Natural Joint Research Articles

Mechanical properties and acoustic emission characteristics of coal samples with a single natural joint of different dip angles

Mechanical properties and acoustic emission characteristics of coal samples with a single natural joint of different dip angles

Characterizing the Native Microbiome Using Next-Generation Sequencing of Bilateral ‘Aseptic’ Knees

BackgroundNext generation sequencing (NGS) has proven ability to identify organisms beyond those identified through traditional culture-based techniques in cases of suspected prosthetic joint infection. However, there is concern that some microorganisms identified may represent the natural joint microbiome rather than pathogenic agents. This work sought to evaluate the presence of microorganisms identified with NGS in bilateral native, presumed “aseptic” knees with osteoarthritis. MethodsThere were 40 patients undergoing primary unilateral (30) or bilateral (10) total knee arthroplasty enrolled prospectively. During surgery, samples of fluid and tissue were obtained from operative knees, and joint fluid was obtained from nonoperative knees. Samples were sent for NGS analysis and processed according to manufacturer protocols. Patient age, body mass index, comorbidities, prior history of injections, and grade of arthritis were evaluated for association with positive NGS results. ResultsThere were 3 of 80 samples (3.8%) that demonstrated positive NGS. There were two of these that had multiple microorganisms identified (1 knee with 4 microorganisms; 1 knee with 2 microorganisms). An additional 2 samples had positive NGS results below the manufacturer's threshold for reporting. The most common organism identified was Cutibacterium acnes, present in 2 of the 3 positive samples. No patient baseline characteristics were associated with positive NGS results. ConclusionsSome native knee joints with osteoarthritis have positive microorganisms identified with NGS. The presence of microorganisms in the native knee has important implications for better understanding the native joint microbiome as well as utilization of NGS in cases of suspected prosthetic joint infection.

Metal ion reinforced hydrogel/Ti6Al4V bionic composite joint bearing interface with extraordinary mechanical and biotribological properties

Artificial joints are facing challenges of high friction and severe wear, which limits their application in the high stress-loading conditions of joint bearing interfaces. Inspired by the soft/hard structure of articular cartilage/subchondral bone in a natural joint and the presence of lubricating proteoglycan/lubricin on cartilage surface, a polyanionic hydrogel coating rich in carboxylates/sulfonates was constructed on a porous Ti6Al4V substrate through ultraviolet radiation combined with metal ion bridging method. In addition, metal ions were adopted to form ionic coordination bonds with the polyanionic hydrogel layer to enhance its mechanical properties. Characterization results showed that the hydrogel layer was firmly adhered to the porous Ti6Al4V surface, and the as-obtained metal ion reinforced hydrogel/Ti6Al4V joint bearing interfaces displayed improved hydrophilicity and mechanical properties. Notably, compared with Al3+ and Fe3+, Ca2+ reinforced PVA-PAA-PSPMK/DT-Ti6Al4V joint bearing interface in deionized water exhibited a lower friction coefficient (∼0.068), which was similar to that of fresh porcine cartilage, and only slight scratches on the worn surface. Moreover, after 4 h of lubrication in phosphate buffer (PBS) or calf serum, its stable and low friction coefficient further revealed its great application potential in physiological environments. The lubrication mechanisms were also discussed in detail. This work presents a simple and effective method to develop hydrogel/Ti6Al4V bionic composite joint bearing interfaces with advanced performance.

Small Joint Organoids 3D Bioprinting: Construction Strategy and Application.

Osteoarthritis (OA) is a chronic disease that causes pain and disability in adults, affecting ≈300 million people worldwide. It is caused by damage to cartilage, including cellular inflammation and destruction of the extracellular matrix (ECM), leading to limited self-repairing ability due to the lack of blood vessels and nerves in the cartilage tissue. Organoid technology has emerged as a promising approach for cartilage repair, but constructing joint organoids with their complex structures and special mechanisms is still challenging. To overcome these boundaries, 3D bioprinting technology allows for the precise design of physiologically relevant joint organoids, including shape, structure, mechanical properties, cellular arrangement, and biological cues to mimic natural joint tissue. In this review, the authors will introduce the biological structure of joint tissues, summarize key procedures in 3D bioprinting for cartilage repair, and propose strategies for constructing joint organoids using 3D bioprinting. The authors also discuss the challenges of using joint organoids' approaches and perspectives on their future applications, opening opportunities to model joint tissues and response to joint disease treatment.

