Joint Mechanics Research Articles

Study on Shear Slip Characteristics of Sandstone Plane Joints under Normal Dynamic Load Disturbance

Abstract Rock joints are susceptible to slip instability due to dynamic load disturbances such as blasting, earthquakes, and fracturation. A series of direct shear tests under the dynamic load were conducted on sandstone plane joints using the RDS-200xl. The work investigated the effects of normal static loads and normal dynamic-load frequencies and amplitudes on plane joints. Besides, the following items were proposed, that is, the peak-to-valley response rate, shear velocity vibration dominant frequency, shear-stress reduction coefficient, and discrete element numerical simulation method for plane-joint direct shear tests. The results were as follows: (1) The normal dynamic load frequency played a role in attenuating the shear stress amplitude with a threshold value of 0.5 Hz. (2) The shear velocity of the plane joint was completely controlled by the high normal dynamic load frequency. Their vibrational dominant frequencies were identical. (3) The amplitude of shear stress increased, and the median stress decreased with the increased normal dynamic load amplitude. The reduction-coefficient equation for sandstone plane joints was proposed to evaluate the shear stress under the normal dynamic load disturbance. (4) The shear-stress hysteresis phenomenon existed in the plane joints under the normal dynamic load, which required excessive shear displacements to reach peak shear strength. The peak shear displacement increased with the increased normal static load. Numerical simulations and indoor tests showed that high- and low-shear-velocity regions were the main reason for shear-stress hysteresis. The findings are conducive to revealing the shear destabilization mechanism of rock joints under dynamic load disturbance.

Two-stage low-carbon optimal dispatch of the power system considering demand response to defend large uncertainties and risks

Introduction: In order to promote the consumption of renewable energy, reduce carbon emissions, and take into account the uncertainty of renewable energy output and load fluctuations in the new power system that can affect the normal operation of market mechanism, a two-stage low-carbon optimization scheduling method for power system that considers demand response under multiple uncertainties is proposed in this paper.Methods: Uncertain scene sets are generated through Latin hypercube sampling and heuristic synchronous backpropagation method is used to reduce scenes to obtain typical scenes and their probabilities. Then, a one-stage optimization model is established with the goal of maximizing energy efficiency and corresponding demand response strategies are obtained. Green certificate carbon trading joint mechanism model consisting of tiered green certificate trading and time-sharing tiered carbon trading are established, and the output of two-stage units are optimized with the goal of minimizing comprehensive operating costs.Result: The simulation results show that the carbon emissions are decreased by 251.57 tons, the consumption rate of renewable energy is increased by 8.64%, and the total costs are decreased by 124.0612 million yuan.Discussion: From this, it can be seen that the dual layer low-carbon optimization scheduling strategy for power system considering demand response under multiple uncertainties can effectively reduce the operating costs and carbon emissions of the system, while balancing the economic and environmental aspects of power system operation.

A novel core-shell C/SiC bolt prepared by chemical vapor infiltration and its fiber strengthening mechanisms

Integrated manufacturing techniques have been extensively utilized to assemble thermal structural components made of continuous fiber reinforced silicon carbide composites (C/SiC) to fabricate large and complex components. The mechanical joint, always in terms of C/SiC bolts, become the weakest link in the components. Laminated C/SiC bolts have been invented to meet the requirements of the high temperature applications. Due to the low shear strengths of C/SiC, the threads are prone to be damaged. In order to fully employ the high tensile strength of carbon fibers, core-shell C/SiC bolt is proposed with the shell prepared by woven fiber architecture. Uniform circumferential microstructure of the threaded teeth has been obtained and the corresponding strength has been improved through fiber bridging mechanism. The results shows that the thread pull-off strength is 17.96% greater than that of the laminated thread tooth, and the stud tensile strength is slightly improved up to 2.96%. The stud shear strength is enhanced by 45.29% and 46.88% with unidirectional C/SiC rod and ZrO2 ceramic rod, respectively. The improvements are mainly caused by the fiber tension-shear coupling effects. Especially the introduction of unidirectional C/SiC rod improves the shear strength of the bolts by fully utilizing the fiber strengthening mechanisms under in-plane shear loading.

