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/3187.jpg (Accessed 19/04/10)

  28. Conclusions • Skin remains a difficult material to model but computational modelling can help to unravel the mechanics behind it • Modelling can help us understand what we can’t investigate experimentally • Blister modelling is a way of testing different hypotheses • Important to correlate computational work to experimental data

  29. Thank you Any Questions?

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