Analysis Of Polyethylene Research Articles

The influence of implant design and limb alignment on in vivo wear rates of fixed-bearing and rotating-platform knee implant retrievals.

Analysis of polyethylene (PE) wear in knee implants is crucial for understanding the factors leading to revision in total knee arthroplasty. Importantly, current experimental and computational methods for predicting insert wear can only be validated against true in vivo measurements from retrievals. This study quantitatively investigated in vivo PE wear rates in fixed-bearing (FB) (n = 21) and rotating-platform (n = 53) implant retrievals. 3D surface geometry of the retrievals was measured using a structured light scanner. Then, a reference surface that included the deformation, but not the wear that the retrievals had experienced in vivo, was constructed using a fully automatic surface reconstruction algorithm. Finally, wear volume was calculated from the deviation between the worn and reconstructed surfaces. The measurement and analysis techniques were validated and the algorithm was found to produce errors of only 0.2% relative to the component volumes. In addition to quantifying cohort-level wear rates, the effect of mechanical axis limb alignment on mediolateral wear distribution was examined for a subset of the retrievals (n = 14 + 26). Our results show that FB implants produce significantly (p = 0.04) higher topside wear rates (24.6 ± 10.1 mm3/year) than rotating-platform implants (15.3 ± 8.0 mm3/year). This effect was larger than that of limb alignment, which had a smaller and nonsignificant influence on overall wear rates (+4.5 ± 11.6 mm3/year, p = 0.43). However, increased varus alignment was associated significantly with greater medial compartment wear in both the FB and rotating-platform designs (+1.7 ± 1.3%/° and +1.8 ± 1.6%/°). Our findings emphasize the importance of implant design and limb alignment on wear outcomes, providing reference data for improving implant performance and longevity.

Extraction and Pyrolysis-GC-MS analysis of polyethylene in samples with medium to high lipid content

While it is recognised that humans are constantly exposed to plastics, there are limitations in understanding the extent of this exposure, particularly dietary exposure. This lack of information is partly due to challenges with the analysis of complicated matrices. This study aimed to assess the impact of medium to high lipid content (> 3%) food samples on the accurate quantification of polyethylene (PE), using pyrolysis-gas chromatography mass spectrometry, and develop an alternative sample processing strategy. Analysis of saturated, monounsaturated and polyunsaturated fats was demonstrated to form the same pyrolysis products as PE, producing a significant interference hindering quantification. An extraction protocol was developed that involves enzyme digestion to break the lipids into smaller chain fatty acids, removal of these interferences with pressurised liquid extraction washes, before a final extraction of the PE by pressurised liquid extraction. This new method was validated through the analysis of three medium- to high-fat content foods: cow’s milk, eggs and lamb meat, where PE recoveries were acceptable (104% to 127%). Method detection limits were also significantly reduced from 1.9 to 0.05 µg/injection (380 to 10 µg/g) with the new protocol, through the removal of matrix background. PE traces were observed in the three food matrices of 72-240 µg/g, significantly reduced as compared to samples extracted with the old method where concentrations of 12-32 mg/g were calculated, demonstrating the potential for overestimation of dietary exposure. Finally, a simple protocol is reported for future studies to (i) determine if an interference is present and (ii) sample processing methods to remove identified interferences.

Comparative retrieval analysis of antioxidant polyethylene: bonding of vitamin-E does not reduce in-vivo surface damage