Mechanics of the foot and ankle joints during running using a multi-segment foot model compared with a single-segment model.

The primary purpose of this study was to compare the ankle joint mechanics, during the stance phase of running, computed with a multi-segment foot model (MULTI; three segments) with a traditional single segment foot model (SINGLE). Traditional ankle joint models define all bones between the ankle and metatarsophalangeal joints as a single rigid segment (SINGLE). However, this contrasts with the more complex structure and mobility of the human foot, recent studies of walking using more multiple-segment models of the human foot have highlighted the errors arising in ankle kinematics and kinetics by using an oversimplified model of the foot. This study sought to compare whether ankle joint kinematics and kinetics during running are similar when using a single segment foot model (SINGLE) and a multi-segment foot model (MULTI). Seven participants ran at 3.1 m/s while the positions of markers on the shank and foot were tracked and ground reaction forces were measured. Ankle joint kinematics, resultant joint moments, joint work, and instantaneous joint power were determined using both the SINGLE and MULTI models. Differences between the two models across the entire stance phase were tested using statistical parametric mapping. During the stance phase, MULTI produced ankle joint angles that were typically closer to neutral and angular velocities that were reduced compared with SINGLE. Instantaneous joint power (p<0.001) and joint work (p<0.001) during late stance were also reduced in MULTI compared with SINGLE demonstrating the importance of foot model topology in analyses of the ankle joint during running. This study has highlighted that considering the foot as a rigid segment from ankle to MTP joint produces poor estimates of the ankle joint kinematics and kinetics, which has important implications for understanding the role of the ankle joint in running.

The Influence of "Super-Shoes" and Foot Strike Pattern on Metabolic Cost and Joint Mechanics in Competitive Female Runners.

The objective of this study is to assess the influence of "super-shoes" on metabolic cost and joint mechanics in competitive female runners and to understand how foot strike pattern may influence the footwear effects. Eighteen competitive female runners ran four 5-min bouts on a force instrumented treadmill at 12.9 km·h -1 in 1) Nike Vaporfly Next% 2™ (SUPER) and 2) Nike Pegasus 38™ (CON) in a randomized and mirrored order. Metabolic power was improved by 4.2% ( P < 0.001; d = 0.43) and metatarsophalangeal (MTP) negative work ( P < 0.001; d = 1.22), ankle negative work ( P = 0.001; d = 0.67), and ankle positive work ( P < 0.001; d = 0.97) were all smaller when running in SUPER compared with CON. There was no correlation between foot strike pattern and the between-shoe (CON to SUPER) percentage change for metabolic power ( r = 0.093, P = 0.715). Metabolic power improved by 4.2% in "super-shoes" (but only by ~3.2% if controlling for shoe mass differences) in this cohort of competitive female runners, which is a smaller improvement than previously observed in men. The reduced mechanical demand at the MTP and ankle in "super-shoes" are consistent with previous literature and may explain or contribute to the metabolic improvements observed in "super-shoes"; however, foot strike pattern was not a moderating factor for the metabolic improvements of "super-shoes." Future studies should directly compare the metabolic response among different types of "super-shoes" between men and women.

Geometry Effects on Joint Strength and Failure Modes of Hybrid Aluminum-Composite Countersunk bolted Joints

This paper presents the effects of geometry parameters (width/hole diameter, and edge distance/hole diameter ratios) on the damage initiation and growth in the CFRP (Carbon Fiber Reinforced Polymer) composite-aluminum countersunk bolted joints. Strain gauge measurements conducted with an Instron testing machine along with a detailed 3D finite element model incorporating geometric, material, and friction-based contact nonlinearities were used to investigate the geometry parameters on the Progressive Damage Analysis (PDA) of the orthotropic material model. The PDA material model integrates the lamina nonlinear shear deformation, Hashin-type failure criteria, and strain-based continuum degradation rules, using the UMAT user subroutine in the MSC Software Corporation Patran-Nastran commercial software. The results showed that the geometry effects on damage initiation and failure modes are quite accurately predicted by the PDA material model, which proved to be computationally efficient, and therefore can predict failure propagation and damage mechanisms. Plate geometry is an important parameter in the design process of an adequate bolted joint while its effects on damage initiation and failure modes were quite accurately predicted by the analysis. The latter proved to be computationally efficient, and could successfully predict failure propagation and damage mechanism in hybrid metal-composite countersunk bolted joints.

