Elongation Mode Research Articles

Phenotypic plasticity in bacterial elongation among closely related species.

Cell elongation is a fundamental component of the bacterial cell cycle and has been studied over many decades, in part owing to its mechanisms being a target of numerous antibiotic classes. While several distinct modes of cell elongation have been described, these studies have largely relied on a handful of model bacterial species. Therefore, we have a limited view of the diversity of cell elongation approaches that are employed by bacteria, and how these vary in response to evolutionary and environmental influences. Here, by employing fluorescent D-amino acids (FDAAs) to track the spatiotemporal dynamics of elongation, we reveal previously unsuspected diversity of elongation modes among closely related species of the Caulobacteraceae , with species-specific combinations of dispersed, midcell and polar elongation that can be either unidirectional or bidirectional. Using genetic, cell biology, and phylogenetic approaches, we demonstrate that evolution of unidirectional-midcell elongation is accompanied by changes in the localization pattern of the peptidoglycan synthase PBP2 and infer that elongation complexes display a high degree of phenotypic plasticity, both among the Caulobacteraceae and more widely among the Alphaproteobacteria. Demonstration that even closely related bacterial species employ highly distinct mechanisms of cell elongation reshapes our understanding of the evolution and regulation of bacterial cell growth, with broad implications for bacterial morphology, adaptation, and antibiotic resistance.

Understanding the effect of physical aging on slip dynamics in soft-glassy materials using pure elongation flow

Slip over a solid surface is a very common occurrence in industrial scale transport and the processing of complex fluids. The knowledge of slip also plays a huge role in the correct estimation of rheological properties. In this work, we have studied the slip dynamics in a model soft-glassy material that exhibits physical aging, wherein the structure evolves gradually toward a more solid-like character via rearrangement of constituents. More precisely, we have investigated the impact of physical aging on slip associated with pure elongation flow of the material. We have allowed the sample to age over different waiting times, followed by the sample being deformed slowly in elongation mode by pulling the top plate to achieve a pure elongation flow. Normal force as a function of gap has been recorded during such pure elongation. These normal force–gap curves demonstrated a remarkable gap-waiting time superposition, manifesting the strong signature of self-similarity in the pure elongation flow of the soft-glassy system. We have adopted a slip layer model, which predicted these normal force–gap flow curves remarkably well. Such prediction also rendered slip layer thickness as a function of waiting time, using which we have explained the intriguing self-similar nature of normal force–gap dependence. Finally, we have established a relationship between the slip layer thickness and the age-dependent bulk rheological properties. We have provided a possible physical reasoning to explain this link between the physical aging-driven state of material and the slip dynamics.

Biomechanical Comparison of Suture-Relay All-Suture Anchors and Conventional Suture Anchors for Posterior Medial Meniscus Root Repair in Porcine Models.

Posterior medial meniscus root (PMMR) tears (PMMRTs) can be repaired using various techniques to promote healing. However, the biomechanical properties of suture-relay all-suture anchor (ASA) versus conventional suture anchor (CSA) and loop-locking transtibial pullout (TTP) have not been well established. To compare the biomechanical properties of PMMR repairs using suture-relay ASA, CSA, and loop-locking TTP. Controlled laboratory study. A total of 33 fresh-frozen porcine knee joints with intact medial menisci were randomly divided into 3 groups, with 11 specimens in each group: ASA, CSA, and TTP. The study involved cyclic loading, with displacement measurements taken after 100, 500, and 1000 cycles. Subsequently, the specimens were loaded until clinical failure (defined as 3-mm displacement) and then to ultimate failure of the construct, with data recorded for displacement after cyclic loading, load to 3-mm displacement, and ultimate load to failure. After 1000 cyclic loadings, the suture-relay ASA group showed considerably less displacement than the loop-locking TTP group (1.8 ± 0.7 mm vs 2.9 ± 0.3 mm; P < .001), but the displacements did not differ considerably between the suture-relay ASA and CSA groups (2.2 ± 0.9 mm; P > .05). The mean loads to clinical failure were significantly greater in the suture-relay ASA and CSA groups (61.3 ± 6.5 and 57.5 ± 9.7 N, respectively) than in the loop-locking TTP group (38.3 ± 9.4 N; P < .05). The ultimate load to failure was significantly greater in the suture-relay ASA group than in the loop-locking TTP group (153 ± 55.1 N vs 102 ± 12.9 N; P < .05). All specimens in the loop-locking TTP group failed by suture elongation mode, whereas only 2 specimens (18%) in the suture-relay ASA group and 5 specimens (45%) in the CSA group failed by suture elongation. Nine specimens (82%) in the suture-relay ASA group and 6 specimens (55%) in the CSA group failed due to suture cutout through the meniscal tissue. The biomechanical properties after PMMR repair did not statistically differ between the suture-relay ASA and CSA groups. The suture-relay ASA technique had a higher load to failure than the loop-locking TTP technique. The suture-relay ASA technique is a promising option for the repair of PMMRTs; its repairing strength is also comparable to that of the CSA technique. Notably, the suture-relay ASA technique can be utilized without establishing a posteromedial portal, resulting in decreased procedure time and mitigating challenges associated with working from the posterior aspect of the knee.

