Abstract:Recently, a novel painless microneedle technology has been developed for transdermal drug delivery, which is believed to be widely applied in clinical therapies. In this review, the development history and current situation of the microneedle technology were first introduced with analysis on existing problems of artificial microneedles. Then, the present researches on biomicroneedles were introduced with discussion on the differences between the artificial micorneedles and biomicroneedles. Due to the limitation of present manufacturing technology, artificial microneedles can not realize such wonderful micro/nanostructures as biomicroneedles and an optimal design as biomicroneedle materials. Moreover, there are differences between the biomicroneedls and artificial microneedles in their penetrating manners. Artificial microneedles can not realize the active control during the penetrating process to reduce the penetrating force. To be as perfect as biomicroneedles, there still exist many problems for artificial microneedles to solve.

Abstract:Objective This study aims at comparing and optimizing postoperative stability and biomechanical compatibility in treating different types of vertically unstable sacrum fractures by using percutaneous posterior-ring tension-band steel plate and percutaneous iliosacral screw. MethodUsing CT and MR images of the second generation of Chinese digitized human “male No. 23”, the finite element models were developed respectively for two groups of vertical sacrum fractures of Denis Ⅰ,Ⅱ,Ⅲ zone with ipsilateral superior and inferior pubis ramus fractures treated with percutaneous posterior-ring tension-band steel plate (P-group) vs percutaneous iliosacral screw (S-group). The multi-solution finite element analysis and experiment validations were adopted on the basis of lumbosacral spinal three-column loading modes and sacroiliac joint physiologic behaviour. Results When simulating vertical sacrum fractures of Denis Ⅰ zone, von Mises stresses of internal fixation device of posterior and anterior rings of P-group were significantly increased, while the sacrum displacements were also increased compared to those in S-group. Whereas as simulating vertical sacrum fractures in Denis Ⅱand Ⅲ zones, von Mises stresses of fixator of both rings in P-group were lower than those of S-group, and the sacrum displacements were also remarkably decreased. Conclusions Considering internal fixation stability, mechanical compatibility for fracture healing and surgical procedure security, percutaneous iliosacral screw is more appropriate for the treatment of vertically unstable pelvis fractures with sacrum Ⅰzone injury, whereas percutaneous posterior tension-band steel plate is in favor of the treatment of vertically unstable pelvis fractures with sacrum Ⅱ and Ⅲ zone injuries.

Abstract:Objective To investigate the biomechanical characteristics 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 was created, including cortical bone, cancellous bone and soft tissue capsule. A rigid plane model was also constructed for ground simulation and constrained in all freedoms. The average hip lateral impact velocity of 2 m/s was applied to the model and the time for simulation analysis was set at 20 ms. The stress and strain distribution on the pelvis-femur complex were obtained by the 3D FE calculation and analysis. ResultsOn the contact surface, the peak impact load reached to 7 656 N at 13 ms, while the maximum Von Mises stress on the soft tissue was 2.64 MPa. Simultaneously, the peak Von Mises stress of 142.64 MPa on the cortical bone occurred in the region of pubic symphysis, which was approximate to the yield stress on the cancellous bone. The Von Mises stress level was higher in the region of the femur neck and greater trochanter. At 13 ms, the peak Von Mises stress on the cortical bone of the femur neck was 76.49 MPa and that on the cancellous bone was 8.44 MPa with the peak compressive principal strain being 0.94%. The peak Von Mises stress on the cancellous bone of greater trochanter was 8.50 MPa, while the peak compressive principal strain was 0.93%. Conclusions Bone fractures of the pelvis-femur complex tend to occur in the region of the femur neck, greater trochanter and pubic symphysis under deceleration impacts during sideways falls.

Abstract:Objective To study the contact mechanics of metal-on-metal hip joint replacements under different walking conditions, particularly for the edge contact behavior between the cup and the head of the bearing due to large range movement. Methods The finite element model of a typical hip joint replacement with conformal spherical bearing was established to simulate the edge contact of hip joint replacement under the given cup inclination angles and vertical loads. Results The maximum contact pressure decreased slightly and the contact area increased when the cup inclination angles increased within the range of 0°~60°. When the cup inclination angles were more than 80°, the corresponding contact area moved to the cup edge, the maximum contact pressure and distribution range increased, but the position of the maximum contact pressure moved from the initial contact point to the new point with 6°~9° in the direction of the increasing cup inclination angle to balance the corresponding contact pressure distribution and the loaded human weight. Conclusions Different edge contact behavior of hip joint replacements tends to occur due to the bigger cup inclination angle. Therefore, much attention should be paid to the problem of edge contact for both the clinical surgery and the manufacturing of hip joint replacements.

