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Addition of high-aspect-ratio (AR) nanofillers can markedly influence flow behavior of polymer systems. As a result, application of graphite nanoplatelets (GNP) allows preparation of microfibrillar composites (MFC) based on PCL matrix reinforced with in-situ generated PLA fibrils. This work deals, for the first time, with preparation of analogous melt-drawn fibers. Unlike other blend-based fibers, the spinning and melt drawing leads to structure of deformed inclusions due to unfavorable ratio of rheological parameters of components. Subsequent moderate cold drawing of the system with dissimilar deformability of components causes strengthening with PLA fibrils. Unexpectedly, high velocity and extent of cold drawing leads to structure with low-AR inclusions, similar to the original melt-drawn blend. Extensive fast deformation of the soft PCL matrix does not allow sufficient stress transfer to rigid PLA. In spite of peculiarities found, the GNP-aided melt spinning allows facile preparation of biodegradable biocompatible fibers with wide range of diameters (80-400 μm) and parameters (2.35-18 cN/tex).
UNLABELLED: PURPOSE OF THE STUDY Ultrahigh molecular weight polyethylene (UHMWPE) is today the most frequently used bearing surface in total joint replacements (TJR) because of its properties, i.e., excellent biocompatibility, good mechanical and tribological performance and high wear resistance. UHMWPE liners are the most loaded TJR components and, therefore, their properties are decisive for TJR longevity. This study had three objectives: 1) to evaluate the oxidative degradation of explanted UHMWPE components; 2) to look for a statistically significant relationship between the extent of oxidative degradation and the durability of joint replacements; and 3) to investigate whether the durability of a TJR was related to the type of sterilisation used in manufacture. MATERIAL AND METHODS The study included 26 acetabular components obtained at revision arthroplasty between 2004 and 2013 from patients in whom a Beznoska/Poldi total hip replacement was used in the period from 1977 to 2002. The average age of the patients at the time of primary implantation was 57.9 years, the average longevity of the components removed was 18.63 years (range, 6.9 to 27.9 years). Samples of worn out and unworn areas from explanted components were processed in a three-step procedure in order to finally obtain 2-mm microtome sections. These were studied by infrared microspectroscopy. Oxidative damage to UHMWPE was determined as the oxidation index (OI); radiation damage to UHMWPE during sterilization was evaluated as the transvinylene index (VI); oxidation-induced changes in the polymer structure and its properties were characterised as the crystallinity index (CI); and local changes in mechanical properties due to oxidative degradation were assessed as microhardness (MH). Spearman's correlation coefficient and the Wilcoxon two-sample test were used for statistical analysis. RESULTS The OI values (average and maximum) in both worn out and unworn surface areas were related to component longevity. The difference between the oxidation index of ruptured components and that of the other components was statistically significant. Significant differences were also found between the average and maximum OI values of worn out areas and those of unworn surfaces. The relationship between the average oxidation index in both the unworn and worn out areas of UHMWPE components and the longevity of cracked components was statistically significant. DISCUSSION Our results show that the OI values obtained by microspectroscopy correlated with both the microscopic damage and the longevity of UHMWPE liners and the correlation was statistically significant also in relation to the longevity of total replacements. Relationships amongst OI, VI, CI and MH values as well as their relation to failure and longevity of total replacements are discussed. CONCLUSIONS It can be concluded that infrared microspectroscopic measurement of OI values is a simple and fast method to characterise UHMWPE liners. In addition, the IR spectra also show other supplementary characteristics, such as VI and CI indices. These values provide information on the quality of various UHMWPE types currently used in TJR surgery. The types of UHMWPE which exhibit high oxidative degradation should be avoided in clinical practice due to increased risk of early TJR failure. Responsible orthopedic surgeons should be aware of this fact and, if possible, collaborate with an independent, noncommercial laboratory in order to evaluate the quality of various UHMWPE liners used in their hospitals. KEY WORDS: UHMWPE, oxidation, total joint replacement, infrared spectroscopy, microhardness.