Study on hydrogen embrittlement sensitivity of 30CrMnSiNi2A steel in electrochemical hydrogen charging

Abstract Electrochemical hydrogen charging was performed on a 30CrMnSiNi2A steel tensile sample, and the difference in hydrogen-charging effect with different hydrogen-charging times, current densities, and toxic agents was compared. The effect of hydrogen on the tensile strength, elongation and failure mode of the material was studied by the tensile test of slow strain rate. Results of the test show that hydrogen can greatly reduce the tensile strength, plastic deformation capacity, and elongation of 30CrMnSiNi2A steel, and the higher the hydrogen concentration in the material is, the more obvious the reduction will be. Hydrogen can make the failure mode of 30CrMnSiNi2A steel change from ductile failure to quasi-joint fracture and intergranular fracture.

The effect of number of knots per throw, knot technique, and suture type on strength properties of suspensory fixation button surgical procedures

Previous studies of the cortical suspensory button (CSB) implant have analyzed fixation strength as a function of suture type and surgical technique, but knot configuration remains an area of interest. This study investigates 4-strand knot configurations in CSB suspensory fixation, specifically comparing the use of 2 separate knots with a single knot. We hypothesize that using 2 knots on the distal side of the CSB with #2 suture will yield the strongest and stiffest suspensory fixation. Two types of knot configurations were compared: a single knot with all 4 suture strands versus 2 independent knots with 2 suture strands each (1 knot from inner strands and 1 knot from outer strands). They were tested using #2 or 2-0 suture, and at distal (on top of the button) or proximal (underneath the button) knot positions. Mechanical testing on the Instron measured ultimate failure load, elongation at failure, and stiffness. Statistical analyses (Shapiro-Wilk, unpaired Student's t-tests, and Chi-square tests) assessed differences in strength, stiffness, elongation, and failure mode between knot configurations within each CSB construct combination. With #2 suture, 2 knots across the CSB resulted in higher load to failure compared to 1 knot in both proximal (467.00 N vs. 554.66 N, P= .026) and distal (395.18 N vs. 526.51 N, P < .001) locations. Furthermore, 2 knots provided higher stiffness than 1 knot in both proximal (53.24 N/mm vs. 67.89 N/mm, P < .001) and distal (47.08 N/mm vs. 56.73 N/mm, P= .041) knot locations. However, using 2-0 suture showed no significant differences in failure load and stiffness regardless of knot location. Using #2 suture and tying 2 independent knots across the CSB increased load to failure and stiffness compared to using only 1 knot regardless of knot position. Thus, if using #2 suture, it is recommended to tie 2 knots to enhance construct strength. However, with 2-0 suture, the number of knots did not impact construct strength. Therefore, if using 2-0 suture, 1 knot can be used to save time. Knot position did not significantly affect the strength or stiffness of the CSB construct, emphasizing the importance of considering knot prominence and surgical approach for determining knot location.

Biomechanical Comparison of Coracoclavicular Fixation Using Metallic Versus All-Suture Anchors.

