In-plane Deformation Research Articles

In-Plane Cyclic Mechanical Properties of CF/PEEK/TPU Flexible Composite with Zero Poisson Ratio

This paper presents the in-plane deformation and cyclic mechanical properties of CF/PEEK (Carbon Fiber-Reinforced Polyetheretherketone)-reinforced TPU (thermoplastic polyurethanes) flexible composites with a zero Poisson ratio. A novel CF/PEEK honeycomb reinforcement with a zero Poisson ratio was fabricated by using 3D-printing technology. Then, TPU was bonded in the two sides of the CF/PEEK honeycomb reinforcement. The in-plane deformation ability and cyclic mechanical properties were evaluated. The results show that the zero Poisson ratio flexible composite can achieve a large in-plane plastic deformation of more than 50% and can better maintain the zero Poisson ratio superstructure. By collecting and comparing the mechanical characteristic values of the CF/PEEK flexible composite under a cyclic load, the CF/PEEK flexible composite MH22-t0.6-CT has the best structural stability. The length of the structure was increased by about 12.53%. By studying the deformation mechanism and failure mechanisms of the flexible composites, the in-plane recyclability of the flexible composites was evaluated, which provides the basic research basis for large-scale in-plane deformation composites.

Ultrafast Time-Domain Spectroscopy Reveals Coherent Vibronic Couplings upon Electronic Excitation in Crystalline Organic Thin Films.

The coherent coupling between electronic excitations and vibrational modes of molecules largely affects the optical and charge transport properties of organic semiconductors and molecular solids. To analyze these couplings by means of ultrafast spectroscopy, highly ordered crystalline films with large domains are particularly suitable because the domains can be addressed individually, hence allowing azimuthal polarization-resolved measurements. Impressive examples of this are highly ordered crystalline thin films of perfluoropentacene (PFP) molecules, which adopt different molecular orientations on different alkali halide substrates. Here, we report polarization-resolved time-domain vibrational spectroscopy with 10 fs time resolution and Raman spectroscopy of crystalline PFP thin films grown on NaF(100) and KCl(100) substrates. Coherent oscillations in the time-resolved spectra reveal vibronic coupling to a high-frequency, 25 fs, in-plane deformation mode that is insensitive to the optical polarization, while the coupling to a lower-frequency, 85 fs, out-of-plane ring bending mode depends significantly on the crystalline and molecular orientation. Comparison with calculated Raman spectra of isolated PFP molecules in vacuo supports this interpretation and indicates a dominant role of solid-state effects in the vibronic properties of these materials. Our results represent a first step toward uncovering the role of anisotropic vibronic couplings for singlet fission processes in crystalline molecular thin films.

Long-term functional outcomes of BIFOLD osteosynthesis in distal femoral fractures with metaphyseal comminution: A retrospective analysis

BackgroundThis retrospective study aimed to evaluate the long-term functional outcomes of BIFOLD osteosynthesis, employing retrograde nailing and distal femoral locked plating, in patients with distal femoral fractures and metaphyseal comminution. MethodsA retrospective analysis was conducted on patients treated for distal femur fractures with metaphyseal comminution between 2012 and 2022, with a minimum follow-up of 2 years. Inclusion criteria encompassed distal femur fractures with metaphyseal comminution, excluding specific conditions. BIFOLD osteosynthesis was employed in all 33 cases, utilizing retrograde SIGN (Surgical Implant Generation Network Nail) and distal femoral locking plates. Primary outcome measures included radiographic and functional outcomes assessed through the Sanders functional evaluation score, with secondary outcomes focusing on perioperative or postoperative complications. ResultsA total of 33 patients (21 male, 12 female) were included, with an average age of 51.4 years. BIFOLD osteosynthesis exhibited an average radiographic fracture healing time of 6.2 ± 2.5 months. The procedure's average operative time was 100 ± 15 min, and blood loss averaged 420 ± 50 ml. According to Sanders criteria, 28 patients (84.84 %) demonstrated well-to-excellent functional outcomes, while 3 patients (9.09 %) reported fair outcomes, and 2 patients (6.06 %) reported poor outcomes. No significant shortening or implant failure occurred, and all patients achieved over 90 degrees of knee range of motion within 8 weeks. One patient experienced superficial infection, and two patients exhibited insignificant coronal plane deformity. ConclusionBIFOLD osteosynthesis, combining intra and extra medullary fixation principles, offers a stable construct for distal femoral fractures with metaphyseal comminution. This approach facilitates faster ambulation, pain relief, early knee joint mobilization, and significant early union, resulting in improved functional outcomes. Additionally, BIFOLD osteosynthesis helps prevent collapse, translational and rotational deformities, as well as shortening.

