Stability improvement of electrospun chitosan nanofibrous membranes in neutral or weak basic aqueous solutions

Further utilization of chitosan nanofibrous membranes that are electrospun from chitosan solutions in trifluoroacetic acid (TFA) with or without dichloromethane (DCM) as the modifying cosolvent is limited by the loss of the fibrous structure as soon as the membranes are in contact with neutral or weak basic aqueous solutions due to complete dissolution of the membranes. Dissolution occurs as a result of the high solubility in these aqueous media of -NH3+CF3COO- salt residues that are formed when chitosan is dissolved in TFA. Traditional neutralization with a NaOH aqueous solution only maintained partial fibrous structure. Much improvement in the neutralization method was achieved with the saturated Na2CO3 aqueous solution with an excess amount of Na2CO3(s) in the solution. We showed that electrospun chitosan nanofibrous membranes, after neutralization in the Na2CO3 aqueous solution, could maintain its fibrous structure even after continuous submersion in phosphate buffer saline (pH = 7.4) or distilled water for 12 weeks.