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Abstract:Objective To investigate the effect of the tibiofemoral joint surface with high conformity on total knee prosthesis motion and insert wear. Methods A type of knee prosthesis with a high coronal conformity was designed and manufactured, and its insert wear was studied by in vitro wear testing combined with finite element simulation. ResultsThe mass wear rates calculated by the in vitro wear testing and finite element simulation were (14.29±3.19) mg/MC and 14.67 mg/MC (MC, million cycle), respectively. After five MCs, the areas of the insert wear obtained by both the methods were basically consistent, and severe wear was found to occur in the middle part of the insert. ConclusionsThe result of the finite element simulation coincided with that of the in vitro testing. The wear rate of the tibiofemoral joint surface of the total knee prosthesis with a high coronal conformity was relatively low. The research outcomes have practical significance for the evaluation and clinical application of the total knee prosthesis with a high conformity.

Abstract:Objective To investigate the trabecular stress distributions on the cortical bone and determine whether the cancellous bone can share the load of the acetabulum with a press-fit acetabular cup. Methods The acetabulum was scanned via micro-computed tomography (CT) to build a three-dimensional micro-finite element analysis (μFEA) model of the acetabulum. The trabecular stress and strain of the bony acetabulum were calculated following total hip arthroplasty (THA) to investigate the biomechanical characteristics of their distributions. Results With the implantation of the press-fit acetabular cup into the acetabulum, the high-stress zone of the articular surface was found to be located in the pubic bone area, with a maximum stress of 1.398 MPa. The largest high-stress zone within the articular surface was at the craniomedial part where it was supported by the iliac. For the cancellous bone within the acetabulum, the high stress was relatively widely distributed on the craniomedial part. When a 1.372 kN load was applied, the high stress was found at the craniomedial and anterior-inferior parts of the articular surface where it was supported by the iliac and pubic bone, with a trabecular micro-damage occurring in the anterior-inferior part. The highest tensile stress at the craniomedial part was 0.604 MPa. For the cancellous bone within the acetabulum, the high stress was mainly distributed on the craniomedial and anterior-inferior parts. Conclusions The high stress near the periphery of the articular surface showed a three-point circular distribution, which was mainly distributed on the iliac, ischial, and pubic bone area. The stress was distributed more uniformly owing to the deformation of the cancellous bone in the acetabulum. The cancellous bone in the acetabulum has the function of load-bearing.

Abstract:Objective To explore the application scope of small splint in the treatment of type-C distal radius fractures. Methods According to CT scan data from the right forearm of a healthy male volunteer, the three-dimensional model of normal distal radius was established. According to AO classification, the fracture line based on normal model was divided to establish nine kinds of high-order tetrahedral mesh models of the upper forearm with C-type fracture. Finite element analysis on nine kinds of fracture models was conducted in ANSYS 15.0 software to obtain the corresponding stress values, and then the stress distribution contours were generated. Results As soft tissues of the wrist were thin with more fracture blocks, after the splint was fixed, the stress on the wrist under 100 N maximum physiological axial load was significantly larger compared with that on the other parts, and the compressive stress was mainly concentrated on the wrist joint. The fixed effect of C2.2, C2.3, C3.2, C3.3-type fracture by small splint was relatively poor, as such comminuted fracture would cause too many and too small fracture blocks, while the fixed effect of C1.1, C1.2, C1.3, C2.1 and C3.1-type fracture was better. Conclusions Through the related finite element study on the treatment of C-type fracture distal radius with small splint, the application scope of small splint was preliminarily determined, which could provide some reference for clinical work.

