In Vivo Degradation and Biomechanical Analysis of Centrum-vertebra-fracture-repairing Absorbable Supporting Plugger

30 March 2009 2 views No Comment

Abstract:

Objective:Use of poly - D,L-lactic acid(PDLLA)andβ-calcium phosphate(β-TCP)on different scales production 6%β-TCP / PDLLA,12%β-TCP / PDLLA and pure PDLLA three kinds of materials which can be absorbed.Manufacture Centrum-vertebra-fracture-repairing absorbable supporting plugger,(CASP)andφ4 mm,the 5 mm long cylindrical material specimen.New Zealand white rabbits were implanted in gluteal Muscle and the femoral condyle.Three of the material in the course of material degradation in appearance,the shape changes,the tissue surrounding materials compatibility,the rate of mass loss,the loss of mechanical strength and speed of the process parameters,and so on.The purpose of evaluating different CASP made of composite materials into the body after implantation the material and degradation products of their own security,degradation rate,biomechanical properties.Selected the materials which more suitable for clinical application.Methods:1.In Vivo Degradation Analysis of Centrum-vertebra-fracture-repairing absorbable supporting pluggerCASP and cylindrical were weight by electronic materials weighing scales,records for the original quality.120 New Zealand white rabbits,2.5±0.3kg,were randomly divided into three groups,namely 6%β-TCP / PDLLA group,12%β-TCP / PDLLA group,PDLLA groups,each 40.CASP and cylindrical materials sample implanted into New Zealand white rabbits gluteus Muscle and the femoral condyle,after experiments on animals to general observation.4,8,12,16 weeks and six months after operation,the experimental animals were killed to observe the material surrounding muscle tissue Femoral condyle and whether to change shape,and contrast with contralateral normal tissue.Remove muscle specimens, released from the attachment organizations to observe the appearance of materials,patterns change.Materials will be weighing again after cleaned,dried,calculating the loss of quality (n=8).Evaluation of different materials in up to six months\’ early to medium-term course\’s materials and degradation security,the rate of degradation of the difference.And filter a material which more suitable for clinical application.2.In Vivo Biomechanical Analysis of Centrum-vertebra-fracture-repairing absorbable supporting pluggerBy Shimadzu AG-1 universal testing machine,three different materials of the CASP and cylindrical material to compress destructive testing,record load - displacement curve, calculated and plotted stress - strain curves,and calculating the initial compressive strength (n=8).4,8,12,16 week and six months after operation,laboratory animals were killed,out muscle specimens,released from the attachment,washing,drying,tested again in universal testing machine,to calculate its compressive strength and compressive Modulus(n = 8). Observed in the degradation process of compressive strength,compressive modulus change and loss of speed,combine the process of degradation of the quality loss rate changes. Evaluation of three different materials in up to six months\’ early to medium-term course\’s degradation and mechanical properties in the process of.Then select a better material which better suited to provide effective support to the vertebral in a certain period.Result:1.All of three group of animas were good after implantation of CASPs and cylindrical materials.The day after operation,animal sober and started drinking water,started eating the next day,the wound I / A healing,no purulent infection,no skin effusion.In the longest period of six months of observation time,the visible material closely with tissue,distal femur no swelling,necrosis,without osteoporosis,muscle tissue wrapped CASP and cylindrical materials close,sample some of the muscles around the materialshave mild fibrosis,no infection,purulent,organizations such as liquefied phenomenon.2.Four weeks,6%β-TCP / PDLLA,group\’s shape,quality loss was not obvious,12%β-TCP / PDLLA group slightly rough surface,mild softening,mass loss was not significant. Pure PDLLAs\’ degradation performance Between these two materials;4-8 weeks,the three materials are gradually emerging softening,such as changes in surface roughness change,and with varying degrees of mass loss,6%β-TCP / PDLLA groups\’ degradation process slightly slower than the other two.8-12 weeks,6%β-TCP / PDLLA degradation process is