Segmental Motion Research Articles

Anterior cervical hybrid constructs reduce superior adjacent segment burden compared to multilevel anterior cervical discectomy and fusion.

Traditional surgical treatment for symptomatic cervical degenerative disc disease is anterior cervical discectomy and fusion (ACDF), yet the increased risk of adjacent segment degeneration (ASD) requiring additional surgery exists and may result in limiting long-term surgical success when it occurs. Disc arthroplasty can preserve or restore physiologic range of motion (ROM), decreasing adjacent level stress and subsequent surgery. For patients with multilevel pathology requiring at least a 1-level fusion, interest is growing in anterior cervical hybrid (ACH) surgery as a partial motion-preserving procedure to decrease the adjacent level burden. This radiographic study compares postoperative superior adjacent segment motion between ACH and ACDF. Secondarily, total global motion, construct motion, inferior adjacent segment motion, and sagittal alignment parameters were compared. This is a single-center, multi-surgeon, retrospective cohort study of 2- and 3-level ACH and ACDF cases between 2013 and 2021. Degrees of motion were analyzed on flexion/extension views using Cobb angles to measure global (C2-C7) construct and adjacent segment lordosis. Neutral lateral X-rays were analyzed for alignment parameters, including global lordosis, cervical sagittal vertical axis (cSVA), and T1 slope (T1S). Differences were determined by independent t-test and Fisher's exact test. Of 100 patients, 38% were 2-level cases (47% ACH, 53% ACDF) and 62% were 3-level cases: (52% ACH, 48% ACDF). Postoperatively, superior adjacent segment motion increased with ACDF and decreased with ACH (-1.3°±5.3° ACH, 1.6°±4.6° ACDF, P=0.005). Postoperatively, the ACH group had greater ROM across the construct (16.3°±8.7° ACH, 4.7°±3.3° ACDF, P<0.001) and total global ROM (38.0°±12.8° ACH, 28.0°±11.1° ACDF, P<0.001). ACH resulted in a significant reduction of motion loss across the construct (-10.0°±11.7° ACH, -18.1°±10.8° ACDF, P<0.001). Postoperative alignment restoration was similar between both cohorts (-2.61°±8.36° ACH, 0.04°±12.24° ACDF, P=0.21). Compared to ACDF, hybrid constructs partially preserved motion across operative levels and had greater postoperative global ROM without increasing superior adjacent segment mobility or sacrificing alignment restoration. This supports the consideration of ACH in patients with multilevel degenerative cervical pathology requiring at least a 1-level fusion and suggests a propensity for long-term success by reducing the superior adjacent segment burden.

On modelling strain gradient viscoelasticity of polymer nanocomposites

Theories of generalized continuum mechanics have found great success in the analysis of nanostructures. However, there exists no work on analysing composites whose constituents are generalized continua. The present work fills this gap and studies the strain gradient viscoelasticity of polymeric nanocomposites. The key problem is to assign the nonclassical boundary condition of the representative volume element (RVE). To resolve it, a perturbation field is superposed on the homogeneous displacement boundary condition. The wavelength of perturbation is comparable to the strain gradient characteristic length. Simulations to obtain the macroscopic effective mechanical properties are performed, which agree well with the experimental data. The frequency dependence of the perturbation field is revealed, and it has a clear physical interpretation in terms of the segmental motions of polymer chains.

KINEMATIC RESPONSES AND SEGMENTAL STIFFNESS OF NORMAL AND DEGENERATIVE L4/L5 MOTION SEGMENTS: FINITE ELEMENT STUDY

In this study, finite element (FE) models of an anatomical normal and a degenerated disc of L4–L5 motion segment, developed using different methodologies of volume mesh constructions, and ways of defining the spinal components’ material properties, were exercised and analyzed. The geometrics details were obtained using digitizing technique and segmentation of computed tomography (CT) scans; with material and structural properties of the spinal components defined based on the literature and greyscale values of CT images for the normal and degenerated L4–L5 motion segments, respectively. The predicted kinematic responses under five different physiological loadings in three anatomical reference planes for both models together with published data were analyzed. The predicted results correlated well within the range and in similar trends with published experimental results. The overall predicted responses showed different volume mesh constructions and the representation of spinal components’ material properties were accurate enough to predict the kinematic responses, although experimental results exhibit considerable divergence due to different experimental techniques. Both models exhibited different rotational and translation segmental stiffness in each corresponding loading configuration. The normal L4–L5 segment exhibited greatest axial torsional stiffness, and least extensional stiffness. The degenerated L4–L5 segment was least flexible (greatest stiffness) in extension and most flexible (least stiffness) in flexion. For compression, the axial stiffness of segment of normal segment was about 10% larger than that of the degenerated segment. The en-bloc efforts of all spinal components have contributed to the different nonlinear kinematic characteristics and segmental stiffness of these different L4–L5 motion segments.

