Polyethyleneterephthalate provides superior retention of endothelial cells during shear stress compared to polytetrafluoroethylene and pericardium

Background

Polyethyleneterephthalate (PET) and polytetrafluoroethylene (PTFE) are polymers successfully used as large diameter arterial grafts for peripheral vascular surgery. However, these prosthetic grafts are rarely used for coronary bypass surgery because of their low patency rates. Endothelialisation of the lumenal surface of these materials may improve their patency. This study aimed to compare the endothelialisation of PET, PTFE and pericardium by examining their seeding efficiency over time and the effect of various shear stresses on retention of endothelial cells.

Methods


Ovine endothelial cells at 4 × 105 cells/cm2 were seeded onto PET, PTFE and pericardium, and cultured for 1–168 hours. Cell coverage was determined via en face immunocytochemistry and cell retention was quantified after being subjected to shear stresses ranging from 0.018 to 0.037 N/m2 for 15, 30 and 60 minutes.

Results

Endothelial cells adhered to all of the materials one hour post-seeding. PET exhibited better cell retention rate, ranging from 66.9 ± 5.6% at 0.018 N/m2 for 15 min to 44.7 ± 1.9% at 0.037 N/m2 for 60 minutes, when compared to PTFE and pericardium (p < 0.0001, three-way ANOVA).

Conclusion

PET shows superior retention of endothelial cells during shear stress compare to PTFE and pericardium.

Effect of cold drawing on subsequent surface strain path and ductility during upsetting

Cold drawing is a process that sizes and smooths the surface of steel before it is cold headed to produce bolts. The effect of the changes in the mechanical properties due to cold drawing on the surface strain and ductility during the upsetting process was analysed showing that the stress and strain state can be more readily altered by changes in the process conditions (friction and height-to-diameter ratio) to cause greater increase in the failure strains than can be achieved by pre-drawing.

Influence of surface mechanical attrition treatment attrition media on the surface contamination and corrosion of magnesium

Surface mechanical attrition treatment (SMAT) is a mechanical peening process used to generate ultrafine grain surfaces on a metal. SMAT was carried out on pure magnesium using different attrition media (zirconia [ZiO2], alumina [Al2O3], and steel balls) to observe the effect on microstructure, surface residual stress, surface composition, and corrosion. Surface contamination from SMAT was characterized using glow discharge optical emission spectroscopy (GDOES). The SMAT process produced a refined grain structure on the surface of Mg but resulted in a region of elemental contamination extending ~10 μm into the substrate, regardless of the media used. Consequently, SMAT-treated surfaces showed an increased corrosion rate compared to untreated Mg, primarily through increased cathodic kinetics. This study highlights the issue of contamination resulting from the SMAT process, which is a penalty that accompanies the significant grain refinement of the surface produced by SMAT. This must be considered if attempting to exploit grain refinement for improving corrosion resistance.

Relationship between processing, surface energy and bulk properties of ultrafine silk particles

Silk particles of different sizes and shapes were produced by milling and interactions with a series of polar and non-polar gaseous probes were investigated using an inverse gas chromatography technique. The surface energy of all silk materials is mostly determined by long range dispersive interactions such as van der Waals forces. The surface energy increases and surface energy heterogeneity widens after milling. All samples have amphoteric surfaces and the concentration of acidic groups increases after milling while the surfaces remain predominantly basic. We also examined powder compression and flow behaviours using a rheometer. Increase in surface energy, surface area, and static charges in sub-micron air jet milled particles contributed to their aggregation and therefore improved flowability. However they collapse under large pressures and form highly cohesive powder. Alkaline hydrolysis resulted in more crystalline fibres which on milling produced particles with higher density, lower surface energy and improved flowability. The compressibility, bulk density and cohesion of the powders depend on the surface energy as well as on particle size, surface area, aggregation state and the testing conditions, notably the consolidated and unconsolidated states. The study has helped in understanding how surface energy and flowability of particles can be changed via different fabrication approaches.