BackgroundWith the Persona® knee system a new polyethylene formulation incorporating vitamin-E which aims to reduce oxidation and maintain wear resistance was introduced. Although in-vitro studies have demonstrated positive effects of the vitamin-E antioxidants on UHMWPE, no retrieval study has looked at polyethylene damage of this system yet. It was the aim to investigate the in-vivo performance of this new design, by comparing it with its predecessor in retrieval analysis.Methods15 NexGen® and 8 Persona® fixed-bearing implants from the same manufacturer (Zimmer Biomet) were retrieved from two knee revision centres. For retrieval analysis, a macroscopic analysis of polyethylene using a peer-reviewed damage grading method was used (Hood-score). The roughness of all articulating metal components was measured using a contact profilometer. The reason(s) for TKA revision were recorded. Statistical analyses (t-test) were performed to investigate differences between the two designs.ResultsThe mean Hood score for Persona® inserts was 109.3 and for NexGen® 115.1 without significant differences between the two designs. Results from the profilometer revealed that Persona® and NexGen® femoral implants showed an identical mean surface roughness of 0.14 μm. The Persona® tibial tray showed a significantly smoother surface (0.06 μm) compared to the NexGen® (0.2 μm; p < 0.001). Both Hood score and surface roughness were influenced by the reasons for revision (p < 0.01).ConclusionsThe bonding of the antioxidant vitamin-E to the PE chain used in the novel Persona® knee system does not reduce in-vivo surface damage compared to highly crosslinked PE without supplemented vitamin-E used in its predecessor knee system NexGen®. However, the Persona® titanium alloy tibial tray showed a significantly smoother surface in comparison to the NexGen® titanium alloy tibial tray. This study provides first retrieval findings of a novel TKA design and may help to understand how the new Persona® anatomic knee system performs in vivo.

Constitutive Equations and Finite Element Implementation of Isochronous Nonlinear Viscoelastic Behavior

We present a phenomenological three-dimensional (3D) nonlinear viscoelastic constitutive model for time-dependent analysis. Based on Schapery's single integral constitutive law, a solution procedure has been provided to solve nonlinear viscoelastic behavior. This procedure is applicable to 3D problems and uses time- and stress-dependent material properties to characterize the nonlinear behavior of material. The equations describing material behavior are chosen based on the measured material properties in a short test time frame. This estimation process uses the Prony series material parameters, and the constitutive relations are based on the nonseparable form of equations. Material properties are then modified to include the long-term response of material. The presented model is suitable for the development of a unified computer code that can handle both linear and nonlinear viscoelastic material behavior. The proposed viscoelastic model is implemented in a user-defined material algorithm in abaqus (UMAT), and the model validity is assessed by comparison with experimental observations on polyethylene for three uniaxial loading cases, namely short-term loading, long-term loading, and step loading. A part of the experimental results have been conducted by (Liu, 2007, “Material Modelling for Structural Analysis of Polyethylene,” M.Sc. thesis, University of Waterloo, Waterloo, ON Canada), while the rest are provided by an industrial partner. The research shows that the proposed finite element model can reproduce the experimental strain–time curves accurately and concludes that with proper material properties to reflect the deformation involved in the mechanical tests, the deformation behavior observed experimentally can be accurately predicted using the finite element simulation.

Role of G-CSF treatment in recurrent miscarriage on the expression of FoxP3, VEGF, VEGF-R2 and c-kit in first trimester pregnancy specimens

Although total shoulder arthroplasty has demonstrated better clinical outcomes than hemiarthroplasty, glenoid component loosening is a common complication. Recently, a novel partially cemented all-polyethylene fluted central peg bone-ingrowth component was introduced.Forty-two consecutive total shoulder arthroplasties from 2003 to 2007 performed by a single surgeon were evaluated radiographically and clinically with American Shoulder and Elbow Surgeons (ASES) scores and range of motion.The average follow-up was 80 months (63-114); the average forward elevation improved from 107° to 137°, and external rotation improved from 30° to 37° at the latest follow-up. The average ASES score improved from 50 to 84. There was a strong correlation with the mean peripheral peg lucent line score (Lazarus score), which was 0.81, with the mean anchor peg lucent line score, which was 0.50 (P < .001). An analysis of polyethylene before and after cross-linking revealed a strong correlation between components with cross-linking and the Lazarus scores and the central fluted peg scores. Overall, there was 97% survivorship at 80 months. On radiographs, 81% of the central fluted pegs had complete incorporation with no lucent lines. These lucent lines correlated with lower ASES scores, suggesting that loosening of the glenoid decreases functional outcome.Care should be taken in preparing the central fluted peg as perforation of the vault can lead to central flute peg lucent line formation, whereas perforation of the peripheral pegs does not seem to negatively affect the outcome.

