Effects of a Q Suture Technique as a Core Suture on Resistance to Gap Formation and Tensile Strength in an Ex Vivo Porcine Flexor Tendon Model

PURPOSE

The Q suture has been reported to be an effective alternative to conventional peripheral sutures in tendon repair. Whether the Q method can be used as a core suture rather than a peripheral suture by adjusting the purchase length is unknown. We tested a double Q suture technique with variable purchase length and studied its effects on gap formation and tensile strength using an ex vivo model.

METHODS

Forty pig flexor tendons were repaired using the double Q sutures with purchase lengths of 2, 4, 6, and 8 mm. Twenty tendons repaired using the double Tsuge and double Kessler sutures with an 8-mm purchase length were used as controls. The tendons were subjected to cyclic loading and load-to-failure. The number of tendons that formed an initial or 2-mm gap between the tendon ends, gap distance at the repair site, stiffness, and ultimate strength were recorded.

RESULTS

During cyclic loading, the double Q suture with a 4-8-mm purchase had fewer tendons form an initial or 2-mm gap and a smaller gap size at the repair site than the Tsuge and Kessler sutures. The stiffness of the double Q suture with a 6-8-mm purchase length and Tsuge suture was greater than those of the double Kessler suture. The double Q suture with a 2-mm purchase length had smaller ultimate strength than the other sutures.

CONCLUSIONS

The Q suture may be an effective tendon repair method whose role can be converted between peripheral and core sutures via adjusting the suture purchase length. With an optimal suture length of 4-6 mm, the double Q method had tensile resistance superior to 4-strand core sutures.

CLINICAL RELEVANCE

The double Q suture may be a viable option as a core suture in flexor tendon repair when the purchase length is appropriately adjusted.

Effect of Al2Cu constituent layer thickness discrepancy on the tensile mechanical behavior of Cu/Al2Cu/Al layered composites: a molecular dynamics simulation

Nano-polycrystalline Cu/Al2Cu/Al layered composites with different layer thicknessesdof single-crystal Al2Cu constituent are constructed. The effects ofdon the strength and fracture modes of nano-polycrystalline Cu/Al2Cu/Al layered composites are systematically investigated by molecular dynamics simulations. The uniaxial tensile results show that the ultimate strength and fracture mode of the nano-polycrystalline Cu/Al2Cu/Al layered composites do not change monotonically with the change of single crystal Al2Cu constituent layer thicknessd, the ultimate strength peaking atd= 2.44 nm, and the toughness reaching the optimum atd= 4.88 nm. The improvement of deformation incompatibility between Cu, Al and Al2Cu components increases the ultimate strength of polycrystalline Cu/Al2Cu/Al laminated composites. Due to the high activity of Cu dislocation and the uniformity of strain distribution of single crystal Al2Cu, the fracture of nano-crystalline Cu/Al2Cu/Al layered composites changes from brittleness to toughness. This study is crucial to establish the organic connection between microstructure and macroscopic properties of Cu/Al layered composites. To provide theoretical basis and technical support for the application of Cu/Al layered composites in high-end fields, such as automotive and marine, aerospace and defense industries.

Behavior of Hybrid Reinforced Concrete Bridge Decks under Static and Fatigue Loading

This paper presents a new bridge deck reinforcement alternative using hybrid reinforced concrete (Hybrid) consisting of Glass Fiber Reinforced Polymer (GFRP) rebar and alkali-resistant fiberglass composite macrofibers added to the concrete mixture. Fiberglass composite macrofibers are a miniaturized GFRP reinforcing bar that is a composite of resin and glass fibers. An experimental testing program and analytical modeling were conducted to evaluate the structural performance at the service and ultimate limit states. Thirteen full-scale bridge deck specimens were constructed and tested under static and fatigue loading. The fatigue loading was applied up to two million cycles at a frequency of 4 Hz. Post-fatigue, the specimens were tested to failure to compare pre-and post-fatigue behavior. Simplified and moment-curvature analytical models were used to predict the specimens' flexural strength at the ultimate level, and both were found to be accurate for predicting pre- and post-fatigue strength. Deflection and crack width were monitored throughout the fatigue loading, and these values were compared to the recommended AASHTO LRFD serviceability limits. Testing and analytical results showed that the Hybrid deck is a viable alternative to steel-reinforced and GFRP-reinforced bridge decks for flexural behavior. The service and ultimate level behavior of each bridge deck type was adequate as compared to the AASHTO LRFD service limits. The exceptional post-peak energy absorption demonstrated by the Hybrid adds ductility to previously elastic GFRP reinforced sections.