Abstract:Objective To analyze the energy-absorption characteristics for four mesomechanical models of the cancellous bone at different locations with different mechanical properties. Methods Under one-way shocks, the finite element method was used to calculate the energy absorption characteristics of the four models. Results According to the energy absorption rate of four models, the model with prismatic structure was found to be an ideal energy absorption model. The buckling and extension analysis was further carried out to comprehensively study mechanical properties of the model with prismatic structure, showing that its first-order buckling load was 248.11 Mpa with little influence on the adjacent pixels. Conclusions Four mesomechanical models of the cancellous bone at different locations can be used as the mesomechanical model for energy absorption materials according to different mechanical properties, particularly as the mesomechanical model for the energy absorption sandwich composite material.

Abstract:Objective To study distributions of the compressive strength on the whole spine endplates by measuring the compressive strength at different locations of the whole spine endplates. Methods Indentation tests were performed at 49 locations in 225 bony endplates of intact human vertebrae (C3 S1) from 5 fresh male specimens to record the failure loads. Results (1) For the whole spine endplates, failure loads of the cervical and lumbar spine were found to be higher than those of the thoracic spine (P<0.01).The failure load was first decreased from C3 to C7 before increasing to T1, and then dropping through T7 and rising again from T8, reaching the maximum at L4, and dropping at L5 before increasing again at S1. (2) The failure load at inferior cervical endplates was significantly higher than that at superior endplates except at C5 and T1 (P＜0.05). (3) Within the intervertebral space, the cranial endplates had a higher yield stress than the caudal endplates except at C5/6, T12/L1 and L5/S1. (4) Failure loads were generally increased from the central to peripheral zones (P＜0.05). (5) For different angular points, failure load distributions were found among the endplates (P<0.01). (6) Distributions of the compressive strength on the endplates varied significantly within the whole spine（P<0.01）. It was found that at C3/4, the failure load at posterior was higher than that at anterior, but at C5/6, the failure load at posterior and anterior was balanced. At T1, the failure load was found to be higher at posterior again, until passing through T2 5, and at T6 L3, the failure load at anterior was higher than that at posterior, and balanced between the anterior and posterior again at L4. At L5 S1, the failure load at posterior was higher than that at anterior. Conclusions The strength distributions on the endplates varied significantly at different locations within the whole spine, which was closely correlated with the physiological curve of the spine. The failure load at inferior endplates was higher than that at superior endplates and it was increased from central to peripheral zones. Within the intervertebral space, the compressive strength at cranial endplates was higher than that at caudal endplates.

Abstract:Objective To study changes and correlations in ultrasound acoustic parameters, bone density and microstructure of the cancellous bone at different stages of decalcification. Methods Fifteen defatted porcine cancellous bone specimens were decalcified at different decalcification stages, and the bone density, microstructure and acoustic parameters were measured by Micro CT and ultrasound system, respectively, before and after the decalcification. Correlations between acoustic parameters, bone density and microstructure were investigated. Results With the loss of calcium in bone specimens, BMD (bone mass density), BS/TV and BV/TV decreased continuously. Microstructure parameters SMI and BS/BV increased, while Tb.Th and Tb.N decreased with Tb. Sp increasing. Degree of anisotropy (DA) increased. Acoustic parameter SOS increased at first, and then decreased, with nBUA slightly decreasing. High correlation was found between acoustic parameters, BMD and bone microstructure parameters. Conclusions Ultrasound acoustic parameters are correlated with BMD and bone microstructure. This study may provide some reference information for the early diagnosis of osteoporosis based on ultrasound.