Fast Field-Cycling Nuclear Magnetic Resonance Relaxometry of Perfluorosulfonic Acid Ionomers and Their Perfluorosulfonyl Fluoride Precursors Membranes.

The spin-lattice relaxation rates (R1) of fluorine nuclei in perfluorosulfonic acid (PFSA) ionomer membranes and their precursor solid perfluorosulfonyl fluoride (PFSF) were measured by fast field-cycling (FFC) NMR relaxometry. The XRD profiles of PFSA and PFSF are similar and show a characteristic peak, indicating the alignment of main chains. While the SAXS profiles of the PFSA membranes show two peaks, those of the solid PFSF lack the ionomer peak which is characteristic of hydrophilic side chains in the PFSA ionomer membranes. The Larmor frequency dependence of R1 obeys power law and the indices are dependent on the sample and temperature. The indices of the PFSA membranes change from -1/2 to -1 along with the Larmor frequency and temperature dependence decrease, which is consistent with the generalized defect diffusion model. Estimated activation energies are in good agreement with those obtained from dynamical mechanical analysis and dielectric spectroscopy, indicating the segmental motion of the backbones as the common origin of these observations. On the other hand, the index changes to -3/4 in the case of the PFSFs, which has been predicted by the reptation model.

Sizing agent induces the oriented attachment of 2D nanosheets for preparing high-performance carbon fiber composites

Inducing highly oriented 2D nanosheets to create a mussel-inspired interface phase on the carbon fiber (CF) surface to enhance its composites’ strength and toughness has become a great challenge. In this study, a novel coating was synthesized to induce the graphene oxide (GO) oriented distributed on the CF surface while constructing a biomimetic "Brick-and-Mortar" structural interface phase, which simultaneously promoted the strength and toughness of CF composites. Acting as a sizing agent, di-pyrene terminated PEG (py-PEG-py) facilitates abundant π-π* stacking interactions, and enables flexible chain segment motion during interface fracture of composites, as well as effectively improving the toughness of composites. Eventually, the formation of a superior mechanism on the CF surface results in remarkable properties for composites, including an interfacial shear strength (IFSS) of 99.3 MPa, interlaminar shear strength of 93.2 MPa, and flexural strength of 1430 MPa. The tensile strength and toughness increased to 1777 MPa and 45.0 MJm−3, respectively. Simultaneously, the continuous thermal conduction pathway produced by the oriented attachment of GO on the CF surface increased in-plane thermal conductivity. The reinforcing mechanisms of the unique mussel-inspired coating were systematically investigated. This work opens up an effective and scalability avenue for obtaining high-performance CF composites.

In vivo study of a novel 3D-printed motion-preservation artificial cervical corpectomy construct: short-term imaging and biocompatibility evaluations in a goat model

BackgroundNonfusion technologies, such as motion-preservation devices, have begun a new era of treatment options in spine surgery. Motion-preservation approaches mainly include total disc replacement for anterior cervical discectomy and fusion. However, for multisegment fusion, such as anterior cervical corpectomy and fusion, the options are more limited. Therefore, we designed a novel 3D-printed motion-preservation artificial cervical corpectomy construct (ACCC) for multisegment fusion. The aim of this study was to explore the feasibility of ACCC in a goat model.MethodsGoats were treated with anterior C3 corpectomy and ACCC implantation and randomly divided into two groups evaluated at 3 or 6 months. Radiography, 3D CT reconstruction and MRI evaluations were performed. Biocompatibility was evaluated using micro-CT and histology.ResultsPostoperatively, all goats were in good condition, with free neck movement. Implant positioning was optimal. The relationship between facet joints was stable. The range of motion of the C2-C4 segments during flexion–extension at 3 and 6 months postoperatively was 7.8° and 7.3°, respectively. The implants were wrapped by new bone tissue, which had grown into the porous structure. Cartilage tissue, ossification centres, new blood vessels, and bone mineralization were observed at the porous metal vertebrae-bone interface and in the metal pores.ConclusionsThe ACCC provided stabilization while preserving the motion of the functional spinal unit and promoting bone regeneration and vascularization. In this study, the ACCC was used for anterior cervical corpectomy and fusion (ACCF) in a goat model. We hope that this study will propel further research of motion-preservation devices.