Estimation of Muscle Forces of Lower Limbs Based on CNN-LSTM Neural Network and Wearable Sensor System.

Estimation of vivo muscle forces during human motion is important for understanding human motion control mechanisms and joint mechanics. This paper combined the advantages of the convolutional neural network (CNN) and long-short-term memory (LSTM) and proposed a novel muscle force estimation method based on CNN-LSTM. A wearable sensor system was also developed to collect the angles and angular velocities of the hip, knee, and ankle joints in the sagittal plane during walking, and the collected kinematic data were used as the input for the neural network model. In this paper, the muscle forces calculated using OpenSim based on the Static Optimization (SO) method were used as the standard value to train the neural network model. Four lower limb muscles of the left leg, including gluteus maximus (GM), rectus femoris (RF), gastrocnemius (GAST), and soleus (SOL), were selected as the studying objects in this paper. The experiment results showed that compared to the standard CNN and the standard LSTM, the CNN-LSTM performed better in muscle forces estimation under slow (1.2 m/s), medium (1.5 m/s), and fast walking speeds (1.8 m/s). The average correlation coefficients between true and estimated values of four muscle forces under slow, medium, and fast walking speeds were 0.9801, 0.9829, and 0.9809, respectively. The average correlation coefficients had smaller fluctuations under different walking speeds, which indicated that the model had good robustness. The external testing experiment showed that the CNN-LSTM also had good generalization. The model performed well when the estimated object was not included in the training sample. This article proposed a convenient method for estimating muscle forces, which could provide theoretical assistance for the quantitative analysis of human motion and muscle injury. The method has established the relationship between joint kinematic signals and muscle forces during walking based on a neural network model; compared to the SO method to calculate muscle forces in OpenSim, it is more convenient and efficient in clinical analysis or engineering applications.

An improved methodology to restrict the range of motion of mechanical joints

Joints with rotational degrees of freedom, for instance, revolute, spherical, or universal joints, are commonly utilized in real-world scenarios. In the multibody systems methodology, mechanical joints usually are formulated as classical kinematic constraints such that there is no restriction of the range of motion (RoM) of the joint. Thus, the formulation must include additional restrictions to prevent the joints from performing unacceptable movements and to avoid unrealistic configurations of the connected bodies. Therefore, the aim of this work is to propose a methodology to restrict the RoM of mechanical joints. Joint resistance moments are applied to the bodies connected by the joint to mimic the dissipative behavior of the materials constituent of joints and to prevent unacceptable configurations of those bodies. The proposed methodology aims to extend and improve a previously published study, specifically in the definition of the RoM limits, calculation of the penalty moments, and establishment of their direction of application. Enhanced methods to deal with the detection of unacceptable joint configurations, namely the elliptical and polynomial approaches, are proposed. A parametrization procedure is described to correctly calculate the direction of the penalty moments to apply to the connected bodies. The methodology is investigated in the dynamic modeling and simulation of one demonstrative example of application, namely a simple pendulum. A parametric analysis is performed to assess the influence of the methodology parameters in the response of the model. The methodology allows the correct restriction of the RoM of joints, while preserving the mechanical energy of the system.

