Design And Related Basic Experiment Research Of Shape Memory Alloy Expandable Vertebral Stent For Minimally Invasive Vertebral Fractures

Part one The Design of Expandable Vertebral Body StentSection one Vertebral Body Anatomy and the Design of Shape Memory Alloy Expandable Vertebral Stent and Analyze the Significance of the Stent Flex VariationObjective : To study the characteristics of Chinese vertebral bodies and nickel-titanium shape memory alloy property,it is to analyze Expandable Vertebral Stent flex variation and to explore the EVS expandable characteristics in vertebral body.Methods:Ten complete sets of Chinese dry spinal specimens,it is to measure the antero-hight and midst-hight and meta-hight of vertebral bodies and survey introversion length “L” and “R” and sagittal longitude “M” in cross-section of terminal plate of vertebral body.The longitude “M” is as design parameter of the stent length.These data are statistical analysis by Microsoft Excel.The EVS flex variation is analyzed in geometry principle.Results: From T4 to L5,the length “L” or “R” is(22.3±2.6/22.4±1.8)mm on terminal plate section of vertebral body(the measuring ranges are from 18 mm to 35mm);siggital longitude “M” is(20.6±1.7~28.8±2.0)mm(the measuring ranges are from 17 mm to 32mm).The “M” longitude is less than “L or R” length.The midst high of vertebral body is(15.7±1.8~22.8±1.3)mm(the measuring ranges are from 12 mm to 26mm).The ratios of middle height “H”and siggital longitude“M” is from 0.70 to 0.80.The 23 mm length of arc“f” is contented EVS design for most Chinese thoraciclumbar compressed fractures.The EVS flex variation range is about from 1.0mm to 4.0mm.The EVS flex variation in thoraciclumbar segments is about from 2.0mm to 3.0mm.The special globular design of repositor stent flex variation is about from 4.0mm to 6.0mm.Conclusions: The length from anterior edge to posterior edge in vertebral body insiggital views could be as stent length design parameter and as application standard selection reference.The stent flex variation of geometry analysis could provide scientific evidence for EVS design and safety in vertebral body.Section Two The Approach of Design Parameters for Shape Memory AlloyExpandable Vertebra StentObjective:It is to measure the surface area and volume and mass of Shape Memory Alloy Expandable Vertebra Stent(SMA-EVS,EVS)with geometry-mathematics principle.The nickel ion liberation scale will be initially measured with ready-made laboratory results in order to explore the EVS clinical application feasibility for implanting into fractures spinal bodies.Methods : The EVS is designed as three or four or five or six lobes whose the thicknesses of plates are from 0.75 mm to 1.2mm.And then,the surface area and volume and mass of EVS could be definited a scale as its design.With the ready-made nickel ion liberation experimental results and the EVS designed surface area,the nickel ion possible liberation of the stent can be calculated and defined its scale.Refering to correlative data of nickel ion intaking minimal request a day and the nickel ion normal concentration in health adults and the nickel ion ingests from food a day,the EVS nickel ion liberation will be initially presumed.The results will be contrasted to the nickel ion of blood concentration and physio-intake in human body.Results : The EVS design surface area ranges are from 420mm2 to 900mm2.Its volume are from 110mm3~280mm3 and its mass are from 772mg~1968mg.The EVS maximum crest scale nickel ion liberation range is calculated from 7517.4×10-6?g to16852.44×10-6?g according to the laboratory measured nickel ion liberation results in Hanks.The nickel ion liberation scale in Hanks is about 0.003% blood nickel ion density.Conclusions:The EVS nickel ion liberation scale is infinitesimal liberation.It can be used an implant in vertebral body.Part Two The Basis of Experiment for Expandable Vertebral StentSection One An initial imaging study of Shape Memory Alloy Expandable Vertebra Stent expanding experiment results in vertebral bodies—Spinal Compression Fractures of Minimally Invasive Dynamic Internal Fixation(MIVDIF)Objective : It is to observe and study with imaging for the shape memory alloyexpandable vertebra stent(SMA-EVS,EVS)expanding results in spinal specimen.It is to explore a new minimally invasive technique for spinal fractures and its clinical application feasibility.Method: The thickness of six lobes EVS was made of 0.75 mm SMA plate.Five EVSs were used in this experiment.Three EVSs were implanted into two levels no compressed vertebra bodies.In order to observe EVS space results the EVS top lobes were revoled was about 90°while inserting into vertebral bodies.Others two EVSs were implanted into one level compressed fracture vertebral