The influence of a nanoparticle gel loaded with siRNA-cyclooxygenase on flexor tendon healing: an in vivo animal study

We investigated the influence of cyclooxygenase (COX)-1 and COX-2 siRNAs delivered through a nanoparticle-gel system on the strength of flexor tendon repairs. Sixteen flexor digitorum profundus (FDP) tendons of chicken toes were transected, repaired and wrapped with gels to evaluate gel adherence. We found that the gel adhered to the tendon surface firmly. Next, 56 tendons were used in a first set of in vivo experiments to compare the therapeutic effects of different doses of COX siRNAs. Another 15 tendons were added in a second set to further assess the effects of a dosage of 12 μg. After 4 weeks, the mean strength of the repaired tendons increased most notably in the toes treated with 12 μg COX siRNAs, and the number of samples with low strength (<35 N) was significantly smaller than in the group without molecular treatment. We conclude that COX-1 and COX-2 siRNAs delivered through a nanoparticle-gel system increased the healing strength of the repaired tendons.

Compressive Behavior of Bamboo Sheet Twining Tube-Confined Concrete Columns

This study experimentally investigated various axial compressive parameters of a new type of confined concrete, which is termed bamboo sheet twining tube-confined concrete (BSTCC). This new composite structure was composed of an outer bamboo composite tube (BCT) jacket and a concrete core. Under axial compression, the parameters of thirty-six specimens include concrete strength (i.e., C30 and C50) and BCT thickness (i.e., 6, 12, 18, 24, and 30 layers). The mechanical properties of the BSTCC specimens from the perspective of the failure mode, stress-strain relationship, effect of BCT thickness and dilation behavior were analyzed. The results showed that, in compression, with an increase in BCT thickness in the range of 18-layers of bamboo sheets, the strength increased remarkably. When the strength of the concrete core was high, the confinement effect of the BCT was reduced. In addition, the BCT thickness relieved the dilation of the BSTCC specimens. Finally, the experimental results were compared with predictions obtained from 7 existing FRP-confined concrete models. All the predictions had good agreement with the test results, which further confirmed that the models developed for FRP-confined concrete can provide an acceptable approximation of the ultimate strength of the BSTCC specimens.

Prediction of the Ultimate Strength of Notched and Unnotched IM7/977-3 Laminated Composites Using a Micromechanics Approach

This paper proposes a multi-scale analysis technique based on the micromechanics of failure (MMF) to predict and investigate the damage progression and ultimate strength at failure of laminated composites. A lamina’s representative volume element (RVE) is developed to predict and calculate constituent stresses. Damages that occurred in the constituents are calculated using separate failure criteria for both fiber and matrix. Subsequently, the volume-based damage homogenization technique is utilized to prevent the localization of damage throughout the total matrix zone. The proposed multiscale analysis procedure is then used to investigate the notched and unnotched behavior of three multi-directional composite layups, [30, 60, 90, −60, 30]_2S, [0, 45, 90, −45]_2S, and [60, 0, −60]_3S, subjected to static tension and compression loading. The specimen is fabricated from unidirectionally reinforced composite (IM7/977-3). The prediction of ultimate strength at failure and equivalent stiffness are then benchmarked against the experimental test data. The comparative analysis with various failure models is also carried out to validate the proposed model. MMF demonstrated the capability to correctly predict the ultimate strength at failure for a range of multidirectional composites laminates under tensile and compressive load. The numerically predicted findings revealed a good agreement with the experimental test data. Out of the three investigated composite layups, the simulated results for the quasi-isotropic [0, 45, 90, −45]_2S layup agreed extremely well with the experimental results with all the percentage errors within 10% of the measured failure loads.

Finite Model Analysis and Practical Design Equations of Circular Concrete-Filled Steel Tube Columns Subjected to Compression-Torsion Load

The objective of this study is to investigate the mechanical properties and the composite action of circular concrete-filled steel tube (CFST) columns subjected to compression-torsion load using finite element model analysis. Load-strain (T-γ) curves, normal stress, shear stress, and the composite action between the steel tubes and the interior concrete were analyzed based on the verified 3D finite element models. The results indicate that with the increase of axial force, the maximum shear stress at the core concrete increased significantly, and the maximum shear stress of the steel tubes gradually decreased. Meanwhile, the torsional bearing capacity of the column increased at first and then decreased. The torque share in the columns changed from the tube-sharing domain to the concrete-sharing domain, while the axial force of the steel tube remained unchanged. Practical design equations for the torsional capacity of axially loaded circular CFST columns were proposed based on the parametric analysis. The accuracy and validity of the proposed equations were verified against the collected experimental results.

Prompt Determination of the Mechanical Properties of Industrial Polypropylene Sandwich Pipes

A simple and prompt method to determine the mechanical properties of industrial multilayer extrusion polypropylene pipes for a gravity sewer network is suggested. The engineering formulas included for calculating the permissible thickness and relative position of a foam core in the pipes are based on a linear-elastic approximation and the rule of mixtures. The applicability of the approximation was justified experimentally during investigation of the effective tensile characteristics of single- and multilayer pipes and each layer specimen by using traditional tests and finite-element calculations. The results obtained were used to formulate engineering recommendations for calculations of this type.