Diagnostic efficacy of complexity metrics from cardiac MRI myocardial segmental motion curves in detecting late gadolinium enhancement in myocardial infarction patients

BackgroundMyocardial segmental motion is associated with cardiovascular pathology, often assessed through myocardial strain features. The stability of the motion can be influenced by myocardial fibrosis. This research aimed to explore the complexity metrics (CM) of myocardial segmental motion curves, observe their correlation with late gadolinium enhancement (LGE) transmural extension (TE), and assess diagnostic efficacy combined with segmental strains in different TE segments. MethodsWe included 42 myocardial infarction patients, dividing images into 672 myocardial segments (208 remote, 384 viable, and 80 unviable segments based on TE). Radial and circumferential segmental strain, along with CM for motion curves, were extracted. Correlation between CM and LGE, as well as the potential distinguishing role of CM, was evaluated using Pearson correlation, univariate linear regression (F-test), multivariate regression analysis (T-test), area under curve (AUC), machine learning models, and DeLong test. ResultsAll CMs showed significant linear correlation with TE (P < 0.001). Six CMs were correlated with TE (r > 0.3), with radial frequency drift (FD) displayed the strongest correlation (r = 0.496, P < 0.001). Radial and circumferential FD significantly differed in higher TE myocardium than in remote segments (P < 0.05). Radial FD had practical diagnostic efficacy (remote vs. unviable AUC = 0.89, viable vs. unviable AUC = 0.77, remote vs. viable AUC = 0.65). Combining CM with segmental strain features boosted diagnostic efficacy than models using only segmental strain features (DeLong test, P < 0.05). ConclusionsThe CM of myocardial motion curves has been associated with LGE infarction, and combining CM with strain features improves the diagnosis of different myocardial LGE infarction degrees.

The effect of suboccipital muscle dysfunction on the biomechanics of the upper cervical spine: a study based on finite element analysis

ObjectiveMuscle dysfunction caused by repetitive work or strain in the neck region can interfere muscle responses. Muscle dysfunction can be an important factor in causing cervical spondylosis. However, there has been no research on how the biomechanical properties of the upper cervical spine change when the suboccipital muscle group experiences dysfunction. The objective of this study was to investigate the biomechanical evidence for cervical spondylosis by utilizing the finite element (FE) approach, thus and to provide guidance for clinicians performing acupoint therapy.MethodsBy varying the elastic modulus of the suboccipital muscle, the four FE models of C0-C3 motion segments were reconstructed under the conditions of normal muscle function and muscle dysfunction. For the two normal condition FE models, the elastic modulus for suboccipital muscles on both sides of the C0-C3 motion segments was equal and within the normal range In one muscle dysfunction FE model, the elastic modulus on both sides was equal and greater than 37 kPa, which represented muscle hypertonia; in the other, the elastic modulus of the left and right suboccipital muscles was different, indicating muscle imbalance. The biomechanical behavior of the lateral atlantoaxial joint (LAAJ), atlanto-odontoid joint (ADJ), and intervertebral disc (IVD) was analyzed by simulations, which were carried out under the six loadings of flexion, extension, left and right lateral bending, left and right axial rotation.ResultsUnder flexion, the maximum stress in LAAJ with muscle imbalance was higher than that with normal muscle and hypertonia, while the maximum stress in IVD in the hypertonic model was higher than that in the normal and imbalance models. The maximum stress in ADJ was the largest under extension among all loadings for all models. Muscle imbalance and hypertonia did not cause overstress and stress distribution abnormalities in ADJ.ConclusionMuscle dysfunction increases the stress in LAAJ and in IVD, but it does not affect ADJ.