body.One was the right top lobes implanting angle,whereas,another was revoled as no compressed fractures specimens.These specimen vertebral bodies were taken X-Ray imaging and and CT three-dimensional reconstruction examining the EVS expectation expanding space inthose vertebral bodies.Results:In no compressed fracture specimens,three EVSs in vertebral bodies got favourable space through the top lobes revoled 90°.There were not obviously bone blocks inserting the EVS spaces.In compressed fracture vertebral body mould,the broken cancellous bone could get into EVS space from the wide lobes latero-interspace in CT three-dimensional reconstruction scan.But bone blocks not enter the EVS space that top lobes were correct angle implanting in CT three-dimensional reconstruction scan.Conclusions:EVS can get expectant space in fractured vertebral body.The six lobes SMA-EVS can effect the created space in fractured vertebral body but the inserting EVS space bone block will not effect the EVS clinical applications.The initial imaging results have provided an experimental foundation for different vertebral compressed fractures in clinical application.Section Two Expandable Vertebral Stent System and the Biological Filler Material Preliminary Researching in VitroObjective: It is to observe absorbable filler materials with shape memory alloy expandable vertebral stent(EVS)system in vitro biomechanical performance.Methods: In this test,three EVSs of three and four and five petallets were made of1.0 mm thickness shape memory alloy plate.Two EVSs of five petallets were made of 0.8mm thickness of shape memory alloy plate.The displacement of stress-displacement curve test in these EVSs was set as 7 mm.Alpha calcium sulfate hemihydrate(SCS)was tested biomechanics as dry module.The biomechanics of filling alpha calcium sulfate hemihydrate with EVSs was dry and tested,too.The displacement of stress-displacement curve test was set as 5 mm.Modulating CP,SCS and HAP into clumps and put them into the water,their changes were observed.Result : In the test results,the biggest mechanics scales of pure EVSs were136.4-246.8N.The biomechanics scales of dry SCS modulation were 128.3N~151.1N.The dry modulation biomechanics of SCS filling with EVSs were 459.9 N ~ 602.5 N.It was significant difference in their biomechanics results,P<0.05.But they couldn't be molded and couldn't be tested as biomechanics while modulating calcium phosphate(CP),calcium sulphate(SCS)and hydroxyapatite(HAP)in the water.Conclusion: EVSs have good biological mechanics.All of CP and SCS and HAP have a good biomechanical strength in dry model.But it can't be stemed node forming in the water and can't achieve to agglutinate and fix for vertebral fractured.Section Three Imaging observation of expandable vertebral stents in vertebral body expansion and biological materials filling effectObjective : To observe imaging results of memory alloys developed expandable vertebral stents(SMA-EVS)expanding in vertebral body and effect of material filling.Methods: There were seven self-developed shape memory alloy six-petal-stents were used in this experiment.Three stents were implanted into two sections of withoutpretreatment fractured vertebral specimens.Another two stent were placed pretreatment vertebral compressed fracture section.To observe the vertebral body stent expanding and produce the cavity and filling with fractured autogenous cancellous bone.A six-petal-stent was inserted the vertebral side and filled with absorbable materials.Another five-petal-stent was twice implanting into pre-perfusion bone cement filled one side of samples to observe the expand influence of the stent in vertebral body.The modified filling biomaterial was implanted into the stent expanding cavity.All of the specimens were observed by radiography and CT three-dimensional reconstruction to observe the stent expanding space results and vertebral specimens filling with material effect.Results: All of the seven implanting stents were eight times in vertebral specimens.They were completely expanded six times and two times were incompletedly expanding.After pretreatment fractured,all of stents were expanding and formed a good cavity.Some fractured cancellous bones were observed implanted into the stent cavity.Closed to the vertebral margins,the stent was portion expanding.After filling absorbable biomaterials,the imaging showed that the filling biomaterials can't be clearly observed.Beforehand filling with PMMA in one side of two vertebrae,the stent only got portion expanding.And then,the self-modified-filler-material were implanted into the stent cavity and obtained a good filling.Then,the vertebra was made fracture treatment,the stent was completedly expanding.Conclusion: Shape memory