Bioinspired microstructures of chitosan hydrogel provide enhanced wear protection

We describe the fabrication of physical chitosan hydrogels exhibiting a layered structure. This bilayered structure, as shown by SEM and confocal microscopy, is composed of a thin dense superficial zone (SZ), covering a deeper zone (DZ) containing microchannels orientated perpendicularly to the SZ. We show that such structure favors diffusion of macromolecules within the hydrogel matrix up to a critical pressure, σ_c, above which channels were constricted. Moreover, we found that the SZ provided a higher wear resistance than the DZ which was severely damaged at a pressure equal to the elastic modulus of the gel. The coefficient of friction (CoF) of the SZ remained independent of the applied load with μ_SZ = 0.38 ± 0.02, while CoF measured at DZ exhibited two regimes: an initial CoF close to the value found on the SZ, and a CoF that decreased to μ_DZ = 0.18 ± 0.01 at pressures higher than the critical pressure σ_c. Overall, our results show that internal structuring is a promising avenue in controlling and improving the wear resistance of soft materials such as hydrogels.