pH-sensitive textile materials as innovative wound dressings

Halochromic (or pH-sensitive) textile materials can give an indication of the pH of the surrounding environment by a visible colour change and can therefore act as first signal systems. A possible application of this textile pH-sensor can be found in wound dressings. In addition to the use of traditional textile materials such as cotton gauze, nanofibrous nonwovens may provide benefits in medical applications. This paper discusses the development of pH-sensitive cotton fabrics by the combination of standard pH-indicator dyes with standard dyeing processes. Also halochromic polyamide nanofibres were produced by adding the pH-indicator dyes to the polymer solution. Both approaches were found to be promising. After the immobilization of the dye on a textile structure, still a clearly visible colour change was present for most of the dye-textile systems. It should however be noted that the behaviour of the pH-indicator dye was dependent on the medium in which it is incorporated

Color change textile materials: a feasibility study on the use of pH-indicator dyes in textile pH-sensors

This paper verifies the possibility of using standard water-soluble pH-indicator dyes in color change textile materials made out of conventional textiles and produced by a dyeing process. After a screening process in which the color depth, levelness and the color change properties of the dyed samples were examined, some dyes were selected to study in more detail. It was found that the behavior of the indicator dyes is different when the dyes are incorporated in textile materials instead of being dissolved in an aqueous solution. Our results show that it is possible to develop a textile pH-sensor using pH-indicators and conventional textiles

Optimum sol viscosity for stable electrospinning of silica nanofibres

Silica nanofibres have, due to their excellent properties, promising characteristics for multiple applications such as filtration, composites, catalysis, etc. Silica nanofibres can be obtained by combining electrospinning and the sol–gel process. To produce silica nanofibres most of the time organic solutions are applied containing a carrying polymer, which is afterwards removed by a thermal treatment to form pure ceramic nanofibres. Although electrospinning of the pure silica precursors without carrying polymer is preferred, the parameters influencing the stability of the electrospinning process are however largely unknown. In addition, this knowledge is essential for potential upscaling of the process. In this study, the optimum viscosity to electrospin in a stable manner is determined and the way to obtain this viscosity is evaluated. Sols with a viscosity between 120 and 200 mPa.s could be electrospun in a stable way, resulting in uniform and beadless nanofibres. Furthermore, this viscosity region corresponded with nanofibres having the lowest mean nanofibre diameters. Electrospinning with diluted sols was possible as well, but electrospinning of the fresh sols was more stable. These results illustrate the importance of the viscosity and degree of crosslinking of the sol for the stable electrospinning of silica nanofibres and demonstrate that upscaling of the electrospinning process of silica nanofibres is feasibl

Polycaprolactone and polycaprolactone/chitosan nanofibres functionalised with the pH-sensitive dye Nitrazine Yellow

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The pH-sensitive properties of azo dyes in aqueous environment

Azo dyes consist of a double nitrogen-nitrogen bond connected to two aromatic moieties, creating a large conjugated pi-system. A relatively simple synthesis and large variety of colours have made azo dyes the most abundant class of colourants. The dye studied in this research, ethyl orange (EO), is a prototypical example of a halochromic (pH-sensitive) azo dye. Halochromic dyes have already proven useful for application in textile sensors since the colour change of such sensors is easy to perceive and the advantages of the parent materials (e.g. flexibility) are maintained.[1] The key to further development of smart materials is combining multiple responses that can be separately addressed by different triggers.[2] To achieve this, we need a full knowledge of the colour changing mechanism and the influence of the environment. Herein, both theoretical and experimental methods were used to unravel the halochromic properties of EO.[3] Experimental UV-VIS and Raman spectra point towards a structural change of EO in water between pH 5 and pH 3. This pH-sensitivity is modeled through a series of ab initio computations on the neutral, various singly and doubly protonated structures. Static calculations (with inclusion of implicit solvation) are successful in assigning the most probable protonation site. However, to fully understand the origin of the main absorption peaks, a molecular dynamics simulation study in a water molecular environment is used in combination with Time Dependent-DFT calculations to deduce average UV-VIS spectra which take into account the flexibility of the dye and the explicit interactions with the surrounding water molecules. The proposed methodology allows to achieve a remarkable agreement between the theoretical and experimental UV-VIS spectrum and enables to fully unravel the pH sensitive behaviour of EO in aqueous environment. References: [1] L. Van der Schueren and K. De Clerck, Textile Research Journal 80(7) 590-603 (2010). [2] M. A. C. Stuart et al., Nature Materials, 9(2) 101-113 (2010). [3] T. De Meyer et al., submitted to Chemistry - A European Journa