Cross-linked Inserts Research Articles

The role of cross-link augmentation on fusion rate and patient satisfaction among patients with traumatic thoracolumbar spinal fracture: A randomized clinical trial.

Most of the studies evaluating the effect of cross links on spinal stability are performed in vitro on porcine or human spine segments and there is limited data regarding clinical benefits of cross link augmentation in traumatic injuries. In this study we aimed to evaluate the effects of cross-links insertion between rods on the fusion rates and post-surgical patients' satisfaction among patients with traumatic thoracolumbar fractures who underwent posterior spinal fixation with pedicle screws. This study was conducted as a randomized clinical trial on 60 patients suffering from traumatic thoracolumbar vertebrae fractures. Patients were randomized into three groups: A (without any cross-link), B (One cross-link insertion) and C (two cross-links insertion). Six months after surgery outcomes were evaluated: fusion rates (plain X-ray and CT scan), Back pain (Visual Analog Scale) and patient satisfaction (fair, good, excellent). In group A 13 (65%) patients had structured bone fusion, but in 7 (35%) patients bone fusion was not observed. In both groups B and C, 19 patients (95%) had bone fusion, but only in 1 patient (5%) fusion failed (p=0.009). In group A, fair satisfaction has the highest rate (8 patients (40%)) compared to the other groups. The highest reported severity of back pain was observed in group A while the lowest reported intensity of back pain was related to group B (p=0.001). Adding cross link to posterior spinal fixations of patients with traumatic thoracolumbar fractures can be associated with better final fusion results and patients' satisfaction. However it is necessary to design studies with greater sample sizes to confirm this theory. IRCT20120527009878N3.

The role of cross-link augmentation on fusion rate and patient satisfaction among patients with traumatic thoracolumbar spinal fracture: A randomized clinical trial

Introduction and objectivesMost of the studies evaluating the effect of cross links on spinal stability are performed in vitro on porcine or human spine segments and there is limited data regarding clinical benefits of cross link augmentation in traumatic injuries. In this study we aimed to evaluate the effects of cross-links insertion between rods on the fusion rates and post-surgical patients’ satisfaction among patients with traumatic thoracolumbar fractures who underwent posterior spinal fixation with pedicle screws. Materials and methodsThis study was conducted as a randomized clinical trial on 60 patients suffering from traumatic thoracolumbar vertebrae fractures. Patients were randomized into three groups: A (without any cross-link), B (One cross-link insertion) and C (two cross-links insertion). Six months after surgery outcomes were evaluated: fusion rates (plain X-ray and CT scan), Back pain (Visual Analog Scale) and patient satisfaction (fair, good, excellent). ResultsIn group A 13 (65%) patients had structured bone fusion, but in 7 (35%) patients bone fusion was not observed. In both groups B and C, 19 patients (95%) had bone fusion, but only in 1 patient (5%) fusion failed (p=0.009). In group A, fair satisfaction has the highest rate (8 patients (40%)) compared to the other groups. The highest reported severity of back pain was observed in group A while the lowest reported intensity of back pain was related to group B (p=0.001). ConclusionsAdding cross link to posterior spinal fixations of patients with traumatic thoracolumbar fractures can be associated with better final fusion results and patients’ satisfaction. However it is necessary to design studies with greater sample sizes to confirm this theory.Trial registration number: IRCT20120527009878N3.

Cyclosporine-loaded cross-linked inserts of sodium hyaluronan and hydroxypropyl-β-cyclodextrin for ocular administration

This work aimed to develop cyclosporine ocular inserts combining sodium hyaluronate (HA) and hydroxypropyl-β-cyclodextrin (HPβCD). Four different formulations, cross-linked with poly(ethylene glycol) diglycidyl ether, were studied to elucidate the role of the HA:HPβCD proportion on the physical characteristics and drug release patterns. The inserts (300 μm thickness) showed porous surfaces, high swelling ratios (∼10), and good cytocompatibility with fibroblasts and chorioallantoic membrane (HET-CAM test). Cyclosporine-loaded inserts (∼0.5% w/w drug content) appeared translucent. Release tests carried out under continuous flow of simulated lacrimal fluid revealed a controlled release of cyclosporine during the first 1 h. Conversely, differences among formulations were evidenced when the inserts were immersed in plenty volume of fluid; inserts with low content in HPβCD released the drug faster. These later inserts also facilitated cyclosporine accumulation into sclera (5.6–32.7 μgdrug/gsclera). Thus, cross-linked HA:HPβCD inserts appear as a suitable platform for peptide drug release to the ocular surface.

Minimum five-year wear rate of metal-on-highly cross-linked polyethylene in primary total hip arthroplasty.