A coracoclavicular (CC) fixation technique using an all-suture anchor with the assistance of fluoroscopy can prevent iatrogenic anterior deltoid detachment from the clavicle; however, soft anchor pullout has been reported as a complication. To compare the biomechanical properties of conventional metallic and all-suture anchors for CC suture fixation. Controlled laboratory study. A total of 24 fresh-frozen cadaveric specimens were divided into 2 groups: metal anchor group (group M) and all-suture anchor group (group A). In group M, 5.0-mm metallic suture anchors were used for CC fixation, whereas 2.8-mm all-suture anchors were used in group A. The prepared specimens were mounted on a materials testing machine. After preconditioning at 0 to 20 N for 10 cycles, the specimens were subjected to cyclic loading from 20 to 70 N for 1000 cycles. Finally, all the specimens were loaded to failure. Cyclic elongation, linear stiffness, ultimate load, and failure modes were recorded, and the Mann-Whitney U test was used to compare nonparametric parameters between the 2 groups. All of the specimens completed the cyclic loading test. The elongation after cyclic loading in group M (1.6 ± 0.6 mm) was significantly smaller compared with that in group A (2.5 ± 1.2 mm) (P = .02). No between-group differences were found in linear stiffness (42 ± 17 N/mm in group M and 41 ± 17 N/mm in group A). The ultimate failure load in group M (263 ± 66 N) was significantly greater than that in group A (177 ± 76 N) (P = .02). All specimens failed because of suture anchor pullout. The use of all-suture anchors in CC fixation resulted in significantly greater cyclic displacement and smaller ultimate failure load than that of metallic anchors. Understanding the most biomechanically sound suture anchor may assist in lowering the risk of clinical failure in CC fixation and repair.

Conserved allosteric inhibitory site on the respiratory syncytial virus and human metapneumovirus RNA-dependent RNA polymerases

Respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) are related RNA viruses responsible for severe respiratory infections and resulting disease in infants, elderly, and immunocompromised adults1–3. Therapeutic small molecule inhibitors that bind to the RSV polymerase and inhibit viral replication are being developed, but their binding sites and molecular mechanisms of action remain largely unknown4. Here we report a conserved allosteric inhibitory site identified on the L polymerase proteins of RSV and HMPV that can be targeted by a dual-specificity, non-nucleoside inhibitor, termed MRK-1. Cryo-EM structures of the inhibitor in complexes with truncated RSV and full-length HMPV polymerase proteins provide a structural understanding of how MRK-1 is active against both viruses. Functional analyses indicate that MRK-1 inhibits conformational changes necessary for the polymerase to engage in RNA synthesis initiation and to transition into an elongation mode. Competition studies reveal that the MRK-1 binding pocket is distinct from that of a capping inhibitor with an overlapping resistance profile, suggesting that the polymerase conformation bound by MRK-1 may be distinct from that involved in mRNA capping. These findings should facilitate optimization of dual RSV and HMPV replication inhibitors and provide insights into the molecular mechanisms underlying their polymerase activities.

Crystal structure of a pre-chemistry viral RNA-dependent RNA polymerase suggests participation of two basic residues in catalysis.

The nucleic acid polymerase-catalyzed nucleotidyl transfer reaction associated with polymerase active site closure is a key step in the nucleotide addition cycle (NAC). Two proton transfer events can occur in such a nucleotidyl transfer: deprotonation of the priming nucleotide 3'-hydroxyl nucleophile and protonation of the pyrophosphate (PPi) leaving group. In viral RNA-dependent RNA polymerases (RdRPs), whether and how active site residues participate in this two-proton transfer reaction remained to be clarified. Here we report a 2.5 Å resolution crystal structure of enterovirus 71 (EV71) RdRP in a catalytically closed pre-chemistry conformation, with a proposed proton donor candidate K360 in close contact with the NTP γ-phosphate. Enzymology data reveal that K360 mutations not only reduce RdRP catalytic efficiency but also alter pH dependency profiles in both elongation and pre-elongation synthesis modes. Interestingly, mutations at R174, an RdRP-invariant residue in motif F, had similar effects with additional impact on the Michaelis constant of NTP (KM,NTP). However, direct participation in protonation was not evident for K360 or R174. Our data suggest that both K360 and R174 participate in nucleotidyl transfer, while their possible roles in acid-base or positional catalysis are discussed in comparison with other classes of nucleic acid polymerases.