Five- to ten-year follow-up with a partially cemented all-polyethylene bone-ingrowth glenoid component

Although total shoulder arthroplasty has demonstrated better clinical outcomes than hemiarthroplasty, glenoid component loosening is a common complication. Recently, a novel partially cemented all-polyethylene fluted central peg bone-ingrowth component was introduced. Forty-two consecutive total shoulder arthroplasties from 2003 to 2007 performed by a single surgeon were evaluated radiographically and clinically with American Shoulder and Elbow Surgeons (ASES) scores and range of motion. The average follow-up was 80months (63-114); the average forward elevation improved from 107° to 137°, and external rotation improved from 30° to 37° at the latest follow-up. The average ASES score improved from 50 to 84. There was a strong correlation with the mean peripheral peg lucent line score (Lazarus score), which was 0.81, with the mean anchor peg lucent line score, which was 0.50 (P<.001). An analysis of polyethylene before and after cross-linking revealed a strong correlation between components with cross-linking and the Lazarus scores and the central fluted peg scores. Overall, there was 97% survivorship at 80months. On radiographs, 81% of the central fluted pegs had complete incorporation with no lucent lines. These lucent lines correlated with lower ASES scores, suggesting that loosening of the glenoid decreases functional outcome. Care should be taken in preparing the central fluted peg as perforation of the vault can lead to central flute peg lucent line formation, whereas perforation of the peripheral pegs does not seem to negatively affect the outcome.

Analysis of Polyethylene by Using Cyclopentadienyl Cobalt Chemical Ionization Combined with Laser-Induced Acoustic Desorption/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

A new mass spectrometric method has been developed for the analysis of low molecular weight polyethylene (PE). Laser-induced acoustic desorption (LIAD), combined with chemical ionization by the cyclopentadienyl cobalt radical cation (CpCo.+) in a Fourier transform ion cyclotron resonance mass spectrometer, produces predominantly a quasimolecular ion, (R + CpCo - 2H2).+, for each PE oligomer (R). An examination of artificial alkane mixtures revealed no mass bias for alkanes of differing molecular weights. However, the success of the LIAD/CpCo.+ CI technique depends greatly upon the LIAD sample preparation method used. Several sample preparation methods were evaluated, and pneumatically assisted spin coating was concluded to provide the best mass spectra as a result of its ability to provide uniform PE coverage on the LIAD foils. The molecular weight distributions measured for several low molecular weight PE samples (200-655) were found to be in good agreement with manufacturers' values as determined by gel permeation chromatography.

Modeling of the Fluid-Structure Interaction in Inelastic Piping Systems

In many engineering applications, compliant piping systems conveying liquids are subjected to inelastic deformations due to severe pressure surges such as plastic tubes in modern water supply transmission lines and metallic pipings in nuclear power plants. In these cases the design of such systems may require an adequate modeling of the interactions between the fluid dynamics and the inelastic structural pipe motions. The reliability of the prediction of fluid-pipe behavior depends mainly on the adequacy of the constitutive equations employed in the analysis. In this paper it is proposed a systematic and general approach to consistently incorporate different kinds of inelastic behaviors of the pipe material in a fluid-structure interaction analysis. The main feature of the constitutive equations considered in this work is that a very simple numerical technique can be used for solving the coupled equations describing the dynamics of the fluid and pipe wall. Numerical examples concerning the analysis of polyethylene and stainless steel pipe networks are presented to illustrate the versatility of the proposed approach.

(N&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;2&lt;/sub&gt;)混合ガス中で部分放電に晒したポリエチレンのAFMとFTIRによる分析

(N&lt;sub&gt;2&lt;/sub&gt;+O&lt;sub&gt;2&lt;/sub&gt;)混合ガス中で部分放電に晒したポリエチレンのAFMとFTIRによる分析

Changing crystallinity of polyethylene in the acetabular cups of Weller hip prostheses

We performed thermal analysis of polyethylene samples obtained from 73 new cups of the Weller hip prosthesis. There were marked individual differences in the degree of their crystallinity, ranging from 37.8% to 67.2% with a mean of 53%. Analysis of polyethylene from removed cups also showed differences in crystallinity in individual cups, with the mean value being higher in the removed implants than in the new ones. This difference in crystallinity between the groups was statistically significant. Marked individual differences in the degree of cup wear may result from these changes.

