An injectable and self-healing novel chitosan hydrogel with low adamantane substitution degree

Chitosan (CS) is a semi-natural polymer with supreme biological function, while the strong interchain hydrogen bonds cause poor water solubility and limit its broader use. To break the semi-rigid structure of CS, a kind of CS modified by adamantane (AD-CS) was successfully synthesized by amidation reaction with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride as catalyst. The chemical structure of AD-CS was characterized by Fourier transform infrared spectroscopy and H-1 NMR. The AD substitution degree of CS is around 2%, calculated by H-1 NMR. A soft and transparent hydrogel composed of hydrogen bonds was obtained directly by simply adding a certain amount of water under mild conditions. Rheological measurements were carried out to research the mechanism of hydrogel formation by measuring the influence of different additives and conditions on the AD-CS hydrogel. Reinforced hydrogels were prepared by freezing and thawing. The mechanical strength and self-healing property of reinforced and pristine hydrogels were assessed with an oscillatory rheometer. The modulus of the reinforced hydrogel was obviously enhanced without much loss of self-healing property. Other properties such as adhesion, injectability and temperature response were also studied. These injectable and self-healing hydrogels show potential value in medical care. Additionally, this is a new method to design CS hydrogels with their original interchain hydrogen bonds. (c) 2019 Society of Chemical Industry