Finite element simulation of femoral stems lightweighted with re-entrant honeycomb lattice structure

Artificial hip joints are used to replace damaged or diseased natural joints. When the stress that is typically applied to the bone changes because the implant and bone are different in stiffness, a phenomenon known as stress shielding occurs. Stress shielding can lead to bone weakening through reduced density and aseptic loosening in the long term. Studies are ongoing to overcome this phenomenon through geometric design, the use of materials with a low modulus of elasticity, or latticed implants. In this study, the effect of lightening the hip prosthesis with lattice structures on stress shielding is investigated using finite element simulation. The femoral stem of a solid hip prosthesis was lightweighted, with a re-entrant honeycomb auxetic cellular lattice structure, and structural analysis was performed. Two different lattice orientations were used, and it was observed that the stress distribution was more homogeneous in both orientations. In these femoral stems, which can be easily produced using additive manufacturing methods, a volume reduction of up to 16% was achieved. The stress transmitted to the bone increased by more than 36%, depending on the orientation, which is a promising result for reducing the stress shield effect.

Calculation method of HJC constitutive model parameters of natural joint angle slate

In the course of underground engineering, layered slate is often encountered. Understanding the mechanical characteristics of layered slate is a prerequisite for engineering construction and disaster prevention and mitigation. As a result, at the beginning of a project, a large number of indoor tests are required, which are time-consuming and laborious. In addition, the natural joint angle of the layered slate is random, so it is extremely difficult to establish a database of the mechanical characteristics of layered slate. Hence, it is necessary to find a simple, feasible, and high-precision method to determine the Holmquist–Johnson–Cook (HJC) constitutive model parameters for naturally jointed layered slate with different dip angles. This study first determines the HJC constitutive model parameters of layered slate with five specific joint dip angles (0°, 30°, 45°, 60°, and 90°) through static tests and the split Hopkinson pressure bar (SHPB) test. Furthermore, by employing sensitivity analysis methods, the influence of key parameters of the HJC constitutive model on the dynamic peak stress of slate is determined. Among them, parameters A and B have the most significant impact on stress, exceeding 50%. Thirdly, a nonlinear fitting regression method is used to determine the HJC constitutive model parameters of naturally jointed angular slate. The relationship between the HJC model parameters and the inclination angle of slate joints is derived, and the accuracy of these parameters is verified through numerical simulation methods. The error between the numerical simulation and indoor experiments is within 10%, indicating a high level of simulation accuracy. The research findings provide a highly precise numerical simulation method for similar projects.

Tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement under frictional heat based on molecular dynamics

Abstract Hip prostheses generate higher frictional heat than natural joints at the joint head-socket interface during in vivo service, resulting in higher temperatures of the contact surfaces and surrounding synovial fluid, which affects the frictional properties of the prosthetic material. In order to clarify the influence mechanism of frictional heat on the tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement, the tribological tests of three contact pairs were carried out under different synovial fluid temperatures in this research. Furthermore, the movement processes of the molecular chain structure of UHMWPE during friction were simulated by Materials Studio (MS), and the mechanism of oxidative degradation was discussed. The results show that the temperature of synovial fluid has a significant effect on the friction and wear resistance of UHMWPE and the lubrication characteristics of synovial fluid. At the same time, the action mechanism of the proteins in the synovial fluid that gradually precipitate with the temperature rise to participate in the friction process is related to the friction pair material and contact mode. The synergistic effect of temperature rise and friction will accelerate the oxidative degradation reaction of UHMWPE and form ketone and alcohol oxides on its surface, thus reducing its wear resistance.

Can the splitting joint reproduce the characteristics of the natural joint in the lab? —A comparison study based on the roughness analysis and shear test