Numerical Analysis of Axial Cyclic Behavior of FRP Retrofitted CHS Joints

This paper aims to numerically investigate the cyclic behavior of retrofitted and non-retrofitted circular hollow section (CHS) T-joints under axial loading. Different joints with varying ratios of brace to chord radius are studied. The effects of welding process on buckling instability of the joints in compression and the plastic failure in tension are considered. The finite element method is employed for numerical analysis, and the SAC protocol is considered as cyclic loading scheme. The CHS joints are retrofitted with different numbers of Fiber Reinforced Polymer (FRP) layers with varying orientation. The results show that the welding process significantly increases the plastic failure potential. The chord ovalization is the dominant common buckling mode under the compression load. However, it is possible to increase the energy dissipation of the joints by utilizing FRP composite through changing the buckling mode to the brace overall buckling.

Ultimate Bearing Capacity Analysis of CFRP-Strengthened Shield Segments Using Bonding Slip Behavior Experiments

Shield segments of subway tunnels are often exposed to the combined actions of several hygrothermal factors that could lead to accidents such as water seepage and tunnel collapse. Further, they often break and deform owing to formation pressure. In addition, uncertainties related to the stress relaxation characteristics and bonding performance of carbon-fiber-reinforced plastics (CFRPs) under a hygrothermal environment make their application in subway systems difficult. This study analyzes the effects of the slip-on-bending strength of CFRP-strengthened shield segments in a hygrothermal environment. In the study, the shield segments are damaged at ambient pressure under a combination of humidity (0%, 5%, and 10%) and temperature (20 °C, 25 °C, 30 °C, and 40 °C). An experimental procedure is designed to evaluate a CFRP-reinforced concrete arch. The method predicts the load-slip relationship and maximum shearing stress and strain. Moreover, confined compression tests are conducted on a tunnel segment lining strengthened with CFRP to evaluate the bearing capacity of the CFRP-strengthened shield segments. An equation for the latter's ultimate bearing capacity is developed based on the elastic layer system theory, stress boundary condition, and bending stress characteristics of axisymmetric elements. It was found that the results from the developed model are compared with the experimental values of CFRP-strengthened shield segments under different humidity values (0%, 5%, and 10%) and a constant temperature. The ultimate strength-the debonding deflection of the CFRP-strengthened shield segment-can be predicted using the proposed ultimate bearing capacity equation with sufficient accuracy.

Mechanical Properties of Cast-in Anchor Bolts Manufactured of Reinforcing Tempcore Steel

The tempcore process is implemented in rolling mills to produce high strength reinforcing steel. Besides being used as reinforcement, rebars are also used as the base material for the manufacturing of anchor bolts. The mechanical properties of reinforcement bars used in Europe are assessed in accordance with Eurocode without the recommendations for cast-in anchor bolts. The material properties of Tempcore rebars are not homogenous over the bar cross section. The European Assessment Document (EAD) for the cast-in anchor bolts does not exactly specify the mechanical properties of the thread part. The aim of these experiments is to show the different mechanical properties of rebars and their thread parts. The experiments were performed on rebars modified by peeling to characterize the reduction of diameter in a thread part. As a possible way to predict mechanical properties in a non-destructive way, the hardness tests were performed. Next, the application of the correlation relationship between hardness and tensile strength has been determined. The paper formulates preliminary recommendations for assessment of the cast-in anchor bolts in practice.

Size Effect on Mechanical Properties and Texture of Pure Copper Foil by Cold Rolling

To study the size effect on the properties of copper, tensile tests were performed with pure copper foil (thickness range from 25 μm to 300 μm) by cold rolling. A pronounced size effect was observed at a thickness of 76 μm. The results showed that ultimate strength increased as sample thickness decreased from 300 μm to 100 μm, however, this was decreased as the thickness changed from 76 μm to 25 μm with ultrahigh strain, with the same trend of dislocation density and micro stain. The rolling texture were consisted of copper {112}<111>, brass {011}<211>, and S {123}<634>. These features seemed to be linked to the increase of fraction of surface grain to volume, which led to lower districting on the dislocation slip.

The deer femur--a morphological and biomechanical animal model of the human femur

BACKGROUND

The need for continued refinement of animal models in orthopaedic studies persists despite decades of research.

OBJECTIVE

This study investigates the merits of deer bone in comparison to the more commonly used pig and sheep bone as an animal model for the human femur.

METHOD

A morphological and biomechanical comparison of deer, pig and sheep rear femurs to those of the human femur is presented. Morphological parameters measured include bone length, cortical and medullary diaphyseal diameters, cortical thickness, cortical cross-sectional area and bone density along the diaphysis. Biomechanical tests included whole-bone four-point flexure tests to determine the bending stiffness (N/mm), Young's modulus of bending (GPa), and ultimate strength in bending (MPa). In addition torsional stiffness (Nm/degree) as well as mid-diaphyseal cortical compressive elastic modulus (GPa) and strength (MPa) is investigated.

RESULTS

On average, deer bone was found to be the least dissimilar from human femur. However, no single bone type consistently resembled the human femur.

CONCLUSION

Deer femora should be considered a suitable animal model for the human femur.