Rapid monitoring of structural deformation based on unsupervised segmentation model

This paper presents a novel approach for rapid structural deformation monitoring using an enhanced segmentation model, SAM-DM (Segment Anything Model-Deformation Monitoring). The method enhances the SAM model by integrating an innovative point prompt generation technique, image fusion, and connected domain analysis, enabling structural deformation monitoring with just a single manual click on the target area in the initial video frame. Specifically, this manual click generates coordinate information for the target area, serving as a point prompt for the SAM-DM model. This process results in the creation of a high-quality binary mask, which is then fused with the original image to isolate only the target area. Subsequently, connected domain analysis is employed to automatically process the mask, extracting the pixel centroid coordinates of the target area, which are then used as prompts for segmenting subsequent frames. This approach allows continuous tracking of changes in the target area's coordinates, thereby facilitating rapid structural deformation monitoring. Experimental results demonstrate that this method can accurately monitor deformation across all target points and adapt to varying lighting conditions and noise levels. Applied to monitor the bending deformation of reinforced concrete beams and the in-plane deformation of concrete slabs, the method achieves results closely aligned with actual measurements, yielding relative errors of 0.95 % and 0.48 %, respectively. Additionally, in monitoring the vibrational deformation of steel frames, the primary frequency of the curve precisely matches measured values, confirming that the SAM-DM-based method delivers both high accuracy and strong robustness.

Surgical Management for Boutonniere Disease

Boutonniere disease is a hand injury causing extension lag or restriction in the proximal interphalangeal joint and hyperextension in the distal interphalangeal joint. This condition often arises from direct laceration or closure damage to the central tendon, rheumatoid arthritis, osteoarthritis, Dupuytren contracture, pulley injury, burns, and other conditions. Surgical management for Boutonniere deformity relies on the expertise of the attending physician and involves both non-surgical and surgical options. In acute cases, conservative therapy should be pursued, while in chronic cases, conservative management may be advised. Surgical intervention is used to transform excessive extension force of the distal interphalangeal joint into extension force of the proximal interphalangeal joint. This is necessary to heal an open rupture of the central tendon. Surgical techniques for chronic deformity are complex due to variables and hand surgeons' expertise. There is no definitive surgical therapy for persistent buttonhole deformity, but several approaches have been documented in case studies. These include terminal tenotomy, collateral band surgery, central tendon surgery, tendon transfer and grafting, stepwise extension mechanism readjustment surgery, and arthrodesis. Central tendon surgery addresses the central tendon, where injured tissue transforms into scar tissue, resulting in delayed extension of the proximal interphalangeal joint. Tendon transfer or grafting have been documented for rotator cuff mechanism rehabilitation, but no definitive guidance exists for these techniques. Curtis treatment introduced a sequential therapy approach for traumatic buttonhole deformity, which involves splinting, excising the transverse reticular ligament, resecting and lengthening the collateral ligament, and repositioning the core tendon. Arthrodesis may be applicable in cases of advanced arthritis, coronal plane deformity, functional impairment, or elderly patients. There are no definitive indications for surgical interventions for persistent buttonhole deformity, and outcomes may be variable or inferior. Understanding the deformity, its progression, and patient's functional constraints is crucial for effective treatment

Biomimetic Modular Honeycomb with Enhanced Crushing Strength and Flexible Customizability.