Highly cross-linked polyethylenes (PE) have been developed with encouraging results in terms of wear. Another body of the literature has indicated potential catastrophic failures related to reduced fatigue properties and oxidation. Each PE available on the market has its own processing characteristics. The aim of this retrospective study was to evaluate the minimum five-year wear properties of an original highly cross-linked PE in a consecutive series of primary THAs. Between August 2005 and December 2007, 80 patients with a mean age of 62.7 years were included. All patients had a 28-mm CoCr femoral head articulating with a highly cross-linked insert (Highcross®, Medacta SA) that was 100 Mrads gamma radiated, remelted at 150 °C, and ethylene oxide sterilized. The primary criterion for evaluation was the femoral head penetration, as measured by Hip Analysis Suite software. The steady state wear was also calculated. Functional results were evaluated according to the WOMAC score. Complete data were available for analysis in 67 patients at a mean follow-up of 5.5 years. The mean femoral head penetration was 0.128 ± 0.62 mm and the steady state wear was-0.025 ± 0.22 mm/year. The WOMAC score significantly decreased from 16.5 ± 5.93 pre-operatively to 4.12 ± 5.5 at the latest follow-up (p <0.001). The minimal five-year results of this retrospective study indicate that this particular highly cross-linked and remelted polyethylene had a low wear rate. Longer-term results are needed to warrant that these mid-term data will generate less osteolysis and resultant aseptic loosening.

Preparation of magnetic, macro-reticulated cross-linked chitosan for tetracycline removal from aquatic systems

A novel adsorbent, magnetic, macro-reticulated cross-linked chitosan (MRC) was synthesised for the removal of tetracycline (TC) from water using a source of biogenic waste (gastropod shells) as a pore-forming agent. The insertion of crosslinks into the chitosan frame was confirmed by FTIR analysis, while the stability of the MRC was demonstrated via a stability test performed in an acidic solution. The enhanced porosity of the MRC was confirmed by the evaluation of its porosity, a swelling test and the determination of its specific surface area. The time–concentration profile of the sorption of TC onto the MRC demonstrated that equilibrium was attained relatively quickly (120min), and the data obtained fitted a pseudo second order (r2>0.99) kinetic equation better than a pseudo first order or reversible first order kinetic equation. The optimisation of process variables indicated that the sorption of TC onto the MRC was favoured at a low solution pH and that the presence of organics (simulated by the addition of humic acid) negatively impacted the magnitude of TC removal. The area of coverage of TC on the MRC (2.51m2/g) was low compared to the specific surface area of the MRC (47.95m2/g). The value of the calculated energy of adsorption of TC onto the MRC was 100kJ/mol, which is far above the range of 1–16kJ/mol stipulated for physical adsorption.

CURE SIMULATION OF LARGE RUBBER COMPONENTS: A COMPARISON OF COMPRESSION AND EXTRUSION MOLDING

ABSTRACT Curing rubber is a complex process that involves the insertion of cross-links to convert the rubber into a useful functional material. The estimation of the cure time needed for product manufacture of small or thin walled products is often arrived at by means of a rheometer trace. Although this has been recognized as adequate for thin walled products, the production of large rubber articles requires a more rigorous analysis of cure kinetics for an essentially non-isothermal process. Often finite element analysis is used to generate non-isothermal temperature histories in a thick component, and then an appropriate cure kinetic equation is solved to predict the state of cure. In addition to generating the capability for cure time prediction, there is a need in the industry to minimize cycle time, improving productivity and therefore costs involved in product manufacture. For large products, the viability of the use of extrusion molding, where the rubber is extruded into a heated mold at the same temperature as the mold, has been demonstrated in previous reported work in this laboratory. The present work explores, via simulation, the feasibility of using extrusion molding as a manufacturing method for large components. The cure simulation module of Autodesk Moldflow has been used to compare the state of cure of a laminated bearing manufactured by conventional compression molding and extrusion molding. Previous experimental data on the temperature histories of a large laminated bearing manufactured using compression molding are compared with simulation data. Simulation data are then presented on manufacturing the bearing using extrusion molding. The aim is to demonstrate the usefulness of extrusion molding for very large components and to illustrate the advantages of using simulation codes to assist in shortening the cycle time in product manufacture.

Simulated Normal Gait Wear Testing of a Highly Cross-Linked Polyethylene Tibial Insert

Polyethylene wear can compromise long-term performance of total knees. We investigated articular and backside wear rate of tibial inserts made from conventional vs highly cross-linked polyethylenes. The inserts were tested on a knee simulator at a frequency of 1.1 Hz using normal gait kinematics with a 7° posterior slope for 7 million cycles. Gravimetrically, the combined articular and backside wear rate was 23 ± 6 and 4.6 ± 2 mm 3 per million cycles for the conventional and cross-linked inserts, respectively. We independently measured articular surface wear rates, which were 15 ± 4 and 5 ± 2 mm 3 per million cycles for conventional and cross-linked inserts, respectively. Electron beam cross-linked and subsequently melted polyethylene reduced the wear rate of polyethylene on articular and backside surfaces in a cruciate-retaining total knee design when tested on a knee simulator under simulated normal gait.

