Abstract:Objective To carry out analysis on the fatigue lifetime prediction of nitinol cardiovascular stents. Method By using the finite element method of fatigure fracture, the three dimensional nitinol cardiovascular stents were established to analyze the structure of cardiovascular stents under a physiological pulsating cyclic loading. Results Great normal stress, low fatigue life and serious fatigue damage were found to be located near the stents’knots, and stents with nitrided surface or shot peened surface were likely to have a longer fatigue life. During miniature fatigue testing, early fatigue cracks or fractures were always formed at locations near stents’knots. Conclusions The simulating results under the physiological loading are matched with related experimental results, which provide a theoretical basis for the reliability and design of the cardiovascular stents.

Abstract:Objective To study the ultra-high cycle fatigue behaviors of the Ti-6Al-4V alloy implant after subjection to simulated body fluid (SBF) environment exceeding 107 cycles, and to predict its service life. Method The Ti-6Al-4V alloy specimens were subjected to SBF in two groups for two days and six days respectively; using the ultrasonic fatigue testing technique, the ultra high cycle fatigue properties of Ti-6Al-4V alloy after subjection to SBF in body temperature were studied and the initiation mechanisms of fatigue cracks were investigated and analyzed with scanning electron microscopy (SEM) and energy dispersive atomic X-ray (EDA X ray). Then, a comparison with corresponding behaviors of the normal Ti 6Al 4V alloy was made. Results The S~N curve of the Ti-6Al-4V alloy after subjection had the similar tendency as that of the normal one, showing that they descended continuously during 104 and 108 cycles and the descending tendency was lower in the region of 107～108 cycles; the life of the specimens after subjection dropped before the fatigue life of 107 cycles and was smaller after the fatigue life of 107 cycles than that of the normal ones; the life of the specimens subjected for six days had little difference with that subjected for two days; fracture could still occur beyond 107 cycles, showing that there was no fatigue limit as the traditional fatigue conception described. Fatigue cracks mainly initiated from the surface of specimen before the fatigue life of 107 cycles and some specimens had multiple crack initiation sites; fatigue failure initiated from internal inclusion where mostly the element Al aggregated after the fatigue life of 108 cycles. Conclusions The ultra high cycle fatigue properties of the Ti-6Al-4V alloy decreas a little with SBF subjection; the initiation site of the fatigue crack changes from the surface to the internal defect with the increase of the number of cycle.

Abstract:Objective To investigate the influence of the location of drug release and the stent spacing on drug deposition in curved artery walls. Method 2D curved artery and strut models were employed to carry out a numerical investigation on drug deposition under different drug release surfaces or stent spacing ( 1 strut length, 3 strut lengths, 7 strut lengths ). The results were compared with those in a straight artery. Results The drug depositions produced by four different surfaces of a single strut were quite different. Compared with the curved artery, the superiority of drug release from the top surface of the straight artery was reduced, while the weakness of drug release from proximal surface was substantially increased. There was no significant change for drug release from the distal surface. The average drug concentration increased with interstrut spacing increasing, but the percentage increase was less than that in the straight artery. Concentration differences were observed between the inside and outside of the curved artery, which on the outside showed much lower. Conclusions The local flow alteration, the drug release location and the stent spacing have significant effects on drug deposition in a curved artery and the result is obviously different from that in a straight artery.

Abstract:Objective In order to provide a reference for analysis of the pathophysiological changes of human arterial tree, the effects of the arterial parameters on input impedance of arterial tree were studied by proposing a recursive algorithm to calculate the input impedance. Method A distributed electric network model was constructed for the arterial tree which consisted of 55 segments accounting for all the central vessels and major peripheral arteries. By setting up the peripheral resistance of the model and constructing a unilateral data link list of the arterial tree, the recursive algorithm was employed to compute the input impedance of ascending aorta in the arterial tree. Then, comparisons of the effects of arterial compliance, peripheral resistance, length, internal radius and wall thickness on the input impedance were made based on the recursive algorithm. Results The computational results were in accord with experimental data and results of other models, and proved the validity of the model and algorithm. The input impedances of the arterial tree showed significant influence with different characteristics for different parameters. Conclusions The input impedance of arterial tree can reflect the changes of the hemodynamic parameters effectively, which is an important reference for the pathophysiological diagnosis of human arterial tree.

