uhmwpe- ultra high molecular weight polyethylene__as a biomaterial
TRANSCRIPT
UHMWPE
• Linear type PE has a branching chain loosely contain in one chain
• Mol.wt 2-6 million (regular 20000-30000)• Due to high mol wt , shows superior
properties
Physical propertiesPROPERTIES HDPE UHMWPE
Mol.wt(million) .05-.2 2-6
MP( oC) 130-137 125-135
Density (g/cc) 0.95-0.96 0.93-0.94
Tensile yield (Mpa) 26.2-33.1 19.3-23
Elongation at break(%) 10-1200 250-450
Tensile modulus(Mpa) 400-4000 600-1500
Izod ipact(Jm-1) 21-210 <1070 no break
Shore d hardness 67-73 60-65
Synthesis
• By use of Ziegler Natta coordination catalyst under low pressure(TiCl-Al.Alk)
• Heterogeneous system(hexane solvent , ethylene gas , catalyst )
• Press. 0.4-0.6 Mpa• Temp. 66-90 oC• Results white granular powder• Calcium sterate is added for isolation
Processing Polymerized
UHMWPE resin
Direct molding
Ram extruded rod
Compression molded block
machining
sterilizationGamma raye- beamPlasma gasEt o
Processing
• Unlike HDPE,LDPE even heating above 200 oC UHMWPE shows high granular structure leads to difficulty in processing
• Proper temp. and high press. Required for achieving proper plastication
• Three methods are 1. Ram extrusion 2. Compression molding 3. Direct compression molding
Ram extrusion
• Temp 180-220 oC
Compression moulding
• Temp. 200-230 oC• press. 2-10 MPa
Direct compression moulding
• 200-240 oC• 5-10 MPa
Sterilization
• Performed after packaging• Available methods are Dry heat, steam under
press. , steam formaldehyde , et.oxide , irradiation…
• Mostly using methods are 1.Gamma radiation . 2.Ethylene oxide
• Gamma radiations can destroy micro organisms and reduce mechanical properties
Oxidation • Occurs after gamma radiation• Gama ray causes breaking of C-H bonds , produces free
radicals• These radical leads further chain scission and introduction of
oxygen containing group• Leads –changes in physical and chemical properties-increase
in modulus and brittleness-increase in density over surfaces-decreace mechanical properties
• Finally turns to regular PE• Prevention – oxidation carried under vacuum or inert gas
atmosphere
Wear properties
• UHMWPE used as bearing surface for artificial joints due to 1 . High toughness . 2. low friction coefficient . 3. low wear in body
• If wearing occurs the generated partcles can cause adverse cellular effects
• Coefficient of friction is very low (0.10-0.22) compared to other materials
Fatigue properties
• Flaking type of wear or delamination is observed
• Initiated by high stress in subsurfaces• Leads to cracking
Modifications
Cross linking
• Increased cross linking results improvement in wear resistance
• vacuum treated implants shows greater cross linking and wear resistance
• UHMWPE is cross linked by low doss gamma radiation in vacuum and directly compression molded at 200 oC and 20 Mpa leads increased orientation and wear resistance
Vitamin E addition
• Prevents crack propagation due to reduced hardness and grain boundaries
• Gamma irradiated vitamin E contain UHMWPE is promising material to prevent flaking like distruction of joints
Bio medical applications
• UHMWPE has been used as the bearing material in total joint prosthesis ( hip , knee , ankle , shoulder , elbow and wrist ) because of unique material properties such as
Low friction coefficientHigh resistance to wearHigh impact resistanceHigh ductilityStability in body
HIP REPLACEMENT INTER VERTEBRAL
ANKLE REPLACEMENT
SHOULDER REPLACEMENT
ELBOW REPLACEMENT
THE END