Micro-pore structure and mechanical properties of porous titanium scaffold using 3D print technology / 医用生物力学

Objective To study the micro-pore architecture and mechanical properties of porous titanium scaffolds with diamond molecule structure produced by 3D print technology, so as to guide the development of 3D-prinited porous titanium orthopedic implants. Methods Selective laser melting (SLM) and electron beam melting (EBM) were used to fabricate porous Ti6Al4V scaffolds with diamond molecule structure. The micro-pore architectures of those scaffolds were observed using optical microscope and scanning electron microscope (SEM), and universal material testing machine was used to conduct compressive test on the scaffolds. Results Both SLM and EBM techniques had machining error and half-melted metal particles were found on the strut surface. The relative error of strut size produced by SLM and EMB was 20.9%-35.8% and －9.1%-46.8%, respectively. The scaffold with strut width of 0.2 mm could not be produced by EBM. The compressive strength and elastic modulus of the scaffold fabricated by SLM was 99.7-192.6 MPa and 2.43-4.23 GPa, respectively. The compressive strength and elastic modulus of the scaffold fabricated by SLM was 39.5-96.9 MPa and 1.44-2.83 GPa, respectively. Conclusions The manufacturing precision of SLM is higher than that of EBM. Porosity is the main factor that affects the compressive strength and elastic modulus of the scaffolds. In the same process, with the increase of porosity, both the compressive strength and elastic modulus decrease. When the porosities are similar, the scaffolds fabricated by SLM possess higher compressive strength and elastic modulus than those by SLM.

Micro-pore structure and mechanical properties of porous titanium scaffold using 3D print technology / 医用生物力学

Objective To study the micro-pore architecture and mechanical properties of porous titanium scaffolds with diamond molecule structure produced by 3D print technology,so as to guide the development of 3D-prinited porous titanium orthopedic implants.Methods Selective laser melting (SLM) and electron beam melting (EBM) were used to fabricate porous Ti6Al4V scaffolds with diamond molecule structure.The micro-pore architectures of those scaffolds were observed using optical microscope and scanning electron microscope (SEM),and universal material testing machine was used to conduct compressive test on the scaffolds.Results Both SLM and EBM techniques had machining error and half-melted metal particles were found on the strut surface.The relative error of strut size produced by SLM and EMB was 20.9％-35.8％ and-9.1％-46.8％,respectively.The scaffold with strut width of 0.2 mm could not be produced by EBM.The compressive strength and elastic modulus of the scaffold fabricated by SLM was 99.7-192.6 MPa and 2.43-4.23 GPa,respectively.The compressive strength and elastic modulus of the scaffold fabricated by SLM was 39.5-96.9 MPa and 1.44-2.83 GPa,respectively.Conclusions The manufacturing precision of SLM is higher than that of EBM.Porosity is the main factor that affects the compressive strength and elastic modulus of the scaffolds.In the same process,with the increase of porosity,both the compressive strength and elastic modulus decrease.When the porosities are similar,the scaffolds fabricated by SLM possess higher compressive strength and elastic modulus than those by SLM.

Micro-pore structure and mechanical properties of porous titanium scaffold using 3D print technology / 医用生物力学

Objective To study the micro-pore architecture and mechanical properties of porous titanium scaffolds with diamond molecule structure produced by 3D print technology,so as to guide the development of 3D-prinited porous titanium orthopedic implants.Methods Selective laser melting (SLM) and electron beam melting (EBM) were used to fabricate porous Ti6Al4V scaffolds with diamond molecule structure.The micro-pore architectures of those scaffolds were observed using optical microscope and scanning electron microscope (SEM),and universal material testing machine was used to conduct compressive test on the scaffolds.Results Both SLM and EBM techniques had machining error and half-melted metal particles were found on the strut surface.The relative error of strut size produced by SLM and EMB was 20.9％-35.8％ and-9.1％-46.8％,respectively.The scaffold with strut width of 0.2 mm could not be produced by EBM.The compressive strength and elastic modulus of the scaffold fabricated by SLM was 99.7-192.6 MPa and 2.43-4.23 GPa,respectively.The compressive strength and elastic modulus of the scaffold fabricated by SLM was 39.5-96.9 MPa and 1.44-2.83 GPa,respectively.Conclusions The manufacturing precision of SLM is higher than that of EBM.Porosity is the main factor that affects the compressive strength and elastic modulus of the scaffolds.In the same process,with the increase of porosity,both the compressive strength and elastic modulus decrease.When the porosities are similar,the scaffolds fabricated by SLM possess higher compressive strength and elastic modulus than those by SLM.

