section 24: articular cartilage mechanical properties
TRANSCRIPT
Section 24: Articular Cartilage Mechanical Properties
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Friction and wearFriction and wear
• Frictional force (F) dependent:Frictional force (F) dependent:• Normal force (i.e., applied load, W)
W t k j i t t d l di– We must know joint geometry and loading• Frictional coefficient
– Surfactant, i.e. surface lubricant• F = μWμ
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Why is the frictional coefficient of il l ?cartilage so low?
• Tissue is mostly waterTissue is mostly water• Relatively large surface asperities provide
A f f t t t l– Are for surfactants to lay– Mechanism for water to be squeezed out of
the cartilage cartilage surfaces are ‘floatingthe cartilage…cartilage surfaces are floating on water’
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Tissue mechanicsTissue mechanics• The composition and structure of cartilage p g
determine the tissue mechanical behaviors• Cartilage tissue mechanics is complex
Viscoelastic part solid part fluid time dependent– Viscoelastic – part solid, part fluid – time dependent behavior
• Fluid flow moving through the matrix• Polymeric interactionsPolymeric interactions
– Nonlinear stress-strain– Compression-tension nonlinearities
Anisotropic– Anisotropic• We will investigate how to model most of these
phenomena this semester
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Material models for articular ilcartilage
• Early: isotropic, linear elasticEarly: isotropic, linear elastic– Doesn’t describe time variation of response
• Later: viscoelastic (springs and dampers)Later: viscoelastic (springs and dampers)– Doesn’t consider influence of fluid (loss in
compression, swelling)p g)• Later still: poroelastic, biphasic
– Doesn’t consider viscous solid, ion effects,• Most recent: biphasic poro-viscoelastic, tri-
phasic theories24-18 From: Grimm and Atkinson
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