Abstract:Objective To develop a set of stretch strain cell loading unit with proprietary intellectual property rights so as to provide a necessary tool for the research of cellular mechanics. Methods Based on the deformation theory of round substrates, the stretch strain cell loading unit could apply the stretch strain to cultured cells in vitro by utilizing digital measuring controlling system and computer software. MTT colorimetric test was adopted to evaluate the ability of human periodontal ligament cells (HPDLCs) to attach and grow on the silastic membrane. The cultured HPDLCs were loaded with 1%, 10% and 20% stretch strain for 0.5, 1 and 24 h, respectively, by the loading unit, and an inverted phase contrast microscope was used to observe the morphology and realignment of HDPLCS. Results The stretch strain cell loading unit could apply the stretch strain of different magnitude, frequency and duration to cultured cells in vitro, with the advantage of a large range strain output, high precision, convenient operation and clear visual monitoring. When cells were seeded for 1, 2, 4, 7, 8 d, respectively, there was no statistical difference between the MTT absorbance value of silastic membrane group and that of control group (P>0.05), showing the good ability of cultured cells to attach and grow on the silastic membrane. After HPDLCs were loaded with 10% and 20% strain for 24 h, the morphology and realignment of HPDLCs changed, and cells became spindle shaped, being parallel to each other with long axis perpendicular to the stretch vector. Conclusions The stretch strain cell loading unit is capable of loading the stretch strain to cultured cells effectively and provides a necessary method for cytomechanical research.

Abstract:Objective To study the pressure field with the single-pulse and the dual-pulse for extracorporeal shock wave lithotripsy (ESWL) by numerical simulation, and to compare and analyze the results. Methods2D axisymmetric Euler equations and hybrid grids improved CE/SE numerical scheme were employed to simulate the pressure field of underwater shock wave in ESWL. Results The CE/SE shock wave dynamics method could successfully track the transmission of shock wave front, and the simulation solution could preferably reveal the focusing properties near the focus of ESWL: the pressure of dual-pulse was about the twice that of the single-pulse near the focus, and the higher lithotriptic efficiency could be achieved when the dual-pulse was much closer to the focus than the single pulse. A negative pressure with high absolute value was observed after the positive pressure occurred near the focus. ConclusionsThe adoption of electro hydraulic lithotripter could effectively improve the efficiency of stone comminution and the cavitation of shock wave focus was unavoidable, which provided a reliable numerical simulation result for the design and application of ESWL lithotripter in clinic.

Abstract:Objective To numerically simulate the blood flow in myocardial bridging parietal coronary artery and investigate the hemodynamics mechanism of the fact that atherosclerosis is more likely to occur in proximal segment of the parietal coronary artery. Methods The model, a straight tube with local stenosis which moved along with heart beating being used in order to simulate the morphology of myocardial bridging parietal coronary artery, was established. The wall of the tube was assumed as a thin wall linear elastomer, and the blood flow was assumed as a series of one dimensional flow equations following incompressible Newtonian fluid. The Lax-Wendroff method was also adopted to solve the governing equations numerically. Results There were significant differences in blood flow, wall shear stress and wall shear stress gradient between parietal coronary artery and normal coronary artery. For parietal coronary artery, the changes of wall shear stress and wall shear stress gradient were more dramatic in proximal segment than those in distal segment. As for two myocardial bridgings in one coronary artery, the trend of the wall shear stress and wall shear stress gradient was essentially the same, but the wall shear stress and wall shear stress gradient in myocardial bridging far from the ventricle were larger than those in myocardial bridging near the ventricle, with a more dramatic change along the time during one cardiac cycle. Conclusions Simulation results indicate that hemodynamics of parietal coronary artery is different from that of normal coronary artery. Changes of wall shear stress and wall shear stress gradient are more dramatic in proximal segment than those in distal segment, thus having an important impact on the local endothelial cells. It might be the hemodynamic mechanism of the fact that atherosclerosis is more likely to be developed in proximal segment of parietal coronary artery.

Abstract:Objective To study the vibration frequencies and resonant peaks of different molecular groups in anti-diabetic drugs and to investigate the absorption spectra of these drugs in the range of terahertz, so as to accurately and efficiently identify similar drugs and provide foundation for understanding the contribution of such vibration in different molecular groups to pharmacology. Methods Using terahertz time domain spectroscopy (THz-TDS), six kinds of similar diabetes pills for treating diabetes mellitus (DM), including gliquidone, glipizide, gliclazide, glimepiride, repaglinide and metformin were tested to obtain their absorption spectra from 0.3~3.0 THz. Support vector machines (SVM) method was employed to separate these anti-diabetic drugs by selecting the experimental data from 1.5~2.0 THz. Results For gliquidone, glipizide, gliclazide, and glimepiride, an obvious resonance peak was found at 1.37 THz. According to the THz spectra, repaglinide and metformin could be easily separated from sulfonylurea drugs. Furthermore, with the help of SVM, the accuracy of discrimination for four kinds of sulfonylurea could reach 100%. Conclusions THz technology, as a new testing method, shall play a positive role in the drugs for their identification, quality control and distinguishing their chemical bonds/functional group.