Micro-frictional contact force properties of articular cartilage / 医用生物力学

Objective To study the frictional contact force properties of articular cartilage by modified silicon probes of the atomic force microscopy (AFM). Methods Modification was conducted on the silicon nitride probes of AFM by the micromanipulator, and the glass microsphere was glued on the probe by glass adhesive as the pinhead. Micro-tribology properties of human and bovine articular cartilage were then investigated by using the modified AFM probes. Results With the increase of load, the friction force of human and bovine cartilage also increased gradually. When the sliding speed increased from 0 to 100 /s, the friction force between specimens and probes increased quickly; when the sliding speed increased from 100 /s to 300 /s, the friction force increased slowly. Conclusions Articular cartilage had an obvious fibrous structure in its surface. There was a direct relationship between the surface roughness of articular cartilage and the measuring range. When the load or sliding speed increased, the friction forces of human and bovine cartilage show an increase with the same variation range. The investigation on mechanical and tribological properties of articular cartilage in micro-frictional experiment will contribute to understanding the injury mechanism of articular cartilage and developing wear-resistant materials for medical artificial joints.

Reinforcement property of collagen fibril in articular cartilage / 医用生物力学

Objective To evaluate and compare the differences in COSMOL articular cartilage (AC) simulation due to the application of collagen fibril reinforcement property. Methods Collagen fiber stress was modeled independently according to its orientation in AC and written into the original poro-elastic AC model. Function call was used to avoid quadric strain term. The iteration of solver was increased for better convergence. Results The initial superficial Y displacement of the reinforced model was 15 μm, which was 17.6% of the non-reinforced model. X normal strain of the reinforced model was 10% of that in the non-reinforced model, but the superficial X normal stress of the reinforced model was 10 times higher than that of the non-reinforced model. Conclusions The application of collagen fibril reinforcement property in COMSOL AC simulation is achieved, which provided the computational model and theoretical analysis for collagen fibril lesion. Lateral reinforcement of collagen fiber can constrain the vertical strain, by which enlarge AC load capacity and improve AC mechanical properties.

Multiscale computation on mechanical environment of chondrocytes / 医用生物力学

Objective To compare the mechanical environment of chondrocytes between superficial zone and deep zone by multiscale computation. Methods The chondrocyte biphasic model was set up and made the results of the articular cartilage (AC) biphasic model mapped to the corresponding borders of the chondrocyte model as the boundary condition. The chondrocyte model was computed to obtain the results of the mechanical environment of chondrocytes and analyzed. Results The results showed that the stress of chondrocytes at deep zone was half of that at superficial zone, but both were much smaller than those outside chondrocytes. The pericellular matrix (PCM) sustained the high stress outside chondrocytes and remarkably reduced the stress inside chondrocytes. Interstitial flow directions adjacent to two chondrocytes were totally the opposite.Conclusions The bearing property of AC reduced the stress near chondrocytes at deep zone prominently and protected the chondrocytes at deep zone and subchondral bone. PCM sustained the high stress outside chondrocytes to provide lower stress environment for chondrocytes living. The opposite interstitial flow direction of two chondrocytes supported the theory that synovia seepage from cartilage surface and nutrient pumped out from subchondral bone constitute the bidirectional nutrient supply in AC.

