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Mattei L.,Largo Lucio Lazzarino | Di Puccio F.,Largo Lucio Lazzarino | Ciulli E.,Largo Lucio Lazzarino
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2016

Although huge research efforts have been devoted to wear analysis of ultra-high molecular weight polyethylene (UHMWPE) in hip and knee implants, shoulder prostheses have been studied only marginally. Recently, the authors presented a numerical wear model of reverse total shoulder arthroplasties (RTSAs), and its application for estimating the wear coefficient k from experimental data according to different wear laws. In this study, such model and k expressions are exploited to investigate the sensitivity of UHMWPE wear to implant size and dimensional tolerance. A set of 10 different geometries was analysed, considering nominal diameters in the range 36-42 mm, available on the market, and a cup dimensional tolerance of +0.2, -0.0 mm (resulting in a diametrical clearance ranging between 0.04-0.24 mm), estimated from measurements on RTSAs. Since the most reliable wear law and wear coefficient k for UHMWPE are still controversial in the literature, both the Archard law (AR) and the wear law of UHMWPE (PE), as well as four different k expressions were considered, carrying out a total of 40 simulations.Results showed that the wear volume increases with the implant size and decreases with the dimensional tolerance for both the wear laws. Interestingly, different trends were obtained for the maximum wear depth vs. clearance: the best performing implants should have a high conformity according to the AR law but low conformity for the PE law. However, according to both laws, wear is highly affected by both implant size and dimensional tolerance, although it is much more sensitive to the latter, with up to a twofold variation of wear predicted. Indeed, dimensional tolerance directly alters the clearance, and therefore the lubrication and contact pressure distribution in the implant. Rather surprisingly the role of dimensional tolerance has been completely disregarded in the literature, as well as in the standards. Furthermore, this study notes some important issues for future work, such as the validation of wear laws and predictive wear models and the sensitivity of k to implant geometry. © 2016 Elsevier Ltd.


Mattei L.,Largo Lucio Lazzarino | Di Puccio F.,Largo Lucio Lazzarino | Ciulli E.,Largo Lucio Lazzarino
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2016

In the present study, numerical and experimental wear investigations on reverse total shoulder arthroplasties (RTSAs) were combined in order to estimate specific wear coefficients, currently not available in the literature. A wear model previously developed by the authors for metal-on-plastic hip implants was adapted to RTSAs and applied in a double direction: firstly, to evaluate specific wear coefficients for RTSAs from experimental results and secondly, to predict wear distribution. In both cases, the Archard wear law (AR) and the wear law of UHMWPE (PE) were considered, assuming four different k functions. The results indicated that both the wear laws predict higher wear coefficients for RTSA with respect to hip implants, particularly the AR law, with k values higher than twofold the hip ones. Such differences can significantly affect predictive wear model results for RTSA, when non-specific wear coefficients are used. Moreover, the wear maps simulated with the two laws are markedly different, although providing the same wear volume. A higher wear depth (+51%) is obtained with the AR law, located at the dome of the cup, while with the PE law the most worn region is close to the edge. Taking advantage of the linear trend of experimental volume losses, the wear coefficients obtained with the AR law should be valid despite having neglected the geometry update in the model. © 2015 Elsevier Ltd.


PubMed | Largo Lucio Lazzarino
Type: | Journal: Journal of the mechanical behavior of biomedical materials | Year: 2015

In the present study, numerical and experimental wear investigations on reverse total shoulder arthroplasties (RTSAs) were combined in order to estimate specific wear coefficients, currently not available in the literature. A wear model previously developed by the authors for metal-on-plastic hip implants was adapted to RTSAs and applied in a double direction: firstly, to evaluate specific wear coefficients for RTSAs from experimental results and secondly, to predict wear distribution. In both cases, the Archard wear law (AR) and the wear law of UHMWPE (PE) were considered, assuming four different k functions. The results indicated that both the wear laws predict higher wear coefficients for RTSA with respect to hip implants, particularly the AR law, with k values higher than twofold the hip ones. Such differences can significantly affect predictive wear model results for RTSA, when non-specific wear coefficients are used. Moreover, the wear maps simulated with the two laws are markedly different, although providing the same wear volume. A higher wear depth (+51%) is obtained with the AR law, located at the dome of the cup, while with the PE law the most worn region is close to the edge. Taking advantage of the linear trend of experimental volume losses, the wear coefficients obtained with the AR law should be valid despite having neglected the geometry update in the model.


