Outline,Introduction: Tribology & Biotribology Biotribology Examples of Biotribology Skin Artificial heart Dental Fracture fixation Flow of red blood cells Ocular system Synovial joints Future 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,http:/www.shef.ac.uk/mecheng/mecheng_cms/tribology/,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,http:/www.maitrise-orthop.com,Dowson et al, J Arthroplasty, 2004,Surfaces,All surfaces are rough:Atomic diameters 1 to 10 Irregularities on mica 20 Quartz crystal 100 Ceramic surfaces 0.005 m (50 ) Metallic surfaces 0.005 to 0.01 m (100 ),1 angstrom () = 10-10 m = 10-4 mm,Surfaces,Surfaces,http:/www.maitrise-orthop.com/corpusmaitri/index_us.html, 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, 1699 The 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 Clean (and dry): 0.25-0.5,Wear,Progressive loss of substance from the operating surface of a body occurring as a result of relative motion at the surface Surface deformation, Pitting, Scratching, Burnishing, Polishing, Delamination, Fretting, Cracking, ,Wear,Laws of wear: Wear increases as the normal load (W) increases Wear increases as the sliding distance (S) increases Wear decreases as the hardness (H) of the softer sliding component increases,K: wear factor, mm3/(Nm),Wear,Wear testing: simple screening Uni-directional pin-on-disc Reciprocating pin-on-plate Multi-directional pin-on-plate,Wear,Wear testing: Leeds hip simulator,Wear,Wear measurements: volume, penetration,Wear,Wear measurements: debris/particles,Lubrication,Abrasive wear Adhesive wearFatigue wear,asperity contactlubricant,Lubrication refers to adding a lubricant between two bearing surfaces in order to control friction and wear,Lubrication,Where hmin : the average film thickness Ra : the composite surface roughness of two bearing surfaces,hmin, ratio,Lubrication,Fluid film lubrication 3Mixed lubrication3 1 Boundary lubrication1 ,Lubrication regimes and ratio,Lubrication,hmin :minimum film thickness R :equivalent radius w :load u :entraining velocity, = (uhead+ucup)/2E :equivalent elastic modulus, :viscosity,Lubrication film thickness, hmin,Hamrock and Dowson, 1978,Lubrication,Radius Rhead,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-shaped Biconcave Axisymmetric Diameter: 8 m Thickness: 1 to 2.5 m Capillaries: 5 to 10 m,Flow of Red Blood Cells:,Lubrication Capillary hemodynamics Mass transfer and supply of oxygen Resistance to shear damage Cell motionElastic deformation Elastohydrodynamic lubrication,Ocular System:,Eye,Ocular System:,Cornea Transparent tissue without blood vessels Approximately spherical at the central portion with a radius about 8 mm Thickness: 0.52mm, increasing to 0.65mm at the limbus Refractive Index: 1.3771 Roughness of epithelial surface: 0.5 m (microridges), covered with a mucus gel further decreasing surface roughness,Ocular System:,Tear films Outmost: lipid (fatty, oily): 0.1 m Middle:aqueous, low viscosity and 7 to 10 m Innermost: mucous (viscous),