Shear deformation characteristics and failure mechanisms of tunnel segment inter-ring joints: Numerical and experimental study

The dislocation of inter-ring joints in tunnel segments poses a significant risk to tunnel structural safety. Therefore, gaining insights into the shear deformation and failure behavior of these inter-ring joints is paramount. In this study, we developed a robust three-dimensional numerical simulation model grounded in the concrete damaged plasticity (CDP) constitutive model. Complementing this, full-scale experiments were conducted on circumferential joints, subjecting them to both positive and negative shear loads. To enhance our understanding, we employed distributed optical fiber sensing (DOFS) and acoustic emission (AE) detection technologies. Our investigation delved into the deformation process, mechanical behavior of bolts, and failure characteristics of inter-ring joints featuring double bolt-tenon and mortise structures. Various parameters were explored, including longitudinal force, bolt preload, and the height-to-thickness ratio of the tenon and mortise (h/t). Notably, our results unveiled distinct stages in the shear deformation process of the joints. In the final failure stage, the tenon exhibited crushing failure, while the mortise underwent shear failure. As the h/t ratio increased, the mortise's failure mode transitioned from overall failure at the root to localized failure at the contact area. Analyzing the mechanical behavior of bolts, we observed more favorable outcomes in positive shear than in negative shear. Bolt preload emerged as a modest factor for enhancing the load-carrying capacity of the joint in positive shear, with minimal impact in negative shear. Furthermore, an increase in longitudinal force was found to positively enhance the joint's load-carrying capacity in both shear conditions. Our findings contribute valuable insights for optimizing the design and safety considerations of tunnel structures.

Integration of Swin UNETR and statistical shape modeling for a semi-automated segmentation of the knee and biomechanical modeling of articular cartilage

Simulation studies, such as finite element (FE) modeling, provide insight into knee joint mechanics without patient involvement. Generic FE models mimic the biomechanical behavior of the tissue, but overlook variations in geometry, loading, and material properties of a population. Conversely, subject-specific models include these factors, resulting in enhanced predictive precision, but are laborious and time intensive. The present study aimed to enhance subject-specific knee joint FE modeling by incorporating a semi-automated segmentation algorithm using a 3D Swin UNETR for an initial segmentation of the femur and tibia, followed by a statistical shape model (SSM) adjustment to improve surface roughness and continuity. For comparison, a manual FE model was developed through manual segmentation (i.e., the de-facto standard approach). Both FE models were subjected to gait loading and the predicted mechanical response was compared. The semi-automated segmentation achieved a Dice similarity coefficient (DSC) of over 98% for both the femur and tibia. Hausdorff distance (mm) between the semi-automated and manual segmentation was 1.4 mm. The mechanical results (max principal stress and strain, fluid pressure, fibril strain, and contact area) showed no significant differences between the manual and semi-automated FE models, indicating the effectiveness of the proposed semi-automated segmentation in creating accurate knee joint FE models. We have made our semi-automated models publicly accessible to support and facilitate biomechanical modeling and medical image segmentation efforts (https://data.mendeley.com/datasets/k5hdc9cz7w/1).

A novel computational workflow to holistically assess total knee arthroplasty biomechanics identifies subject-specific effects of joint mechanics on implant fixation

Computational studies of total knee arthroplasty (TKA) often focus on either joint mechanics (kinematics and forces) or implant fixation mechanics. However, such disconnect between joint and fixation mechanics hinders our understanding of overall TKA biomechanical function by preventing identification of key relationships between these two levels of TKA mechanics. We developed a computational workflow to holistically assess TKA biomechanics by integrating musculoskeletal and finite element (FE) models. For our initial study using the workflow, we investigated how tibiofemoral contact mechanics affected the risk of failure due to debonding at the implant-cement interface using the four available subjects from the Grand Challenge Competitions to Predict In Vivo Knee Loads. We used a musculoskeletal model with a 12 degrees-of-freedom knee joint to simulate the stance phase of gait for each subject. The computed tibiofemoral joint forces at each node in contact were direct inputs to FE simulations of the same subjects. We found that the peak risk of failure did not coincide with the peak joint forces or the extreme tibiofemoral contact positions. Moreover, despite the consistency of joint forces across subjects, we observed important variability in the profile of the risk of failure during gait. Thus, by a combined evaluation of the joint and implant fixation mechanics of TKA, we could identify subject-specific effects of joint kinematics and forces on implant fixation that would otherwise have gone unnoticed. We intend to apply our workflow to evaluate the impact of implant alignment and design on TKA biomechanics.