The integration of biomimetic principles into the sophisticated design of honeycomb structures has gained significant traction. Inspired by the natural reinforcement mechanisms observed in tree stems, this research introduces localized thickening to the conventional honeycombs, leading to the development of variable-density honeycomb blocks. These blocks are strategically configured to form modular honeycombs. Initially, the methodology for calculating the relative density of the new design is meticulously detailed. Following this, a numerical model based on the plastic limit theorem, verified experimentally, is used to investigate the in-plane deformation models of modular honeycomb under the low- and high-velocity impact and to establish a theoretical framework for compressive strength. The results confirm that the theoretical predictions for crushing strength in the modular honeycomb align closely with numerical findings across both low- and high-velocity impacts. Further investigation into densification strain, energy absorption, and gradient strategy is conducted using both simulation and experimental approaches. The outcomes indicate that the innovative design outperforms conventional honeycombs by significantly enhancing the crushing strength under low-velocity impacts through the judicious arrangement of honeycomb blocks. Additionally, with a negligible difference in densification strains, the modular honeycomb demonstrates superior energy dissipation capabilities compared to its conventional counterparts. At a strain of 0.85, the modular honeycomb's energy absorption capacity improves by 36.68% at 1 m/s and 25.47% at 10 m/s compared to the conventional honeycomb. By meticulously engineering the arrangement of sub-honeycombs, it is possible to develop a modular honeycomb that exhibits a multi-plateau stress response under uniaxial and biaxial compression. These advancements are particularly beneficial to the development of auto crash absorption systems, high-end product transportation packaging, and personalized protective gear.

Solution and Surface Solvation of Nitrate Anions with Iron(III) and Aluminum(III) in Aqueous Environments: A Raman and Vibrational Sum Frequency Generation Study.

Hydrated trivalent metal nitrate salts, Fe(NO3)3·9H2O and Al(NO3)3·9H2O, in both solid and aqueous phases are investigated. Raman and surface-selective vibrational sum frequency generation (SFG) spectroscopy, are used to shed light on ion-ion interactions and hydration in several spectral regions spanning low frequency (440-550 cm-1) to higher frequency modes of nitrate and water (720, 1050, 1250-1450, and 2800-3750 cm-1). These frequencies span the metal-water mode, nitrate in-plane deformation, nitrate symmetric and asymmetric modes, and the OH stretch of condensed phase water molecules. Comparison to NaNO3, and in some cases KNO3, is also shown, providing insight. Splitting and frequency shifts are observed and discussed for both the solid state and solution phase. The Lewis acidity of Fe3+ and Al3+ ions plays a significant role in the observed spectra, in particular for the nitrate asymmetric band splitting and frequency shift. The spectral response from water solvation for iron and aluminum nitrates is nonlinear as compared to linear for sodium nitrate, suggesting significantly different solvation environments that are limited by water hydration capacity at higher concentrations. Moreover, a non-hydrogen bonded OH, dangling OH, from hydrating water molecules is observed spectroscopically for Al and Fe nitrate solutions. Furthermore, aluminum nitrate perturbs the surface water structure more than iron nitrate despite aluminum being a weaker Lewis acid. The surface water structure is thus found to be unique for the Al(NO3)3 solutions as compared to both Fe(NO3)3 and NaNO3, such that surface solvation is more pronounced. This observation exemplifies the nature of the Fe(III) and Al(III) ions and their substantial influence on the surface water structure.

Noble gases in shocked igneous rocks from the 380 Ma-old Siljan impact structure (Sweden): A search for paleo-atmospheric signatures

Finding direct records of the ancient Earth's atmosphere is key to understand the evolution of the entire planet. Nevertheless, such records are scarce, and only a few geological samples with preserved paleo-atmospheric signatures are available today. In this study, we analyzed noble gases contained in shocked granitic and volcanic rocks collected across the 380 Ma-old Siljan impact structure (in Sweden) to investigate the potential of shocked quartz crystals with planar deformation features (PDFs), often decorated by fluid inclusions, to preserve atmospheric signatures.Our results reveal that most of the investigated samples show relative elemental abundances of noble gases falling between those of air and meteoric water values. Atmospheric gases are present in the samples but excesses in radiogenic, nucleogenic, and fissiogenic noble gas isotopes highlight interactions of fluids with crustal rocks during the impact-generated hydrothermal circulation of fluids after the impact. Such fluid circulation event(s) could also have remobilized older fluids originally present in fluid inclusions preserved in the mineral lattices. Furthermore, results obtained on the two pure quartz fractions highlight a stronger atmospheric signature correlated with the presence of PDFs. The atmospheric component detected in this study could represent either a paleo-atmospheric signature trapped shortly after the Siljan impact event, or it may result from modern atmospheric contamination. Future studies of noble gases contained within shocked quartz crystals from other impact structures will unveil if such samples present advantages compared to other paleo-atmospheric proxies.

