Study of the Behavior of a Bell-Shaped Colonic Self-Expandable NiTi Stent under Peristaltic Movements

Managing bowel obstruction produced by colon cancer requires an emergency intervention to patients usually in poor conditions, and it requires creating an intestinal stoma in most cases. Regardless of that the tumor may be resectable, a two-stage surgery is mandatory. To avoid these disadvantages, endoscopic placement of self-expanding stents has been introduced more than 10 years ago, as an alternative to relieve colonic obstruction. It can be used as a bridge to elective single-stage surgery avoiding a stoma or as a definitive palliative solution in patients with irresectable tumor or poor estimated survival. Stents must be capable of exerting an adequate radial pressure on the stenosed wall, keeping in mind that stent must not move or be crushed, guaranteeing an adequate lumen when affected by peristaltic waves. A finite element simulation of bell-shaped nitinol stent functionality has been done. Catheter introduction, releasing at position, and the effect of peristaltic wave were simulated. To check the reliability of the simulation, a clinical experimentation with porcine specimens was carried out. The stent presented a good deployment and flexibility. Stent behavior was excellent, expanding from the very narrow lumen corresponding to the maximum peristaltic pressure to the complete recovery of operative lumen when the pressure disappears

Tribological and mechanical properties of graphene nanoplatelet/PEEK composites

Poly(ether ether ketone) (PEEK) is a relevant thermoplastic in industry and in the biomedical sector. In this work, the lubricant capability of graphene nanoplatelets (GNPs) is used for improving the PEEK wear properties. Nanocomposites were prepared by solvent-free melt-blending and injection molding at various compositions between 1 and 10 wt. % of GNPs. The Raman G band shows a progressive increment proportional to the bulk GNP percentage. From calorimetric data, the polymer matrix structure is interpreted in terms of a 3-phase model, in which the crystalline phase fluctuates from 39 to 34% upon GNP addition. Thermal conductivity varies in accordance with the polymer crystallinity. Tensile and flexural tests show a progressive increase in the modulus, as well as a decrease in the fracture strength and the work of fracture. Most important, the composite surface undergoes a substantial improvement in hardness (60%), together with a decrease in the coefficient of friction (-38%) and a great reduction in the wear factor (-83%). Abrasion and fatigue wear mechanisms are predominant at the lowest and highest GNP concentrations respectively. In conclusion, GNPs are used without any chemical functionalization as the filler in PEEK-based materials, improving the surface hardness and the tribological properties

Tribological behavior of functionalized 1-2 layered graphene/uhmwpe composites

In this work we present the evaluation of pristine and functionalized graphene as reinforcements for UHMWPE-based composites. These composites were manufactured by physically blending graphene particles and medical grade UHMWPE powder followed by a thermo-compression process. Mechanical behaviour by means of uniaxial tension and biaxial load by small punch were carried out. Friction coefficient and wear rate were measured. In some cases composites enhanced stiffness and yield stress, although with loss of toughness. This mechanical behaviour was recuperated after a thermal treatment. Small positive changes were obtained with some graphene concentrations respect to the friction coefficient. However, 20 % of reduction in wear rate was obtained when the graphene was functionalized. In general these composites present a good trend to be a potential alternative to the current highly crosslinked polyethylenes.We thank the Ministry of Science and Education of Spain by means of the projects MAT2010-16175) and CONSOLIDER CSD2008-00023 (FUNCOAT) for financial suppor

Tribological Behavior and Mechanical Properties of Graphene/PEEK Composites

PEEK has been implemented in various orthopaedic applications due to its many beneficial mechanical, tribological, and radiolucent properties. These properties can be further tailored by introducing fillers into the PEEK matrix. In this work, graphene has been incorporated due to its high mechanical resistance, intrinsic stiffness, and lubricating properties [2]

Influence of processing conditions on microstructural, mechanical and tribological properties of graphene nanoplatelet reinforced UHMWPE