Abstract:Objective To study the load distribution of muscles for those having long period stance training during traditional chinese Gongfu stance, and evaluate the effectiveness of such stance. Method Seven traditional Chinese Gongfu stance trainers and seven normal adults for the control were enrolled in the experiment. The sEMG (surface electromyography) signals of five muscles (brachioradialis, triceps brachii, deltoid, latissimus dorsi, triceps surae) were tested by Flexcomp Infiniti 10 channel sEMG collector. The value of IEMG (integral electromyography) were processed. Results With the increase of load, the ratio between deltoid IEMG and latissimus dorsi IEMG for the stance trained group stabilized in the range from (0.372±0.258) to (0.257±0.146), while that of the control was in the range from (1.313±0.698) to (0.800±0.405). Conclusions When the traditional Chinese Gongfu stance is processed with or without load, the trained group distributed major load on the dorsal muscle, while the control on the shoulder.

Abstract:Objective To measure the interstitial fluid pressure (IFP) on low hydraulic resistance channel along meridians and observe the difference and fluctuation. Method Low hydraulic resistance points (LHRP) and non LHRP were measured on anesthetized mini pigs by a scanning hydraulic resistance measuring device. The IFP was then measured by wick in needle method on these two regions. Results The stomach meridian, kidney meridian and conceptual vessel meridian on mini pigs were measured. The IFP were significantly lower than non LHRP region on the above three meridians(P<0.05), the differences of which were 1.06，0.70，3.69 mmHg respectively with the total pressure difference of 1.44 mmHg and pressure gradient of 1.44~2.88 mmHg/cm（1 mmHg=0．133 kPa）. Conclusions Among the peripheral subcutaneous tissues, there exists a difference of IFP toward the meridian which may drive the flow of interstitial fluid toward the meridians.

Abstract:Objective To evaluate neck muscular strength（NMS） of the air force pilots and its role in the circumstance of aerial dynamics. Method The tests were performed by using CME-1 Neck Muscle Training Machine with 149 pilots volunteered as test subjects. Each individual’s maximal isometric NMS was evaluated in the extension, flexion, left and right lateral bending directions within a single day. The NMS in each direction was tested for 10 times to choose the maximal peak value in each direction as the NMS for data analysis. The mean of overall peak value in each direction was calculated as the mean neck muscular strength (MNMS). The ratio(r) between MNMS and NMS was calculated to reflect the neck muscular endurance in pilots. Results The NMS in the flexion, extension, and left and right lateral bending directions was （132.0±42.2)N, （205.2±82.2)N, （174.3±76.4)N and （191.2±78.3)N respectively，the NMS in the extension or flexion direction was significantly different (P<0.001) compared with NMS in all the other directions，and the right NMS was significantly higher than the left NMS(P<0.001). The ratios between MNMS and NMS in the flexion, extension and left and right lateral bending directions were 74.24%,72.86%,72.75% and 68.72% respectively. Conclusions To Maximize the efficiency in flight performance and minimize neck injuries induced by +Gz, fighter pilots should be encouraged to perform more on land neck muscle strengthening exercises and improve their head positioning techniques during flight.

Abstract:Objective To study the methods of reducing the shock response of surface ship crew by under water explosion. Method The shock response lumped parameter models were established to study the influence on surface ship crew with different structure parameters in standing, sitting and walking posture. Results For ship crew with sitting posture, the shock response of the pelvis could be reduced by enlarging the damping ratio and stiffness ratio between the deck and the chair. For ship crew with both standing posture and walking posture, the shock response of the limb could be reduced by enlarging the damping coefficient of the deck. Conclusions By adding anti shock chairs or laying anti-shock material on the deck, the damping ratio and stiffness ratio between the deck and the chair, or the damping coefficient of the deck could be enlarged, and the shock response of the surface ship crew could be reduced.

Abstract:Objective To provide reference for understanding the stress state of the aortic arch，select the appropriate constitutive relation, further analyze the biomechanical properties of human aortic arch so as to offer the biomechanical basis for treating aortic arch in clinic. Method Under two different constraints(the first constraint: the constraint along with the direction of ascending aorta; the second constraint: the ascending aorta could move freely, but the end was closed with a hemisphere), three constitutive relationships (linear constitutive, exponential function constitutive, M-R constitutive) and two loads(10.67 kPa and 26.66 kPa), the circumferential stress on human aortic arch were studied by the finite element method, and the results were also discussed. Results The models under two constraints were established and the contour plot of circumferential stress and its distribution along the arc of aortic arch under two constraints, three constitutive relationships and two loads were obtained respectively. Conclusions The exponential function constitutive model could reflect the mechanical properties of aortic arch more comprehensively and the mechanical properties of aortic arch could be reflected more factually under the second constraint.

