Burçak Karagüzel Kayaoğlu

Microfluidic device on a nonwoven fabric: A potential biosensor for lactate detection

In the present study, a novel, wearable textile based microfluidic device was developed that provides a non-invasive, rapid, semi-quantitative detection of the lactate level in simulated sweat solution. The potential application was envisioned to be a biosensor that can monitor an athlete’s physical status during exercise. A photolithography technique was used for the fabrication of hydrophilic micro channels and reservoirs surrounded by hydrophobic barriers made from SU-8 negative photoresist. The reservoirs were functionalized by co-immobilization of lactate oxidase (LOX) and horseradish peroxidase (POX) enzymes. LOX uses L-(+)-Lactic acid as substrate and produces H2O2 which is a POX substrate. Then, POX oxidases H2O2 in the presence of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) and results in color formation. The studies showed that excess amount of analyte presence resulted in analyte inhibition. It was also shown that analyte pH and temperature were effective on the color formation. For effective results, analyte pH and temperature should be ≥5℃ and 25–30℃, respectively. Lower pH and higher temperature values resulted in a decrease in the enzyme activity. The textile based biosensor system could make a semi-quantitative visual detection to differentiate between the normal (<5 mM) and high (≥5 mM) lactate level: while a high lactate level led to a denser purple color formation, normal levels led to a light purple formation and a green color started to be observed.

Electrospun antibacterial nanofibrous polyvinylpyrrolidone/cetyltrimethylammonium bromide membranes for biomedical applications

Nanoscale structures with large surface area-to-volume ratios are used as biomaterial scaffolds for vascular grafts, wound dressings, and air purifying filters. Using electrospinning, nanofibers containing an antibacterial agent, cetyltrimethylammonium bromide, were prepared for wound healing application. Polyvinylpyrrolidone, known as a biocompatible additive in food and drug industries, has been used as fiber processing agent with the organic active ingredient, cetyltrimethylammonium bromide. A series of samples with different polyvinylpyrrolidone/ cetyltrimethylammonium bromide ratios were successfully prepared by this method. The morphology and electroactive characteristics of nanofibers were investigated using scanning electron microscopy, atomic force microscopy, and electrochemical impedance spectroscopy. Fiber diameters and charge transfer resistances were found to decrease with salt content, while the double-layer capacitance increased with no apparent effect on the specific capacitance providing favorable conditions for the fabrication of biomaterials. In addition, the quaternary ammonium compound (cetyltrimethylammonium bromide) with a minimum ratio of 2.5 wt% showed reduction in bacterial activity of Klebsiella pneumonia, Staphylococcus aureus, and Escherichia coli.

Adhesion strength behaviour of plasma pre-treated and laminated polypropylene nonwoven fabrics using acrylic and polyurethane-based adhesives

The adhesion strength enhancement of oxygen plasma pre-treated laminated polypropylene nonwoven fabrics using two different types of adhesives was investigated in this study. Fabric surface modification was performed using low-pressure, radio-frequency oxygen plasma treatment. Effect of plasma treatment on fabric surface wettability was determined by vertical wicking measurements. Wettability of highly hydrophobic polypropylene nonwoven samples dramatically increased with increasing plasma power and exposure time. Plasma-treated polypropylene fibers showed rougher surfaces with increased plasma power and treatment times. X-ray photoelectron spectroscopy (XPS) analysis showed that oxygen plasma treatment of polypropylene fiber surface led to a significant increase in atomic percentage of oxygen compound responsible for hydrophilic surface. Peel strength enhancement of produced laminated fabrics was observed for plasma-treated samples compared to untreated samples. PU-based adhesive attached on the surface of both plasma-treated and untreated polypropylene nonwoven, filling the spaces between the fibers due to the penetration of the adhesive agent. The improvement in surface wettability of polypropylene nonwoven and the introduced sites through oxygen plasma treatment resulted in good adhesive bonding. For both adhesives, peel strength improvement of produced laminated fabrics was observed for plasma-treated samples compared to untreated ones. After lamination with polyurethane-based adhesive and 20 wash cycles, decrease in peel bond strength was between 22% and 25% for plasma-treated samples, while it was 36% for untreated fabrics. Laminated samples using acrylic-based adhesives showed much lower peel strength values and washing resistance than samples laminated with polyurethane-based adhesives.

