Thermosensitive PNIPAM grafted alginate/chitosan PEC

Smart biomaterial functionality such as controlled adhesion properties is crucial to limit strip-off injuries. Among functional polymers, poly-N(isopropylacrylamide) (PNIPAM) allows surface properties to be changed depending on the temperature, with a transition of its properties that occurs around 32 °C, called the lower critical solution temperature (LCST). This transition is expected to modify surface interactions. Alginate and chitosan are biocompatible polymers commonly combined as polyelectrolyte complex (PEC) and are suitable for wound dressing applications. As a complex system, however, it is not so trivial to achieve an efficient functionalization. Herein, we elaborated a procedure to functionalize the surface of alginate/chitosan PECs without altering their intrinsic properties. FTIR revealed that acidic treatment led to a partial decomplexation of the PECs. Therefore, while the N-Hydroxysuccinimide/N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (NHS/EDC) coupling usually requires an intermediate pH, we showed that a preliminary acidification seemed to increase the surface grafting efficiency. Water contact angle increased from 51° to 72°, showing that PNIPAM enhanced the surface hydrophobicity. The LCST transition modified the interaction forces between PNIPAM and model surfaces: it revealed an unexpected thermosensitive behaviour as hydrophobic transition favoured interactions with hydrophilic surfaces. It was presumably due to PNIPAM/PEC substrate interactions. Finally, the surface modification did not affect the release properties of the PEC biomaterial.