Structural response of glass fiber-polymer composite bending-active elastica beam under long-term loading conditions

Bending-active elastica beams represent structural members which are initially installed as straight beams and then bent into arched shapes by applying horizontal displacements to one support. Designing such members for permanent structures made of fiber-polymer composites involves complex viscoelastic responses, which have not yet been thoroughly investigated. An experimental investigation of medium-scale bending-active elastica beams, consisting of pultruded glass fiber-polymer composite profiles, was thus conducted to investigate the long-term structural behavior of such members under imposed sustained bending and axial compression. The results revealed that viscoelastic responses are based on an interaction of stress relaxation and creep with their effects increased with increasing bending degree and time of exposure to sustained strains and stresses. The imposed horizontal displacement to one of the supports to maintain the bent beam shape induced sustained bending stresses in the beam. Beneficial relaxation of these stresses occurred with relaxation predicted to reach 12 % during a targeted 50-year design service life. Furthermore, the likelihood of the curved beam exhibiting in-plane deformations under sustained stresses enabled creep to occur simultaneously, with associated in-plane creep deformations and strength reduction. While creep deformations remained insignificant, progressive creep rupture occurred at highest bending degrees, exhibiting sequential creep rupture in the outer combined mat layers, delamination, crack opening and final fiber failure. Creep rupture can be prevented by postponing crack initiation in the combined mat layer beyond the targeted design service life. This can be achieved by limiting the bending degree to 50 % of the bending degree at which short-term crack initiation occurs.

Detorsional guided growth — modern concepts and perspectives of clinical application: a review

Background. Torsional deformities of the long bones in children are usually treated using correcting detorsional osteotomies with different types of osteosynthesis. However, this method is highly traumatic and can cause severe complications. Guided growth is the gold standard for frontal and sagittal planes deformities treatment in growing children. The technique is effective, minimally invasive, enables early weight-bearing and has lower complication rate. Recently, application of guided growth technique has been actively studied for horizontal plane deformities correction as well. The aim of the review — based on a scientific literature analysis, to present possibilities of using guided growth technique for correcting torsional deformities of the long bones, as well as to define the ways of its improvement for further clinical application. Methods. The search was performed in PubMed/MEDLINE, Google Scholar and eLIBRARY databases. For review, we included 8 articles (five animal experimental studies and three clinical studies), which were published from 2013 to 2023. Results. Analyzed studies demonstrated the possibility of applying detorsional guided growth for horizontal plane deformities correction in growing children. Three main surgical techniques were suggested. Correction efficiency mainly depends on the interplate angle, proper plate positioning and longitudinal growth potential. Limitations of these studies were: a small group number; absence of preoperative CT scans in animal studies; torsional profile measurement using computed tomography was performed only in one of three clinical studies. There was also no preoperative planning of deformity correction/creation amount, so it was not possible to evaluate the accuracy of the suggested methods. The main complications were secondary deformities and limb length discrepancy. Conclusions. Further clinical application of detorsional guided growth in children may be possible after solving the problem of secondary deformities and shortening and providing preoperative planning of the deformity correction amount.

Iterative Method of Determining Stress Intensity Coefficients Under Dynamic Loading of the Crack System

An elastic isotropic body in a state of plane deformation, which contains a system of randomly placed cracks under the action of a dynamic (harmonic) loading, is considered. The authors set the problem of determining the stress field around the cracks under the conditions of their wave interaction. The solution method is based on the introduction of displacements in the body in the form of a superposition of discontinuous solutions of the equations of motion constructed for each crack. With this in mind, the initial problem is reduced to a system of singular integro-differential equations with respect to unknown displacement jumps on the crack surfaces. To solve this system, a new iterative method, which involves solving a set of independent integro-differential equations that differ only in their right-hand parts at each iteration, is proposed. For the zero approximation, solutions that correspond to individual cracks under the action of dynamic loading are chosen. Such a new approach allows to avoid the difficulties associated with the need to solve systems of integro-differential equations of large dimensions that arise when traditional methods are used. Based on the results of the iterations, formulas for calculating the stress intensity coefficients for each crack were obtained. In the partial case of four cracks, a good agreement between the results obtained during the direct solution of the system of eight integro-differential equations by the mechanical quadrature method and the results obtained by the iterative method was established. In general, numerical examples demonstrate the convergence and stability of the proposed method in the case of systems with a fairly large number of densely located cracks. The influence of the interaction between cracks on the stress intensity factor (SIF) value under dynamic loading conditions was studied. An important and new result for fracture mechanics is the detection of the absolute maximum of the normal stresses at certain frequencies of the oscillating normal loading. The number of interacting cracks and the configuration of the crack system itself affect the values of the frequencies at which SIF reaches a maximum and the maximum values. These maximum values significantly (by several times) exceed the SIF values of single cracks under a similar loading. At the same time, under conditions of static or low-frequency loading, it is possible to reduce the SIF values compared to the SIF for individual cracks. When cracks are sheared, the values of the tangential stresses have a tendency to decrease with increasing frequency, and their values do not significantly differ from the values of the tangential stress for an individual crack.