Kinetostatic Analysis of a Spatial Cable-Actuated Variable Stiffness Joint

Abstract The demand for robots capable of performing collaborative tasks requiring interactions with the environment is on the rise. Safe interactions with the environment require attributes such as high dexterity and compliance around obstacles, while still maintaining the requisite stiffness levels for payload manipulation. Such attributes are inherent to biological musculoskeletal systems. Motivated by this realization, this paper proposes a cable-actuated spatial joint with variable stiffness, inspired by the tensegrity principles found in biological musculoskeletal systems. The paper provides a detailed analysis of the joint’s mobility and mechanism kinematics. Based on the limits of the actuation forces, the paper also presents the wrench-feasible workspace of the joint. The paper also outlines the conditions that the cable actuation forces must satisfy to maintain the static equilibrium of the joint. The stiffness modeling presented in this work demonstrates the modulation of stiffness bounds as a function of cable actuation forces. Furthermore, the stiffness modulation as a function of the geometrical parameters is also presented.

The Impact of Forward Head Posture on Neck and Ankle Joint Position Sense: A Cross-Sectional Study.

Forward head posture (FHP) decreases the neck position sense and creates tension in the neck muscles, which inversely affects the mechanics of the distal joints through body myofascia. Thus, this study investigated the effects of FHP on neck and ankle joint position sense, and conducted a comparison between the joint position sense of the right and left ankle. Fifty-seven subjects were assigned according to the craniovertebral angle (CVA) into the FHP group (CVA <49°; n = 27) or the control group (CVA >49°; n = 30). Head and ankle joint repositioning accuracy was measured by using a cervical range-of-motion device and an isokinetic dynamometer, respectively. There was a significant increase in the joint position error (JPE) of the cervical flexion, extension, and right and left side bending motions of the FHP group compared to the control group (P < .05). There were significant increases in the JPE of the right and left ankle dorsiflexion and plantarflexion of the FHP group compared to the healthy group (P < .05). Moreover, the JPE of the right ankle dorsiflexion and plantarflexion of the FHP group were significantly higher than the left ankle (P < .05). The FHP decreases the position sense of cervical flexion, extension, and right and left side bending motions, and the plantarflexion and dorsiflexion of both ankle joints, especially the right ankle joint.

Microstructure and Mechanical Properties of IN690 Ni-Based Alloy/316LN Stainless-Steel Dissimilar Ring Joint Welded by Inertia Friction Welding.

Inertia friction welding (IFW) was used to join large-diameter hollow bars made of Inconel 690 and 316LN successfully. The interfacial characteristics, microstructure, mechanical properties and fracture mechanism of welded joints under different process parameters were investigated. The results indicated that a joining mechanism with mechanical interlocking and metallurgical bonding was found in IFW joints. There was a significant mechanical mixing zone at the welding interface. The elemental diffusion layer was found in the "wrinkles" of the mechanical mixing zone. A tiny quantity of C elements accumulated on the friction and secondary friction surfaces. The tensile strength and impact toughness of the joints increased with the total welding energy input. Increasing the friction pressure could make the grain in all parts of the joint uniformly refined, thus enhancing the mechanical properties of welded joints. The maximum tensile strength and impact toughness of the welded joint were 639 MPa and 146 J/cm2, reaching 94% and 68% of that for Inconel 690, respectively, when the flywheel was initially set at 760 rpm, 200 MPa for friction pressure, and 388 kg/m2 for rotary inertia. Due to the Kirkendall effect in the welded joint, superior metallurgical bonding was at the welding interface close to the Inconel 690 side compared to the 316LN side.

The unintentional effect of unicompartmental knee arthroplasty on extraarticular deformity and of high tibial osteotomy on intraarticular deformity for the treatment of anteromedial osteoarthritis.