Comparative Biomechanical Stability of the Fixation of Different Miniplates in Restorative Laminoplasty after Laminectomy: A Finite Element Study

A novel H-shaped miniplate (HSM) was specifically designed for restorative laminoplasties to restore patients’ posterior elements after laminectomies. A validated finite element (FE) model of L2/4 was utilized to create a laminectomy model, as well as three restorative laminoplasty models based on the fixation of different miniplates after a laminectomy (the RL-HSM model, the RL-LSM model, and the RL-THM model). The biomechanical effects of motion and displacement on a laminectomy and restorative laminoplasty with three different shapes for the fixation of miniplates were compared under the same mechanical conditions. This study aimed to validate the biomechanical stability, efficacy, and feasibility of a restorative laminoplasty with the fixation of miniplates post laminectomy. The laminectomy model demonstrated the greatest increase in motion and displacement, especially in axial rotation, followed by extension, flexion, and lateral bending. The restorative laminoplasty was exceptional in preserving the motion and displacement of surgical segments when compared to the intact state. This preservation was particularly evident in lateral bending and flexion/extension, with a slight maintenance efficacy observed in axial rotation. Compared to the laminectomy model, the restorative laminoplasties with the investigated miniplates demonstrated a motion-limiting effect for all directions and resulted in excellent stability levels under axial rotation and flexion/extension. The greatest reduction in motion and displacement was observed in the RL-HSM model, followed by the RL-LSM model and then the RL-THM model. When comparing the fixation of different miniplates in restorative laminoplasties, the HSMs were found to be superior to the LSMs and THMs in maintaining postoperative stability, particularly in axial rotation. The evidence suggests that a restorative laminoplasty with the fixation of miniplates is more effective than a conventional laminectomy due to the biomechanical effects of restoring posterior elements, which helps patients regain motion and limit load displacement responses in the spine after surgery, especially in axial rotation and flexion/extension. Additionally, our evaluation in this research study could benefit from further research and provide a methodological and modeling basis for the design and optimization of restorative laminoplasties.

Phase behavior of rubber and supercritical CO2: Operating parameters and swelling characteristics

AbstractThis study aims to compare the difference in the swelling process between styrene butadiene rubber (SBR) and natural rubber (NR) in ScCO2. A high‐pressure visual stainless‐steel autoclave was used to carry out swelling measurements based on the sample dimensions. The swelling rates for both rubbers followed a first‐order kinetic model. The diffusion coefficient for CO2 was determined from the change in the swelling degree with time. The shrinking process for the expanded rubber obeyed a second‐order kinetic model. A 2‐level full factorial experimental design was employed to discuss the influence of variables on rubber swelling and CO2 diffusion. Temperature and pressure were found to have a great influence on the equilibrium swelling degree, swelling rate and diffusion coefficient. For both SBR and NR, the maximum equilibrium swelling degrees were observed at 120°C and 20 MPa, yielding values of 1.18 and 1.16, respectively. The maximum diffusion coefficient reached approximately 3 × 10−9 m2 s−1 for both types of rubber at 120°C and 8 MPa. The crosslink density failed to affect these three responses, but the volume of expansion and the shrinkage rate were found to significantly decrease and increase, respectively, with increasing crosslink density. The motion of polymer segments forced by ScCO2 led to rearrangement of the material structure, which governed the nature of swelling, expansion, and shrinkage. Due to a lower number of entanglements and a weak electrostatic interaction exists between CO2 and the π‐system, SBR can absorb more CO2 and easily restructure than NR under the same conditions, resulting in higher equilibrium swelling degree, larger expansion and faster shrinkage than NR.Highlights Swelling of nature rubber and styrene‐butadiene rubber in ScCO2 is compared. Swelling degree is positively correlated with temperature and pressure. Diffusion coefficient increases with temperature but decreases with pressure. Swelling degree varies with rubber type, while CO2 diffusion dose not. Crosslink density significantly affects expansion and shrinkage of rubber.