Splitting joints have been widely used to study the morphology characteristic and shear behavior of rock joints in the laboratory. There are some differences between the splitting joint and natural joint both in morphology characteristic and shear behavior. To quantitatively compare the differences, the present study used several splitting joints and natural joints to carry out the roughness analysis and direct shear test. Six profiles were extracted from each joint surface with a 30° interval to calculate the 2D roughness parameters (i.e., amplitude roughness parameter, average asperity inclination, root-mean-square of profile slope, and joint roughness coefficient). These parameters of the natural joints have a wide range and have obvious fluctuation. On the contrary, these parameters of the splitting red sandstone joints converge on a small range with tiny fluctuation, even calculated from different joint surfaces. The directional parameter (θ⁎max(C + 1)) was adopted to calculate the 3D roughness with a 5° interval. The directional parameter of the natural joints in range of 0° ∼ 360° forms a peanut, a prolate ellipse, or a gourd shape, presenting significant anisotropy. For the splitting joints, it forms a circle or a roughly circular shape, presenting insignificant anisotropy. The asperity heights of natural joints mainly present an irregular distribution, and they present an approximately normal distribution in few joints. For the splitting joints, the asperity heights generally obey a normal distribution. It indicates that there are huge differences between natural joint and splitting joint in morphology characteristic. To study the shear behavior, two types of joint were reconstructed for repeated test. The mechanical performance and failure characteristic of the splitting joint under different shear directions are similar. On the contrary, those of the natural joints under different shear directions are different, presenting obvious anisotropy. Based on the comparative analysis of the natural joints and the sandstone splitting joints in the present study, there is substantial difference between two types of joints both in morphology characteristic and shear behavior. The splitting joints cannot reproduce the characteristics of the natural joints well.

Morphological classification method and data-driven estimation of the joint roughness coefficient by consideration of two-order asperity

Abstract The roughness of the joint surface plays a significant role in evaluating the shear strength of rock. The waviness (first-order) and unevenness (second-order) of natural joints have different effects on the characterization of joint surface roughness. To accurately quantify the influence of the two-order asperity on the joint roughness coefficient (JRC) prediction of joint surface profile curve, the optimal sampling interval of the asperity was determined through the change of the R p {R}_{{\rm{p}}} value of the joint surface profile curve. The separation of the two-order asperity of 48 joint surface profile curves was completed at the optimal sampling interval, and morphological parameters of the asperity such as i ave {i}_{{\rm{ave}}} , R max {R}_{{\rm{\max }}} , and R p {R}_{{\rm{p}}} were counted from three aspects: asperity angle of the profile curve, asperity degree, and the trace length. Based on the statistical results of the morphological parameters considering the two-order asperity, the new nonlinear prediction models were proposed. The results showed that the curve slope mutation point SI = 2 mm is the optimal separation distance of the two-order asperity of the joint surface profile curve. The refined separation method that considers the waviness and unevenness of morphological parameters can characterize the detailed morphological features of the joint surface in more dimensions. The support vector regression (SVR) and random forest (RF) models that take into account a two-order asperity separated results have higher accuracy than traditional models. The prediction accuracy has improved by 7–8% in SVR model compared with SVR(SO) and RF(SO). The SVR nonlinear model that considering separation of two-orders of joint surface roughness is more suitable for the prediction of JRC.

Combining Piezoelectric Stimulation and Extracellular Vesicles for Cartilage Regeneration

Numerous patients experience articular cartilage defects (ACDs), which are characterized by progressive cartilage degradation and often lead to osteoarthritis (OA). Consequently, 44.7% of OA patients suffer from dyskinesia or disability. Current clinical drug treatments offer limited effectiveness in fully curing the disease. In this study, we propose a collaborative approach that combines physical and biological cues to promote cartilage regeneration. A biodegradable piezoelectric poly (l-lactic acid) (PLLA) nanofiber scaffold facilitates in situ, battery-free electrical stimulation under natural joint loading, while extracellular vesicles (EVs) serve as communication mediators between cells and promote cell proliferation, migration, and secretion of type II collagen. In this combined approach, EVs attached to PLLA are gradually released by localized piezoelectric electrical stimulation and taken up by chondrocytes. This process results in the organization of type II collagen along the PLLA fiber surface, ultimately forming cartilage lacunae that facilitate the residence of new chondrocytes. As an outcome, a significant round cartilage defect (diameter: 3 mm and depth: 1 mm) in the PLLA/EVs group (rat and knee) was rapidly restored within six weeks. In contrast, individual EVs and PLLA groups demonstrated considerably weaker cartilage regeneration capabilities. This research suggests that the synergistic effect of electromechanical stimulation and EVs-based biological cues is a crucial intervention method for treating OA.