Shank-localized cell wall growth contributes to Arabidopsis root hair elongation.

Root hairs are highly elongated tubular extensions of root epidermal cells with a plethora of physiological functions, particularly in establishing the root-rhizosphere interface. Anisotropic expansion of root hairs is generally thought to be exclusively mediated by tip growth-a highly controlled apically localized secretion of cell wall material-enriched vesicles that drives the extension of the apical dome. Here we show that tip growth is not the only mode of root hair elongation. We identified events of substantial shank-localized cell wall expansion along the polar growth axis of Arabidopsis root hairs using morphometric analysis with quantum dots. These regions expanded after in vivo immunolocalization using cell wall-directed antibodies and appeared as distinct bands that were devoid of cell wall labelling. Application of a novel click chemistry-enabled galactose analogue for pulse chase and real-time imaging allowed us to label xyloglucan, a major root hair glycan, and demonstrate its de novo deposition and enzymatic remodelling in these shank regions. Our data reveal a previously unknown aspect of root hair growth in which both tip- and shank-localized dynamic cell wall deposition and remodelling contribute to root hair elongation.

A Spring-Based Inductive Sensor for Soft and Flexible Robots

The development of flexible and soft robots generates new needs in terms of instrumentation, as large encountered deformations require highly stretchable strain sensors. In this regard, we contribute to the adoption of inductive sensors by providing tools to model and exploit them and showing their relevance experimentally. First, strain estimation based on voltage measurement is proposed. Compared to direct inductance evaluation, the principle is easier to implement and opens the possibility to optimize the measurement performances by tuning the circuit components and interrogation frequency. The possibility of performing a single sensor calibration independently via the elongation mode during strain sensing is outlined. A detailed characterization is then performed, which shows that the sensor produces a low hysteresis of 0.1%, a precision in the order of 0.14%, and an accuracy of 0.9%. Finally, two proofs of concept are proposed: 1) the integration with a pneumatic artificial muscle (PAM) that demonstrates the added value of the sensor for a model-free precise control of a soft system and 2) the closed-loop control of a flexible bending manipulator using the inductive sensor. The performance in the closed-loop control is demonstrated, with a sensing element that is easy to integrate mechanically, strengthening its potential to be used as a structural element as well.

Geomorphology of sand dunes in the Taklamakan Desert based on ERA5 reanalysis data

The characteristics of the wind regime and the development of dune morphology in the Taklamakan Desert have been the focus of scholars. In this study, we used ERA5 reanalysis wind data at a height of 10 m from 1979 to 2019 to examine the sand transport and wind regime characteristics of the entire Taklamakan Desert. We combined the two latest dune development modes, i.e., bed instability and elongation modes, and determined that: (1) Taklamakan Desert is overall characterized by a lower wind energy environment; the wind and sand activity intensities are highest in the eastern part of the desert, with a decreasing trend from the east to the west. The wind direction in the eastern region shows unimodal characteristics due to the backward easterly wind; the wind regime gradually becomes complicated from the northeast to the southwest; (2) the morphological alignments of dunes can be predicted by such modern wind regimes combined with the latest dune development modes. Large longitudinal dunes in the middle of the desert can be predicted with the elongation mode, whereas secondary transverse dunes, which derive from these composite dunes, can be predicted using the bed instability mode. Collectively, this paper fills the gap of the lack of uniform and standardized macro-scale wind data in the Taklamakan Desert, and the two modes of dune development derived from ERA5 reanalysis data can match the morphology and trend of most modern dunes.

Insight into the mechanism of DNA synthesis by human terminal deoxynucleotidyltransferase.

