生物摩擦学BiotribologyGeneral.ppt
Outline,Introduction:Tribology&BiotribologyBiotribologyExamples of BiotribologySkinArtificial heartDentalFracture fixationFlow of red blood cellsOcular systemSynovial jointsFuture Developments,Definition,the study of tribes?the study of hair as in Trichology?Try-biology?,Tribology,Definition,Tribology:Tribo-,Gr.Tribos-(is):rubbing;-logy:names of sciences or departments of study“The branch of science and technology concerned with interacting surfaces in relative motion and with associated matters(as friction,wear,lubrication,and the design of bearings).Oxford English Dictionary“The science and technology of interacting surfaces in relative motion and the practices related thereto”Jost Report(1966)Surfaces,friction,wear and lubrication,Definition,Definition,Biotribology:All aspects of tribology related to biological systems(Professor Duncan Dowosn and Professor Verna Wright,University of Leeds,1973)Dental,skin,clothes,hair,footwear,contact lens and eye,replacement heart valves,fracture repair,pleural and pericardium,and natural synovial joints and artificial replacements.,Surfaces,God made materials but surfaces were the work of the Devil.Pauli,Nobel Prize for Physics,1945,Dowson et al,J Arthroplasty,2004,Surfaces,All surfaces are rough:Atomic diameters1 to 10 Irregularities on mica20 Quartz crystal100 Ceramic surfaces 0.005 m(50)Metallic surfaces0.005 to 0.01 m(100),1 angstrom()=10-10 m=10-4 mm,Surfaces,Surfaces,A Dambreville*,M Phillipe*,A Ray*,*Clinique St-Michel,29000 Quimper,*Hpital de Carpentras 4200 CARPENTRAS,*Clinque du Parc 69458 LYON CEDEX-France,Surfaces,Profilometry Non-contacting such as laser or white light Contacting such as stylus method,Surfaces,Same Ra,but not same tribology and other roughness parameters are also required!,Use of Ra with caution!,Friction,Friction is loosely defined as the resistance to motion.Leonardo da Vinci(AD 1452 1519),Friction,Amontons,1699The force of friction(F)is directly proportional to the applied load(w)The force of friction(F)is independent of the apparent area of contact,Friction,Coefficient of friction(),Friction,Transporting an Egyptian colossus from the tomb of Tehuti-Hetep,El-Bersheh,(c.1880 B.C.),Dowson,History of tribology,2nd ed,1998,Wet:0.2,Wear,Progressive loss of substance from the operating surface of a body occurring as a result of relative motion at the surfaceSurface deformation,Pitting,Scratching,Burnishing,Polishing,Delamination,Fretting,Cracking,Wear,Laws of wear:Wear increases as the normal load(W)increasesWear increases as the sliding distance(S)increasesWear decreases as the hardness(H)of the softer sliding component increases,K:wear factor,mm3/(Nm),Wear,Wear testing:simple screeningUni-directional pin-on-discReciprocating pin-on-plateMulti-directional pin-on-plate,Wear,Wear testing:Leeds hip simulator,Wear,Wear measurements:volume,penetration,Wear,Wear measurements:debris/particles,Lubrication,Abrasive wear Adhesive wear Fatigue wear,asperity contact lubricant,Lubrication refers to adding a lubricant between two bearing surfaces in order to control friction and wear,Lubrication,Where hmin:the average film thicknessRa:the composite surface roughness of two bearing surfaces,hmin,ratio,Lubrication,Fluid film lubrication 3 Mixed lubrication 3 1 Boundary lubrication 1,Lubrication regimes and ratio,Lubrication,hmin:minimum film thicknessR:equivalent radiusw:loadu:entraining velocity,=(uhead+ucup)/2E:equivalent elastic modulus,:viscosity,Lubrication film thickness,hmin,Hamrock and Dowson,1978,Lubrication,RadiusRhead,Radial clearance,c,Equivalent radius,Rcup,Summary,Friction,Wear,Lubrication,Biotribology:Examples,Skin friction,Biotribology:Examples,Lubrication in total artificial heart,Biotribology:Examples,Wear of heart valves,Biotribology:Examples,Dental wear,Biotribology:Examples,Fracture fixation,Flow of Red Blood Cells:,Disk-shapedBiconcaveAxisymmetricDiameter:8 mThickness:1 to 2.5 mCapillaries:5 to 10 m,Flow of Red Blood Cells:,LubricationCapillary hemodynamicsMass transfer and supply of oxygenResistance to shear damageCell motionElastic deformationElastohydrodynamic lubrication,Ocular System:,Eye,Ocular System:,CorneaTransparent tissue without blood vesselsApproximately spherical at the central portion with a radius about 8 mmThickness:0.52mm,increasing to 0.65mm at the limbusRefractive Index:1.3771Roughness of epithelial surface:0.5 m(microridges),covered with a mucus gel further decreasing surface roughness,Ocular System:,Tear filmsOutmost:lipid(fatty,oily):0.1 mMiddle:aqueous,low viscosity and 7 to 10 mInnermost:mucous(viscous),Ocular System:,Tear filmsNon-newtonian shear thinningViscosity at high shear rates0.0013 Pas,Ocular System:,Function of tear filmsSmooth motion and optical qualityOxygen supply due to diffusion and pumping(hydrodynamic action)Comfort and eliminate debris,Ocular System:,BlinkingOnce every 5 s(2 to 10)and 12 per minDuring closure:upper eyelid moves down with an approximate speed of 15 cm/s(10 to 12 mm during 0.08s)During opening:0.17 sLoad between the eyelid and the globe is quite small,less than a few grams 0.2 to 0.25 N in the normal direction0.0004 to 0.0005 N in the tangential direction,Ocular System:,Lubrication mechanismsBoundary,Ehlers(1965)Hydrodynamic,Holly(1970)10 m tear film,the surface roughnesslow coefficient of friction,0.005high shear rate 15,000 1/s during blinkinglow shear stress on the ocular surfacebut sufficient high to remove the dead cells and mucous threads contaminated with lipid from the ocular surface in the aqueous layer,Ocular System:,Dry eyeBoundary lubricationSurface roughness increased by 10 timesThinner tear films and increased shear stresses,Ocular System:,Importance of lubricationNormal lubrication mechanismsDiseases such as dry eyeArtificial tear filmsFunction of contact lens,Synovial Joints:,Synovial jointsHipKneeAnkleShoulderElbow,Synovial Joints:,FunctionRelative motion between two surfaces with low friction and negligible wearTransmit high load(3 to 6 times bodyweight)without damaging any of its structural components.,Synovial Joints:,Synovial jointArticular cartilageSynovial fluidBone,Synovial Joints:,Synovial joint,Future Developments:,Many more applications!Unification of lubrication mechanisms in different biological systems Tribological approach to understand the wear mechanism in different artificial hip joints Promoting fluid film lubrication in artificial hip joints,