Unicompartmental Knee Arthroplasty (UKA) and High Tibial Osteotomy (HTO) are two valid options in the treatment of Anteromedial Osteoarthritis (AMOA) of the knee with UKA being mainly performed in cases of Intraarticular deformity (IA) and HTO in cases of Extraarticular deformity (EA). The exact unintentional effect of UKA on EA deformity and HTO on IA deformity is still not well understood. The aim of this study was to assess this unintentional effect of UKA on EA and HTO on IA deformities respectively. This a single-center retrospective study in which 50 patients who underwent UKA and 50 patients who underwent medial opening wedge HTO (MWOHTO) for the treatment of AMOA were included. Overall, 35 males and 15 females underwent HTO with a mean age of 44.3 ± 11.2 years while the mean age of the UKA group was 71.8 ± 7.9 years in 23 males and 27 females. The radiological effect of UKA and HTO on each of the following angles: Hip-Knee-Ankle angle (HKA), Medial Proximal Tibial Angle (MPTA), mechanical Lateral Distal Femoral Angle (mLDFA) and Joint Line Convergence Angle (JLCA) on long film radiographs both pre- and postoperatively was measured. The postoperative values were compared to the preoperative values to detect the expected and unintended effects of each technique on IA and EA deformities. In the HTO group, the MPTA has changed significantly as expected from 83.1 ± 4.5 preoperatively to 88.9 ± 3.9 postoperatively (p value < 0.001) correcting the existing preoperative EA varus without overcorrection. Similarly in the UKA group, the JLCA has also changed significantly as expected to correct the IA varus from 3.8 ± 1.7 preoperatively to 0.9 ± 1 postoperatively (p value < 0.001). On the other hand, the JLCA was unintentionally changed in the HTO group from 2.6 ± 2.1 preoperatively to 1.6 ± 2.4 postoperatively (p value = 0.03) partly correcting the IA varus deformity. Similarly, the MPTA showed a significant change that occurred inadvertently in the UKA group from 84.8 ± 2.1 to 86.3 ± 1.6 postoperatively (p value < 0.001). This unintentional increase in the MPTA also partly corrected the preexisting EA varus deformity. The mLDFA did not show a significant change neither in the HTO group (p value = 0.96) nor in the UKA group (p value = 0.94). In addition to intraarticular varus correction, UKA can partly correct the extraarticular varus deformity in AMOA even when resurfacing is exclusively attempted. Additionally, intraarticular deformity can be also partially managed by HTO along with the extraarticular varus correction even without performing overcorrection.

Design, Testing, and Sensitivity Analysis of a Torsional Cyclic Test Adapter

In this article, a torsional adapter is designed and evaluated through the comparison of analytical, numerical, and experimental tools. The adapter converts a conventional tension–compression test machine for cyclic loading to a modified application of both force-controlled and displacement-controlled torsional loading. The mechanism ensures a uniform distribution of loading application on both sides of the specimen. The determination of the durability curve can therefore be consistently carried out by acknowledging the geometric relation between the displacement of the test rig and the strain on the specimen. However, friction and clearance in the mechanism joints can cause energy dissipation; therefore, a detailed evaluation of this effect is mandatory before the use of the adapter. Here, it is shown that, using the current version of the adapter, the energy dissipation during torsional testing can be measured and later successfully considered during the determination of the torsional cyclic curve. Future improvements of the adapter will involve the reduction of the friction between the components of the mechanism.

Shear fracture behavior and damage constitutive model of rock joints considering the effect of pre-peak cyclic loading

The research on mechanical properties and fracture nalysed of rock joints under dynamic loading disturbance is essential for the stability analysis of rock mass engineering. In this work, a series of pre-peak cyclic shear tests considering the number of cycles and cycle amplitude are conducted for rock joints. Firstly, the shear fracture nalysed and damage evolution law of rock joints are investigated in detail. Then, based on the statistical damage theory, the novel damage constitutive model of rock joints under pre-peak cyclic shear loading is established assuming that the microscopic element damage of rock joints material obeys the Weibull distribution. Finally, the real-time response of acoustic emission and the failure mode of joint surface are nalysed. The results demonstrate that the peak and residual shear stress are positively correlated with the cyclic amplitude. The cumulative cyclic displacement grows with the increase in the number of cycles and cycle amplitude. Moreover, the developed damage model considering the effect of pre-peak cyclic loading is verified by comparing the shear test results with the theoretical values, which are in good agreement. The variation of the shear wear zone of joint surface with cyclic parameters is discussed by binarization calculations. The results of this work can provide a valuable theoretical basis for further research on the shear fracture mechanism of rock joints under dynamic loading disturbance and mitigating geological disasters.