Terminal deoxynucleotidyltransferase (TdT) is a member of the DNA polymerase X family that is responsible for random addition of nucleotides to single-stranded DNA. We present investigation into the role of metal ions and specific interactions of dNTP with active-site amino acid residues in the mechanisms underlying the recognition of nucleoside triphosphates by human TdT under pre-steady-state conditions. In the elongation mode, the ratios of translocation and dissociation rate constants, as well as the catalytic rate constant were dependent on the nature of the nucleobase. Preferences of TdT in dNTP incorporation were researched by molecular dynamics simulations of complexes of TdT with a primer and dNTP or with the elongated primer. Purine nucleotides lost the "summarised" H-bonding network after the attachment of the nucleotide to the primer, whereas pyrimidine nucleotides increased the number and relative lifetime of H-bonds in the post-catalytic complex. The effect of divalent metal ions on the primer elongation revealed that Me&lt;sup&gt;2+&lt;/sup&gt; cofactor can significantly change parameters of the primer elongation by strongly affecting the rate of nucleotide attachment and the polymerisation mode.

Elongatable Gripper Fingers With Integrated Stretchable Tactile Sensors for Underactuated Grasping and Dexterous Manipulation

The ability to grasp a wider range of objects in size and shape directly relates to the performance of robotic grippers. Adapting to complex geometries of objects requires large degrees of freedom to allow complex configurations. However, complexity in controlling many individual joints leads to introduction of underactuated mechanisms, in which traditional finger designs composed of revolute joints allow only flexion/extension motions. In this article, we propose a length-adjustable linkage mechanism in the underactuated finger controlled by an antagonistic tendon pair. The resulting gripper can elongate the fingers for an increased task space or shorten them for a finer spatial resolution. For tactile sensing, hyperelastic soft sensors are used to stretch with finger elongation. Contact pressures measured by the soft sensors are used in force-feedback control for which either the joint angles or the link lengths are adjusted. Lastly, a multimodal control scheme that combines elongation and flexion modes is demonstrated with tasks of dexterous manipulation.

Variability in fluvially‐dominated, fine‐grained, shallow‐water deltas

AbstractFluvially‐dominated, fine‐grained, shallow‐water deltas are more variable than is generally recognized. Studies of the Mississippi River imply rather persistent river‐mouth jet dynamics, resulting in either progressive channel bifurcation around middle‐ground mouth bars on lobate deltas, or steady channel progradation to form elongate deltas akin to the modern Mississippi Delta. By contrast, satellite imagery and historical maps of less well‐known fluvially‐dominated deltas show diverse river‐mouth deposits, with plan‐form shapes ranging from river‐mouth fans, through splay, triangular, frond and tongue‐shaped mouth bars, to elongate channels with prominent subaqueous levées. Critically, such deposits may vary along individual channels and across or between individual lobes suggesting that jet variability can be normal, and that a spectrum of jets forms a suite of stable river‐mouth deposits. Channel elongation can also be common. In addition to high‐inertia jets and delta‐head or backwater‐mediated avulsion, two further mechanisms are recognized to form elongate channels. Following channel splitting, dominant splits can shoulder aside mouth bars, so that subordinate splits wither and dominant splits extend the parent channel. Alternatively, river‐mouth fans, subordinate distributary networks and lobes may be abandoned, so that a dominant parent distributary is rejuvenated by receiving an increase in discharge, allowing progradation to continue. Individual real‐world deltas are expected to be characterized by a range of river‐mouth deposits, both laterally and over time. However, such variable river‐mouth deposits, and different modes of channel elongation, are not generally considered in models of fluvially‐dominated deltas – omissions that may have significant impact for land remediation projects on modern deltas, and descriptions of the subsurface constructed to aid resource extraction.

A phylogenetic assessment of Endocalyx (Cainiaceae, Xylariales) with E. grossus comb. et stat. nov.

