Section 24: Articular Cartilage Mechanical Properties

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Section 24: Articular Cartilage Mechanical Properties 24-1

Transcript of Section 24: Articular Cartilage Mechanical Properties

Page 1: Section 24: Articular Cartilage Mechanical Properties

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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p

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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

p