Objective To predict the tissue-level failure strain of the cortical bone and discuss the effects of different running speeds on the mechanical properties of rat femoral cortical bone.Methods The threshold for cortical bone tissue-level failure strain was assigned,and fracture simulation under three-point bending was performed on a rat femoral finite element model.The predicted load-displacement curves in each simulation were compared and fitted with the experimental data to back-calculate the tissue-level failure strain.Results The cortical bone tissue-level failure strains at different running speeds were statistically different,which indicated that different running speeds had certain impacts on the micromechanical properties of the cortical bone structures.At a running speed of 12 m/min,the cortical bone structure expressed the greatest tissue-level failure strain,and at a running speed of 20 m/min,the cortical bone structure expressed the lowest tissue-level failure strain.Conclusions Based on the changing trends of tissue-level failure strain and in combination with the changes in macro-level failure load and tissue-level elastic modulus of cortical bone structures,the effects of different running speeds on the mechanical properties of cortical bone structures were discussed in this study.The appropriate running speed for improving the mechanical properties of the cortical bone was explored,thereby providing a theoretical basis for improving bone strength through running exercises.

BACKGROUND:Current fracture simulation for cortical bone structure is mainly based on three numerical methods:the element instantaneous failure,continuum damage mechanics,and extended finite element methods.Although many studies focus on cortical bone fracture simulation,few have compared the differences in prediction accuracy using the three numerical methods. OBJECTIVE:To probe the accuracy and applicability of the three numerical methods in simulating cortical bone fracture under bending load. METHODS:The rat femur samples were primarily used to perform the three-point bending experiment.The rat femoral finite element models were established based on the micro-CT images of the femur samples and the three numerical methods were used to conduct the fracture simulations under three-point bending loads.The predicted fracture loads and fracture patterns were compared with the experimental data to determine the accuracy of various numerical methods in simulating cortical bone fracture. RESULTS AND CONCLUSION:(1)The discernible differences in the failure processes could be observed in the same finite element model under the three numerical simulations due to different element failure strategies.(2)The simulation results showed that the fracture simulation using the continuum damage mechanics method was in better agreement with the experimental results.(3)The numerical method that was suitable for simulating cortical bone fracture under bending load could be determined by comparing it with experimental results.The variations in the fracture parameters were observed,and the reason for the differences in the predicted results using different numerical methods was also discussed,which aided in determining the range of applicability of structural fracture simulation for each numerical method and then improving the simulation accuracy.

BACKGROUND:Critical energy release rate is a global fracture parameter that could be measured during the failing process,and its value may change under different failure modes even in the same structure. OBJECTIVE:To propose an approach to predict the critical energy release rate in the femoral cortical bone structure under different failure modes. METHODS:Three-point bending and axial compression experiments and the corresponding fracture simulations were performed on the rat femoral cortical bone structures.Different critical energy release rates were repeatedly assigned to the models to perform fracture simulation,and the predicted load-displacement curves in each simulation were compared with the experimental data to back-calculate the critical energy release rate.The successful fit was that the differences in the fracture parameters between the predicted and experimental results were less than 5%. RESULTS AND CONCLUSION:(1)The results showed that the cortical bone structure occurred tensile open failure under three-point bending load,and the predicted critical energy release rate was 0.16 N/mm.(2)The same cortical bone structure occurred shear open failure under axial compression load,and the predicted critical energy release rate was 0.12 N/mm,which indicates that the critical energy release rate of the same cortical bone structure under different failure modes was different.(3)A comprehensive analysis from the perspectives of material mechanical properties and damage mechanism was conducted to reveal the reasons for the differences in the critical energy release rate in the cortical bone structure under different failure modes,which provided a theoretical basis for the measurement of the energy release rate and the accurate fracture simulation.

Objective To explore the feasibility and safety of kidney transplantation for pre-sensitized infants using deceased donors and summarize the relevant literature reports .Methods A second kidney transplantation was successfully performed for an 8-month-old pre-sensitized girl in July 2017 .She had a low level of donor specific antibody (DSA ) against human leucocyte antigen (HLA ) B62 due to severe acute rejection (AR) after her first kidney transplantation .For desensitization , plasmapheresis and intravenous immunoglobulin plus anti-CD20 antibodies were offered on operative day .Clinical data and outcomes were retrospectively analyzed .Results Renal graft regained immediate function after transplantation .Preformed DSA could be detected at 1 week .However ,there was no de novo DSA .At 1 year post-transplantation ,preformed DSA turned negative .During a follow-up period of 2 years ,renal graft showed an excellent function with a serum creatinine of 31 μmol/l and eGFR of 110 ml/min/1 .73m2 .No AR episode or proteinuria occurred .DSA stayed negative .Simultaneously physical development also caught up .Her height of 93 cm tall and weight of 13 .5 kg at month 24 & 8 months corresponded to normal grow th curve of her age .Conclusions Pre-sensitized infant could tolerate desensitization therapy well and achieve satisfactory outcomes .With surgical precisions and optimized managements ,kidney transplantation provides excellent renal functions and survivals for infants with organs from deceased donors .

Objective To evaluate the efficacy of tigecycline plus prolonged high-dose meropenem infusion in the prevention and treatment of early carbapenem-resistant Klebsiella pneumoniae (CRKP) infection after renal transplantation .Methods From January 2016 to December 2018 ,clinical data were retrospectively analyzed for 13 renal transplant recipients with graft-carried CRKP .The relevant clinical data included treatments and outcomes of grafts and recipients .KPC-2 gene was the only resistance gene detectable in all isolates of CRKP . Among 13 CRKP positive recipients ,there were positive cultures of graft preservation solution ,recipient blood & urine (n=1) , positive cultures of graft preservation solution & urine (n=1) ,positive cultures of graft preservation solutions & peri-graft drainage (n=3) ,continuous positive cultures of peri-graft drainage more than twice (n= 3) and positive culture of graft preservation solution (n= 5).All patients received tigecycline plus prolonged high-dose meropenem infusion-based antibiotics .Results Five patients with CRKP positive in preservation solution were successfully prevented from infection after a treatment period of (12 .4 ± 2 .1)days .Among another 8 cases ,additional topical medications (n= 3) and surgical debridement (n= 1) were used .It took a median time of 16 (7～60) days until a negative culture and the total antibiotic treatment course was 20 (10～93) days .The average hospitalization duration was (50 ± 35) days .During a median follow-up period of 25 (6～28) months ,there was no onset of renal arterial rupture ,graft nephrectomy or death .The survival rate was 100％ for recipients and 92 .3％ for grafts .Conclusions For post-transplant infections due to graft-carried KPC-2 producing CRKP ,rapid diagnostics and tigecycline plus prolonged high-dose meropenem infusion may optimize clinical outcomes by decreasing the rate of graft nephrectomy and the recipient mortality .