The phylogenetic affinities of four representative Endocalyx taxa at the species and variety levels are studied based on materials collected on different palm hosts in Japan and the states of Hawaii and Texas, USA. They include specimens and their isolates belonging to E. cinctus, E. indumentum, E. melanoxanthus var. grossus, and E. melanoxanthus var. melanoxanthus. Phylogenetic analyses of nuclear ribosomal DNA sequence data (ITS-LSU nrDNA) confirmed that Endocalyx belongs to the order Xylariales (Sordariomycetes) where all species and varieties treated form a strongly supported monophyletic lineage within the family Cainiaceae. They were also phylogenetically well resolved and consistent with their morphological and ecological circumscription. Species status is proposed for E. melanoxanthus var. grossus under the name E. grossus comb. et stat. nov. on the basis of its distinct morphological, molecular, cultural, and ecological characteristics. The putative placement of Endocalyx within the family Apiosporaceae (Amphisphaeriales), based on the presence of basauxic conidiophores, is rejected considering that all species treated clustered within the distant Cainiaceae (Xylariales). This characteristic mode of conidiophore elongation is determined to have evolved independently within distantly related ascomycetous lineages. Novel morphological and cultural features of Endocalyx taxa based on new isolates are described and commented. The recently described E. metroxyli is reduced to a synonym with E. melanoxanthus.

Elaboration and characterization of ferroelectric materials Sr2(1-x)Na(1+x)GdxNb5O15 synthesized by solid process

The solid solutions Sr2(1-x)Na(1+x)GdxNb5O15 (SNGN) with substitution rates of Sr2+ by Gd3+ varying between 0 and 1 were prepared and have undergone several heat treatments. The XRD spectra show that the powders calcined at 650 °C for 6 h exhibit a mixed structure consisting of orthorhombic-quadratic phases. On the other hand, calcination at 1200 °C for 12 h ensures complete crystallization of the SNGN compounds in the TTB structure of quadratic symmetry. The SEM images show grains of regular and spherical shapes. The Raman spectra of the solid SNGN solution calcined at 1200 °C (x = 0; 0.2; 0.4 and 0.6), show two broad bands attributed to the transverse deformation modes of the O-Nb-O bond and of elongation modes of the Nb-O bond of octahedra (NbO6). IR spectroscopy highlights the existence of absorption bands corresponding to the elongation and deformation vibrations of some bonds. The temperature measurements of the dielectric permittivity εr of the ceramic (SNN; x = 0) show for all the frequencies used, the presence of a narrow peak during the heating and the cooling phases with a maximum located respectively at the Curie temperature Tc ∼ 235.07 °C and Tc ∼ 224.84 °C. The dielectric losses tan (δ) values are very weak in the ferroelectric phase (T < Tc), then an increase, which reaches 2.3 for the lowest frequency, occurs in the paraelectric phase. The maximum permittivity ε'rmax undergoes a decrease as the frequency increases; this diffusive behavior can be associated to the domains walls in the micro-domains of the ferroelectric phase.

Helium effects on tensile properties of powder metallurgical-processed tungsten for fusion reactor applications

• Effects of He concentration on tensile properties of SR-W were clarified. • Suppression of recovery and recrystallization by He caused the mechanical properties. Powder metallurgical processing of Tungsten (W) followed by thermomechanical treatment, including rolling and stress relief (SR) heat treatment, is a candidate fabrication process for W materials for fusion applications. Helium (He) is insoluble in almost all metals, and grain boundary embrittlement occurs on the accumulation of He on their grain boundaries. In this study, the effects of He concentration, test temperature, and strain rate on the mechanical properties of SR-W were investigated using tensile tests. The He effects were studied by the uniform implantation of high-energy He-ions into specimens by cyclotron accelerator irradiation and by tensile tests from 300 °C to 1300 °C. The examined He concentration was below 20 appm. Vickers hardness tests on an isochronal annealed specimen up to 1500 °C showed that the threshold concentration of He for suppressing the recovery and recrystallization of the microstructure of SR-W by annealing was between 2 and 20 appm. The tensile test showed a slight increase in the ultimate tensile strength (UTS) at He concentrations up to 20 appm; however, no clear effect on the elongation or fracture mode was observed. The results of the tensile test conducted at 1300 °C on a 20-appm He-implanted specimen showed that its softening and ductility by recrystallization were suppressed; however, there was no observation of grain boundary embrittlement by He implantation. The results suggest that the mechanism of the mechanical response of He-implanted SR-W was He suppression of the recovery and recrystallization of the layered structure unique to SR-W up to 1500 °C. Moreover, at the level of He concentration introduced by nuclear transmutation in the divertor of a fusion reactor without displacement damage, no severe effect occurred to promote the embrittlement of SR-W.