Medial open wedge osteotomy yields comparable stability to lateral open wedge procedure on the distal femur.

Supracondylar osteotomies are a frequently and successfully used technique in the treatment of coronal plane deformities and unicompartmental osteoarthritis of the knee. While lateral open wedge techniques are common for valgus deformities, the data about medial open wedge techniques for varus deformities is sparse. The aim of this study was to compare the biomechanical properties of medial and lateral open wedge osteotomies using a locking Tomofix® plate (DePuy Synthes, Oberdorf, Switzerland). Our hypothesis was that there would be no difference regarding biomechanical outcome parameters between these two groups. Medial and lateral open wedge osteotomies were performed in composite bone model as routine. Each experimental group contained 6 constructs. Standardized osteotomy gaps of ten millimeters were performed and Tomofix® plates were fixed to third generation composite bones. The constructs were subsequently mounted into a servohydraulic testing machine. Axial and torsional loadings were applied as described in previous experimental studies. All specimens were subject to a load to failure mode with the mechanism of failure being noted. Both experimental groups showed comparable biomechanical properties under axial and torsional loadings. Mean high force axial stiffness was 3772 N/mm for lateral and 4185 N/mm for the medial construct. Significant differences were noted for torsional stiffness under low- (0 N) and mid-force (150 N) loadings (P = 0.002; P = 0.009), favoring the medial open wedge constructs. Medial open wedge osteotomy yields comparable biomechanical stability to the lateral open wedge procedure on the distal femur in a composite bone model.

A hyperelastic model considering the coupling of shear-compression for the forming simulation of 3D orthogonal composite preforms

The shear-compression coupling phenomenon is vital in the forming process of complex 3D woven composite components, but has not been effectively considered in existing macroscopic material models. A hyperelastic material model considering shear-compression coupling is developed here. Firstly, in-plane shear tests on pre-compressed specimens and compression tests on pre-sheared specimens were carried out, respectively. The results show that pre-compression can hinder and promote the in-plane shear deformation before and after shear locking occurs in the fabric, respectively. In-plane shear can contribute to compression. Then, a nonlinear hyperelastic constitutive model is presented and implemented in an Abaqus/Explicit user subroutine. Finally, a simulation study of the hemispherical forming of 3D orthogonal woven fabric was conducted using this model. The simulation results considering shear-compression coupling show more accurate in-plane shear angles and edge shapes compared to those without considering coupling. Moreover, since the shear-compression coupling is considered, the friction between the fabric and the tool needs to be reasonably discussed in the moulding simulation.

Buckling of planar curved beams with finite prebuckling deformation

The serpentine structure with a sufficiently thick cross section has recently been proposed as an important design concept in stretchable electronics, which features mechanically stable in-plane deformation mechanism and very low electrical resistance, bringing unique advantages for devices compared with the traditional thin ribbon layout. However, unduly increasing the thickness is well known to sacrifice the overall flexibility and functionality of devices. Such a contradiction leads to challenges in structural stability, as a relatively thick but insufficient serpentine structure may eventually undergo the out-of-plane buckling after significant in-plane prebuckling deformation and appreciable alterations in initial configuration, which is ignored by most conventional buckling theories (CBTs) and linear buckling analysis in commercial finite element analysis software, producing intolerable errors when predicting the critical loads. In this paper, a systematic and straightforward theory considering the finite prebuckling deformation (FPD buckling theory) is established to investigate the underlying mechanism. Two sets of governing equations related to the prebuckling and FPD buckling behavior are obtained. Four representative examples, including two classical problems of planar curved beams and two typical loading conditions of serpentine structures, have been carefully studied. Comparisons with the accurate geometrically-nonlinear-analysis-based (GNAB) buckling analysis have amply demonstrated the validity of our theory in predicting the reinforcement effect of prebuckling deformation on the buckling resistance of structures. Key dimensionless geometric parameters that govern this effect have also been identified, providing direct and effective guidance for the design and optimization of stretchable electronic devices.