Solving the Lamé problem in the quasi-brittle setting to substantiate the solution scheme for rock breaking by the blast-hole method

Introduction. The blast-hole method of mining and preparing rocks for excavation has been used by mankind since ancient times. However, there are no generally accepted and generally recognized design and calculation methods for this process, which was established in the review part of this work. Research objective is to develop a basic analytical model for hard rock quasi-brittle materials breaking by a blast-hole method using static thrusts. Methods of research. A detailed analysis of the breaking mechanism through the transition state from the rock material continuity to its separation is the methodological basis of the developed quasi-static model for calculating the energy-power indicators of the process of separating volumes (pieces) of rock into separate parts. It makes it possible to justify and determine: the irreversible energy of rupture through the energy constant rock material in relation to the process energy efficiency, critical load resulting in local breaking, the size and number of the primordial tension cracks, as well as the number of through cracks. Result. The obtained indicators and parameters formed the body of the energy balance equation of the irreversible energy of rupture of rock pieces. The developed methodology for setting and solving the problem of the limiting state of quasi-brittle materials rupture in the form of a thickwalled cylinder (the Lamé problem) that simulates a certain solid volume deformed by a uniformly distributed blast-hole pressure of thrusts, is universal and can serve as a base for assessing a set of issues related to mining. The resulting interrelation of indicators made it possible to derive an equation for the energy balance of the rock volumes rupture. Due to the solution for this equation, the critical value of the blast-hole pressure that results in local breaking, the size of primordial cracks, and the corresponding limiting burst pressure were obtained for the first time. Theoretical novelty. Within the framework of the general approach of the quasi-brittle materials breaking linear theory, based on the developed methodology, the problem of the limiting state of the rock in the form of natural joint loaded with a static thrust through a single blast-hole, was correctly stated and solved by the energy method for the first time. As a result of the research, an analytical dependence of the rock static breaking energy intensity was obtained, which includes both the volumetric specific energy of potential deformation and the specific surface energy

Localizable points in the support of a multiplier ideal and spectra of constrained operators

A unitarily invariant, complete Nevanlinna–Pick kernel K on the unit ball determines a class of operators on Hilbert space called K-contractions. We study those K-contractions that are constrained, in the sense that they are annihilated by an ideal of multipliers. Our overarching goal is to identify various joint spectra of these constrained K-contractions through the vanishing locus of their annihilators. Our methods are based around a careful analysis of a subset of the ball associated to the annihilator, which we call its support. For the functional models, we show how this support completely determines several natural joint spectra. The picture is more complicated for general K-contractions, as their spectra can be properly contained in the support. Nevertheless, the “localizable” portion of the support always consists of spectral points. When the support is assumed to be small in an appropriate sense, we manage to effectively detect points of localizability.

The flexion–extension gap is predictive of patient-reported outcome measures after cruciate-retaining total knee arthroplasty

BackgroundWe aimed to evaluate the association between the flexion–extension gap difference and patient-reported outcome measures after total knee arthroplasty (TKA). MethodsThis was a retrospective case–control study of 60 cruciate-retaining single-radius TKAs. Soft tissue balancing was measured using an offset seesaw tensioner and centre-type digital knee balancer under joint distraction forces of 20–50 lbf and 1.5 times body mass index (1.5 BMI). At the last follow up of 2.0–6.5 (mean, 4.5) years postoperatively, patients were asked if they perceived their knee joint as ‘natural’ (26 knees) or ‘artificial’ (34 knees). Age, sex, and the flexion–extension gap were compared between the two groups. A receiver operating characteristic curve was used to determine cut-off values of variables predictive of a natural joint perception. ResultsNatural joint perception was associated with a greater flexion–extension gap difference under a distraction force of 1.5 BMI (P = 0.016), higher knee function (Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, P = 0.019), and quality of life (EuroQol 5-Dimension, P = 0.029). A gap difference of 0.95 mm under 1.5 BMI distraction predicted a natural joint perception post-TKA (sensitivity, 97.1%; specificity, 88.5%). Using a gap threshold of 1.0 mm under a 1.5 BMI distraction force yielded significant between-group differences in postoperative flexion (P = 0.040), satisfaction (P = 0.043), knee joint function (P < 0.001), quality of life (P = 0.032), and posterior femoral condylar offset (P = 0.037) ConclusionA flexion–extension gap difference ≥1.0 mm under a distraction force of 1.5 BMI predicted superior outcomes, including patient satisfaction, after cruciate-retaining TKA. It was suggested that posterior femoral condylar offset could influence this finding.