Biomechanical Comparison of 2 Patellar Fixation Techniques in Medial Patellofemoral Ligament Reconstruction: Transosseous Sutures vs Suture Anchors.

Background:Multiple techniques for fixing a graft to the patella in medial patellofemoral ligament (MPFL) reconstruction have been described; however, no single technique has been shown to be superior to another.Purpose/Hypothesis:The purpose of this study was to compare the biomechanical performance of 2 different patellar fixation techniques: suture anchor (SA) and transosseous suture (TS) fixation. The hypothesis was that there would be no significant differences between the groups in ultimate failure load, stiffness, or elongation.Study Design:Controlled laboratory study.Methods:In this study, a new TS technique was biomechanically compared with the SA technique for MPFL reconstruction using 24 fresh-frozen mature porcine patellae and porcine flexor profundus tendons. The specimens were randomized into 2 groups undergoing MPFL reconstruction using either the SA technique or the TS technique (n = 12 per group). Fixation with TS was completed using 3 No. 2 UltraBraid sutures and three 2-mm transosseous tunnels. SA reconstruction was completed using 2 parallel 3.5-mm titanium SAs with 2 No. 2 UltraBraid sutures. We preconditioned each graft using a force between 5 and 20 N before cyclic loading. Then, the specimens were biomechanically tested (1000 cycles; 5-100 N; 1 Hz) and loaded under tension at 200 mm/min until failure. The ultimate failure load, stiffness, elongation, and failure mode were recorded for each specimen. The Shapiro-Wilk test and independent t tests were used to assess the data.Results:The TS technique resulted in a significantly higher mean failure load than did the SA technique (496.18 ± 93.15 vs 399.43 ± 105.35 N; P = .03). The TS technique resulted in less stiffness than did the SA technique (55.42 ± 7.92 vs 72.11 ± 10.64 N/mm; P < .01). There was no significant difference between the groups in elongation. None of the graft fixation/patellar complexes failed during cyclic testing in either group. During the load-to-failure test, the most common mode of failure in the SA group was an anchor being pulled out of the bone, whereas that in the TS group was rupture of the suture material.Conclusion:MPFL reconstruction with 3 TSs provided a higher load to failure than did the commonly used fixation method involving SAs.

Three-dimensional migration of human amniotic fluid stem cells involves mesenchymal and amoeboid modes and is regulated by mTORC1.

Three‐dimensional (3D) cell migration is an integral part of many physiologic processes. Although being well studied in the context of adult tissue homeostasis and cancer development, remarkably little is known about the invasive behavior of human stem cells. Using two different kinds of invasion assays, this study aimed at investigating and characterizing the 3D migratory capacity of human amniotic fluid stem cells (hAFSCs), a well‐established fetal stem cell type. Eight hAFSC lines were found to harbor pronounced potential to penetrate basement membrane (BM)‐like matrices. Morphological examination and inhibitor approaches revealed that 3D migration of hAFSCs involves both the matrix metalloprotease‐dependent mesenchymal, elongated mode and the Rho‐associated protein kinase‐dependent amoeboid, round mode. Moreover, hAFSCs could be shown to harbor transendothelial migration capacity and to exhibit a motility‐associated marker expression pattern. Finally, the potential to cross extracellular matrix was found to be induced by mTORC1‐activating growth factors and reduced by blocking mTORC1 activity. Taken together, this report provides the first demonstration that human stem cells exhibit mTORC1‐dependent invasive capacity and can concurrently make use of mesenchymal and amoeboid 3D cell migration modes, which represents an important step toward the full biological characterization of fetal human stem cells with relevance to both developmental research and stem cell‐based therapy.

Thermosetting supramolecular polymerization of compartmentalized DNA fibers with stereo sequence and length control

Thermosetting supramolecular polymerization of compartmentalized DNA fibers with stereo sequence and length control