Ultra-high molecular weight polyethylene (UHMWPE) is a relevant thermoplastic in industry and a well-proven standard biomaterial in joint replacements. To enhance its tribological properties while preserving its bulk ones, composite coatings on a UHMWPE substrate were prepared using non-functionalised graphene nanoplatelet (GNP) at reinforcement concentration of 0.1–5 wt% and two mechanical mixing techniques (ball mill or blade mixer) with different consolidation temperatures of 175–240 °C. Changes in morphology and size of the UHMWPE particles before hot-pressing were observed in function of the mechanical mixing techniques applied. Wear rate was affected by graphene content, reaching a minimum at 0.5 wt% GNP, with a reduction of 20 and 15%, for ball milling and blade mixer, respectively. However, blade mixer increased the wear rate by around twice respect the ball milling results, for all the studied materials. The coefficient of friction decreased notably, by ~25%, below 3 wt% GNP content, and hardness increased by 24%, regardless of the mechanical mixing process used. Finally, consolidation temperature had a positive influence on wear rate at temperatures of around 195 °C, which could be related to the free radical scavenger effect of the GNP

A methodology for the customized design of colonic stents based on a parametric model

The choice of necessary stent properties depends mainly on the length of the stenosis and degree of occlusion. So a stent design with variable radial stiffness along its longitudinal axis would be a good option. The design proposed corresponds to a tube-based stent with closed diamond-shaped cells made from a NiTi alloy. By acting independently on different geometric factors, variable geometries can be obtained with different radial force reactions. A design adjustment according to specific requirements, in order to get a better fit to ill-duct and reduces complications, is possible. A parametric analysis using finite element has been conducted to determine the influence of slot length, number of circumferential slots, tube thickness and shape-factor on stent mechanical behavior, which allow eliminating the need for extensive experimental work and knowing and quantifying the influence of those factors. The results of finite element simulations have been used, by means of least-squares fit techniques, to obtain analytical expressions for the main mechanical characteristics of the stent (Chronic Expansive Radial Force and Radial Compression Resistance) in terms of the different geometrical factors. This allows the stent geometry to be customized without launching an iterative and costly process of modeling and simulation for each case

Estructura y morfología de las regiones degradadas del polietileno de ultra alto peso molecular en prótesis articulares

Se realiza el presente estudio en material de 3 prótesis articulares de rodilla para valorar las diferencias morfológicas y estructurales entre las zonas degradadas y no degradadas encontradas en el polietileno de ultra alto peso molecular (PEUAPM). Los implantes estudiados comprenden material degradado tras implante y retirada, material degradado sin implantar y material no degradado sin implantar. Mediante microscopía electrónica de barrido, se analiza la morfología de la zona degradada que explica la pérdida de transparencia del material en la llamada banda blanca. Mediante FTIR, se comprueba la degradación química de la zona de banda y se obtiene el índice de degradación del material, correlacionado con su cristalinidad. Mediante DSC y difractogramas de rayos X, se manifiesta en el material degradado la presencia de fase ortorrómbica pero también monoclínica, cuya cuantificación mediante rayos X abre un nuevo camino para investigar la relación entre degradación del material y fracaso del implante.Peer Reviewe

Aplicación de aleaciones con memoria de forma en el diseño y fabricación de ferulajes para corrección de las deformidades articulares de los dedos de la mano

OBJETIVO: Se propone un prototipo de férula para la corrección de las deformidades articulares de los dedos de la mano, basados en las propiedades de las aleaciones de níquel-titanio, con el fin de mejorar la aplicación de las ortesis dinámicas de acción constante, empleadas habitualmente en ortopedia. MATERIAL Y MÉTODOS: Para ello, se han diseñado diferentes prototipos de láminas y varillas, variando sus grosores. Los prototipos se han aplicado a 15 pacientes con su consentimiento, deformidad en Boutonnière, entre 40 y 60º de angulación de la articulación interfalángica proximal (IFP) del dedo y edades comprendidas entre 18 y 39 años (media 31 años), midiendo cuando empieza a notarse un cambio en la fuerza tensil de la férula sobre la deformidad del dedo con el equipo Xpresion. RESULTADOS: Los valores obtenidos, son de 3291,67 ± 222,30 gr./mm 2, guardando relación directa con el diámetro del dedo. Los resultados obtenidos hasta conseguir una corrección superior al 75 %, han sido buenos en 9 pacientes, 5 regulares (corrección entre 30 % y 75 %) y uno malo (inferior al 30 %). CONCLUSIONES: Las férulas de Níquel Titanio con tensiones constantes durante largos periodos de tiempo, hasta recuperar la posición original, con su diseño, mejoran el ajuste inicial facilitando el manejo por parte del paciente y del especialista.Peer Reviewe