Influence of hydrogen on deformation and embrittlement mechanisms in a high Mn austenitic steel: In-Situ neutron diffraction and diffraction line profile analysis

Austenitic steels have relatively high resistance to hydrogen embrittlement and play a critical role in hydrogen service applications. In particular, high Mn austenitic steels are considered economically viable alloy alternatives for these applications. The current study employed in-situ and ex-situ neutron diffraction techniques combined with diffraction line profile analysis (DLPA) to investigate the influence of hydrogen on deformation and embrittlement mechanisms in a high Mn (approximately 30 wt pct) austenitic steel. Investigation using both neutron diffraction and electron backscatter diffraction revealed the presence of extensive deformation twins and stacking faults within the steel microstructure after tensile deformation in the non-charged condition. These microstructural features suggest planar deformation behavior, which is expected from the relatively low stacking fault energy (SFE) of the alloy (approximately 29 mJ/m2). Hydrogen pre-charging resulted in apparent increases in both dislocations and stacking faults, contributing to macroscopic hardening and embrittlement mechanisms. Overall, numerical parameters obtained through neutron DLPA were used to elucidate the underlying mechanisms associated with hydrogen effects on the mechanical behavior, i.e. macroscopic strengthening, strain hardening rate, and embrittlement.

Distal Tibial Dome Osteotomy With Ilizarov Fixation in Correction of Ankle Deformity Resulting From Malunited Ankle Fusion

Background: Distal tibial osteotomy is used in the treatment of ankle deformities. Many methods of fixation of this osteotomy were described, including plates, pins, and ilizarov. Dome osteotomy is a cylindrical osteotomy with no bone loss, with the axis of bone is rotated around the center of the circle. We conducted a case series of treatment of ankle deformity due to malunited ankle fusion with distal tibial dome osteotomy. Methods: Eight patients with a history of poliomyelitis with ankle deformity due to a malunited ankle fusion underwent distal tibial dome osteotomy with ilizarov fixation for deformity correction. Postoperative follow up was done up to 12 months postoperatively. We intended to follow up the union of the osteotomy, the axis of the limb, the external clinical appearance, and patient satisfaction. Results: Deformity correction was achieved in all patients regarding the clinical alignment, with no apparent clinical residual deformity in coronal, sagittal plane, or rotational deformity, the limb was cosmetically straight with a plantigrade foot satisfactory to the patients with improving quality of gait. The osteotomy fully united in all patients in a period of 8 to 11 weeks with an average of 9.3 weeks, after which frame was removed. No patient had nonunion or delayed union of the osteotomy. Three patients had pin tract infection during the period of the fixator which was treated by local dressings and antibiotics. Conclusion: Distal tibial focal dome osteotomy fixed by ilizarov is an effective treatment option in malunited ankle fusion deformities.

Analyzing the back-face deformation of curved UHMWPE composite laminate under high-speed impact

Ballistic protection extensively employs curved ultra-high-molecular-weight polyethylene (UHMWPE) laminates to conform to protective targets. However, ballistic tests have indicated that the curvature of laminates increases back-face deformation, diminishing ballistic performance, while the mechanism behind this curvature effect on back-face deformation remains unclear. In this paper, the back-face deformation of curved UHMWPE laminates, including apex displacement and the boundary of the deformation region, are systematically studied through numerical simulation and theoretical analysis. Firstly, a numerical model of curved UHMWPE laminates under the high-speed impact is established. The numerical results indicate that as the curvature increases, the deformation region becomes more concentrated, resulting in a larger apex displacement. Secondly, as the curvature increases from zero, the deformation mode of curved laminates changes from membrane stretching dominated to a combination of membrane stretching and bending. Finally, considering the change in the deformation mode, a theoretical analysis for the propagation of bending waves in an orthotropic curved plate is conducted to reveal the relationship between curvature and back-face deformation. The theoretical analysis shows that increasing curvature slows bending wave speed, reducing in-plane deformation region movement, thus increasing apex displacement. This study is expected to help design curved UHMWPE laminates with better ballistic performance.