Abstract:Objective To compare biomechanical effects of Zero-Profile anterior cervical intervertebral fusion system and Cage-Plate fusion system on the adjacent segments, so as to provide references for the long-term clinical efficacy of single segment cervical spondylosis. Methods The finite element model of cervical spine C1-7 was established based on CT scan data of normal people. After the validity of the model was validated, two finite element models of C5-6 segment implanted with Zero-P fusion system and Cage-Plate fusion system were built. The physiological torque 1.5 N·m was loaded respectively on the normal model, Zero-P implanted model and Cage-Plate implanted model to simulate cervical flexion, extension, lateral bending and rotation. Changes in the ranges of motion (ROMs) of adjacent segments and stresses on nucleus pulposus, endplate and annulus, facet joints of intervertebral disc were compared for the three models. Results After the two kinds of anterior cervical intervertebral fusion systems were implanted, ROMs of C4-5 segments increased by 20%, but ROMs of C6-7 segments increased up to 120%. The stresses on C4-5 nucleus increased by 78%, while the stresses on C6-7 nucleus increased up to 110%. The stresses on the adjacent endplates and the fiber ring also increased. Conclusions The implantation of Cage-Plate and Zero-P fusion system both increased the ROMs of the adjacent segments, and the stresses on annulus, fiber rings and facet joints of the adjacent discs increased as well, which would cause lesions of the adjacent segments in the long run. However, there was no essential difference in biomechanical effects of the Cage-Plate and Zero-P cage fusion system on the adjacent segments.

Abstract:Objective To investigate the biomechanical properties and clinical effects of the unilateral/bilateral percutaneous vertebroplasty (PVP) on the treatment of osteoporotic vertebral compression fractures in elderly patients. Methods The finite element models of the unilateral/bilateral percutaneous vertebroplasty (PVP) in osteoporotic vertebral compression fractures were established to evaluate changes in strain and stress of the fractured vertebra after surgery. Eighty patients with osteoporotic vertebral compression fractures underwent unilateral or bilateral PVP were collected for retrospective analysis. The operation time,intraoperative fluoroscopy times,injected bone cement volume, bone cement leakage rate and visual analogue scales (VAS) score between the two groups were analyzed. Results The maximum strain and stress in unilateral PVP group were 1.18 times and 1.15 times of those in bilateral PVP group,respectively.The operation time and intraoperative fluoroscopy times in unilateral PVP group were obviously smaller than those in bilateral PVP group (P<0.001). There was no statistical significance in the injected bone cement volume, bone cement leakage rate, and VAS score between the two groups (P>0.05).Conclusions The biomechanical effect of unilateral PVP was similar to that of bilateral PVP. The puncture needle localization of unilateral PVP for treating elderly patients with osteoporotic vertebral compression fractures had the advantage of less operation time and limited X-ray exposure.

Abstract:Objective To investigate the effect of different adhesive materials on all-ceramic restoration. Methods The all-ceramic restoration system model of mandibular first molar was established by spiral computed tomography (CT) scanning and computer-aided design (CAD) modeling. Four types of resin adhesive materials (Duo Cement,Lute-It,Rely-X ARC,Variolink II) used in clinics were selected, and the stress distribution was calculated using the ABAQUS software. Results The stress at the bonding interface was the highest when low filler adhesive Lute-It was used. Based on the viscoelasticity analysis, resin adhesives with a larger storage modulus and loss modulus could yield lower stress extremes. Conclusions The study suggests that high-filler type resin adhesives with a large energy storage modulus and loss modulus should be used clinically.

Abstract:Objective To investigate the hemodynamic changes in a tortuous coronary to elucidate the effects of tortuosity on coronary perfusion and wall shear stress (WSS). Methods A single tortuous and non-tortuous patient-specific left anterior descending (LAD) coronary artery cases were selected. Two LAD models with and without coronary tortuosity were reconstructed in Mimics software and then transferred to the ANSYS Fluent software for performing computational fluid dynamics (CFD) simulation. The hemodynamic characteristics of both the LAD models were compared. Results The vessel WSS of the tortuous coronary artery clearly decreased in the bend section where the maximum curvature was larger than 1 mm-1.Such a scenario could led to an inadequate blood supply in the downstream vessels. A low WSS (0-26 Pa) acted on the outer wall of the bend, whereas the inner wall of the bend had a high WSS (>100 Pa). The mean WSS of the non-tortuous and tortuous models was 10.79 Pa and 36.12 Pa, respectively. The overall WSS of the tortuous model was larger compared with that of the non-tortuous model. Conclusions Coronary tortuosity increased the overall WSS, which could delay the progress of coronary atherosclerosis.