Abstract:Objective To investigate the cooling effect of blood flow on living tissue heating. MethodThe ultrasonic tissue phantom with a U-tube was used to simulate the living tissue with counter-current vessels. The distilled water with constant temperature (37.5 °C) was pumped into the phantom through the U-tube. The phantom was then immersed in another water bath and heated from 37.5 °C to 43.5 °C with a constant heating rate in order to simulate the environment of hyperthermia. Meanwhile, 46 thermocouples were employed to measure the temperatures of liquid flow, tube wall and the phantom. Finally, the experimental results of the temperature distribution were visualized by AVS (Advanced Visual System) software. ResultsWith the increase of flow velocity, the temperature of tissue was reduced, especially in the area surrounded by the U-tube. Moreover, the temperatures in the U tube bounded area reduced more significantly when the Reynolds number varied from 50 to 130. ConclusionsThis perfusion phantom experiment was successful to simulate the influences of the counter-current flow on the characteristics of the heat transfer. It showed that because of the existence of the counter-current vessels, the cooling effect of internal tissue surrounded by U-shaped tube was more evident.

Abstract:Objective To analyze the axial stiffness of human pelvis that were set with the double support standing posture and subjected to gradient vertical loads. Method Nine intact embalmed cadaver specimens were marked from 1# to 9# according to the test sequence, and then subjected to vertical static loads in the gradient of 100 N from 0 N to 500 N. The load displacement data were collected by using the beam sensor of electronic universal testing machine to calculate the axial stiffness of human pelvis. Results The differences of axial stiffness among individual pelvis were large (P=0.815), ranging from 240 N/mm to 776 N/mm. All the pelvic specimens were divided into three groups by cluster analysis (the first group: 1#、2#、3#、5#、9#, the second group: 4#、6#、8#, the third group: 7#). According to the processed results, there were statistical differences among the groups (P<0.05). The trends of pelvic axial stiffness were different under gradient loads. The axial stiffness of the first and third group, totally six specimens, increased with loads increasing; while the axial stiffness of the second group including three specimens increased first, but then decreased with the loads increasing. Conclusions There are significant individual differences in pelvic axial stiffness and its changing discipline within the physiological range; the cluster analysis can be used to analyze the changing discipline between the load and stiffness of human pelvis; as a whole, the pelvic axial stiffness increased with the loads increasing.

Abstract:Objective To compare the stresses on the end plate of adjacent lumbar vertebrae between intra-segmental fixation and inter-segmental fixation in treating lumbar spondylolysis by three-dimensional finite element analysis. Method Based on the established finite element model of L4 lumbar spondylolysis, the lumbar internal fixation such as rods and trans-pedicle screws were reconstructed to make the finite element models of intra segmental and inter segmental internal fixation with the same constraint and loading conditions. The stresses on endplate of adjacent lumbar vertebrae of finite element models were measured under three mechanical conditions:spondylolysis, intra-segmental fixation and inter-segmental fixation. Results High stresses were observed under two kinds of internal fixation conditions compared with the spondylolysis condition at the lower endplate of L4 under axial loading(P<0.05). The stresses at the lower endplate of L4 under intra segmental fixation condition were similar as that of the spondylolysis condition under flexion, extension and lateral bending loading. With the same loading, higher stresses were observed under inter-segmental fixation condition compared with the spondylolysis condition, and so did the lower stresses at upper endplate of S1(P<0.05). The lower stresses at the upper endplate of S1 under intra-segmental fixation condition were observed compared with the other two conditions under rotating loading (P<0.05). Conclusions The intra segmental fixation can not only provide stability for lumbar spondylolysis under axial, flexion, extension, lateral bending,but also preserve the normal activity at adjacent disc levels, especially under rotating loading.

Abstract:Objective To explore the influence of femoral tunnel placement on the isometry of grafts in the reconstruction of posterolateral corner of the knee (PLC). Method Knee specimens from 9 frozen human cadavers were used in the study. Five points of femoral attachment sites, including the central, proximal, distal, anterior and posterior points, were selected as femoral test points for both lateral collateral ligament（LCL）and popliteus tendon（PT）. The fibular/tibial attachment sites of LCL, PT and popliteofibular ligament（PFL） were connected to the corresponding 5 test points using the brass wire, respectively. Changes in distance between each pair of fibular/tibial and femoral points were measured during the passive knee flexion extension test (0°~90°). Results The maximal changes of distances between the LCL’s anterior, distal points and LCL’s fibular attachment site were not greater than 3 mm, and there was no significant difference between these two points; the maximal change of distance between the PT’s anterior point and PFL’s fibular attachment site were not greater than 3 mm. All of the maximal changes of distances between the PT’s 5 test points and tibial point of musculotendionous junction were greater than 3 mm. Conclusions Under the condition of fibular tunnels locating at center points of LCL and PFL attachment site, the femoral tunnel should be located at the anterior edge of LCL’s attachment site (anterior point) for LCL reconstruction, and at the anterior edge of PT’s attachment site (anterior point) for PFL reconstruction.