Knee-simulator testing of conventional and cross-linked polyethylene tibial inserts

We compared the resistance to delamination and to adhesive/abrasive wear of conventional and highly cross-linked polyethylene tibial inserts of a cruciate-retaining total knee design using a knee simulator. Both groups were tested after aggressive, accelerated aging, and 1 set of conventional inserts was studied without aging. Aging oxidized the conventional, but not the highly cross-linked, inserts. The simulated normal gait testing lasted for 5 and 10 million cycles for the conventional and highly cross-linked inserts, respectively. Aged conventional inserts showed delaminations, whereas none were observed in the unaged conventional and aged cross-linked inserts. Wear rates measured by the gravimetric method were 9 ± 2 mm 3, 10 ± 4 mm 3, and 1 ± 0 mm 3 per million cycles; by the metrologic method, they were 8 ± 1 mm 3, 9 ± 2 mm 3, and 3 ± 0 mm 3 for the unaged conventional, aged conventional, and aged highly crosslinked inserts, respectively. In the test model used, oxidation led to delamination, whereas increased cross-link density resulted in reduced adhesive/abrasive wear of tibial inserts.

Aggressive wear testing of a cross-linked polyethylene in total knee arthroplasty.

Recently, highly cross-linked polyethylenes with high wear and oxidation resistance have been developed. These materials may improve the in vivo performance of polyethylene components used in total knee arthroplasty. To date, the in vitro knee wear testing of these new polyethylenes has been done under conditions of normal gait. However, their critical assessment also must include aggressive in vitro fatigue and wear testing. In the current study, an aggressive in vitro knee wear and device fatigue model simulating a tight posterior cruciate ligament balance during stair climbing was developed and used to assess the performance of one type of highly cross-linked polyethylene tibial knee insert in comparison with conventional polyethylene. The highly cross-linked inserts and one group of conventional inserts were tested after sterilization. One additional group of conventional inserts was subjected to accelerated aging before testing. The articular surfaces of the inserts were inspected visually for surface delamination, cracking, and pitting at regular intervals during the test. The aged conventional polyethylene inserts showed extensive delamination and cracking as early as 50,000 cycles. In contrast, the unaged conventional and highly cross-linked polyethylene inserts did not show any subsurface cracking or delamination at 0.5 million cycles. The appearance and location of delamination that occurred in the aged conventional inserts tested with the current model previously have been observed in vivo with posterior cruciate-sparing design knee arthroplasties with a tight posterior cruciate ligament.

Measurement of cross linked fibrin derivatives in plasma: an immunoassay using monoclonal antibodies.

Fibrinogen degradation, fibrin polymerisation, and the insertion of cross links into fibrin by fibrin stabilising factor lead to the appearance of new antigenic determinants. Antibodies against these antigenic sites may react specifically with the derivatives but not with the parent molecules. We have utilised a monoclonal antibody, which interacts with the cross linked fragment D dimer and related high molecular weight fibrin derivatives, to develop an enzyme immunoassay which measures cross linked fibrin derivatives in plasma and serum using D dimer as standard. Mean concentration in plasma from normal subjects was 75 ng/ml with an upper limit of about 144 ng/ml. Concentrations in patients with pulmonary embolism, deep venous thrombosis, arterial thromboembolism, and disseminated intravascular coagulation were raised in all cases. Confirmation of the specific increase of cross linked fibrin derivatives in patients with disseminated intravascular coagulation was obtained by parallel monitoring of their fibrin degradation products in serum using affinity chromatography and sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. In many patients the plasma concentrations greatly exceeded the serum values of cross linked fibrin degradation products, suggesting that the procedure can measure fibrin derivatives in plasma which are absent from serum.

Investigation, by cross-linking, of conformational changes in F-actin during its interactions with myosin.

The hypothesis that the subunits of F-actin rotate during interactin with myosin and ATP has been tested by using the specific cross-linking reagent p-phenylene-N,N'-bis(maleimide) (PM). The insertion of cross-links between F-actin subunits does not change the ability of the F-actin to activate the ATPase of either myosin subfragment-1 (S-1) or heavy meormyosin, and its ability to superprecipitate with myosin is unimpaired. We conclude that large-scale rotations of actin subunits are not required for activity. The cross-linking of F-actin by PM is, however, inhibited in a noncooperative fashion by S-1 binding, suggesting that a small local change in actin structure may accompany the binding of S-1 or that S-1 sterically blocks the cross-linking by binding near the contact region between actin subunits.