Retos y nuevas perspectivas en la revegetación de sistemas forestales

Entre los días 21 y 23 de noviembre de 2007 tuvo lugar la I Reunión del Grupo de Trabajo de Repoblaciones Forestales de la Sociedad Española de Ciencias Forestales (SECF) y el grupo de trabajo de Restauración Ecológica de la Asociación Española de Ecología Terrestre, y IV Reunión del Grupo de Trabajo de Repoblaciones Forestales de la SECF en las instalaciones del Rectorado de la Universidad de Alcalá. A la reunión asistieron 74 participantes, y se presentaron un total de 39 comunicaciones orales, 18 paneles y 8 ponencias invitadas. Además, se presentó el libro “Calidad de Planta Forestal para la Restauración en Ambientes Mediterráneos” y se organizaron dos mesas redondas, una sobre “Necesidades reales de investigación en calidad de planta y cultivo de planta forestal en vivero” (Tabla 1) y otra sobre “Necesidades reales de la investigación en reforestación” (Tabla 2, 3). Una densa agenda para alcanzar los principales objetivos de la reunión, la presentación de investigación de calidad en el ámbito de la revegetación de sistemas forestales, y el intercambio de experiencias e inquietudes entre los diversos colectivos implicados en la misma. Pero ¿qué imagen podemos extraer del estado actual de nuestros conocimientos en esta área a partir de las comunicaciones presentadas

Chronostratigraphy and new vertebrate sites from the upper Maastrichtian of Huesca (Spain), and their relation with the K/Pg boundary

The transitional-continental facies of the Tremp Formation within the South-Pyrenean Central Unit (Spain) contain one of the best continental vertebrate records of the Upper Cretaceous in Europe. This Pyrenean area is therefore an exceptional place to study the extinction of continental vertebrates across the Cretaceous/Paleogene (K/Pg) boundary, being one of the few places in Europe that has a relatively continuous record ranging from the upper Campanian to lower Eocene. The Serraduy area, located on the northwest flank of the Tremp syncline, has seen the discovery of abundant vertebrate remains in recent years, highlights being the presence of hadrosaurid dinosaurs and eusuchian crocodylomorphs. Nevertheless, although these deposits have been provisionally assigned a Maastrichtian age, they have not previously been dated with absolute or relative methods. This paper presents a detailed stratigraphic, magnetostratigraphic and biostratigraphic study for the first time in this area, making it possible to assign most vertebrate sites from the Serraduy area a late Maastrichtian age, specifically within polarity chron C29r. These results confirm that the vertebrate sites from Serraduy are among the most modern of the Upper Cretaceous in Europe, being very close to the K/Pg boundary.Spanish Ministry of Economy and Competitiveness (grant numbers CGL2014-53548-P, CGL2015-64422-P and CGL2017-85038-P), cofinanced by the European Regional Development Fund; and by the Department of Education and Science of the Aragonese Government (grant numbers DGA groups H54 and E05), cofinanced by the European Social Fund (ESF). The paleomagnetic study was possible thanks to the complementary grants (beneficiaries of FPU, grant number CGL2010-16447/BTE: Brief Stays and Temporary Transfers, year 2015) supported by the Spanish Ministry of Culture, Education and Sports; and the Laboratory of paleomagnetism of the University of Burgos (Spain). Eduardo Puértolas Pascual is the recipient of a postdoctoral grant (SFRH/BPD/116759/2016) funded by the Fundação para a Ciência e Tecnologia (FCT-MCTES)