The Impact of Scaling Methods and Strong Ground Motion Segments on the Seismic Behaviour of a Low-Rise Tunnel-Form System Building

The Impact of Scaling Methods and Strong Ground Motion Segments on the Seismic Behaviour of a Low-Rise Tunnel-Form System Building

Structural Relaxation Time of a Polymer Glass during Deformation.

In order to determine the structural relaxation time of a polymer glass during deformation, a strain rate switching experiment is performed in the steady-state plastic flow regime. A lightly cross-linked poly(methylmethacrylate) glass was utilized and, simultaneously, the segmental motion in the glass was quantified using an optical probe reorientation method. After the strain rate switch, a nonmonotonic stress response is observed, consistent with previous work. The correlation time for segmental motion, in contrast, monotonically evolves toward a new steady state, providing an unambiguous measurement of the structural relaxation time during deformation, which is found to be approximately equal to the segmental correlation time. The Chen-Schweizer model qualitatively predicts the changes in the segmental correlation time and the observed nonmonotonic stress response. In addition, our experiments are reasonably consistent with the material time assumption used in polymer deformation modeling; in this approach, the response of a polymer glass to a large deformation is described by combining a linear-response model with a time-dependent segmental correlation time.

Spinal articulation exercise using an exercise ball enhances dynamic postural control

PurposeWe hypothesized that exercises that selectively utilize local muscles responsible for segmental movements of the spine might promote local muscle activity and dynamic postural balance. In this study, we examined the effects of selective local muscle exercises (spinal articulation exercise) on dynamic postural control in healthy subjects. MethodsThe effects of spinal articulation exercise were examined using a deflated exercise ball for the postural sway in healthy students who were assigned to an exercise or control group. The independent variable was the extent of exposure to selective local muscle exercise, and the dependent variable was dynamic postural control. A stabilometer, which measures dynamic postural control, was used to evaluate the effectiveness of the exercises. In addition, center of gravity movements were assessed using a Gravicorder G-620 stabilometer in which the subject was asked to shift their center of gravity between 2 circles on a computer monitor. Pre- and post-intervention dynamic postural control was statistically evaluated between the exercise group and control group using the Mann-Whitney test. ResultsThe post-intervention average COUNTS were significantly higher in the exercise group than in the control group (p = 0.003, r = 0.78). ENV. AREA was significantly smaller in the exercise group than in the control group (p = 0.036, r = 0.54). Furthermore, LNG/COUNTS were significantly smaller in the exercise group than in the control group (p = 0.024, r = 0.58). ConclusionsSpinal articulation exercise may be used to enhance the dynamic postural balance of healthy young adults.

Hydroxyl‐terminated polybutadiene(HTPB) propellants cross‐linked by dimer acid diisocyanate (DDI): Cross‐linking network and properties

AbstractConsidering the high toxicity of toluene diisocyanate (TDI) and the low reactivity of isophorone diisocyanate (IPDI), a low‐toxicity curing agent, dimer acid diisocyanate (DDI), was used to cross‐link HTPB elastomers and propellants. The unique long‐chain structure of DDI not only ensures the elastic modulus and tensile strength of the elastomer, but also improves the flexibility to some extent. The long flexible chains promote the segment movement, which is very important for the formation of hydrogen bonds between segments. The chemical cross‐linking network and hydrogen bonding association play a significant role in the mechanical properties of the HTPB/DDI system. The relationship between the mole ratio of ‐NCO to ‐OH (R‐value) and the mechanical properties of HTPB/DDI elastomers were also investigated. In the range of R‐value from 0.85 to 1.2, the elastic modulus and tensile strength first increase and then decrease, and the elongation at break first decreases and then increases. Under the same curing conditions, the elastic modulus and tensile strength of the HTPB/DDI propellant are similar to the HTPB/TDI propellant. For the HTPB/AP/Al propellants and HTPB/AP/RDX/Al propellants, the HTPB/DDI system has lower burning rates in the range of 5–19 MPa than the HTPB/TDI system and HTPB/IPDI system. The application of DDI can reduce the burning rates of the propellant without adding any burning rate modifiers. It is considered that DDI can replace TDI and IPDI as a new curing agent with low toxicity and moderate reactivity for HTPB systems.