Wear analysis and diagnostic reasoning on clinical failure of artificial hip joints / 医用生物力学

Objective To investigate the wear mechanism of artificial hip joints and the criteria for wear life definition, analyze the causes of abnormal wear and the clinical manifestations of wear failure, establish the reasoning route of failure incidents. Methods The wear process and early factors on abnormal wear in artificial hip joints were studied through elastohydrodynamic lubrication computation and finite element analysis; the service life of artificial hip joints was determined through establishing criteria for wear life definition; the clinical manifestations of wear failure were introduced and classified through wear-osteolysis morphological matrix; the reasoning logic of failure incidents was established through clinical investigation. Results The minimal synovium thickness and contact stress between the femoral head and the acetabular cup were calculated, and the effect of relevant parameters was studied as theoretical references for wear analysis; the criteria on wear life definition of artificial hip joints were proposed, namely the mechanistic failure due to geometric change in artificial hip joints and the biological failure due to osteolysis; nine kinds of clinical manifestation for wear failure were found; the reasoning route for failure incidents was presented. Conclusions Primary wear process in artificial hip joints includes boundary and mixed friction, adhesive, ploughing and third-body wear; surface quality, fit clearance between the acetabular cup and the femoral head, and roundness have great impact on early abnormal wear; normal mechanistic life of metal-UHMWPE artificial hip joint can reach 40 years, but its maximum biological life is no more than 10-15 years, which is the constraint of prosthesis life today; the diversity of clinical manifestations for wear failure is the morphological Results of mechanical wear and osteolysis, which is helpful for the reasoning route of failure incidents.

Effects of hip protector on biomechanical response of the pelvis-femur complex under lateral pelvic impacts during sideways falls / 医用生物力学

Objective To investigate the effect of hip protector on biomechanical response of the human pelvis-femur complex under lateral pelvic impacts during sideways falls using three dimensional (3D) finite element (FE) method. Methods Based on the model database of China Mechanical Virtual Human, a 3D FE model of the pelvis-femur-soft tissue complex including cortical bone, cancellous bone and soft tissue capsule and the pelvis-femur-soft tissue complex with a two layer hip protector were created, respectively. The rigid plane model was also constructed in the two models for ground simulation and constrained in all freedoms. The average hip lateral impact velocity of 2 m/s was applied to the two models, and the time for simulation analysis was set at 20 ms. The stress and strain distribution on the two models under lateral impacts could be obtained by the 3D FE calculation. The comparative analysis was performed to study the effect of the hip protector on biomechanical response of the pelvis-femur complex. Results The hip protector made the peak Von Mises stress appeared 4 ms more earlier in the pelvis-femur complex with a significant decrease in the stress and strain level. The average Von Mises stress peak was decreased by 67.88% and 69.34% in the cortical bone and in the cancellous bone, respectively, and the compressive principal strain peak was decreased by 63%. Conclusions Under lateral pelvic impacts, the two-layer hip protector could act as safeguard for pelvis-femur complex, thus effectively prevent the occurrence or reduce the risk of bone fracture.

Biomechanical analysis and reasoning on dislocation failure after total hip arthroplasty / 医用生物力学

Objective To propose a detailed method on the diagnosis of dislocation failure by studying the mechanism of mechanical failure and causes of dislocation occurrence after the total hip arthroplasty (THA). Methods The correlation between dislocation failure and clinical situation, product design and patients was analyzed by establishing the dislocation model to study the biomechanical mechanism of dislocation procedure. Results The reasoning route for dislocation analysis after THA was proposed and the visual hip prosthesis motion analysis software was developed and validated. Conclusions Case study on dislocation failure after THA shows that the proposed method and developed software can judge the cause of dislocation incidence in detail, and determine the relationship between implanting position for the hip prosthesis and dislocation incidence. Meanwhile, it can find the best implanting position before operation and analyze the risk of dislocation incidence, which will be helpful for the prosthesis design.