Plasma-induced adhesion improvement of cotton/polypropylene-laminated fabrics

In this study, improvement in the adhesion strength of plasma-pretreated and laminated cotton/polypropylene (PP) fabrics using acrylic-based adhesive was investigated. Low-temperature, low-pressure oxygen plasma was utilized for surface modification of cotton/PP-laminated fabrics. Water absorption time was measured on plasma-treated cotton fabrics at different plasma power and treatment time conditions. The plasma conditions providing the fastest liquid absorption on the surface were selected and applied during plasma pretreatments. Surface wettability increased with increasing plasma power and plasma exposure time. Plasma-induced surface morphology changes were observed via Scanning Electron Microscope (SEM) images. X-ray Photoelectron Spectroscopy (XPS) analysis showed that oxygen content on the surface increased with plasma treatment, which contributed to the surface polarity and hydrophilicity. Peel bond strength results of untreated and plasma-treated samples were analyzed to determine the effect of plasma pretreatment process. Adhesion strength values of laminated samples, before washing and after 40 wash cycles, were determined by peel bond strength tests. Before washing, adhesion strength of plasma pre-treated, laminated samples was 28–60% higher than that of untreated laminated fabrics. After 40 wash cycles, adhesion strength of plasma pre-treated and laminated samples was about 40–69% higher than the untreated laminated fabrics. Peel bond strength values decreased with the increased number of wash cycles. Plasma pretreatment enhanced both the adhesion strength and washing resistance of laminated samples.

Microfluidic Nonwoven-Based Device as a Potential Biosensor for Sweat Analysis

Monitoring body fluids such as sweat composition can provide useful information about the physiological status. Physiological monitoring of body fluids such as sweat with a textile-based system has the advantage of being non-invasive and easily accessible and such monitoring is beneficial to indicate information about bodys physiological status. In the present study, it is aimed to design a textile-based system with non-invasive methods which can be used to monitor a sportsmans performance. A novel, disposable and wearable biochemical analytical device was designed and fabricated by patterning micro channels and reservoirs using SU-8 photoresist through photolithography technique on an absorbant bicomponent Evolon® nonwoven substrate. It was obtained that hydrophilic reservoirs were well defined and demarcated by hydrophobic barriers. Therefore, no liquid leakage was observed around the reservoirs which was crucial for achieving a proper enzyme immobilization and the successful detection of the color change after the simulated sweat was deposited on the hydrophilic reservoir areas. Analyte optimization studies revealed that color change became more evident with the increasing analyte concentration until 20 mM and started to decrease with further increase due to analyte inhibition. Also, on textile fabrics, color densities started to decrease after 40 mM analyte concentration.

Seam properties of ultrasonic welded multilayered textile materials

This study examined the effects of ultrasonic welding parameters on bond strength, seam thickness and seam stiffness, as well as water permeability. For study purpose, two types of four-layered fabrics with same compositions and different areal densities suitable for inner part of sport shoes were used. Two different types of seams, lapped and superimposed, were applied for ultrasonic welding and also compared by traditional seam applied by shoe manufacturer. The morphology of different type of seams was also analyzed to observe the influence of welding parameters on the layers during the ultrasonic welding process. Bonding strength was found to depend on the seam type and composition of the joined fabric layers. It was confirmed by the shoe manufacturer that all the produced welded seams provided the requested minimum bond strength to be suitable for the use of the shoes. The traditional seams applied by the shoe manufacturer were thicker but had lower stiffness in comparison to all welded seams. It was also found out that ultrasonic welding damaged the membrane, which was confirmed by no water resistance of welded seams. Statistical analysis showed that ultrasonic welding parameters, such as welding frequency and velocity, influence the bond strength, thickness, and bending stiffness of welded seams, but the obtained results were statistically insignificant.

Utility of polyvinyl alcohol fiber-based needle punched nonwoven fabric as potential reinforcement in cementitious composites:

This study reports on the use of polyvinyl alcohol–based needle punched nonwoven fabrics in cement-based composites as a low-cost reinforcement. In this study, a nonwoven reinforcement using crimped polyvinyl alcohol fibers for cement-based composites was developed. The incorporation of nonwoven fabric in composites improved tensile and flexural properties compared to a discrete polyvinyl alcohol fiber-reinforced composite. Formation of multiple fine cracks, crimped fibers and mechanical interlocking of fibers in the nonwoven fabric structure resulted in superior mechanical performance. The failure mode was due to a single macro-crack for the discrete fiber reinforced composite as opposed to a number of fine cracks for the nonwoven reinforced composite.