Abstract:Objective To study the mechanical properties and biological characteristics of 3D-printed porous β-tricalcium phosphate ［β-Ca3(PO4)2, β-TCP］ scaffolds, so as to provide guidance for the design of composite scaffolds in animal experimentation. Methods Poly 1,8-octanediol citrate (POC), a kind of novel biodegradable materials, was used as the adhesive. The 3D-printed porous β-TCP scaffolds were fabricated by fused deposition modeling (FDM) technology, and Gly-Arg-Gly-Asp-Ser (GRGDS), a kind of polypeptides, was added into the scaffolds to improve the adhesive property of cells. The optical microscope and scanning electron microscope (SEM) were used to observe the micro-pore architectures of those scaffolds. The material testing machine was used to conduct compressive test on the scaffolds, and the water contact angles of the scaffolds were measured. The cell adhesion rate and proliferation rate of the scaffolds were also tested by in vitro cell experiment. The model of SD rat skull defects was repaired by the scaffolds, and the osteogenic ability in vivo was further studied. Results The GRGDS, remaining active, was evenly distributed in the composite scaffolds. The micro-pore architectures of the polypeptide modified scaffolds changed, with improvement in cell adhesion rate, while the compressive modulus, water contact angle and osteogenic ability in vivo of the scaffolds were not obviously affected. Conclusions The cell adhesion capacity of β-TCP composite scaffolds modified by polypeptide improved significantly, while the mechanical properties and hydrophilicity, osteogenic ability in vivo of the scaffolds were not affected very much. These research results provide new ideas for reconstruction of scaffolds for repairing bone defects in clinic, and a laboratory basis for further clinical application of this scaffold.

Abstract:Objective To investigate the mechanical response of Emerin, a nuclear envelope protein, and its role in apoptosis of vascular smooth muscle cells (VSMCs) during cyclic stretch, and the potential effect of transcriptional factors in this process. Methods Physiological cyclic stretch with the magnitude of 5% and frequency of 1.25 Hz was subjected to VSMCs in vitro by using FX-5000T cyclic stretch loading system. VSMCs cultured under the same conditions but without applying mechanical stretch were used as the static control. The apoptosis of VSMCs was detected by using Cleaved-caspase3 ELISA kit, and the expression of Emerin was revealed by using Western blotting. The effects of Emerin on activities of 345 kinds of transcriptional factors in VSMCs were demonstrated with Protein/DNA array after Emerin specific RNA interference (RNAi) under static condition, and the potential transcriptional factors involved in VSMC apoptosis were analyzed with Ingenurity Pathway Analysis (IPA) software. Furthermore, the binding abilities of Emerin to the motif of 2 kinds of apoptosis-related transcriptional factors were detected with chromatin immunoprecipitation (CHIP) and qPCR. ResultsCompared with the static control, the apoptosis of VSMCs was significantly decreased by 5% cyclic stretch, which suggested a protective effect of physiological cyclic stretch. The expressions of Emerin in VSMCs was remarkably increased with 5% cyclic stretch applied for 6 h, 12 h and 24 h. Specific RNAi under static condition decreased the expressions of Emerin but increased the apoptosis of VSMCs. Emerin siRNA transfection remarkably increased (more than 2 times) the activities of 10 transcriptional factors that participated in cellular apoptosis, i.e. CREB-BP1, p300, p55, MAX, NRF-1, STAT1, STAT3, TEF1, TR and BZP. CHIP-qPCR result revealed that the binding ability of Emerin to specific mofit of STAT1 or STAT3 was significantly repressed with Emerin RNAi. Conclusions Physiological cyclic stretch could increase the expression of Emerin which might modulate the binding of Emerin to motifs of apoptosis-related transcriptional factors such as STAT1 and STAT3, regulate the activities of these factors, and then subsequently repress the VSMC apoptosis. The investigation on mechanobiological mechanisms of VSMC apoptosis induced by cyclic stretch may contribute to further understanding the physiological and pathological mechanisms of vascular homeostasis and vascular remodeling.