Cam-Type Impingement: Ensuring an Ideal Femoroplasty

When conservative measures have failed, arthroscopic femoroplasty has proven highly efficacious in treating femoroacetabular impingement (FAI) and improving hip joint mechanics. It is best to approach this in a systematic manner with preoperative planning and intraoperative confirmation. Plain radiographs, MRI and/or CT are helpful in the preoperative assessment with identifying the location and shape of the cam deformity. Understanding the extent of the cam lesion prior to surgical intervention will aid in the resection process. The resection can then be confirmed by an intra-operative fluoroscopic exam and arthroscopic dynamic motion evaluation under direct visualization. Using the trough technique, the resection can be marked using the cortical-cancellous border as a depth landmark. When performing the resection, a smooth contour should be performed, with an understanding that both over and under resection can be problematic. Adequate resection should be ensured by testing range of motion, with fluoroscopic imaging, to obtain a circumferential view of the resected area. It is essential to understand how to position the lower extremity in order to obtain different fluoroscopic views of the femoral head neck junction clock-face. Once complete, a thorough irrigation of the joint should be performed to remove bony debris. An ensuing capsular closure should be performed to minimize the risk of iatrogenic hip instability.

A method for manufacturing a mechanically strong and durable hybrid structure of polyethylene–hydroxyapatite composite and titanium alloy

AbstractThe integration of polymer, metal, and ceramic materials in hybrid structures represents a potential but underexplored alternative for biomedical applications. Here, we present a methodology for manufacturing a mechanically strong and durable hybrid overlap structure from a composite of green high‐density polyethylene (HDPE) and hydroxyapatite (HA) compatibilized with HDPE‐g‐MAH joined to a substrate of Ti6Al4V alloy. This process involves laser structuring of micro‐scale grooves on the metal surface, followed by injection overmolding of the polymer composite. A hybrid overlap joint with strong interfacial anchoring was achieved, resulting in outstanding joining strength and fatigue life. This achievement holds significant promise for future biomedical applications.Highlights Joining of composite of HDPE–HA with Ti6Al4V alloy via injection overmolding Laser texturing was effective in improving mechanical interlocking A hybrid joint with high shear strength and fatigue life was developed The hybrid joint is promising for biomedical applications

Chondroitin sulfate and caseinophosphopeptides doped polyurethane-based highly porous 3D scaffolds for tendon-to-bone regeneration

Tendon disorders are common injuries, which can be greatly debilitating as they are often accompanied by great pain and inflammation. Moreover, several problems are also related to the laceration of the tendon-to-bone interface (TBI), a specific region subjected to great mechanical stresses. The techniques used nowadays for the treatment of tendon and TBI injuries often involve surgery. However, one critical aspect of this procedure involves the elevated risk of fail due to the tissues weakening and the postoperative alterations of the normal joint mechanics. Synthetic polymers, such as thermoplastic polyurethane, are of special interest in the tissue engineering field as they allow the production of scaffolds with tunable elastic and mechanical properties, that could guarantee an effective support during the new tissue formation. Based on these premises, the aim of this work was the design and the development of highly porous 3D scaffolds based on thermoplastic polyurethane, and doped with chondroitin sulfate and caseinophosphopeptides, able to mimic the structural, biomechanical, and biochemical functions of the TBI. The obtained scaffolds were characterized by a homogeneous microporous structure, and by a porosity optimal for cell nutrition and migration. They were also characterized by remarkable mechanical properties, reaching values comparable to the ones of the native tendons. The scaffolds promoted the tenocyte adhesion and proliferation when caseinophosphopetides and chondroitin sulfate are present in the 3D structure. In particular, caseinophosphopeptides’ optimal concentration for cell proliferation resulted 2.4 mg/mL. Finally, the systems evaluation in vivo demonstrated the scaffolds’ safety, since they did not cause any inflammatory effect nor foreign body response, representing interesting platforms for the regeneration of injured TBI.