A systematic study of carbon fibre surface grafting via in situ diazonium generation for improved interfacial shear strength in epoxy matrix composites

A recently established means of surface functionalization of unsized carbon fibres for enhanced compatibility with epoxy resins was optimised and evaluated using interfacial shear stress measurements. Interfacial adhesion has a strong influence on the bulk mechanical properties of composite materials. In this work we report on the optimisation of our aryl diazo-grafting methodology via a series of reagent concentration studies. The fibres functionalised at each concentration are characterised physically (tensile strength, modulus, coefficient of friction, and via AFM), and chemically (XPS). The interfacial shear strength (IFSS) of all treated fibres was determined via the single fibre fragmentation test, using the Kelly-Tyson model. Large increases in IFSS for all concentrations (28-47%) relative to control fibres were observed. We show that halving the reagent concentration increased the coefficient of friction of the fibre and the interfacial shear strength of the composite while resulting in no loss of the key performance characteristics in the treated fibre.

Effects of commercial diets and temperature on the growth performance and stress response of hapuku (Polyprion oxygeneios)

There is a growing interest in the development of hapuku (Polyprion oxygeneios) for aquaculture in New Zealand and Australia. This is driven by the high value of this species prized for its excellent flesh quality, texture and its rapid growth capability. As a relatively new aquaculture candidate, little is currently known about their thermal tolerance and stress response. Juveniles inhabit surface waters, have a high rate of growth and move into a demersal habitat at an age between 3 and 4 years, where water temperature is cooler (7-15. °C) and more stable. The sea surface temperature in New Zealand can reach 22. °C during the summer months in more northerly locations, and captive rearing has indicated that during periods of high temperature, growth is reduced and it is possible that the physiological response is compromised. We examined the effects of two rearing temperatures (18. °C and 22. °C) and three commercial diets on the growth of P. oxygeneios during a 14 week trial. At the end of this trial, fish were exposed to a crowding stressor, and their stress response (plasma cortisol, glucose and cholesterol levels) determined. In addition, we examined the temporal stress response of P. oxygeneios acclimated to 18. °C and 22. °C subjected to a single acute handling stress. Specific growth rate and condition factor significantly increased over time in fish reared at 18. °C, but not at 22. °C. Plasma cortisol levels in hapuku prior to and after application of the stressors were within the range observed in other teleost species and the magnitude of the cortisol response was higher in hapuku subjected to crowding than handling stress. In summary, the results indicated that rearing P. oxygeneios at temperatures of 22. °C compromised their growth and that all three diets tested promoted growth in hapuku reared at 18. °C but not at 22. °C.Statement of relevanceHapuku over 1 kg had better growth rates at 18. °C than 22. °C.

Motorcycle clothing fabric burst failure during high speed impact with an abrasive surface

High energy is involved when a rider impacts a road surface in a crash. Rider speed, height of fall and road surface morphology all contribute to the level of initial impact energy. Impact can cause fabrics and seams of protective garments to burst rendering their protective value void. The Cambridge abrasion tester tests protective clothing with a fall height of 50mm and abrasive belt speed of 28km/hr, far below what can happen in a “high side” motorcycle crash at 100km/hr. This work addresses the mechanics of what occurs in the first few microseconds of an impact and provides insight into the effect that speed has on fabric burst. This work used a Cambridge impact abrasion test to evaluate two different protective motorcycle clothing fabrics (a denim and brushed fleecy fabric over a p-aramid protective liner). It measured their abrasion resistance at an abrasion speed of 28km/hr and standard impact height. It used a high speed camera to measure the impact displacement of the test head. Fabrics with high stretch were more prone to burst failure on initial impact. Fabric burst is caused by a high speed tensile stress between the fabric coupled with the abrasion surface and the inertia of the body dragging against it. Stretch fabrics are pushed into the abrasion surface for a longer period by the body before the tensile stress occurs so the coupling force is higher. If the transition to abrasion occurs early in the impact then a fabric is less likely to burst.

Effect of bulk microstructure of commercially pure titanium on surface characteristics and fatigue properties after surface modification by sand blasting and acid-etching

Surface modification techniques are widely used to enhance the biological response to the implant materials. These techniques generally create a roughened surface, effectively increasing the surface area thus promoting cell adhesion. However, a negative side effect is a higher susceptibility of a roughened surface to failure due to the presence of multiple stress concentrators. The purpose of the study reported here was to examine the effects of surface modification by sand blasting and acid-etching (SLA) on the microstructure and fatigue performance of coarse-grained and ultrafine-grained (UFG) commercially pure titanium. Finer grain sizes, produced by equal channel angular pressing, resulted in lower values of surface roughness in SLA-processed material. This effect was associated with greater resistance of the UFG structure to plastic deformation. The fatigue properties of UFG Ti were found to be superior to those of coarse-grained Ti and conventional Ti-6Al-4V, both before and after SLA-treatment.

