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The effects of irradiation and artificial aging on the wear behaviour of UHMWPE.
No full textUltra-high-molecular-weight-polyethylene (UHMWPE) for hip implants can present serious clinical problems: the cyclic nature of the contact stresses at the articular surface can lead to pitting, delamination and crystallinity changes of the polymer with formation of PE debris, which may lead to extensive bone loss around the implant and consequently osteolysis and implant loosening.
The effects of different sterilization methods have been studied by various authors, but no one produced a full conclusive verdict (1,2). To assess long term stability of polymers, various accelerated aging methods have been developed. In this study, an internal protocol was developed to evaluate the effects of the accelerated aging on wear.
Three EtO-sterilised and six gamma-irradiated (standard 3 Mrads dose in air) UHMWPE acetabular cups (Chirulen GUR 1050, POLY HI SOLIDUR, France) were aged in air at 80°C for 4 weeks and thereafter tested in conjunction with twelve 28-mm CoCrMo femoral heads.
Wear tests were carried out using a 12-station hip joint simulator (Shore Western, USA) run for 3 million cycles, with bovine calf serum as lubricant. A frequency of 1 Hz, according to the rotation test frequency, was applied with a sinusoidal load having a peak magnitude of about 2 kN.
Wear behaviour was evaluated by gravimetric measurements and Raman analysis. Since Raman spectra reflect PE morphology, Raman spectroscopy was used to investigate the crystallinity changes induced by aging and wear testing. Micro-Raman spectra were obtained in a non-destructive way using a Jasco NRS-2000C instrument (exc=488 nm, 20× magnification). For each cup, 12 spectra were recorded in the inner surface within 1.5 mm from the centre, the most worn area. Crystallinity (C%) was determined from Raman spectra using the partial least-squares (PLS) regression.
Significant differences were observed between the wear behaviours of the two sets of acetabular cups after 3 million cycles ( = 0.0001).
The mean C% values obtained for untreated gamma and EtO-sterilised UHMWPE unworn cups were significantly different (62 and 60%, respectively).
Upon ageing significant changes in C% were observed for all the cups and were more pronounced for gamma-sterilised cups (meanly from about 62% to 65%) than for EtO-sterilised cups (meanly from 60% to 61%). Upon wear testing of the gamma-sterilised cups, only three samples showed significant increases in C%. Conversely, all the EtO-sterilized cups showed significant C% changes: one cup showed a C% increase (from (60.9±0.2)% to (61.9±0.4)%), while the other two underwent a C% decrease (from (60.3±0.3)% to (56.4±0.7)% and from (60.9±0.3)% to (59.4±0.4)%).
The higher crystallinity found for the gamma-sterilised cups can be explained by considering that the energy of the gamma rays is sufficiently high to break the UHMWPE polymeric chains, resulting in a reduction of molecular weight and in a corresponding increase in crystallinity. Raman spectroscopy proved a valid tool to non-destructively monitor the C% changes the samples underwent upon aging and wear tests. By Raman-PLS analysis it was confirmed that aging affected more significantly the morphology and wear behaviour of the gamma-sterilised cups; also the EtO-sterilised cups underwent detectable C% changes, which, however, did not affect so dramatically wear behaviour
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Comparative study on the wear behaviour of different conventional and cross-linked polyethylenes for total hip replacement
No full textIn this study, five different types of conventional and cross-linked polyethylene (XLPE) (γ-sterilised PE GUR1020, EtO-sterilised PE GUR1020, γ-sterilised PE GUR1050, EtO-sterilised XLPE GUR1020, EtO-sterilised XLPE GUR1050) acetabular cups were tested on a hip joint simulator run for 5 million cycles in order to compare the relative long-term wear resistance in relation to material properties (PE grade, conventional or cross-linked) and sterilisation method (EtO treatment or γ-irradiation).
Gravimetric measurements revealed significant differences between the wear behaviours of the five sets of acetabular cups. Weight loss was found to decrease along the series: γ-sterilised PE GUR1020>EtO-sterilised PE GUR1020>γ-sterilised PE GUR1050>EtO-sterilised XLPE GUR1050>EtO-sterilised XLPE GUR1020. The wear results were discussed in relation to the crystallinity degree of the cups which was determined by micro-Raman spectroscopy coupled to partial least-squares analysis. Within both conventional and cross-linked PE series, it appeared that higher crystallinity samples (i.e. γ-sterilised PE GUR1020 and EtO-sterilised XLPE GUR1050, respectively) were characterised by higher wear rates. The higher weight loss observed for PE GUR1020 was explained in relation to its lower molecular weight with respect to PE GUR1050. Raman analysis showed that wear testing did not significantly modify the crystallinity degree of any of the tested acetabular cups. The most worn cup, i.e. γ-sterilised PE GUR1020, appeared the most homogeneously polished upon wear testing, as confirmed by the lowest standard deviation associated to the crystallinity value recorded in the centre of the cup. The results of this investigation have clearly shown a dramatic wear reduction in favour of the cross-linked polyethylene
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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