Studying the Effect of Temperature on the Tensile Strength of an Intravascular Catheter Using a Degradation Model / Estudiando el Efecto de la Temperatura en la Resistencia Tensil de un Catéter Intravascular Usando un Modelo de Degradación

ABSTRACT The accelerated aging process is incorporated into the design and development of intravascular catheters to assess their reliability assuring that this medical device is safe and effective for the intended use during their shelf life. The accelerated aging process is based on a common approach that assumes that the rate of aging increases by a factor of 2^(∆T/10), where ∆T is the temperature increment. However, with the life data obtained from this empirical method is difficult to do inferences about reliability. This paper presents an accelerated destructive degradation test using thermal stress to obtain degradation data directly relates reliability to critical performance characteristic, which is the tensile strength in the intravascular catheter tip considered as a critical concern in patients' safety. The degradation data model is given by a stochastic Wiener process with the drift parameter being represented as Arrhenius function. The parameters of the Wiener process and Arrhenius function are estimated using maximum likelihood; these parameters are used to estimate the first-passage time (time to failure) distribution when the intravascular catheters degradation path reaches a tensile strength critical value in each thermal stress level. Based on this, a complete product reliability assessment is performed and presented.

RESUMEN El proceso de envejecimiento acelerado es incorporado en el diseño y desarrollo de catéteres intravasculares para evaluar su confiabilidad y asegurar que el dispositivo medico es seguro y efectivo para su uso durante su vida de estante. Este proceso está basado en un enfoque que asume que la tasa de envejecimiento se incrementa por un factor de 2^(∆T/10), en donde ∆T es el incremento de temperatura. Sin embargo, con los datos de vida obtenidos de este método empírico resulta complicado realizar inferencias sobre la confiabilidad del dispositivo. Este articulo presenta una prueba de degradación acelerada destructiva que considera un estrés termal para obtener datos de degradación que se relaciona directamente la confiabilidad con la resistencia tensil de la punta de un catéter intravascular y que es considerada como una característica critica para la seguridad de los pacientes. El modelo de degradación esta dado por un proceso estocástico Wiener, con el parámetro de deriva representado la relación de Arrhenius. Los parámetros del proceso Wiener y la relación de Arrhenius son estimados mediante máxima verosimilitud; estos parámetros son usados para estimar la distribución de primer paso, la cual se caracteriza cuando la resistencia de un catéter alcanza el nivel crítico de resistencia en cada nivel de estrés. Considerando esto, se lleva a cabo y se presenta una evaluación de confiabilidad completa del producto.

Screening and characterization of medicinal plants extracts with bactericidal activity against Streptococcus mutans.

The aim of the present study was to perform a screening of extracts obtained from 15 medicinal plants using water (at 25 and 90 °C) or ethanol (at 25 °C), to bactericidal activity against cariogenic S. mutans ATCC 25175, as well as to carry out the preliminary phytochemical characterization of the extracts and HPLC/MS assay for selected extracts. The extractions were carried out for 5 h at 400 rpm. Only five from 45 tested extracts were selected based on their antibacterial activity. The IC50 varied from of 28 ppm for Quercus ilex up to 250 ppm for Jatropha dioica. Different polyphenolic and quinic acids, flavonoids, anthocyanin or tyrosol were identified by HPLC/MS in selected extracts from Rosa gallica L., Jatropha dioica Sessé, Mimosa tenuiflora (Willd.) Poir, Quercus ilex L., and Solanum nigrum. The obtained results confirm that selected extracts are good candidates to be used for cariogenic bacteria control.

Synthesis of glycerol-derived diallyl spiroorthocarbonates and the study of their antishrinking properties in acrylic dental resins.

In this work was evaluated the efficiency of an antishrinkage additive in a dental resin. This additive was a mixture 1:1 of five and six-membered ring spiroorthocarbonates functionalized with allylic groups (SOC DA). The aim of this study was to reduce the shrinkage of a typical dental resin composed of a blend of the dimethacrylates, Glycerolate bisphenol A dimethacrylate (Bis-GMA)/2-[(3,5,5-trimethyl-6-[2-(2-methyl prop-2-enoyloxy) ethoxycarbonylamino] hexyl) carbamoyloxy] ethyl, 2-methyl prop-2-enoate, (UDMA)/triethyleneglycol dimethacrylate (TEGDMA) in a 50:30.20 molar ratio, and silicon dioxide as filler. SOC DA was added at 5, 10 and 20 mol% to the already mentioned formulation. It was found that the addition of 20 mol% of SOC DA decreased 53 % the shrinkage of the cured composite material, in comparison with a formulation where it was not added the antishrinkage additive. Besides, the kinetics of photopolymerization determined by Real-Time infrared spectroscopy, demonstrated that the addition of increasing concentration of SOC DA improved the conversion of double bonds of dimethacrylates. Additionally, the presence of SOC DA at 10 % mol, helped to increase the flexural strength and the compressive strength of the composite, as a consequence of the augment of the crosslink density, induced by the ring opening polymerization of SOC DA.