Abstract:Objective To compare the stress relaxation and mechanical properties of creep viscoelasticity in the young and old’s spine and to provide the reference for the mechanical mechanism of viscoelasticity of yellow ligament degeneration. Method Twenty specimens of elderly patients with degenerative lumbar yellow ligament degeneration as the older group, and twenty specimens of young patients with lumbar yellow ligament injuries as the youth group were used respectively. All the yellow ligament specimens were from the yellow ligament between the fourth and fifth of lumbar vertebra (L4~L5). Stress relaxation experiment and creep experiment were conducted on the specimens by the strain increasing speed as 1%/s and the stress increasing speed as 0.5 MPa/s respectively. The experimental temperature was (36.5±0.5) ℃ and the experimental time was 7 200 s. Ninety stress relaxation and creep data were collected, and the data were dealt with the statistical analysis and normalization methods. Results The 7 200 s stress of yellow ligament in the youth group decreased by 1.42 MPa, while the 7 200 s stress of yellow ligament in the older group decreased by 1.91 MPa. The 7 200 s strain of yellow ligament in the youth group increased by 3.39%, while the 7 200 s strain of yellow ligament in the older group increased by 2.07%. The 7 200 s stress in two groups all increased and the increased strain data showed statistically significance (P<0.05). The stress relaxation curve changed in the form of logarithm and the creep curve changed in the form of index. Conclusions The 7 200 s stress relaxation and creep in the yellow ligament of the older group all decreased and the mechanical properties of viscoelasticity changed.

Abstract:Objective To evaluate the biomechanical stability of pectin/polyvinyl alcohol composite （CoPP）hydrogel and to assess the range of motion(ROM) and intradiscal pressure (IDP) changes at the above adjacent segment after the anterior implantation of CoPP hydrogel and cage. Method Six fresh cadaveric lumbar spine specimens（L3～L5）were biomechanically tested on the robotic testing machine. ROM at L3/4 and L4/5 and intradiscal pressure at L3/4 were measured. All measurements were made with initially intact and followed by both CoPP and cage implantations. Results At the implanted level (L4/5), the CoPP spine showed no significant change in the other five motion directions except left lateral bending motion compared with the intact spine (P>0.05), whereas the cage spine decreased significantly in all motion directions when compared with the intact spine or CoPP spine (P<0.05). At the above adjacent level of L3/4, the CoPP revealed a minor change in all motion directions except left lateral bending motion compared with the intact spine (P>0.05), whereas the ROM of cage spine significantly increased in all motion directions compared with the intact spine (P<0.05). The IDP of the CoPP spine did not increase under any condition compared with the intact spine (P>0.05). While the IDP of cage spine significantly increased in flexion/extension and left/right lateral bending compared with the intact spine or CoPP spine (P<0.05). There was no significant increase in axial rotation compared with the intact spine or CoPP spine (P>0.05). Conclusions The implantation of CoPP prosthetic nucleus can preserve the motion function at the operated level and maintain the lumbar stability. Compared with the lumbar fusion, the nucleus replacement has no significant effect on the ROM and IDP at adjacent level, which may decrease or avoid the adjacent segment degeneration.

Abstract:Mechanical stimulation plays an important role in the normal metabolism and reorganization of bone. Many kinds of stress sensitive cells, including osteoblasts, can perceive and transduce the mechanical signals. As the fibrous framework throughout a cell, cytoskeleton as well as extracellular matrix and integrin is one of the critical components in mechanotransduction. Mechanical stimulation can induce the rearrangement of the cytoskeleton, and the signals are transduced and transformed by the second messagers, finally resulting in the changes of gene expression.The family of Rho, protein kinase C and focal adhesion kinase are the main messages involved in this process. This paper summarizes the recent advances about the effects and possible mechanism of mechanical stimulation on osteoblast cytoskeleton.

Abstract:Relative movement between the spine segments has close connection with spinal surgery. Understanding the spinal range of movement is crucial to advance our understanding about the biomechanical function of spine injury, spinal degeneration, and the development of new surgical treatments and implants for spinal disorders. The measurement of spinal movement has gone through the process from two dimensional plane to three dimensional measurement, from simple to complex, from rough estimation to precise calculation. This paper will describe the major achievements and deficiency of various methods of spinal movement measurement to provide reference and help for the research of spinal movement measurement.