Qazi T.H.,Friedrich - Alexander - University, Erlangen - Nuremberg | Qazi T.H.,Charité - Medical University of Berlin | Rai R.,Friedrich - Alexander - University, Erlangen - Nuremberg | Dippold D.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 5 more authors.
Acta Biomaterialia | Year: 2014

Cardiovascular diseases, especially myocardial infarction, are the leading cause of morbidity and mortality in the world, also resulting in huge economic burdens on national economies. A cardiac patch strategy aims at regenerating an infarcted heart by providing healthy functional cells to the injured region via a carrier substrate, and providing mechanical support, thereby preventing deleterious ventricular remodeling. In the present work, polyaniline (PANI) was doped with camphorsulfonic acid and blended with poly(glycerol-sebacate) at ratios of 10, 20 and 30 vol.% PANI content to produce electrically conductive composite cardiac patches via the solvent casting method. The composites were characterized in terms of their electrical, mechanical and physicochemical properties. The in vitro biodegradability of the composites was also evaluated. Electrical conductivity increased from 0 S cm-1 for pure PGS to 0.018 S cm-1 for 30 vol.% PANI-PGS samples. Moreover, the conductivities were preserved for at least 100 h post fabrication. Tensile tests revealed an improvement in the elastic modulus, tensile strength and elasticity with increasing PANI content. The degradation products caused a local drop in pH, which was higher in all composite samples compared with pure PGS, hinting at a buffering effect due to the presence of PANI. Finally, the cytocompatibility of the composites was confirmed when C2C12 cells attached and proliferated on samples with varying PANI content. Furthermore, leaching of acid dopants from the developed composites did not have any deleterious effect on the viability of C2C12 cells. Taken together, these results confirm the potential of PANI-PGS composites for use as substrates to modulate cellular behavior via electrical stimulation, and as biocompatible scaffolds for cardiac tissue engineering applications. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


D'Andrea E.,Largo Lucio Lazzarino | Pagnotta S.,CNR Institute of Chemistry of organometallic Compounds | Grifoni E.,CNR Institute of Chemistry of organometallic Compounds | Lorenzetti G.,CNR Institute of Chemistry of organometallic Compounds | And 3 more authors.
Spectrochimica Acta - Part B Atomic Spectroscopy | Year: 2014

The usual approach to laser-induced breakdown spectroscopy (LIBS) quantitative analysis is based on the use of calibration curves, suitably built using appropriate reference standards. More recently, statistical methods relying on the principles of artificial neural networks (ANN) are increasingly used. However, ANN analysis is often used as a 'black box' system and the peculiarities of the LIBS spectra are not exploited fully. An a priori exploration of the raw data contained in the LIBS spectra, carried out by a neural network to learn what are the significant areas of the spectrum to be used for a subsequent neural network delegated to the calibration, is able to throw light upon important information initially unknown, although already contained within the spectrum. This communication will demonstrate that an approach based on neural networks specially taylored for dealing with LIBS spectra would provide a viable, fast and robust method for LIBS quantitative analysis. This would allow the use of a relatively limited number of reference samples for the training of the network, with respect to the current approaches, and provide a fully automatizable approach for the analysis of a large number of samples. © 2014 Elsevier B.V.


PubMed | Largo Lucio Lazzarino and Northumbria University
Type: | Journal: Journal of the mechanical behavior of biomedical materials | Year: 2016

Although huge research efforts have been devoted to wear analysis of ultra-high molecular weight polyethylene (UHMWPE) in hip and knee implants, shoulder prostheses have been studied only marginally. Recently, the authors presented a numerical wear model of reverse total shoulder arthroplasties (RTSAs), and its application for estimating the wear coefficient k from experimental data according to different wear laws. In this study, such model and k expressions are exploited to investigate the sensitivity of UHMWPE wear to implant size and dimensional tolerance. A set of 10 different geometries was analysed, considering nominal diameters in the range 36-42mm, available on the market, and a cup dimensional tolerance of +0.2, -0.0mm (resulting in a diametrical clearance ranging between 0.04-0.24mm), estimated from measurements on RTSAs. Since the most reliable wear law and wear coefficient k for UHMWPE are still controversial in the literature, both the Archard law (AR) and the wear law of UHMWPE (PE), as well as four different k expressions were considered, carrying out a total of 40 simulations. Results showed that the wear volume increases with the implant size and decreases with the dimensional tolerance for both the wear laws. Interestingly, different trends were obtained for the maximum wear depth vs. clearance: the best performing implants should have a high conformity according to the AR law but low conformity for the PE law. However, according to both laws, wear is highly affected by both implant size and dimensional tolerance, although it is much more sensitive to the latter, with up to a twofold variation of wear predicted. Indeed, dimensional tolerance directly alters the clearance, and therefore the lubrication and contact pressure distribution in the implant. Rather surprisingly the role of dimensional tolerance has been completely disregarded in the literature, as well as in the standards. Furthermore, this study notes some important issues for future work, such as the validation of wear laws and predictive wear models and the sensitivity of k to implant geometry.