High temperature electrical breakdown and energy storage performance improved by hindering molecular motion in polyetherimide nanocomposites

Polyetherimide (PEI) is widely used as a material for high temperature and high power energy storage capacitors in new energy vehicles and other fields. However, as the temperature increases, the electrical conductivity increases and the breakdown strength decreases, which greatly reduces the energy storage density of the capacitor and limits the application range. In order to clarify the influence mechanism of high temperature on the breakdown and energy storage performance of dielectrics, this paper established a charge capture and molecular displacement (CTMD) breakdown model based on the expansion motion of molecular segments to study the charge transport and molecular chain motion process of PEI nanocomposites (PNCs) at high temperature. The results show that at 100 °C, compared with pure PEI, the internal maximum molecular displacement of PEI PNCs with appropriate doping content (3 wt%) is reduced by 28.79 %, and the breakdown strength is increased by 11.20 %. Appropriate nano-doping can effectively increase the movement difficulty of molecular chains and reduce the activation volume that provides energy for charge transport. Thus, charge transport is inhibited, current density is reduced, and Joule heat accumulation is avoided. Finally, the high temperature breakdown and energy storage performance are improved.

Understanding the Impact of Chain Mobility on Conformational Evolution and Kinetics of Mesophase Formation in Poly(ʟ-lactide) under Low-Pressure CO2.

Although the mesomorphic phase as an intermediate state has been introduced to understand polymer crystallization, the understanding of the mesomorphic phase is far from complete. Here, the effect of chain mobility on the mesophase structuring in melt-quenched poly(ʟ-lactide) (PLLA) treated in low-pressure CO2 at 1.6-2.0 MPa and 0 °C was investigated using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and atomic force microscopy (AFM). The IR and AFM results demonstrated that the final degree of order and the kinetics of structural evolution during the CO2-induced mesophase formation were critically dependent on the CO2 pressure. This was attributed to the distinct dynamics of conformational evolution (gg to gt conformer transition) due to the different CO2 pressures. The thermal behavior from the DSC results showed that CO2 pressure dominated both the scale and dynamics of the chain motion of PLLA. At a lower CO2 pressure of 1.6 MPa, smaller-scale segmental motion was not replaced by the larger-scale cooperative motion that occurred at a relatively higher CO2 pressure of 2 MPa, which was favorable for faster mesophase formation. Consequently, by inhibiting direct crystallization under limited mobility conditions, it was demonstrated that different chain mobility controlled by CO2 pressure and thus CO2 solubility impacted the dynamics of the mesophase formation of PLLA. The present results have implications for understanding the role of chain mobility in determining the intermediate structural phases in semicrystalline polymers.

High energy-dissipation PDMS polymer-fluid-gels over an ultra-wide temperature range

Viscoelastic polymers exhibit strong energy dissipation in the glass transition region due to the motion of chain segments. Yet, the damping temperature ranges are pretty narrow, and the damping effect is poor at low frequencies. Here, we report two PDMS polymer-fluid-gels prepared by traditional curing and solvothermal polymerization, both of which exhibit excellent energy-dissipation capacity with loss factor larger than 0.7 at 1 Hz both covering 255 K (−55 °C to 200 °C), and larger than 1.0 at 1 Hz covering 134.7 K and 146.7 K, respectively, exceeding all the literature reports. Furthermore, solvothermal polymerization realizes large cross-linking meshes in which polymer fluids can stretch with less restriction and have longer relaxation time, which is conducive to low-frequency damping. The lower the frequency, the more pronounced the relative increase in damping, with the ratio of the two being greater than 4 times in the measuring low-frequency range. Moreover, the gels can absorb impact in extreme environments and protect raw eggs from breaking at temperatures as low as −50 °C when dropped from a height of 2 m.

