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

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Presentation on theme: "Some Aspects of Skin Tribology: Friction Blister Holly Sibley MEng Supervisor: Dr. Georges Limbert University of Southampton."— Presentation transcript:

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

2 Main Functions of Skin Protective FunctionExamples Mechanical Abrasions Blunt Impacts Cutting BiologicalInvasion from foreign organisms RadioactiveUV ChemicalPenetration ThermalInsulation 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 D 3 Production of pheromones

5 Variability of Skin Location Age Ethnicity Hydration levels (Accesseed 09/04/10) (Accesseed 09/04/10) https://www.storesonlinepro.com/files/ /uploaded/baby%20face.jpghttps://www.storesonlinepro.com/files/ /uploaded/baby%20face.jpg (Accesseed 09/04/10) (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. (Accessed 24/03/10)

8 Structures within skin Blood Vessels and Lymphatics Sweat Gland Hair Follicle Sweat Glands and Hair Follices Nerves (Accessed 25/03/10)

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

10 There are different types of blisters and each ‘splits’ the skin at a different histological level Pemphigoid Bullosa Pemphigus Vulgaris (Accessed 10/04/10) (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 (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 VariableSymbol Volume Fluid Fraction Volume Solid Fraction Velocity of Fluid Velocity of Solid Coefficient of Growth Permeability Pressure Stress Strain Bulk Modulus Viscosity Biot’s Coefficient Fluid conservation Eqn: Solid conservation Eqn: Darcy’s Law:

17 Poroelastic Model Force Balance Equation: VariableSymbol Volume Fluid Fraction Volume Solid Fraction Velocity of Fluid Velocity of Solid Coefficient of Growth Permeability Pressure Stress Strain Bulk Modulus Viscosity Biot’s Coefficient Poroelastic Response: Strain:

18 Which Value to Use? Hydraulic Conductivity ValuesUnitsSourceSubject MaterialPublicationNotes 5.33(Swartz and Fleury 2007)Rat DermisReview ArticleMeasurement made Ex Vivo. 15 to 78(Swartz and Fleury 2007)Rat Abdominal MuscleReview ArticleMeasurement made In Vivo. 70 to 150(Swartz and Fleury 2007)Mouse Tail SkinReview ArticleMeasurement made In Vivo. 70(Swartz, Kaipainen et al. 1999)Mouse Tail SkinJournal Article Measurement estimated from the fluorescent characteristic length approximation. 41 to 253(Swartz and Fleury 2007)MesenteryReview ArticleMeasurement made Ex Vivo. 190(Intaglietta and de Plomb 1973)MesenteryJournal ArticleFlow across tissue slice In Vitro 31(Winters and Kruger 1968)MesenteryJournal ArticleFlow across tissue slice In Vitro 21(Swabb, Wei et al. 1974)HepatomaJournal ArticleFlow across tissue slice In Vitro 20(Granger, Dhar et al. 1975)Wharton’s JellyJournal Article- 8(Swabb, Wei et al. 1974)Rat HepatomaJournal Article Darcy’s law analysis of In Vitro filtration data. 5(Swabb, Wei et al. 1974) Rat Subcutaneous Tissue Journal Article Darcy’s law analysis of In Vitro filtration data. 9(Swabb, Wei et al. 1974) Rabbit and Human Sclera Journal Article Darcy’s law analysis of In Vitro filtration data. 2.5(Swabb, Wei et al. 1974) Human and Rabbit corneal Stroma Journal Article Darcy’s law analysis of In Vitro filtration data. 7.75(Swabb, Wei et al. 1974) Human Articular Cartilage Journal Article Darcy’s law analysis of In Vitro filtration data. 7(Swabb, Wei et al. 1974)Pig AortaJournal ArticleDarcy’s law analysis of In Vitro filtration data.

19 COMSOL Model 10mm 1.750mm 1.150mm 0.085mm Free Fixed Free 1000 MPa 5 MPa MPa 50 N/m 2 Inward Flux: 0.01 mm/s Atmospheric Pressure Zero Flux/ Symmetry

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 (Accessed 19/04/10) (Accessed 19/04/10) (Accessed 19/04/10) (Accessed 19/04/10) (Accessed 19/04/10) (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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