PubMed | Friedrich - Alexander - University, Erlangen - Nuremberg and Largo Lucio Lazzarino
Type: | Journal: Materials science & engineering. C, Materials for biological applications | Year: 2016

Nano- and micro-scale topographical features play a critical role in the induction and maintenance of various cellular properties and functions, including morphology, adhesion, gene regulation, and cell-to-cell communication. In addition, recent studies have indicated that the structure and function of heart tissue are also sensitive to mechanical cues at the nano- and micro-scale. Although fabrication methods exist for generating topographical features on polymeric scaffolds for cell culture, current techniques, especially those with nano-scale resolution, are typically complex, prohibitively expensive and not accessible to most biology laboratories. Here, we present a simple and tunable fabrication method for the production of patterned electrospun fibers that simulate the complex anisotropic and multi-scale architecture of cardiac tissue, to promote cardiac cell alignment. This method is based on the combination of electrospinning and soft lithography techniques, in which electrospun fibers, based on a blend of poly(glycerol sebacate) and poly(caprolactone), were collected on a patterned Teflon-coated silicon wafer with imprinted topographical features. Different surface topographies were investigated, such as squares and grooves, with constant or different interspatial distances. In vitro cell culture studies successfully demonstrated the alignment of both C2C12 myoblasts and neonatal rat cardiomyocytes on fabricated electrospun patterned surfaces. C2C12 cells were cultured over a period of 72h to study the effect of topographical cues on cell morphology. Cells attached within the first 8h after seeding and after 24h most of the cells started to align responding to the topographical cues. Similarly, cardiomyocytes responded to the topographical features by aligning themselves and by expressing Connexin 43 along cellular junctions. Summarizing, we have developed a new method with the potential to significantly promote cardiac tissue engineering by fabricating electrospun fibers with defined topographical features to guide and instruct donor and/or host cells.


Bertini L.,Largo Lucio Lazzarino | Frendo F.,Largo Lucio Lazzarino | Marulo G.,Largo Lucio Lazzarino
International Journal of Fatigue | Year: 2016

A series of tests have been carried out using specimens made of a tube, having a thickness of t=10 mm, joined to a plate by fillet welding. Two different kinds of specimen were employed, differing in the plate geometry (stiffness). Both kinds of specimen were tested under bending (prevalent load) and shear loading in as welded conditions. Different initiation regions for the fatigue cracks were found and significantly different fatigue resistances were obtained for the two geometries in terms of the nominal stress approach (or in terms of applied load vs cycles to failure). Two local methods for the fatigue life assessment were then applied to independently analyse the experimental results: the fictitious notch rounding approach proposed by Radaj, which is also recommended by some international standards and the more recently proposed peak stress method, which is based on the NSIF concept. It is shown that the nominal stress method, which is by far the simplest method among those recommended in standards for analysing the joint under study, fails to explain the observed different endurances. On the other side, the methods based on local stresses account for the different joint stiffness and provide a reduced scatter in the results. However, even if local approaches, accounts for differences in the structural behaviour of the joint, the knowledge of the actual geometry of the weld need to be accounted for, in order to be able to identify the fatigue crack initiation region. For a design purpose, a safe prediction of the fatigue endurance of the joint can be obtained by all the analysed methods, if the corresponding recommended design curve is used. © 2016 Elsevier Ltd. All rights reserved.


Frendo F.,Largo Lucio Lazzarino | Bertini L.,Largo Lucio Lazzarino
International Journal of Fatigue | Year: 2015

The fatigue resistance of a pipe-to-plate welded joint was investigated under combined in-phase and out-of-phase (changing principal directions) bending and torsion. The specimen consisted of a pipe having 64 mm outer diameter and 10 mm thickness, which is joined by fillet welding to a 25 mm thickness plate. The pipe and plate were made of S355 steel and the joint was not subjected to any after welding relieve treatment. This work represent an extension of a previous work by the authors, in which the fatigue resistance of the same joint was investigated under bending, torsion and combined in-phase loading. A new experimental arrangement, making use of two independent hydraulic actuators, was developed to have the possibility of making out of phase tests. Four series of tests were then carried out in the life range 105-2·106, with two bending to torsion ratios (i.e. σ/τ=3.25 and σ/τ=0.88) and two load ratios (i.e. R=-1 and R=0). For the examined joint, failures originated from the weld root, where a severe notch is present. The results confirmed a lower fatigue endurance in case of out-of-phase loading, by a factor ranging from 2 to 8 depending on the number of cycles and on the adopted failure hypothesis. © 2015 Elsevier Ltd. All rights reserved.


Bertini L.,Largo Lucio Lazzarino | Cera A.,Trenitalia S.p.A. Direzione Tecnica | Frendo F.,Largo Lucio Lazzarino
International Journal of Fatigue | Year: 2014

The fatigue resistance of pipe to plate fillet welding connections was experimentally investigated. The specimens consisted of steel tubular elements, having 10 mm wall thickness and 64 mm external diameter, joined by seam welding to a plate of 25 mm thickness and were designed in order to reproduce a typical joint used in railway bogie frames. Tests were carried out under pure bending, pure torsion and under combined in-phase loading, with two different bending-to-torsion ratios. For each loading condition, tests were conducted with R=0 (i.e. pulsating fatigue) and R=-1 (i.e. alternating fatigue). The results, obtained on the basis of the nominal stress method, show an almost independent behaviour on the load ratio R for the torsion loading and a significant effect of the load ratio R in case of bending loading. A modified equivalent stress, based on the results obtained under pure bending/torsion, is demonstrated to fit all the experimental results with a reduced scatter and a higher slope, with respect to the frequently used von Mises equivalent stress. © 2014 Elsevier Ltd. All rights reserved.

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