alloy expandable vertebral stent can be self-expanding in vertebral fracture and produce an anticipated space.Without pretreatment vertebral body fracture specimens may be influence of strength and other factors(vertebral strengthening)by cortical and cancellous bone.The stent can't completely expand.The traditional filling material can't be good cavity filling in vertebral stents.Modified filler material has a good operability.Part Three The Biomechanical Study of Expandable Vertebrae StentSection One Preliminary Mechanical Properties of the Independently Developed Shape Memory Alloy Expandable Vertebrae Stents(SMA-EVS)Objective : Observe the preliminary mechanical properties of the independentlydeveloped Shape Memory Alloy Expandable Vertebrae Stent(SMA-EVS).Methods: Conduct preliminary pressure tests respectively to one three-petal EVS,one four-petal EVS and one five-petal EVS made of SMA with the thickness of 1.0mm and two five-petal EVS and one six-petal EVS made of SMA with the thickness of 0.8mm,and observe the change of stress-displacement curve.Results: The shape of EVS stress-displacement curve is like “S” and the power of stent increases when pressure increases;when the stent is compressed 7mm,the tension limit is 100 to 246N;all tested stents haven't broken when being compressed completely;when the compressed stents are put into warm water,they expand completely without the loss of heights of stents.Conclusion: SMA-EVS has good initial tension and terminal elasticity,which can provide the broken centrum with initial restoration and expansion and support.Section Two Biomechanics characteristic of shape memory alloy expandable vertebrae stents(SMA-EVS)and kyphon balloon in spine surgeryBackground:The improved surgical techniques and the emerging new biomaterials have brought promising development for the treatment of spinal trauma and vertebralfracture.For the advantages that rigid stability,maintaining power lines,restore lordosis,reduce postoperative braking time,increase fusion rate,early rehabilitation,rigid internal fixation has become the standard non-surgical treatment for spinal disorders.Purpose:In this study,we observed the preliminary mechanical properties of the independently developed Shape Memory Alloy Expandable Vertebrae Stent(SMA-EVS)and kyphon balloon for the spinal surgery.Methods:We conducted preliminary pressure tests on one threepetal SMA-EVS,one four-petal SMA-EVS and one five-petal SMA-EVS with the thickness of 1.0 mm,two five-petal SMA-EVS and one six-petal SMA-EVS with the thickness of 0.8 mm.Then,the change of stress-displacement curves were observed respectively and compared to that of kyphonballoon.Results:The results showed that the stress-displacement curve of SMA-EVS was sigmoid while the curve of kyphon balloon was linear.For SMA-EVS,the tension of stent increased when pressure increased.When the stents were compressed by 7 mm to the maximum extent,the range of tension was 100-246 N.All the tested SMA-EVS haven't broken when being compressed completely.When the compressed stents were put into warm water,they expanded completely without the loss of heights.Conclusions:In conclusion,the biomechanics characteristics of SMA-EVS were different from kyphon balloon.SMA-EVS could be the good candidate for initial restoration,expansion and support of the broken centrum because of its good initial tension and terminal elasticity.Section Three The Biomechanics Preliminary Tests for Different Technology of Expandable Vertebral StentsPurpose:The early development of shape memory alloy expandable vertebral stents(EVSs)had expanded in vertebral bodies.To test the mechanical strength for these EVSs through improved the process parameters and different petallets technology in order to further explore the relationship between stent technology and biomechanical strength of design parameters and manufacturing technology,to seek the best technology of stents.Stent process can be made of memory alloy plate and tubular materials.Initial stent of successfully expanding in vertebral body was made of plate process.These stents mechanical properties were basis on the test and improve design parameters.Methods:In this experiment,the detection of these stents biomechanical strength was following these groups:Reference group: batch successfully expanding in vertebral body,the six-petals-stentof 0.8mm memory alloy plate biomechanical strength was as the control group: the memory alloy plate thickness stent design was 0.8mm and the petals width about 1.2 mm.Therefore,its biomechanical strength was as the initial referenceThe first group: Three stents were made of 1.0mm memory alloy plate(each one with three-petals,four-petals and five-petals)and two stents were made of 0.8mm memory alloy