The role of the interfaces and cross-links on the mechanical behavior of mineralized collagen fibrils. A numerical approach

Mechanical properties of bone tissue are highly dependent on its hierarchical structure. The presence of microcracks and diffuse damage in lamellar bone is correlated with the failure of the collagen-mineral interface in mineralized collagen fibrils (MCF). The main goal of this work is to evaluate the mechanical behavior of the interfaces and quantify the stiffness loss of the MCF associated with different failure mechanisms, under controlled in-plane displacement. Additionally, we aim to study the role of the cross-links on the fibril mechanical response, beyond the interface failure. Inter- and intra-microfibrilar cross-links are analyzed. In order to address the first issue, a detailed representative volume of the MCF is analyzed by means of the finite element method, under the assumption of plane strain and periodic boundary conditions. In this model the interfaces between constituents are modeled with an exponential cohesive law. Enzymatic cross-links, located at the molecular terminals connecting each 4D (D=67nm) staggered molecules, are represented by non-linear springs. Three in-plane controlled deformations are applied. The results of this work provide the anisotropic stiffness loss of the tissue involved in the different failure mechanisms at the nano-scale length. The initiation of microcracks and the presence of damage zones are compatible with the failure mechanisms observed at interfaces. Interface failure entails a progressive stiffness loss, bringing a non-linear behavior of bone. The strength obtained for the longitudinal maximum deformation is more than 20 times the transverse strength and 3.5 times the shear strength. The quantification of the reduction percentage in the elastic moduli and the shear stiffness when the fibril is damaged, has a potential application in improving failure criteria based on degradation of elastic constants. When longitudinal elongation is applied, the mechanical contribution of the cross-links in delaying the failure initiation of the interface is shown. Likewise, results of this work confirm the scarce influence of the cross-links in the strain range analyzed. Additionally, a three-dimensional numerical model of several microfibrils is defined with the aim of analyzing the mechanical relevance of inter- and intra-microfibrilar cross-links, beyond the interface failure. Results confirm that cross-links transfer the load when strain increases, being highlighted the mechanical competence of the trivalent cross-links.

Total ankle arthroplasty in valgus ankle osteoarthritis

The valgus total ankle replacement (TAR) presents a considerable challenge and tests the skill and ingenuity of even the most accomplished foot and ankle surgeon. Coronal plane deformity used to be considered a relative contra-indication for TAR, however with implant innovation and greater surgical understanding, the indications for TAR in deformity continue to expand. Success requires a bespoke approach to each patient to ensure that intra- and extraarticular deformities and imbalance are adequately addressed to avoid TAR failure. The overall goal in TAR surgery is achieving a well aligned and stable ankle with a well aligned and stable foot below. This article presents some of our strategies to achieve this when considering TAR in the valgus ankle.10.1016/j.fuspru.2024.08.002

Anterior Column Release: With Great Lordosis Comes Great Risk of Complications-A Case Series.

Retrospective review. We sought to characterize complications associated with anterior column release (ACR). Correction of positive sagittal imbalance was traditionally completed with anterior column grafts or posterior osteotomies. ACR is a minimally invasive technique for addressing sagittal plane deformity by restoring lumbar lordosis. We conducted a retrospective review of consecutive patients who underwent ACR in a prospectively kept database at a tertiary care academic center from January 2012 to December 2018. The prespecified complications were hardware failure (rod fracture, hardware loosening, or screw fracture), proximal junctional kyphosis, ipsilateral thigh numbness, ipsilateral femoral nerve weakness, arterial injury requiring blood transfusion, bowel injury, and abdominal pseudohernia. Thirty-eight patients were identified. Thirty-five patients had ACR at L3-4, 1 had ACR at L4-5, and 1 patient had ACR at L2-3 and L3-4. Eighteen patients (47.4%) had one of the prespecified complications (10 patients had multiple). Ten patients developed hardware failure (26.3%); 8 patients (21.1%) had rod fracture, 4 (10.5%) had screw fracture, and 1 (2.6%) had screw loosening. At discharge, rates of ipsilateral thigh numbness (37.8%) and hip flexor (37.8%)/quadriceps weakness (29.7%) were the highest. At follow-up, 6 patients (16.2%) had ipsilateral anterolateral thigh numbness, 5 (13.5%) suffered from ipsilateral hip flexion weakness, and 3 patients (5.4%) from ipsilateral quadriceps weakness. Arterial injury occurred in 1 patient (2.7%). Abdominal pseudohernia occurred in 1 patient (2.7%). There were no bowel injuries observed. ACR is associated with a higher than initially anticipated risk of neurological complications, hardware failure, and proximal junctional kyphosis.