Determinations of stress wave velocity in a timber pole using wavelet transform

This paper presents an application of Wavelet Transfonn (WT) for determination of stress wave velocity for Non-destructive Testing of timber utility poles in service. For surface Non-destructive Testing (NDT), the hammer impact, which produces generally broadband frequency excitation, is used to generate stress wave. Moreover, due to practicality the impact location for field testing of a utility pole is on the side of the pole and 1.5 m above ground level. And the geometry of utility pole could not guarantee non-dispersive longitudinal wave. All of these issues have resulted in lack of accuracy and reliability of results from surface NDT in field testing. In recognition of such problem, this research explores methods to reliably calculate desired wave velocity by isolating wave mode and studying dispersive nature of utility pole. Fast Fourier Transfonn (FFT) is firstly conducted to determine the suitable frequency from a stress wave data. Then WT is applied on the wave data mentioned to perfonn time-frequency analysis. Velocity can be detennined by time history data of desired frequency from WT results which will be compared with the available analytical solution for longitudinal wave velocity. The results of the investigation showed that wavelet transfonn analysis can be a reliable signal processing tool for non-destructive testing in tenns of velocity detennination, which in tum also helps to detennine the embedded length of the timber pole.

An inverse routine to predict residual stress in sheet material

A method is presented to determine residual stress distribution in sheet material from data collected in a free bending test. It may be used where the residual stress distribution is symmetrical about the mid-surface as it is usually the case for frequently-used sheet metal post-processing techniques such as skin-pass or temper rolling, tension- and roller leveling. An existing inverse technique is used to obtain a residual stress profile and material constants that provide the best fit in a finite element analysis of bending with the experimentally derived moment-curvature relation. The method is verified for bending of a low-carbon stainless steel using measurement of residual stress by X-ray diffraction. The residual stresses were induced in the sheet by cold rolling. The technique described here can be used industrially as a rapid method of investigating residual stresses in incoming sheet. In processes where the deformation is principally one of bending, such as cold roll forming, it is known that residual stresses have an influence on shape defects and springback and the method presented here can be used to determine whether incoming sheet is suitable for further processing and also as a means of obtaining improved material data input for numerical simulation.

Bio-conjugation of antioxidant peptide on surface-modified gold nanoparticles: a novel approach to enhance the radical scavenging property in cancer cell

BACKGROUND: Functionalized gold nanoparticles are emerging as a promising nanocarrier for target specific delivery of the therapeutic molecules in a cancer cell, as a result it targeted selectively to the cancer cell and minimized the off-target effect. The functionalized nanomaterial (bio conjugate) brings novel functional properties, for example, the high payload of anticancer, antioxidant molecules and selective targeting of the cancer molecular markers. The current study reported the synthesis of multifunctional bioconjugate (GNPs-Pep-A) to target the cancer cell. METHODS: The GNPs-Pep-A conjugate was prepared by functionalization of GNPs with peptide-A (Pro-His-Cys-Lys-Arg-Met; Pep-A) using thioctic acid as a linker molecule. The GNPs-Pep-A was characterized and functional efficacy was tested using Retinoblastoma (RB) cancer model in vitro. RESULTS: The GNPs-Pep-A target the reactive oxygen species (ROS) in RB, Y79, cancer cell more effectively, and bring down the ROS up to 70 % relative to control (untreated cells) in vitro. On the other hand, Pep-A and GNPs showed 40 and 9 % reductions in ROS, respectively, compared to control. The effectiveness of bioconjugate indicates the synergistic effect, due to the coexistence of both organic (Pep-A) and inorganic phase (GNPs) in novel GNPs-Pep-A functional material. In addition to this, it modulates the mRNA expression of antioxidant genes glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) by two-threefolds as observed. CONCLUSIONS: The effects of GNPs-Pep-A on ROS reduction and regulation of antioxidant genes confirmed that Vitis vinifera L. polyphenol-coated GNPs synergistically improve the radical scavenging properties and enhanced the apoptosis of cancer cell.