- MeSH
- biokompatibilní materiály chemie MeSH
- lidé středního věku MeSH
- lidé MeSH
- náhrada kyčelního kloubu přístrojové vybavení MeSH
- oxidační stres fyziologie MeSH
- polyethyleny chemie MeSH
- reoperace MeSH
- selhání protézy MeSH
- senioři MeSH
- spektrofotometrie infračervená MeSH
- testování materiálů metody MeSH
- Check Tag
- lidé středního věku MeSH
- lidé MeSH
- senioři MeSH
- Publikační typ
- časopisecké články MeSH
Ultrahigh-molecular-weight polyethylene (UHMWPE) has been used as a liner in total joint replacements (TJR) since the 1970's. One of the main lifetime-limiting factors of contemporary TJRs is the long-term oxidative stability of UHMWPE, as the oxidative degradation results in chain scissions and deterioration of mechanical properties, including the most important one – wear resistance. In order to maximize the oxidation and wear resistance of UHMWPE components, the manufacturers apply various procedures, such as crosslinking by ionizing radiation, thermal treatment and stabilization. Almost each manufacturer uses its own UHMWPE modification procedure and there is a number of different types of UHMWPEs on the market. Clinical practice stressed the need for an objective comparison of different UHMWPE types and the influence of oxidative damage on the lifetime of TJR. Due to the small size and irregular shape of UHMWPE components and inhomogeneous nature of oxidative degradation in vivo, their properties should be studied by microscopic methods. We tested the sensitivity and accuracy of two microscopic methods – infrared microscopy (IR) and microhardness (MH) measurements supplemented by DSC in relation to UHMWPE characteristics. The methods help to analyze reasons for TJR failures, to detect differences in molecular and supramolecular structures and properties of various UHMWPE types, and to characterize aging of various UHMWPE components in vitro.
- MeSH
- artroplastiky kloubů MeSH
- lidé MeSH
- mikroskopie metody MeSH
- nestabilita kloubu MeSH
- oxidace-redukce MeSH
- polyethyleny chemie MeSH
- protézy kloubů MeSH
- testy tvrdosti MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
PURPOSE OF THE STUDY: Each method of sterilisation has some effect on the structure and properties of UHMWPE and thus also on joint replacement longevity. This study was designed to compare, using objective methods of measurement, several kinds of sterilisation and to recommend the one which has the best prospect for making joint replacements last longer. MATERIAL AND METHODS: Two groups of UHMWPE samples were tested. Group 1 included virgin GUR 1020 polyethylene, non-modified and non-sterilised (Meditech, Germany). Group 2 comprised of three sets of samples sterilised with formaldehyde, gamma irradiation and ethylene oxide, respectively. In both groups, physicochemical properties were assessed by infrared spectroscopy (IR), and the oxidation (OI) and trans-vinyl (VI) indices, which show the degree of oxidation of a material, were determined. Free-radical concentrations were measured by the method of electron spin resonance (ESR). The mechanical properties of each sample were studied using small punch tests (SPT) and testing microhardness (MH). Any change in mechanical properties can affect, to various degrees, the quality and longevity of a prosthetic joint. RESULTS: The samples sterilised by gamma irradiation showed higher values of both the OI (0.37) and the VI index (0.038) than the other samples (OI, 0.02 to 0.05 and VI, 0). Also, the free-radical concentration was detectable only in the gamma-sterilised sample. Values obtained for mechanical properties were as follows: peak load in the range of 58.48 N (gamma irradiation) to 59.60 N (ethylene oxide); ultimate load in the range of 46.69 N (gamma irradiation) to 57.50 N (ethylene oxide); ultimate displacement in the range of 4.29 mm (gamma irradiation) to 4.58 mm (virgin polyethylene and formaldehyde); and work to failure in the range of 185.18 mJ (gamma irradiation) to 205.89 mJ (virgin polyethylene). Microhardness values were obtained in the following ranges: 41.2 to 44.6 MPa (virgin polyethylene); 40.2 to 44.1 MPa (formaldehyde); 46.1 to 49.3 MPa (gamma irradiation); and 40.3 to 44.2 MPa (ethylene oxide). DISCUSSION: The samples sterilised with formaldehyde and ethylene oxide have mechanical properties very similar to virgin polyethylene, they are not damaged by oxidation and do not contain free radicals. Owing to these characteristics, the immediate and long-term oxidation stability of the three samples is higher. The sample sterilised by gamma irradiation showed the presence of free radicals and immediate and long-term oxidative degradation. This results in the deterioration of mechanical properties and the growth of crystallinity due to enhanced oxidation and leads to higher polyethylene microhardness. CONCLUSIONS: Sterilisation with gamma irradiation results in oxidative degradation and mechanical property deterioration, which is one of the potential risks of a shorter life span of joint replacements. The use of ethylene oxide or formaldehyde does not change polymer properties nor has any effect on oxidation of materials. Therefore, a longer life expectancy of the joint replacements sterilised with ethylene oxide can be expected. The life span of their joint replacements is a key issue for the patients. Prosthetic joint loosening is painful and the patient often requires re-implantation. A higher number of re-implantations is associated with higher costs for the institution involved and, consequently, for the whole health care system. Although this study basically deals with chemical issues, it informs the surgeon of the latest developments leading to the improvement of implanted materials, which can increase the life expectancy of joint replacements and patients' satisfaction.