Assessment of Hip Joint Function and Limb Load in Patients after Cementless Hip Arthroplasty During 14-day Rehabilitation

Abstract Background Arthoplasty is a surgical procedure consisting in replacing a natural joint altered by the disease process with an artificial joint. This surgery allows you to restore the lost function of the hip joint. Comprehensive rehabilitation plays an essential role after surgery. Objectives The aim of the study was to assess the impact of rehabilitation on patients on the 1st and 14th day of rehabilitation after cementless hip arthroplasty on the load on the operated limb and to assess the function of the hip joint. Material and methods The studies were performed on a group of 44 patients with post-surgery rehabilitation.The studies were performed twice: on the 1st and 14th day of rehabilitation. The standardized questionnaires was used: Harris Hip Score and WOMAC. The reaction of ground forces was assessed using the Alpha stabilometric platform. Results The average point value indicated on the Harris Scale significantly increased in the measurement on the 14th day of rehabilitation by 8.57 ± 6.56 points (p &lt; 0.001). On the other hand, the WOMAC Scale showed a decrease in point values in the second measurement by 9.67 ± 6.76 points (p &lt; 0.001). A significant increase in the average load on the operated lower limb by 3.68 ± 3.18% was indicated as measured on the 14th day of rehabilitation (p &lt; 0.001). The difference between the average load of the right and left limbs in the measurement on the first day of rehabilitation was an average of 9.77%, while on the fourteenth day of rehabilitation the difference between the average load of the right and left limbs decreased to an average of 3.5%. Conclusions Postsurgery rehabilitation allows to obtain physiological load ranges of the lower limbs, striving for a 50% share in the load of each of the lower limbs. The effectiveness of the implemented rehabilitation is confirmed on the basis of the analysed limb load parameters and the analysis of patients’ subjective assessments made using standardized questionnaires.

Method for visualizing the shear process of rock joints using 3D laser scanning and 3D printing techniques

This study presents a visualized approach for tracking joint surface morphology. Three-dimensional laser scanning (3DLS) and 3D printing (3DP) techniques are adopted to record progressive failure during rock joint shearing. The 3DP resin is used to create transparent specimens to reproduce the surface morphology of a natural joint precisely. The freezing method is employed to enhance the mechanical properties of the 3DP specimens to reproduce the properties of hard rock more accurately. A video camera containing a charge-coupled device (CCD) camera is utilized to record the evolution of damaged area of joint surface during the direct shear test. The optimal shooting distance and shooting angle are recommended to be 800 mm and 40°, respectively. The images captured by the CCD camera are corrected to quantitatively describe the damaged area on the joint surface. Verification indicates that this method can accurately describe the total sheared areas at different shear stages. These findings may contribute to elucidating the shear behavior of rock joints.

Cartilage-bioinspired, tough and lubricated hydrogel based on nanocomposite enhancement effect.

The maintenance of high load-bearing tissues and joint lubrication is essential for suppressing osteoarthritis. The lubrication of natural joints is mainly attributed to the hydration lubrication mechanism of articular cartilage. Phospholipids on the cartilage surface attract water molecules to form a tough hydrated layer to reduce friction. In this work, inspired by the phosphatidylcholine lipids, we synthesized lubricated nanospheres by grafting hydrophilic polymer brushes and further synthesized a nanocomposite hydrogel. The addition of the lubricated nanospheres enhanced both the mechanical and lubricated properties of the hydrogel. The nanocomposite-lubricated hydrogel exhibited a friction coefficient 81.7% lower than the blank hydrogel because of grafting the polymer brushes. Also, the nanocomposite enhancement helped the hydrogel achieve high mechanical properties with a compressive strength of 6.63 MPa (50%). The nanocomposite hydrogel developed here could be a promising candidate material in bionic articular cartilage substitute materials.

Minimally Invasive Inferior Intra-Articular Sacroiliac Joint Fusion: Successful Application of Osseous Stabilization Using Allograft Bone.

Minimally invasive sacroiliac joint (SIJ) fusion is the preferred surgical method for managing patients with recalcitrant, chronically severe SIJ pain and dysfunction refractory to conservative medical measures. The primary surgical objective of all minimally invasive SIJ fusion procedures is to provide immediate stabilization within the joint space to support osseous consolidation and the development of a mechanically solid arthrodesis. The intra-articular surgical approach to the SIJ with allograft bone placement utilizes a trajectory and easily identifiable landmarks that allow the surgeon to control the risk of violating important neuro-vascular structures. The intra-articular approach can employ a superior or inferior operative trajectory, with the former restricted to allograft placement in the ligamentous portion of the SIJ. The inferior approach utilizes decortication to surgically create a channel originating in the purely articular portion of the joint space allowing for truly intra-articular implant placement within the osseous confines of the ilium and sacrum. Positioning the implant along the natural joint line and securing it within the underlying sub-chondral bone, mortise and tenon fashion provides stabilization and large surface area contact at the bone implant interface. The inferior, intra-articular approach also places the implant perpendicular to the S1 endplate, near the sacral axis of rotation, which addresses the most significant biomechanical forces across the joint. Short-term, post-surgical observational data from a 57 patient multi-center registry using the inferior, intra-articular approach show uniform and statistically significant improvement in all clinical outcomes (p < 0.001 for all comparisons), including an average 3-point improvement in back pain severity from 6.8 preoperatively to 3.8 at 6 months. Further clinical evaluation with longer-term follow-up of the inferior, intra-articular SIJ fusion procedure is encouraged.

