Shear Thickening—Shear Thinning Transitions in Chitosan Hydrogel

Shear-Thickening or dilatant behavior is difficult to observe because it is frequently confused with mechanical oscillation or with experimental deviation. In appropriated shear rate range this behavior can be identified in samples that behave as a pseudo-plastic or Newtonian fluid in large shear rate range, evidencing what is currently called the shear-thickening – shear-thinning transition, ST–ST transition, even though this transition is less common than the shear-thinning – shear-thickening transition, in which dilatancy occurs at considerably higher shear rates. Chitosan hydrogels have gained significant attention due to their potential applications in various fields, in-cluding biomedical engineering, drug delivery, and tissue regeneration. These hydro-gels due to its peculiar structure often exhibit ST-ST behavior if the shear rate applied is low enough that this transition can be observed. In this work, chitosan hydrogels obtained from chitosan with different molar masses, degrees of acetylation, degree of crosslinking, preparation methods and aging conditions prior to rheological tests at shear rates between 0.03 s-1 and 1.5 s-1, at temperatures of 22°C, 23°C and 37°C were analyzed and the ST-ST transition related to these parameters. It was found that the ST-ST transition is more influenced by pH, molarity and chitosan concentration than by thermal aging.