- MeSH
- artroplastiky kloubů metody MeSH
- ethylenoxid farmakologie MeSH
- formaldehyd farmakologie MeSH
- lidé MeSH
- polyethylen terapeutické užití MeSH
- protézy kloubů * škodlivé účinky klasifikace MeSH
- selhání protézy MeSH
- spektrofotometrie infračervená metody MeSH
- srovnávací výzkum účinnosti MeSH
- sterilizace metody MeSH
- testování materiálů metody MeSH
- záření gama * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- anglický abstrakt MeSH
- časopisecké články MeSH
- srovnávací studie MeSH
BACKGROUND: At present time the number of implantations of joint replacements as well as their revisions increases. Higher demands are required on the quality and longevity of implants. The aim of this work was to determine the degree of oxidative degradation and the amount of free/residual radicals in selected ultra-high molecular weight polyethylene (UHMWPE) components of the joint replacements and demonstrate that the measured values are closely connected with quality and lifetime of the polymer components. METHODS: We tested both new (4 samples) and explanted (4 samples) UHMWPE polymers for total joint replacements. The samples were characterized by infrared spectroscopy (IR), electron spin resonance (ESR) and microhardness (MH) test. The IR measurements yielded the values of oxidation index and trans-vinylene index. The ESR measurements gave the free radicals concentration. RESULTS: In the group of new polyethylene components, we found oxidation index values ranging from 0.00-0.03 to 0.24. The trans-vinylene index values ranged from 0.044 to 0.080. The value of free radical concentration was zero in virgin and also in sample of Beznoska Company and non-zero in the other samples. In the group of explanted components, the measured values were associated with their history, micromechanical properties and performance in vivo. CONCLUSIONS: We demonstrated that measuring of oxidative damage may help the orthopaedic surgeon in estimating the quality of UHMWPE replacement component and thus radically to avoid early joint replacement failure due to worse polyethylene quality.
- MeSH
- biokompatibilní materiály chemie MeSH
- elektronová paramagnetická rezonance MeSH
- krystalizace MeSH
- kyčelní protézy * MeSH
- lidé MeSH
- oxidace-redukce MeSH
- polyethyleny chemie MeSH
- protézy kolene * MeSH
- reoperace MeSH
- selhání protézy MeSH
- spektrofotometrie infračervená MeSH
- testování materiálů MeSH
- tvrdost MeSH
- volné radikály analýza MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
Ultrahigh molecular weight polyethylene (UHMWPE) is a key component of modern total joint replacements (TJR). The most frequently replaced human joints are hips and knees, followed by shoulders, elbows, etc. However, UHMWPE liners are the most loaded components of the implants. Consequently, the main materialrelated reasons of TJR failures are wear and oxidative degradation of the polymer. Resistance to wear (i.e. release of microscopic particles from the polymer surface) is increased by radiation-induced crosslinking. Oxidation stability (i.e. resistance of polymer to chain scissions and deterioration of mechanical properties) is enhanced by means of suitable thermal treatment and sterilization protocols. The most recent trend is to employ a biocompatible stabilizer – vitamin E – for further improvement and finetuning of UHMWPE performance. This review summarizes the recent developments in UHMWPE modifications, which come both from the author’s institute and from the world, and which should further increase lifespan of total joint replacements.