Can Knees be Forgotten 2 Years After Total Knee Arthroplasty?

Background: There have been multiple ways to measure outcomes post total knee arthroplasty. Ultimate goal is to replicate a natural joint to allow patients to perform most activities of daily living and give high satisfaction rates. Patient reported outcome measures (PROM) like Forgotten Joint Score (FJS), Oxford Knee Score (OKS)and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) have been validated and used for evaluation of TKA patients. FJS helps to evaluate how natural a prosthesis feels post surgery. Our aim was to study how natural a joint felt or was forgotten 2 year after surgery and how FJS correlates with OKS and WOMAC scores. Materials and Methods : We evaluated 254 total knee replacements with minimum 2 year post TKA. All the patients who were at least 2 year post operative, completed FJS questionnaire where scores are ranged from 0-100; OKS questionnaire where scores are ranged between 0-48; Short – form WOMAC questionnaire where scores are ranged between 0-28. Correlation analysis was performed for FJS with OKS and short - form WOMAC scores. Results: 254 patients with mean age of 65.01 years of which 83 males and 171 females were evaluated with minimum of 24 months follow up and average follow-up of 30.85 months. Average FJS, OKS and SF WOMAC were 77.24, 38.75 &amp; 79.97 respectively. FJS showed good correlation with OKS and SF WOMAC scores. Conclusion : FJS is an easy and equally effective outcome measure, which is valid and reliable like the other common well know measures like OKS and WOMAC. Patients experience a marked improvement in the FJS over the first two years. Patients in our series had good outcomes who had more natural feel of knees or a feeling of “forgotten knees” in their day to day activity after 2 years of surgery.

Human-like redundancy resolution: An integrated inverse kinematics scheme for anthropomorphic manipulators with radial elbow offset

As a mimic of the human arm structure, anthropomorphic manipulators with radial elbow offset (AMREO) are often deployed on humanoid service robots. However, the unique offset leads to difficulties in solving the analytical inverse kinematics (IK), which poses a challenge for further anthropomorphic control. This paper presents an integrated scheme for solving the path-wise IK problem of a 7-DoF AMREO in the position domain. Unlike other approaches, special attention is paid to the naturalness of the arm configuration, with the aim of making AMREO exhibit human-like behavior in human-centered environments. First, an analytical IK solution of AMREO for a single end-effector pose is derived based on the arm angle parameterization. Then, inspired by the habitual arm configurations in human reaching movements, the natural arm configuration mapped to wrist position is proposed for AMREO. To learn the patterns implied therein, a LSTM-based natural arm angle prediction network (NAPN) is designed and trained based on a human demonstration dataset. Finally, a redundancy resolution framework embedded with NAPN is built to generate smooth and natural joint configurations in the path-wise IK tasks. Comparative experiments show that the proposed analytical IK algorithm has better computational efficiency and precision than conventional methods, and can give complete results for one IK call within 4 μs. In addition, continuous path tracking experiments on a real robot validate the effectiveness and anthropomorphism of the redundancy resolution scheme based on NAPN.

Explant analysis of a Discocerv cervical disc: A case study for a ceramic-on-ceramic cervical disc

Explant analyses are key to better understanding the effectiveness of medical implants in replacing natural joints. For the first time, an explanted Discocerv cervical disc was examined. The implant utilised the articulation of a caudal zirconia cup (inferior component) and a cephalic alumina head (superior component). The articulating surface of the superior alumina head had an average surface roughness of 0.016 ± 0.003 μm (Sa) and the articulating surface of the inferior zirconia cup had an average surface roughness of 0.015 ± 0.002 μm (Sa). Both articulating surfaces had negative skewness, indicating the removal of local peaks. The difference between the average surface roughness of the components was not significant (p-value: 0.741). Dark grey marks were observed on both of the articulating surfaces, which were found to be adhered titanium debris that was generated due to component impingement. This titanium debris may explain the small amount of metallosis that was reported at explantation. Some transfer of zirconium to the alumina articulating surface was also seen.