Crosslinked chitosan-based nanofilms (thickness approximately 40 nm) were prepared using a naturally occurring and nontoxic reagent, genipin, and the surface properties were studied as a function of crosslinking degree and pH, by combining three techniques: dynamic contact angle of sessile drops, quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM). The results showed a pH-response of these crosslinked chitosan nanofilms, which swelled at pH 3 and shrank at pH 6. This transition was facilitated by chitosan crosslinking, although the wettability, studied by contact angle measurements, decreased with crosslinking. QCM-D and AFM were used to study the swelling capacity and elastic properties of crosslinked chitosan nanofilms, demonstrating that the response of the nanofilms was fully reversible between pH 3 and 6, but irreversible changes occurred at pH 9. QCM-D showed variations in frequency (Δf) generated by the processes of swelling/shrinkage and variations in dissipation (ΔD), related to the changes in the structure of chitosan nanofilms under different pH values. Under various pH conditions, the AFM results also showed swelling at pH 3 and shrinking at pH 6, observing an increase in the elastic modulus from ≈500 MPa at pH 3 to ≈700 MPa at pH 6. These results allowed us to understand the pH-sensitive properties of genipin-crosslinked chitosan nanofilms, which can be very useful in smart biomaterial-based textiles.

The authors acknowledge the financial support from the InForm grant (FP7-CSA-CA 233533) and the support of the Surface and Corrosion Science division from Royal Institute of Technology (KTH) in Stockholm (Sweden), where these experiments were carried out. The authors also greatly thank the Spanish Ministry of Science and Innovation (CTQ2017-84998-P project) and the Catalan Government (2017SGR1778 grant). In addition, the European Regional Development Fund (“Fondo Europeo de Desarrollo Regional”, FEDER) is also appreciated. The “Grupo de Nanotecnología Farmacéutica”, of the Faculty of Pharmacy and Food Sciences, at the University of Barcelona (UB), which forms an R&D Associated Unit to CSIC, is also acknowledged. Moreover, the authors are very grateful to Karin Persson (RISE Research Institutes of Sweden, Stockholm) and Per Claesson (Royal Institute of Technology, KTH, Sweden), for their support and useful discussions, as well as facilitating experimental equipment.

Peer reviewed