Statistical analysis on artificial joint failure and its role in technology development / 医用生物力学

This paper expounds the statistical work on artificial joint failure and their primary results in China and abroad. From the view of clinical demand, biomechanics and engineering, the paper proposes that it is the basic technology, manufacturing techniques and clinical conditions that lead to artificial joint failure. The paper also elaborates the demand on further improving the clinical medicine of artificial joint and prosthesis technology, and presents some suggestions to promote the domestic statistics work on artificial joint failure.

Mechanical analysis and reasoning on fractured stem failure after total hip arthroplasty / 医用生物力学

Objective To propose some detailed methods for diagnosis of fractured stem failure in clinic by studying the mechanical mechanism of fractured stem failure and the specific causes of fracture occurrence after the total hip arthroplasty (THA). Methods The correlations between fracture stem failure and production, clinical situation and patients were analyzed by 2D and 3D finite element analysis (FEA) method to study the biomechanical mechanism of fracture processes. Results The reasoning route for fractured stem failure analysis after THA was proposed, and mechanical analysis and validation on fractured stem failure were conducted by FEA methods successfully. Conclusions Fracture should not occur on the artificial stem, for those that gone through the strength design and experimental test; statistical analysis on fractured stem failure showed that the occurrence of such fractured stem is a kind of little probability random event, which could be induced by a variety of non-normal factors, such as fluctuations in product quality, technical errors in clinic, patient accidents and so on. Strict controls on these factors can reduce the fractured stem occurrence; the reasoning route for fractured stem failure can help to discover the reasons of failure occurrence; the mechanical mechanism of specific fracture stem occurrence can be detected by 2D and 3D FEA methods.

Biomechanical analysis and reasoning on aseptic loosening failure after total hip arthroplasty / 医用生物力学

Objective To propose some detailed methods for diagnosis of aseptic loosening failure in clinic by studying the mechanical mechanism and the specific causes of aseptic loosening failure after the total hip arthroplasty (THA). Methods The causes of aseptic loosening were investigated from the view of biomechanics, such as strength of the bone cement layer, interface fretting, stress shielding, wear and osteolysis; the relationships between aseptic loosening failure and products, clinical and patient factors were analyzed; the method to detect loosening before the revision surgery was also studied. Results The reasoning route for aseptic loosening failure analysis after THA was proposed, and detection of aseptic loosening with fluoroscopic analysis (FSA) technique before the revision surgery was conducted successfully. Conclusions The reasoning route for aseptic loosening failure analysis can help to discover reasons of failure occurrence. Loosening can be detected and confirmed in vivo by FSA method, which can also assist the clinician for diagnosis and treatment of aseptic loosening after the THA.

Dislocation risk after total hip arthroplasty / 医用生物力学

Objective To investigate and analyze the risk of dislocation failure after total hip arthroplasty (THA). Methods The optical motion capture system was used to obtain the kinematic data of the lower limbs during actions of daily living (ADLs) from normal people. The visual hip prosthesis motion analysis software was designed and developed to measure the maximum safe motion space of the hip prosthesis with different design parameters and judge the safety of the hip prosthesis by analyzing the relative motion relation between the cup and prosthetic stem. Results Based on the measured kinematics data, the motion analysis software could compare the range of motion of the natural joints and that after THA. Thus, the relationship between the dislocation of hip prosthesis and ADLs was obtained and the dislocation risk after THA was investigated. Conclusions There is a high risk when activities that require a high flexion motion are performed, especially for the kneeling and squatting activity.