Versatile morphology transition of nano-assemblies via ultrasonics/microwave assisted aqueous polymerization-induced self-assembly based on host–guest interaction

Nano-assemblies have wide applications in biomedicine, functional coatings, Pickering emulsifiers, hydrogels, and so forth. The preparation of assemblies mainly utilizes the polymerization-induced self-assembly (PISA) method, which can produce high-concentration nanoscale assemblies in one step. However, the initiation processes of most reported PISA are limited to thermal initiation. Here, we reported two green and efficient methods for synthesizing nano-assemblies with various morphologies using ultrasound (20 kHz)/ microwave (500 W) assisted aqueous-phase RAFT-PISA in 3 h and 1 h. Cyclodextrin (CD) and styrene (St) nucleating monomer were complexed in a 1:1 ratio. Then, using Poly (ethylene glycol) methyl ether as the macromolecular reversible addition-fragmentation chain transfer (RAFT) agent (PEG-CTA) to control the CD/St complexes, the conversion rate of St monomer was respectively 27 %–60 %, 20 %–30 % within 3 h and 1 h under ultrasonics/microwave assisted PISA. Results showed that the morphologies of the assemblies are not only related to the length of PS block, but also to the assistance types and the remaining monomer concentration. The results showed that only PEG45-b-PS90 and PEG45-b-PS241 assemblies prepared by ultrasonics assisted PISA form evolved lamellaes and vesicles (100 nm), which break through the limitation of kinetic freezing. But the ultrasonic reaction on morphology of assemblies is not all favourable. For one thing, it can promote the movement of particles; for another, it makes reverse morphology transformation and sphere is preferred morphology. Therefore, the main reason of morphology evolution is the remaining monomer concentration of PEG45-b-PS90 and PEG45-b-PS241 assemblies reaches to 55 %–65 %, which promoting the segment movement. The results showed that the morphology of the assemblies prepared by microwave assisted PISA changed from spherical micelles to short rods, and finally to vesicles (120–140 nm) as the length of hydrophobic PS block increases. The kinetic freezing problem was solved in microwave-assisted PISA due to the action of microwaves and more remaining monomer concentration. Both them can boost particles movement.

Numerical investigation on the behaviour of Post-Tensioned Mechanically Stabilised Earth Walls (PT-MSEW)

This study reports on a numerical investigation on the behaviour of an innovative retaining wall system named Post Tensioned Mechanically Stabilised Earth Wall (PTMSEW). In the proposed system, Post-Tensioning (PT) technique was integrated into the common retaining wall and the Mechanically Stabilised Earth Wall (MSEW) construction method to improve the performance of MSEWs and limit their failure modes. The variables of this study were wall height, PT force, pre-cast segment size, surcharge load, foundation size, and soil reinforcement length. The study found that incorporating PT stress into the MSEW improved the performance of the retaining wall by decreasing horizontal displacement of the wall face, soil reinforcement tensile forces, and backfill settlements and significantly enhanced the passive resistance of the wall. The introduction of a small amount of PT force prevented local failures caused by the relative movement of face segments. It was observed that by applying only a small level of post-tensioning, the lateral load-carrying capacity and passive resistance of the proposed PT-MSEW system can be significantly improved over that of its conventional counterpart. This opens new possibilities for the use of MSEW in the construction of taller retaining walls.

Preoperative low Hounsfield units in the lumbar spine are associated with postoperative mechanical complications in adult spinal deformity.

To determine the most valid bone health parameter to predict mechanical complications (MCs) following surgery for adult spinal deformity (ASD). This multicenter study retrospectively examined the records of patients who had undergone fusion of three or more motion segments, including the pelvis, with a minimum two-year follow-up period. Patients with moderate and severe global alignment and proportion scores were included in the study and divided into two groups: those who developed MCs and those who did not. Bone mineral density (BMD) of the lumbar spine and femoral neck was measured using dual-energy X-ray absorptiometry, and Hounsfield units (HUs) were measured in the lumbar spine on computed tomography. Radiographic parameters were evaluated preoperatively, immediately after surgery, and at final follow-up. Of 108 patients, 30 (27.8%) developed MCs, including 26 cases of proximal junctional kyphosis/failure, 2 of distal junctional failure, 6 of rod fracture, and 11 reoperations. HUs were significantly lower in patients who experienced MCs (113.7 ± 41.1) than in those who did not (137.0 ± 46.8; P = 0.02). BMD did not differ significantly between the two groups. The preoperative and two-year postoperative global tilt, as well as the immediately postoperative sagittal vertical axis, were significantly greater in patients who developed MCs than in those who did not (P = 0.02, P < 0.01, and P = 0.01, respectively). Patients who experienced MCs following surgery for ASD had lower HUs than those who did not. HUs may therefore be more useful than BMD for predicting MCs following surgery for ASD.