Viscosity characterization and flow simulation and visualization of polytetrafluoroethylene paste extrusion using a green and biofriendly lubricant.

Polytetrafluoroethylene (PTFE) and expanded PTFE (ePTFE) are ideal for various applications. Because PTFE does not flow, even when heated above its melting point, PTFE components are fabricated using a process called paste extrusion. This process entails blending PTFE powder particles with a lubricant to form PTFE paste, which is subsequently preformed, extruded, expanded (in the case of ePTFE), and sintered. In this study, ethanol was proposed as an alternative green lubricant for PTFE processing. Not only is ethanol benign and biofriendly, it provides excellent wettability and processing benefits. Using ethanol as a lubricant, the shear viscosity of PTFE paste and its flow behavior during paste extrusion were investigated. Frequency sweeps using a parallel-plate rheometer were performed on PTFE paste samples and various grits of sandpaper were used to reduce wall slip of PTFE paste. A viscosity model was generated and a multiphysics software was used to simulate PTFE paste extrusion. The simulated extrusion pressure was compared to experimental data of actual paste extrusion. Flow visualization experiments using colored PTFE layers were conducted to reveal the flow profile of the PTFE paste. The morphology of the expanded ePTFE tubes was examined using scanning electron microscopy and the effect of expansion ratio on ePTFE morphology was quantified.

Biologically Functionalized Expanded Polytetrafluoroethylene Blood Vessel Grafts.

Cardiovascular diseases plague human health because of the lack of transplantable small-diameter blood vessel (SDBV) grafts. Although expanded polytetrafluoroethylene (ePTFE) has the potential to be used as a biocompatible material for SDBV grafts, long-term patency is still the biggest challenge. As discussed in this paper, by virtue of a novel material formulation and a new and benign alcohol/water lubricating agent, biofunctionalized ePTFE blood vessel grafts aimed at providing long-term patency were fabricated. Compared to the most prevalent modification of PTFE, namely surface treatment, this method realized bulk treatment, which could guarantee homogeneous and long-lasting performance throughout PTFE products. These blood vessel grafts included embedded functional biomolecules, such as arginylglycylaspartic acid, heparin, and selenocystamine, using water as a solvent in paste extrusion and in the expansion of ePTFE. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscope results confirmed the existence of these targeting biomolecules in the as-fabricated ePTFE blood vessel grafts. Meanwhile, the greatly improved biological functions of the grafts were demonstrated via live and dead assays, cell morphology, CD31 staining, nitric oxide (NO) release, and anticoagulation tests. This novel and benign material formulation and fabrication method provides an opportunity to produce multibiofunctional ePTFE blood vessel grafts in a single step, thus yielding a potent product with significant commercial and clinical potential.

QT dynamicity, microvolt T-wave alternans, and heart rate variability during 24-hour ambulatory electrocardiogram monitoring in the healthy newborn of first to fourth day of life.

BACKGROUND: Twenty-four hour ambulatory electrocardiogram (AECG) monitoring is an established technique for integrated assessment of heart rhythm; however, comprehensive description of serial changes in cardiac electrophysiology over the first days of life in humans is lacking. The aim of this study was to determine the patterns of circadian heart rhythm based on AECG evaluation in newborns. METHODS: Twenty healthy newborns (14 boys and 6 girls) were serially examined with AECG at days 1, 2, and 4 after birth. Heart rate (HR), arrhythmias, QT dynamicity, microvolt T-wave alternans, and various indices of HR variability (HRV) including deceleration/acceleration capacity analysis were analyzed. RESULTS: There were no sex differences in HR. Supraventricular premature beats were noted in 35%, ventricular-in 15 % of newborns. Slope QT/RR was 0.35 (0.3-0.5); intercept QT/RR was 124 (93-148), QT/RR correlation coefficient (r) was 0.63 (0.53-0.85). Peak value of T-wave alternans was 32 +/- 8 (12-55) muV. Low level of HRV was typical for all parameters of time-domain analysis compared with normal limits for older children. The overall mean values of deceleration/acceleration capacity were 3.38 +/- 0.57 (2.16-4.13) and -3.58 +/- 0.67 (-2.13 to -4.38) milliseconds, respectively. CONCLUSION: The healthy newborns exhibit peculiarities of 24-hour cardiac rhythm with isolated premature beats, pauses of sinus rhythm less 1000 milliseconds, steep slope of QT/RR by analysis of QT dynamicity. There are low HRV, and symmetrical AC/DC capacity was typically for autonomic regulation of HR, probably due to high sympathetic activity at this age.

Assessing college-level learning difficulties and "at riskness" for learning disabilities and ADHD: development and validation of the learning difficulties assessment.

This article describes the development and validation of the Learning Difficulties Assessment (LDA), a normed and web-based survey that assesses perceived difficulties with reading, writing, spelling, mathematics, listening, concentration, memory, organizational skills, sense of control, and anxiety in college students. The LDA is designed to (a) map individual learning strengths and weaknesses, (b) provide users with a comparative sense of their academic skills, (c) integrate research in user-interface design to assist those with reading and learning challenges, and (d) identify individuals who may be at risk for learning disabilities and attention-deficit/hyperactivity disorder (ADHD) and who should thus be further assessed. Data from a large-scale 5-year study describing the instrument's validity as a screening tool for learning disabilities and ADHD are presented. This article also describes unique characteristics of the LDA including its user-interface design, normative characteristics, and use as a no-cost screening tool for identifying college students at risk for learning disorders and ADHD.