stabilizing, no obvious change in appearance;12%β-TCP / PDLLA groups\’ degradation rate increase, formed on the surface of visible crack,blunt edge Intensified,a form of bending at the same time,serious loss of quality;pure PDLLA material degradation process slightly slower than the former,the rough surface,the blunt edge of change,accomplish with turbidity,accelerated loss of quality;12-16 weeks,6%β-TCP / PDLLA Group material degradation process is smooth,surface cracks increased,a curved shape,changed blunt teeth;12%β-TCP / PDLLA degradation rate was even more rapidly,material distortion,seriously deformed.The doublewall CASP was compressed.Sharp teeth changed significantly blunt;very fragile materials that can be broken by hand force;purely PDLLA materials become more turbid,the blunt edge of change,obviously bent shape,materials to soften significantly,shorten the length of columnar,Volume shrinking,degradation at both ends of a circular shape.16 weeks - half a year,6%β-TCP / PDLLAs\’ degradation accelerated.The appearance further bending, deformation,blunt teeth sharp change significantly.Surface fissures increasing,loss of quality intensified.12%β-TCP / PDLLA complete loss of material strength,and become a serious softening of gum-like,muscle tissue was surrounded by CASP and can not be totally removed. Late,material in the muscle tissue fragments for amorphous granular,can not fully removed; pure PDLLA material softening Obviously,further narrow shape,CASP twisted serious, columnar materials appearance of similar to spherical.3.Three kinds of materials\’ CASP can withstand the initial state of the compression load for 6551±316N、6433±251N、6865±244N,much larger than day-to-day activities of lumbar by axial loading.12 weeks,its strength is still to 3128.9±147N/cm2,1287.1±107N/cm2, 3209.9±176N/cm2,still higher than the lumbar limit compressive strength.Compressive strength of the initial three core materials were 106.121±7.651MPa,104.240±10.407MPa, 109.803±12.089MPa,much larger than cancellous bone strength(1-17 MPa);12 weeks, respectively,compressive strength Dropped to 90.601±16.626MPa,39.401±4.720MPa, 81.529±6,662MPa,although 12%TCP / PDLLA group showing a sharp downward trend, but still higher than the strength of trabecular bone;six months,6%TCP/ PDLLA and PDLLA-strength materials decreased to 37.248±4.771MPa,19.735±2.328MPa,still slightly higher than the spongy bone strength.Compressive modulus,the three initial modulus materials were 12.311±0.888GPa,12.093±1.207GPa,12.738±1.402GPa,much higher than the vertebra elastic modulus(2 GPa);12 weeks,were down to 10.511±1.929GPa,4.571±0.548GPa,9.458±0.773GPa,still higher than the vertebral bone-compression modulus; half a year later,has been unable to measure 12%TCP / PDLLA group of compressive modulus,but 6%TCP / PDLLA and pure PDLLA group,compressive modulus materials for 4.321±0.553GPa,2.289±0.270GPa,still slightly higher than the vertebral compression modulus.Conclusion:1.First time report that add ceramic materialsβ- TCP into biodegradable polymer PDLLA to prepare biodegradable composite implants and manufacture the Centrum-vertebra-fracture-repairing absorbable supporting plugger(CASP),which for thoracolumbar burst fracture of the vertebral reconstruction.2.Three kinds of materials have good biocompatibility,can be absorb by body safely. Degradation of early and mid-term material itself and its degradation product does not have a negative impact on test animals.Muscle tissue and bone surrounding material have no abnormal performance.3.Accomplish mass loss,all kinds of materials display more or less biodegradation behavior,and they can be absorb by body safely and completely.4.Three of their initial strength and modulus of elasticity higher than vertebra cancellous bone,but compared to metallic implant,the compressive modulus closer to normal vertebral cancellous bone,and further decline accompanied by degradation.Can be meet the requirements of support within the vertebrae,avoid stress shielding to promote fracture healing and prevent osteoporosis or refracture.5.No matter what kind of materials,their respective mass loss rate and the rate of decline in strength apparent inconsistency,the intensity decreased significantly faster than the loss of quality.6.6%β- TCP/PDLLA materials\’mass loss and biomechanical decrease is more satisfactory than the other two.Maybe batter biodegradable composite material for thoracolumbar reconstruction.