Abstract:Objective To investigate the effect of calcium on the stability of VWF-A2 domain. Methods The crystal structures of A2 (not containing calcium) and A2/Ca2+ (with calcium bound) were downloaded from protein data bank. For A2 domain, the conformational changes, unfolding pathway differences and the exposure degree variance of cleavage sites caused by calcium binding were observed and analyzed by steered Molecular Dynamics simulations under constant force. Results The unfolding pathway of A2 domain and exposure process of cleavage sites were force-dependent. Calcium binding did not affect the unfolding process of A2 in the early stage. As the conformational rearrangement of α3β4-loop reduced its localized dynamic properties, the movement among β1-β4-β5 strands was restrained, which suppressed its further unfolding to stay in the intermediate steady state and delayed the cleavage-site exposure. Conclusions Stretch force could induce β5 strand of A2 unfolding and the cleavage-site exposure, while calcium binding inhibited ADAMTS13 proteolysis efficiency through stabilizing A2 hydrophobic core and covering its cleavage sites. These results way help to understand how ADAMTS13 cleavages the VWF-A2 domain and regulates the hemostatic potential of VWF, and further provide useful guidance on the design of related anti-thrombus drugs.

Abstract:Objective To study the effects of osteopontin (OPN) on the nuclear mechanics of bone marrow-derived mesenchymal stem cells (BMSCs) as well as its involved mechanisms. Methods The BMSC migration was evaluated using the Transwell assay. An atomic force microscope (AFM) was used to determine the elastic modulus of the BMSC nucleus and analyze the changes in the nuclear mechanics of the BMSCs after treatment with OPN. The activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase1/2 (ERK1/2) was measured by Western blot. The role of the FAK-ERK1/2 signaling pathway in mediating the OPN-affected BMSC nuclear mechanics was investigated by employing a specific inhibitor. RT-PCR and Western blot were used to detect the expression of Lamin A/C at mRNA and protein levels in the BMSCs, respectively. Results The elastic modulus of the BMSC nucleus exhibited a significant decrease after OPN treatment compared with that of the control group. OPN could upregulate the phosphorylation level of FAK and ERK1/2, but the inhibitor of FAK or ERK1/2 restored the OPN-decreased elastic modulus of the BMSC nucleus and inhibited the BMSC migration significantly. After treatment with OPN, the expression of Lamin A/C in the BMSCs reduced significantly, and such a reduced expression could be suppressed by the inhibitor of FAK or ERK1/2. Conclusions OPN could probably downregulate the expression of Lamin A/C of the BMSCs via the FAK-ERK1/2 signaling pathway, decrease the stiffness of the BMSC nucleus, and promote the migration of the BMSCs. The research outcomes provide the experimental evidence for further understanding the mechanism of the OPN-regulated BMSC migration and its potential clinical application.