Imparting hydrophobicity to natural leather through plasma polymerization for easy care effect

This study reports on the deposition of a hydrophobic coating on natural leather through a plasma polymerization method and investigates the hydrophobic behavior of the plasma coated substrate. The silicon compound of hexamethyldisiloxane (HMDSO), inactive gas argon (Ar) and toluene were used to impart surface hydrophobicity to a natural leather substrate. Surface hydrophobicity was analyzed by water contact angle, absorption time, and surface free energy measurements. The water contact angle and absorption time results showed that the surface hydrophobicity of natural leather sample was clearly improved after plasma polymerization of HMDSO on the material surface. XPS analysis showed that plasma polymerization of HMDSO/toluene compositions led to a significant increase in atomic percentage of Si compound responsible for hydrophobic surface. These atomic ratios showed that the highest amount of Si and lowest amount of N were obtained with 100 % HMDSO plasma process, confirming the higher degree of plasma polymerization than the other plasma processes. A decrease was observed in total surface free energies of the natural leather samples after plasma deposition indicating improvement in surface hydrophobicity.

Structural properties of graphene oxide fibers: from graphene oxide dispersion until continuous graphene oxide fiber

Abstract Continuous graphene oxide fiber focused for the last seven years have a very large application area such as electronic textiles, photovoltaics, batteries, fuel cells, sensors, filters. This study reports the effect of processing parameters such as time, temperature of the exfoliation together with dispersion preparation methods of graphene oxide on the properties of continuous graphene oxide fibers produced by coagulation bath. Relationship between changing parameters and structural properties of graphene oxide fiber, fiber morphology, roughness, crystalline structure have been discussed. It has been shown that crystalline structures and responses to changing parameters are different when it is an exfoliated state, dispersion state, and fiber state. For example, crystalline sizes and number of layers of GO fiber were higher than those of GO dispersion, while the crystallinity degrees and d-spaces at the GO fiber were always less than that of GO dispersion. Higher exfoliation time leads to an increase of Tex count of fiber, while longer ultrasonic time resulted in lower value compared to both shorter ultrasound time and mechanical homogenization. Shorter ultrasonic treatment and shorter exfoliation time leads to higher electrical conductivity compared to mechanical homogenization. Shorter ultrasonic treatment results in vaguely tendency of an increase of breaking strength.

Electromagnetic shielding effectiveness of carbon fabric/epoxy composite with continuous graphene oxide fiber and multiwalled carbon nanotube:

Carbon fabric composite is used in technical applications such as aircrafts in which electromagnetic shielding (electromagnetic interference–shielding effectiveness) is required. Traditionally, metallic coatings or metal plates are used for electromagnetic shielding, however, conductive filler-filled composite is also alternative to metal sheets due to its light weight. In the literatures, there are studies about effect carbon nanotube and graphene oxide flakes on electromagnetic interference; however, there are no studies encountered that search the effect of carbon nanotube/graphene oxide fiber and alignment of graphene oxide fiber on electromagnetic interference. Thus, in this study, fabrication of light-weight carbon fabric/epoxy composite filled with graphene oxide fiber, reduced graphene oxide fiber and multiwalled carbon nanotube and alignment of graphene oxide fiber was studied for the first time for both electromagnetic shielding (electromagnetic interference–shielding effectiveness) and electrical conductivity. It was found that reduced graphene oxide with two layers at the same alignment (0–0) leads to increment in the electromagnetic interference–shielding effectiveness value, while reduced graphene oxide with opposite alignment (0–90) leads to decrease in the electromagnetic interference–shielding effectiveness value. Opposite to literatures for graphene oxide flakes, highly rough surface of graphene oxide fiber and reduced graphene oxide fiber causes a deterioration in electromagnetic interference–shielding effectiveness due to disruptive multiple reflections resulted from highly rough surface of graphene oxide fiber, which causes multiple reflection effect. Multiwalled carbon nanotube generally provides higher electromagnetic interference–shielding effectiveness than graphene-based fiber because it has higher conductivity and has no disruptive effect of crimpy surface as graphene oxide fiber. Multiwalled carbon nanotube loading of 15 wt% results to 32 dB electromagnetic interference–shielding effectiveness, which is considered an adequate and moderate level of shielding for many applications.