Phase diagrams of polyethylene blends by Raman spectroscopy

The Raman internal mode region analysis of polyethylene (PE) is extended to studies of blends of different PEs so as to obtain a phase diagram showing the magnitude of crystalline (Pc), amorphous (Pa) and interfacial (Pb) phases at different compositions. The non-cocrystallizable HDPE/LDPE blends shows additivity in phase structure with blend composition. Enlarged share of Pb is seen for compatible blends of HDPE/LLDPE and especially for HDPE with VLDPE of low crystallinity. This method offers an easy access to direct observing compatibility of different PEs on a molecular level.

High Performance Size Exclusion Chromatograph with Computerized Data Reduction for Analysis of Polyethylene and Oligomers

Abstract A liquid chromatograph is described for the size exclusion chromatography (SEC) of polyethylene and oligomers. The rigid column packing material was 10 µm diameter porous silica. An infrared spectrophotometer was used as the detector. The chromatograph was designed and operated to minimize the degree of chromatographic peak shape distortion resulting from factors such as system dead volume, detector cell design, sample injection volume, and sample concentration. To compensate for peak spreading and skewing, the chromatographic data were analyzed with an IBM 370/168 computer using an APL program. The molecular weight range covered by this SEC system was 100-500 000. Precision and accuracy of Jhe calculated weight average molecular weight (Mw) values for polyethylene standards over this range were ±3 and s±4%, respectively.

Plastoelasticity of high polymers based on the analysis of polyethylene stretched till natural draw ratio

A theory of the plastoelasticity of high polymers is developed, which takes into account the essential structural details explored with X-ray diffraction and electron micrographs. The structure consists of small microparacrystallites (mPC's), which are the nodules of a threedimensional network. This is deformed affine under stress. The theory takes into account the stretching phenomenon of affine transformation and retransformation down to colloidal dimensions and can solve therefore directly the differential equations of non-linear deformation behaviour. Within the microdomains of less than 0.1 mm diameter affine phenomena do not occur, because the microparacrystallites are disintegrated and plastically deformed. The theory is applied to the profile analysis of the shoulders in the neck of partically at room temperature drawn polyethylene. The retardation time of the microdomains reaches near the half width of the shoulder a minimum value of 2.5 min. Studying the stress-strain curve the rod firstly is deformed “homogeneously” till to an elongation of 8∼25% beyond the yield point. Till here those microdomains, which are plastically deformed, mostly are distributed randomly over the sample. In this way the deviation from the Hooke-law (linearity and immediate reversibility) can be explained, which becomes larger with increasing strain and increasing number of deformedmPC's. Above γ=25% cooperative deformations of adjacent microparacrystallites arise in planes orthogonal to the stretching direction as consequence of stress fields generated by the network knotted with plastically deformable knots. Now the macroscopically visible necking begins. At γ ∼ 2 both shoulders are separated and have gained their final profile, if the stretching velocity is constant and not too large and the temperature not too low. The Kelvin-elements, which represent the microdomains, are frozen in our example before they have reached the equilibrium elongation because outside of the shoulder the rod has become so cold that the plasticity of themPC's has decreased. This determines the so-called natural draw ratio. The deformation to natural draw ratio is absolutely reversible, if the time of passing of the microdomains the shoulder is small enough compared with the relaxation time of the Maxwell-elements. The effective Young-modulus in the phenomenological Hooke-part of the stress-strain curve has a maximal value of 5000 kp cm−2, whilst the entropy driven spring constant of the reversible deformable microdomains is much smaller with a value of 15 kp cm−2. The word “viscoelasticity” is not sufficiently descriptive.

Differential thermal analysis of polyethylene obtained by radiation-induced polymerization

Abstract The fine structure of polyethylene prepared by radiation-induced polymerization of ethylene at room temperature is investigated by differential thermal analysis (DTA). This polyethylene is difficult to affect by annealing, but does show a tendency to reorganize during heating. A double endotherm on the DTA heating curve is observed in samples annealed at temperatures between 121 and 125°C. The structure represented by the endotherm at the lower temperature shows a strong tendency to reorganize, but that represented by the endotherm at the higher temperature does not. These double endotherms do not disappear from the heating curve of a sample oxidized by fuming nitric acid. It is proposed that polyethylene prepared by radiation-induced polymerization has a large crystalline fraction but small crystallite size and a small amorphous part; the polymer molecules, in both parts, may be strained with some hindrance to thermal movement, for example, by the existence of long-chain branches.