plate(two stent with five-petals).It was sum to five stents.In this group,it was the first batch stents biomechanical testing.The petals were nearly compressed state during the biomechanical strength testing.So its stress-displacement was set to 7mm.The group of biomechanical strength result was its reference group.The second group: one six-petals stent was made of 1.0 mm thickness of memory alloy plate.One eight-petals stent was made of 0.8mm thick memory alloy tubular.Two six-petals and three five-petals stents were made of 0.8 mm thickness memory alloy plate.This test group of biomechanical strength as the designed stents was as biomechanical strength interval that stress-displacement was set to 5 mm.The third group: One six-petals and one eight-petals stent were test that was made of o.8mm thickness of memory alloy tubular.It was to explore design expected optimal with tube material development performance and biomechanical strength of stents.In this group the stress-displacement was 9mm.The fourth group: the six-petals stent of 1.0mm thickness and eight-petals stent of0.8mm tubular material of the corresponding petals repeating test.It was to observe memory effects.The stress-displacement was set to 5mm.The fifth group: One six-petals stent of 1.0 mm thickness tubular was test biomechanical strength changes in different petals placed.Heng Yi biomechanics tester was to record the pressure-displacement curve changes.Results:Reference group: batches expanding the vertebral body of six-petals stent biomechanical strength,while the compression displacement was 7mm.The biomechanical strength was 90 N.The first group: It is each type petal stent biomechanical strength reference group.In this results of press-displacement test for plate process EVS,the stress displacement was set to 7 mm.The corresponding biomechanical strength was from 136 N to 236 N.Ellipsoid stent street-displacement curve was about "S" shape changes.While theStress-displacement was about 2mm,these stents biomechanical strength were about from50 N to 75 N.Then these stents mechanical strength would increase as an arc.The displacement curve showed as a "plateau".With stress-displacement further increasing,the stress-displacement curve curvature showed a steep change again.Their terminal pressure strength was about from 136 N to 236 N.Their average was 168 N.The 1.0 mm plate three-petals-stent biomechanical strength was the largest in the whole testing process.The second was four-petals-stent.The 0.8mm plate of six-petals-stent biomechanical strength curve corresponding was minimum.The second group: The stents biomechanical strength was about interval groups.In this group result,the six-petals-stent biomechanical strength result was the largest for 1.0mm thickness memory alloy plate in the whole testing process.While the stress-displacement was 5mm,the terminal value was about 238 N.The third group: It was tubular process biomechanical strength test results.The0.8mm thickness tubular stent was about diamond shape that the petal was not ellipsoid shape structure.The petal was about a single arc structure.While the stress-displacement was at 1 mm,the biomechanical strength was from 45 N to 65 N.While the stress-displacement was at 2 mm,the biomechanical strength was about 73 N.In this displacement process,the stent stress was higher than the corresponding plate technology.Then stress-displacement of these stents was going into the "plateau".Eight-petals-stent increased in the end-stage stress-displacement and six-petals-stent was decreased.As the maximum stress-displacement of 9 mm,the pressure value was from 72 N to 110 N.It was not as plate process of ellipsoid structure "S" shape biomechanical strength terminally increased.The fourth group: It was repeated stress tests for six-petals-stent of 1.0 mm plate process and eight-petals-stent of 0.8mm thickness tubular stent.These stents biomechanical strength test results were almost overlap.The fifth group: It was the biomechanical strength changes of 1.0 mm thickness six-petals-stent in different petal placed.Its test curve result was not obviously different.Conclusions:Stent has a good biological mechanics performance and memory characteristic.It was shown some difference biomechanical properties in different thickness and different process of stent.Section four Biomechanical finite element analysis of expandable vertebral stent implanted into vertebraObjective: To study the mechanical strength of expandable vertebral stent made of shape memory alloy along with the vertebra by using finite element analysis(FEA)after stenting.Method: CT scan of L1 vertebra was performed for elderly females with senile osteoporosis.The 3D FEA model of the L1 osteoporotic vertebral body was reconstructed