- MeSH
- alfa-tokoferol MeSH
- artroplastiky kloubů * MeSH
- biokompatibilní materiály chemická syntéza chemie terapeutické užití MeSH
- biomechanika MeSH
- dávka záření MeSH
- lidé MeSH
- polyethyleny * chemická syntéza chemie terapeutické užití MeSH
- polymery * chemická syntéza chemie terapeutické užití MeSH
- protézy kloubů MeSH
- testování materiálů MeSH
- záření gama MeSH
- Check Tag
- lidé MeSH
PURPOSE OF THE STUDY The orthopaedic community has unanimously adopted the view that ultra high molecular weight polyethylene (UHMWPE) wear particles are a very frequent cause of aseptic implant loosening. Some studies have tried to provide objective evidence for this. We have found descriptions of particle distribution or morphology, but no report that would objectively correlate the number of particles in zones surrounding an implant with the extent of damage to these zones. The aim of this study was to develop a method allowing us to evaluate a number of samples with polyethylene abrasive wear large enough to find association between the extent of damage around a THA and the number of biologically active UHMWPE wear particles, 0.1 to 10 μm in size . MATERIAL AND METHODS In 28 patients undergoing revision total hip arthroplasty (THA) at the 1st Orthopaedic Clinic, 1st Faculty of Medicine, Charles University, we took samples of typical osteoaggressive granuloma from defined zones around the implant; the zones corresponded to those described by Gruen and DeLee. The extent of tissue damage in each zone was evaluated on the basis of pre-operative radiographs and by the extent of osteolysis and damage to soft tissues actually observed during revision THA. The volume of wear particles in each zone was assessed by the IRc method developed by us; this is based on a quantitative evaluation of infrared spectra. To verify the methodology, a comparison between tissue damage and the number of particles in each zone was made in three randomly selected patients. RESULTS We introduced a method of detailed orthopaedic evaluation which enabled us to categorize zones around a revised THA according to the extent of damaged tissue. As a result, a series of zones ranked by the extent of damaged tissue, or an "orthopaedist?s statement" (OS), was obtained. At the same time we adopted a method, based on infrared spectroscopy and termed IRc, by which the number of particles in the samples of damaged tissues and osteoaggressive granulomas collected from the area around a revised THA was determined. The results of evaluation were presented as numerical data that, in a defined way, were converted into a series of zones ranked according to the number of wear particles, i.e., the "result of measurement" (RM). In this study we verified the methods described above and made a comparison of OSs and RMs for three randomly selected patients. The very good agreement found confirmed the reliability of both methods which will soon be used to evaluate a group of patients large enough to provide statistically significant results. DISCUSSION The IRc method determines a total volume of UHMWPE wear particles, 0.1 to 10 μm in size, which are generally considered to be most biologically active. This study suggests that the distribution of particles around a THA is uneven and that relation between tissue damage and the number of wear particles in individual zones surrounding a THA does exist. The major conclusion from the orthopaedic point of view is a confirmation of the assumption that UHMWPE wear particles are one of the chief causes of THA failure. Although this fact is generally accepted, studies correlating the number of particles with tissue damage and osteolysis in individual zones are very scarce. CONCLUSIONS The quick and simple IRc method offers a possibility to quantify polyethylene wear particles in soft tissues. The number of 0.1 to 10 μm wear polyethylene particles correlated with pre-operative radiographic findings and orthopaedic evaluation of revision THAs in three randomly selected patients. The confirmed correlation between the extent of tissue damage in individual zones surrounding a THA and the volume of wear particles detected in these zones supports the view that UHMWPE wear particles are one of the main causes of THA failure.
- MeSH
- financování organizované MeSH
- granulom etiologie MeSH
- kyčelní kloub patologie MeSH
- kyčelní protézy škodlivé účinky MeSH
- lidé MeSH
- mikroskopie elektronová rastrovací MeSH
- náhrada kyčelního kloubu MeSH
- polyethylen terapeutické užití MeSH
- reoperace MeSH
- selhání protézy MeSH
- spektrofotometrie infračervená využití MeSH
- spektrometrie rentgenová emisní MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- hodnotící studie MeSH
In a combined experimental and theoretical approach, the interactions of valinomycin (Val), macrocyclic depsipeptide antibiotic ionophore, with sodium cation Na(+ )have been investigated. The strength of the Val-Na(+ )complex was evaluated experimentally by means of capillary affinity electrophoresis. From the dependence of valinomycin effective electrophoretic mobility on the sodium ion concentration in the BGE (methanolic solution of 20 mM chloroacetic acid, 10 mM Tris, 0-40 mM NaCl), the apparent binding (stability) constant (K(b)) of the Val-Na(+ )complex in methanol was evaluated as log K(b) = 1.71 +/- 0.16. Besides, using quantum mechanical density functional theory (DFT) calculations, the most probable structures of the nonhydrated Val-Na(+) as well as hydrated Val-Na(+).H(2)O complex species were proposed. Compared to Val-Na(+), the optimized structure of Val-Na(+).H(2)O complex appears to be more realistic as follows from the substantially higher binding energy (118.4 kcal/mol) of the hydrated complex than that of the nonhydrated complex (102.8 kcal/mol). In the hydrated complex, the central Na(+) cation is bound by strong bonds to one oxygen atom of the respective water molecule and to four oxygens of the corresponding C=O groups of the parent valinomycin ligand.
Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.
- MeSH
- chemické modely MeSH
- crown ethery MeSH
- izotopy uhlíku MeSH
- kvantová teorie MeSH
- magnetická rezonanční spektroskopie metody normy MeSH
- molekulární struktura MeSH
- oniové sloučeniny MeSH
- počítačová simulace MeSH
- protony MeSH
- referenční standardy MeSH
- spektroskopie infračervená s Fourierovou transformací metody MeSH
- vodíková vazba MeSH