Articular cartilage simulation using depth-dependent mechanical parameters / 医用生物力学

Objective To evaluate the difference in articular cartilage simulation due to the application of either homogeneous or depth-dependent mechanical parameters. Method The nonlinear， biphasic， porous model of articular cartilage was built using poroelasticity module in COMSOL. Under the static load, the model was computed using homogeneous and depth dependent parameter, respectively. The difference between the results was analyzed. Results For the total stress of cartilage， there was no remarkable difference between two parameter configurations. However, for the analysis such as solid phase stress, fluid pressure and flow velocity， the difference between two parameter configurations must be considered. Conclusions Different parameter configuration has negligible effect on the total stress of cartilage, but it is influential to the flow velocity. Therefore， homogeneous mechanical parameters should be used in order to simplify the total stress computation problem. The other more detailed analysis should be based on the depth dependent parameters. These conclusions could be referred to for future cartilage modeling and numerical computation and thus laying a foundation for the design and computation of artificial joint.

Joint angles and muscle activations in the lower limb of young women during slope walking / 医用生物力学

Objective To illustrate the influences of walking speed and road slope on lower limb motions by quantitative analysis on the changes of joint angles and muscle activation. Method Five walking speeds and three road slopes were selected from slow to fast according to the related measurement. The gaits of 15 young women were measured using the motion capture system and the EMG signals of 8 major muscles in lower limbs were collected simultaneously. The mean joint angles of hip, knee and ankle in sagittal plane at different speeds and different slopes were calculated. The subject whose data was closest to the mean value could be easily found. Results The joint angles of the subject’s hip, knee and ankle in sagittal plane at different speeds and different slopes in a gait cycle were presented and the activation curves of the 8 major muscles during lower limb movements were obtained. Conclusions In each gait cycle, the curves of joint angles and muscle activations varied little with 5 different speeds, while curves for 3 different road slopes only showed similar tendencies but with different peaks.

Measurement and analysis of the joint angle in lower limb during stair ascent / 医用生物力学

Objective To obtain the statistical data from the range of motion in lower limb of the Chinese people during their stair ascent so as to provide references for the design of artificial joints with large range flexion. Methods Common staircase as an experimental device was designed, and motion capture system（Optotrak Certus, NDI）and 3D force plate（AMTI, Bertec）were used to establish a systematic method to measure the lower limb motion from 40 subjects during stair ascent. Results The variation of joint angle and range of motion in hip, knee and ankle joints for the 40 subjects in different directions within one cycle were obtained and calculated. The range of motion in hip, knee and ankle joints at the sagittal plane were -1.6°~66.7°, 0°~91.4°,-20.8°~22.4°, respectively. Conclusions During the movement of stair ascent, the range of motion at the sagittal plane in hip, knee and ankle joints reached the maximum, with the most flexion in hip and knee. Compared with the movement during walking and jogging on flat road, the range of motion in joints both in hip and knee at the sagittal plane were larger during stair ascent.

JCS-based method on coordinate transformation of attachment points between muscle and bone / 医用生物力学

Objective In order to avoid potential injuries imposed to human body, it can be feasible to use the musculoskeletal models which can be reconstructed from the cadaver color cryosection (CCC) images, computerized tomography (CT) images, magnetic resonance (MR) images or other images to analyze the dynamic properties of muscles in vivo during human movement. Methods We reconstruct the lower limb musculoskeletal model and define the uniform joint coordinate system (JCS) on the model and the subject. The coordinate transformation of the muscle attachment points both on the model and the subject is described in detail. Results The length and the moment arm of the biceps femoris (short head) during knee flexion are calculated and analyzed. Conclusion This method plays an important role in improving the kinematics and dynamic simulation and the muscle force estimation.

Influence of jogging speed on lower limb joints and muscles of young women / 医用生物力学

Objective To study the effect of reasonable jogging speed on body shape and walking gait to make people acquire graceful posture through jogging. Method Five jogging speeds were selected according to related measurements. Kinematical data of subjects (15 young women volunteers) in jogging were measured by the motion capture system, while the EMG signals of 8 major muscles in lower limb were collected simultaneously. The mean angles of hip, knee and ankle joints in sagittal plane at different speeds were calculated. The subject whose data was closest to the mean value was chosen as the research subject and analyze the kinematical data. Results The angles of the subject's hip, knee and ankle joints in sagittal plane at different speeds in a gait cycle were presented, and activation curves of her 8 major muscles were obtained during lower limb movements. Relationships between the jogging speed, jogging stage, muscle activation and joint angle were described by the scoring method. Conclusions The range of joint angle and maximum of muscle activation don't change with jogging speed monotonously. The study provides a reference for young women to choose their own jogging speed.