using computer-aided design software.Stress changes of the stent and the L1 vertebra were measured before and after stenting under 5 load states,namely,axial compression,anteflexion,backward extension,lateral bending and lateral rotation.Results: In simple load simulation test before stenting,the stress of the vertebra under the five load states,lateral bending,backward extension,anteflexion,rotation and standing,was 17.1MPa,21.1MPa,44.0MPa,13.1MPa and 11.4MPa,respectively.No changes in stress acting on the vertebra were detected after stenting in the load simulation test.The stent implanted into the vertebra was subjected to the stress of 82.7MPa,49.8MPa,42.6MPa,79.1MPa and 22.8MPa,respectively.With the removal of the stent,the groove left in the vertebra was subjected to the stress of 82.7MPa,49.8MPa,39.2MPa,79.1MPa and 22.8MPa in the five motions,respectively.According to 3D FEA,changes in stress were detected for the vertebra after stenting only in anteflexion position.The maximum stress of the vertebra occurred in this position in the absence of stent with the value of44.0MPa.After stenting,the maximum stress also occurred in the anteflexion position with the value of 42.6MPa.With the stent removed,the maximum stress acting on the vertebra was 39.2MPa.Conclusion: Vertebra underwent no obvious changes in stress during the majority of the motions tested after implanting the expandable vertebral stent made of shape memory alloy.The maximum stress of the vertebra changed before and after stenting in the anteflexion position.This indicated the need to reduce the pressure acting on the anterior edge of the vertebral body in anteflexion position so as to prevent recompression of the treated vertebra.Part Four The Infrastructure Study of SpineSection One The Principles of Mathematical Analysis for Vertebral Sections And the Researching of Spinal LesionsSummary of Background Data : The spinal structure is made up of alternate connection of the vertebral body and intervertebral disc.It can be more clearly know the spine law of disease through collective studies.Purpose: To analyze stress transmission rule of spinal vertebral body-intervertebral disc with mathematical and physical principles;to analyze the correlation between stress transmission rule of spinal vertebral body-intervertebral disc and clinical pathology.Methods: the transverse diameter(L)and sagittal diameter(H)of the upper and lower sections on each vertebral body of C2-S1 in 10 intact spinal specimens were measured.Similarity principle of geometry was used: the area changes of upper and lower sections of vertebral body/intervertebral disc could be expressed in mathematical equations S1/S2=(a*b)/(A*B)and S=?/4*L*H to analyze the structure law of upper and lower sections of vertebral bodies;According to the structure of the intervertebral disc,principle of hydrostatic pressure F1/F2=S1/S2 was used to analyze the law of intervertebral disc pressure change.Results: With regard to spinal vertebral body section structure,the area increased in a S shape curve from the lower section of C2 to lower section of L4.The section area decreased from the lower section of L4 to the upper section of S1.The transverse diameter and sagittal diameter of the vertebral body-intervertebral disc determined the section area of the vertebral body and pressure coefficient K,K=L*H.Conclusion: The structure of spinal vertebral body-intervertebral disc itself determines the specific mechanical transmission and distribution characteristics of the spine;Establishment of mathematical equations to recognize the structure and mechanical transmission law of the spine can help more intuitively understand and observe spinal mechanical characteristics and patterns of clinical spinal lesions.Section Two Spinal Fracture Classification ResearchingFollowing the clinical researching and the development of imaging technology,especially the spiral CT imaging reconstruction technology and MRI progress,these clinical diagnoses provide a more intuitive imaging basis for spinal fracture.Following the further development of clinical technology and especially for minimally invasive treatment technology popularizing and applying of the spine during the nearly 30 years,the clinical treatment and cognition of spinal fractures have more profound changes.According to the spinal structure and fracture rules and since more than half a century the recent advances in the treatment of clinical spinal fractures,we introduce a neural spine fractures column concept and propose spinal fractures into three columns and types as well as comprehensive consideration on the basis of clinical symptom,physical examination,imaging,combined with spinal fracture type,imaging diagnosis and nerve damage degree.