Blend electrospinning of dye-functionalized chitosan and polycaprolactoe : towards biocompatible pH-sensors

The development of so-called smart materials, i.e. materials that are able to sense and respond to changes in their environment, is a hot topic in today’s research. Halochromic dyes show high potential within this field as pH-changes are visualized by a fast and simple change of color.[1] A smart halochromic sensor can be fabricated by incorporating such halochromic dye into a suitable matrix material, resulting in a custom, user-friendly product, providing clear information in a non-destructive way. Polymer nanofibers are a very well suited matrix material since nanofibrous nonwovens are characterized by a high specific surface area, small pore size, high pore volume and high absorbance capacity, making them ideal candidates for advanced, fast-responding sensor applications.[2] Dye-immobilization is, currently, a major challenge in nanofibrous sensor design as dye-doped solvent electrospinning, i.e.the most commonly applied processing technique, suffers from leaching of the dye out of the nanofibrous network.[3] Our research focuses on dye-immobilization through covalent dye-modification, where the polymer backbone is modified with a halochromic dye before the electrospinning process, providing a covalent linkage between the dye and the polymer. This technique is of particular interest for the application of natural (bio)polymers, such as chitosan.[4] The nanofibrous structure is ideally produced via blend electrospinning, which allows for the selection of a suitable carrier polymer that is widely available and well electrospinnable along with an appropriate amount of dye-modified polymer for the specific application. Of course, the question arises, if the modification of the polymer has a significant influence on the electrospinning process and, moreover, if the halochromic properties of the dye are maintained within the nanofibrous network. Within our research, chitosan was successfully modified and blend electrospun for the production of halochromic nanofibers. We found that the covalent modification could both positively as well as negatively affect the electrospinnability of the polymer. Additionally, dye-migration was significantly reduced within the entire pH-range, without majorly affecting the halochromic properties of the dyes. Future work will include the selection of a dye with a suitable pH-range for the intended application, without negatively affecting the electrospinning process. Nevertheless, our research already showed the great potential of the combination of covalent modification with electrospinning, especially for natural (bio)polymers, as it provides a universal method for versatile dye-functionalization of large-area nanofibrous nonwovens