Phase I study of TPF neoadjuvant chemotherapy followed by radical radiotherapy in advanced nasopharyngeal carcinoma / 癌症

<p><b>BACKGROUND AND OBJECTIVE</b>PF regimen is the standard chemotherapy for advanced head and neck cancers including nasopharyngeal cancer. Recently PF has been found to enhance the tumor control by addition of Taxotere. The purpose of this study was to evaluate the dose-limiting toxicity (DLT) and maximum tolerated dose (MTD) of TPF neoadjuvant regimen (taxotere, cisplatin (DDP) and 5-fluorouracil (5-FU)) followed by radical radiotherapy in advanced nasopharyngeal carcinoma (NPC).</p><p><b>METHODS</b>Between December 2006 and May 2008, 41 patients with newly diagnosed UICC stage III or IV advanced nasopharyngeal cancer were enrolled. There were 29 male and 12 female patients, with a median age of 47 years (range, 29-60 years), and ECOG performance status < or = 2. The initial dose was taxotere 40 mg/m(2) d1, DDP 40 mg/m(2) d1, and 5-FU 400 mg/m(2) d1-5. The treatment was repeated every 3 weeks for two cycles. Each dose of taxotere and DDP was increased by 5 mg/m(2) and 5-FU by 50 mg/m(2), respectively. The dose was escalated after six patients completed two cycles at the initial dose and DLT was assessed. Radiotherapy was started from the 5th week, with 68-72 Gy/34-36 fractions delivered to the nasopharynx and 60-66 Gy/30-33 fractions to the node-positive area.</p><p><b>RESULTS</b>Forty patients (79 cycles) were evaluated for toxicity and efficacy of the therapy. No DLT occurred at the dose levels 1-4. At dose level 5, three of six patients experienced DLT including grade III/IV neutropenia lasting more than 1 week. Two of them also had grade III mucositis, leading to the interruption of radiotherapy for more than 1 week. Three more new patients were retreated with the same dose (at dose level 6) under the G-CSF support, and no DLT occurred. Dose escalation continued to level 7, and DLT was found in all of the four patients, including three grade IV neutropenia, one of them had fever and pneumonitis; three grade III diarrhea; and one grade III mucositis lasting 10 days. Dose escalation was stopped and three more new patients were treated again at dose level 5 and no DLT was found. Other severe toxicities included grade III anemia (1 patients), grade III vomiting (4 patients), and grade III weight loss (9 patients). No severe hepatic and renal toxicities were found.</p><p><b>CONCLUSION</b>TPF neoadjuvant chemotherapy is a safe and effective regimen in the treatment of advanced NPC, with recommended doses of taxotere 60 mg/m(2) d1, DDP 60 mg/m(2) d1, and 5-FU 600 mg/m(2) d1-5.</p>

JCS-based method on coordinate transformation of attachment points between muscle and bone / 医用生物力学

Objective In order to avoid potential injuries imposed to human body,it could be feasible to use the musculoskeletal models which can be reconstructed from the cadaver color cryosection(CCC)images,computerized tomography(CT)images,magnetic resonance(MR)images or other images to analyze the dynamic properties of muscles in vivo during human movement.Mothod We reconstruct the lower limb musculoskeletal model and define the uniform ioint coordinate system(JCS)on the model and the subject.The coordinate transformation of the muscle attachment points both on the model and the subject is described in detail.Results The length and the moment arm of the biceps femoris(short head)during knee flexion are calculated and analyzed.Conclusion This method plays an important role in improving the kinematics and dynamic simulation and the muscle force estimation.