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

Nanofibres functionalised with pH-sensitive dyes could greatly contribute to the development of stimuli-responsive materials. However, the application of biocompatible polymers is vital to allow for their use in (bio)medical applications. Therefore, this paper focuses on the development and characterisation of pH-sensitive polycaprolactone (PCL) nanofibrous structures and PCL/chitosan nanofibrous blends with 20% chitosan. Electrospinning with added Nitrazine Yellow molecules proved to be an excellent method resulting in pH-responsive non-wovens. Unlike the slow and broad response of PCL nanofibres (time lag of more than 3h), the use of blends with chitosan led to an increased sensitivity and significantly reduced response time (time lag of 5 min). These important effects are attributed to the increased hydrophilic nature of the nanofibres containing chitosan. Computational calculations indicated stronger interactions, mainly based on electrostatic interactions, of the dye with chitosan (ΔG of -132.3 kJ/mol) compared to the long-range interactions with PCL (ΔG of -35.6 kJ/mol), thus underpinning our experimental observations. In conclusion, because of the unique characteristics of chitosan, the use of PCL/chitosan blends in pH-sensitive biocompatible nanofibrous sensors is crucial.