软骨生物力学特性课件

12.1 Introductionn nBone works in small strain range,biology sensitive to strain(stress)n nAnisotropic,stress-strain&strain-displacement are linearn nCartilage related to bone(calcified cartilage);small friction coefficient,n nLubrication&shock absorption,multi-phasic structure(fluids,ions,solids)triphasic theory12.1.1 Anatomy of a long bonen nShaft(diaphysis),expansion(metaphysis),for immature,metaphysis surmounted by epiphysis united to metaphysis via growth plate(epiphyseal plate)n nCoefficient of friction between articulate cartilage 0.0026!n nGrowth plate-place where calcification of cartilage occur.For matured,epiphyses fused with metaphyses n nDiaphysis:hollow tube,wall Diaphysis:hollow tube,wall dense cortex(compactum)dense cortex(compactum)n nMedulla or medullary cavity:Medulla or medullary cavity:central space,contains bone central space,contains bone marrowmarrown nPeriosteum:covering external Periosteum:covering external surface of long bone,except surface of long bone,except articulationarticulationn nInner layer,active cells Inner layer,active cells enlargement&remodeling;enlargement&remodeling;osteogenic layerosteogenic layern nOuter layer,fibrous comprised Outer layer,fibrous comprised almost entire periosteumalmost entire periosteumn nOver most of diaphysis,periosteum is tenuous&loosely attached&blood vessels are capiliary;n nAt expanded ends,ligaments are attched firmly&can convey large size blood vessels;Same at ridges along diaphysis.n nNote:mechanical properties depend on which part of bone is considered.n nTable 12.1:1NotesNotesn ncortical region of cortical region of diaphysisdiaphysisn nSpecimens taken Specimens taken from compactumfrom compactumMicroscopic observationn nComposite materialComposite materialn nBasic unit:Haversian system(osteon)Basic unit:Haversian system(osteon)n nArtery or vein at centerArtery or vein at centern nBlood vessels connected by Volkmanns canals(transverse)Blood vessels connected by Volkmanns canals(transverse)n nWeight%Weight%n n2/3 inorganic material,mainly hydroxyapatite,3Ca3(PO4)2.2/3 inorganic material,mainly hydroxyapatite,3Ca3(PO4)2.Ca(OH)2&small quantity of other ionsCa(OH)2&small quantity of other ionsn nTiny crystals 200 A long,area 2500 A2,Tiny crystals 200 A long,area 2500 A2,n nCollagen,HA crystals arranged along length of collagen Collagen,HA crystals arranged along length of collagen fibrils.fibrils.Arrangement in fibersn nWoven-fiber bonen nLamallae in osteons:concentric n nLamallae in surface:parallel to surface12.1.2 Bone as a Composite Materialn nCollagen&hydroxyapatiten nYoungs modulus of fluorapatite 165GPan nSteel 200GPa,6061 Aluminum alloy 70GPan nCollagen tangent modulus 1.24 GPan nYoungs modulus of human femur 18GPan nBones strength is higher than either HA or collagen:softer component prevent stiff one from brittle cracking,stiff component prevent the soft from yieldingn nMechanical properties depend on:n ncomposition composition n n structure of bone structure of bone n ngeometric shape of componentsgeometric shape of componentsn nbond between fibers&matrixbond between fibers&matrixn nbonds at points of contact of fibersbonds at points of contact of fibersn nStrength of bone correlates with mass density of bone looselyn nCorrelation coefficient between strength&density Correlation coefficient between strength&density 0.40-0.420.40-0.42n nDensity&strength are non-unifromly distributed in Density&strength are non-unifromly distributed in femur;density 2.20-2.94;strength 1.35 xfemur;density 2.20-2.94;strength 1.35 x12.2 Bone as a Living Organn nBone is living blood circulation;transport materials to and from Bone is living blood circulation;transport materials to and from bone&bone can change,grow,removed by resorption,(stress-bone&bone can change,grow,removed by resorption,(stress-dependent)dependent)n nUnder-stressed or over-stressed bone becomes weakened,proper Under-stressed or over-stressed bone becomes weakened,proper range of stress is required;range of stress is required;n nLocal stress concentration imposed by improper tightening of Local stress concentration imposed by improper tightening of screws,nuts&bolts in bone surgery may cause resorption and screws,nuts&bolts in bone surgery may cause resorption and resulted in loosening!resulted in loosening!n nEvolution process has resulted in optimum design of bone:Evolution process has resulted in optimum design of bone:n nGeneral shaping to minimize stressGeneral shaping to minimize stressn nDistribution of material to achieve minimum-weightDistribution of material to achieve minimum-weightn nTheoriesn nUniform strength under a specified set of loading Uniform strength under a specified set of loading conditionsconditionsn nTrajectory architecture,put material only in the paths Trajectory architecture,put material only in the paths of transmission of forces and leave voids elsewhere.of transmission of forces and leave voids elsewhere.n nExamples of optimum structure designn n