Abstract:Objective To study the mechanical properties of ballistic gelatin and establish a dynamic constitutive model by a numerical method to lay the foundation for the related research on wound ballistics. Methods First, 20% ballistic gelatin samples at 10°C were prepared, and then, the quasi static and dynamic compressive mechanical properties of the ballistic gelatin were tested using a universal material testing machine and an aluminum Hopkinson bar, respectively. Results The quasi-static and dynamic compressive stress-strain curves of 20% ballistic gelatin at 10 ℃ were obtained. When the strain was 0.45, the true stress was 0.041, 0.083, 0.194, 14.515, 31.496, 55.597, and 96.678 MPa at a strain rate of 10-3, 10-2, 10-1, 5 800, 7 900, 10 400, and 13 000 s-1, respectively. When the strain rate was 13 000 s-1 and the strain increased from 0.4 to 0.5, the stress increased rapidly from 53.558 MPa to 164.417 MPa, equivalent to an increase by over 3.07 times. Conclusions The ballistic gelatin had a remarkable strain rate effect in the range of both low and high strain rates. The constitutive model with strain rate was established based on the experimental results with the form of σ=kε·mεn, and the material constants of 20% ballistic gelatin were obtained.

Abstract:Objective To explore the differences in the static balance ability of elderly women performing Tai Chi, square dance, and fitness walking as long-term exercises. Methods A total of 128 healthy elderly women were selected as the subjects. The subjects were classified into the Tai Chi, square dance, fitness walking, and control groups based on their daily main fitness items. The average swing speed (avg.v) of the subjects, swing angle, outer area (area), and total length of the swing (TL) were measured by a balance tester during double-feet standing with eyes closed and right-foot standing with eyes opened, and the test time was 10 s. Results There were significant differences in the values of each balance index of the Tai Chi, square dance, fitness walking, and control groups during double-feet standing with eyes closed and right-foot standing with eyes opened(P<0.05). There were significant differences in the avg.v, TL, and area index values of the Tai Chi and square dance groups (P<0.05) in case of right-foot standing with eyes opened. In both the states,the four balance indices of the Tai Chi group were significantly smaller than those of the fitness walking group (P<0.05).There were significant differences in the area, TL, and avg.v index values of the square dance and fitness walking groups (P<0.05) for the right-foot standing with eyes opened. Conclusions The static balance abilities of elderly women performing Tai Chi, square dance, and fitness walking over a long term were better than those in the absence of regular exercises. The elderly women associated with long-term Tai Chi exercises exhibited a better static balance ability than those performing square dance and fitness walking exercises, and elderly women associated with long-term square dance exercises showed a better static balance ability than those with fitness walking exercises.

Abstract:Cortical bone is a kind of natural biological composite materials, which is mainly composed of tropocollagen molecules and nanoscale hydroxyapatite mineral crystals. It possesses high strength, stiffness and fracture toughness and has the ability to tolerate damage and self-heal. In the long process of evolution, bone tissues form the biomechanical strength and toughness to meet its functional needs. The excellent mechanical properties of cortical bone are closely related to its hierarchical microstructure. This paper reviewed the hierarchical microstructure of cortical bone and its toughening mechanisms, which would contribute to understanding the diagnosis, prevention and treatment of aging-related osteoporosis and the pathological mechanism of bone diseases.

Abstract:As an effective implant for bone fracture, bone screws are widely used in clinic. Based on the clinical application of bone screws, this study summarized different kinds of bone screws according to their structures and materials, analyzed 3 kinds of common screw failure (loosening, breaking, corrosion) and the influencing factors. The common testing methods of screws were summarized, especially the key points and difficulties during the testing process for bone screws were analyzed, which was important for improving the design of product, selection of materials and development of in vitro testing technology. The development trend for testing method of bone screws was prospected as well.

Abstract:MicroRNA (miRNA) is a kind of important gene expression regulatory molecules during biological process, but its regulation mechanism in metabolic process of bone tissues has not been completely clarified. In this review, the regulation of miRNA on osteoblast differentiation in microgravity environment was discussed. The positive and negative regulation of miRNA was summarized, respectively, with focus on introducing the mechanism of different genes. Some miRNA molecules that have important effects on bone metabolism under microgravity were enumerated. MiRNA plays an important role in regulating and controlling bone metabolic diseases in microgravity environment, and its related studies are significant for the prevention and treatment of bone loss induced by weightlessness.