Abstract:Objective To exert different substrate strain stimulation on rabbit myofibroblasts (MFs) (proto-) at different differentiation stages so as to study the variation of α-SMA expression. MethodsBy implanting heterologous protein into rabbits’ peritoneal cavity, 5 d and 7 d MFs (proto-) were obtained and cultured on the elastic substrates. Strain of 0%-3% and 3%-6% as well as strain of 0%-6% were applied by substrate static stretch. Results α-SMA expression was not found in 3 d MFs (proto-), while α-SMA expression could be detected in 5-7 d MFs (proto-), and α-SMA expression was significantly enhanced in 10-15 d MFs (proto-) (P<0.01). Under the two loading modes, α-SMA expression was both significantly improved, and higher α-SMA expression was presented under sectioned loading. Conclusionsα-SMA expression of MFs（proto-） is increased after the substrate static stretch in response to different loading modes, which suggests that mechanical factors can play an important role in the process of MFs differentiation and wound healing response.

Abstract:Objective To investigate the cause of tumor cell migration by comparing the effect of substrate stiffness on hepatic and hepatoma carcinoma cell migration so as to understand the invasive characteristics of tumor cells. Methods Immunofluorescence staining, morphological analysis and transwell were employed to observe the morphological characteristics of HCCLM3 and L02 cells on different substrates and test their migration characteristics with the quantitative analysis. Results (1) The migration rate and net translocation of HCCLM3 and L02 cells on 4 kPa substrate was higher than those both on 0.5 kPa(most soft one) and on glass (the hardest one) substrates, and L02 cells also displayed higher migration efficiency than HCCLM3 cells on such substrates. (2) The mean squared displacement of HCCLM3 and L02 cells on different substrates showed consistent tendency, and the directional persistence of L02 cells on the softer substrate was significantly higher than that of HCCLM3 cells. (3) In 0.5 and 1 mg/mL three dimensional collagen environment, the number of invasive cells of HCCLM3 was remarkably more than that of L02 cells. After adding MMPs inhibitor GM6001 (40 μg/mL), the number of invasive cells was notably increased in HCCLM3 cells, but notably decreased in L02 cells. Conclusions (1) In two dimensional comparatively soft environment, L02 cells displayed an efficient migration due to its higher directional persistence. (2) In three-dimensional collagen environment, the invasion efficiency of HCCLM3 cells was significantly higher due to the various modes of migration adaptation to the microenvironment.

Abstract:Objective To investigate the effect of intermittent tensile strain on the proliferation and osteogenic differentiation of rBMSCs (rat bone mesenchymal stem cells). Methods Intermittent tensile strain was applied on rBMSCs in vitro by Flexcell 4 000 Tension System (10% elongation amplitude, 0.5 Hz, twice every day, 4 h every time), then effects of the strain after 1, 3, 5, 7 d on cell morphology, cell proliferation, and the relative expression of Cbfα1（core binding factor α1），ALP and collagen I mRNA as well as Cbfα1 protein were measured. Results Intermittent tensile strain slowed the proliferation of rBMSCs from the first day to the seventh day. The relative expression of ALP and collagen I mRNA increased by 3~6 times from the third day（P＜0.05）, meanwhile the expression of Cbfα1 mRNA and protein was up-regulated under the mechanical stimulation. Conclusions Mechanical stretch plays an important role in the proliferation and differentiation of rBMSC, and approprite intermittent tensile strain can slow the proliferation of rBMSC and promot its osteogenic differentiation.

Abstract:Muscle atrophy of the stumps after lower limb amputation has always been a crucial factor resulted in inefficient clinical rehabilitation and athletic recovery for the amputated patients. Therefore, understanding the initiating and developing mechanism of muscle atrophy is very important for the improvement of amputation，restoration training and prosthetic design，which is also widely concerned in the prosthetic rehabilitation field. This paper will review the advances of residual limb muscle atrophy researches on the approaches and models，the mechanical properties of the residual limb，the micro pathologic characteristics as well as the prevention strategies of muscle atrophy in recent years. It can be concluded that further researches are needed to study the special physiologic and mechanical environment in residual limb, which affected the growth of muscle cells as well as the dynamic balance of the muscle protein synthesis and decomposition before completely understanding the mechanism of residual limb muscle atrophy and definitely clarifying its real cause.