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

Abstract

Highlights pH-sensitive PCL and PCL/chitosan nanofibres are successfully electrospun. pH-sensitive PCL and PCL/chitosan nanofibres show a clear halochromic response. Chitosan addition results in a significantly increased water sorption. Chitosan addition is indispensable for a sensitive and rapid response. Theoretical modelling on the dye-polymer interactions underpins the experimental findings. Highlights (for review)Polycaprolactone and polycaprolactone/chitosan nanofibres functionalised with pH- Polycaprolactone (PCL) is an aliphatic polyester, often used in (bio)medical applications 56 because of its biocompatibility, slow biodegradability, low-cost, non-toxicity and good 57 mechanical properties (Moghe et al., 2009; Van der Schueren et al., 2011). However, PCL is Prabhakaran et al., 2008;Yang et al., 2009; Bhattarai et al., 2009; Hong & Kim, 2011; 63 Cooper et al., 2011). Contact angle measurements were carried out with the drop-shape analysis system DSA 10- 168Mk2, coupled to a control unit G120 Mk1/G140-Mk1 and with the drop-shape analysis 169 software DSA1 (v1.80, Krüss). 171Dynamic Vapour Sorption (DVS) measurements were conducted in a Q-5000SA instrument 172(TA-instruments, Zellik, Belgium). All measurements were performed at 23 °C ± 0.1 °C. 173Deliquescent salts (sodium bromide and potassium chloride) were used to verify the humidity 174 of the instrument. 4 mg of nanofibres were placed in the quartz sample pans. At the start of 175 each moisture sorption cycle, the fibres were dried at 0 % relative humidity (RH) until the 176 weight change was stabilised to be less than 0.05 % for a period of 15 minutes. After the 177 stabilisation, the moisture sorption cycle was started and the humidity was increased hydroxide were used to adjust the pH. 196The UV-Vis spectra were recorded with a Perkin-Elmer Lambda 900 spectrophotometer. For suggests an increased interaction with water when chitosan blend nanofibres are used. 287As a final step prior to the halochromic study, the dye leaching of the samples is 288 characterised ( The nanofibrous samples were all yellow just after the electrospinning process, in agreement 306 with the acidic conditions during their production (acetic acid-formic acid solvent system). compared to the sharp transition of NY in aqueous solutions, which occurs between pH 6 and 346 8 (Fig. 3a), the response of PCL nanofibres is less sensitive (response between pH 4 and 10, observed. All PCL/chitosan samples showed a sharp transition between pH 4 and 6 (Fig. 3c). 362Also the wavelength maxima did not alter and remained constant at 474 nm and 605 nm in proposed, which will then be validated by theoretical results. After electrospinning pure PCL (Fig. 5b) with NY, no halochromic behaviour is observed, structures. The chitosan model (Fig. 5e) has a PA of 908 kJ/mol, which is much higher than 429 the value of 841 kJ/mol obtained for the PCL model (Fig. 5d). This suggests that the chitosan ( Fig. 7) is much higher, -132.3 kJ/mol. The value for dye leaching was, however, much larger...

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