Preparation And Properties Of Thermosensitive, Injectable Alkylated Chitosan Hydrogel

As a kind of soft scaffolds in tissue engineering, thermosensitive and injectable hydrogels which show sol-gel transition in response to temperature have gained great interest because the cell or drug can be easily loaded into them and can be injected into the needed place to form in-situ gel. This method can avoid the surgery and relieve the suffering of patients. Chitosan/sodium-β-glycerophosphate (CS/GP) hydrogel has some advantages such as biocompatibility and injectability. However, there are some problems for CS/GP hydrogel, for example the low rate of the response to temperature, the ambiguous mechanism and so on.In this research, alkylated chitosan (ACS-4, ACS-6, ACS-8, ACS-4i) was prepared by using CS and different kinds of aldehyde. The degree of substitution of the derivative (DS) was mainly controlled by CS/aldehyde ratio. The structure and DS of ACS was investigated by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. Results showed that the obtained DS ranged from 5% to54.8%. All of the obtained alkylated chitosan was water soluble.The sol-gel transition of CS/GP and ACS/GP were studied by the test tube inverted method and rheometer. The gelation temperature (Tgel) decreased as the concentration of GP increased for both CS/GP and ACS/GP. As for ACS/GP, Tgel firstly increased and then decreased when DS increased. However, if SD was too large, ACS/GP could not gel but precipitate. When DS was about 5%, the alkyl chain length had little effect on Tgel. During cooling process, the gel-sol transition could occur for ACS/GP when DS was large enough, whereas CS/GP hydrogel was only partially thermoreversible. The mechanism of sol-gel transition was speculated as follows. As for CS/GP, CS was stabilized by the formation of the shield of water around CS at the lower temperature, which was promoted by the interaction between CS and GP. At Tgel, the water shield was destroyed and thus all kinds of the interaction between CS began forming, including the entanglement, hydrogen bond, hydrophobic interaction and so on. Hydrogen bond played an important role. As for ACS/GP, hydrophobic forces played more and more important role on sol-gel transition as the amount of hydrophobic group increased.Properties of the hydrogel were investigated by SEM and gravimetric method. It was found that xerogel showed irregular porous structure. The largest swelling degree (SD) of xerogel was about 118.9%-310% and reached equilibrium after about 334 minutes. The wet weight remaining of the hydrogels in PBS were 90%-95% after 14 days, indicating the stability of these gels. The released profile of bovine serum albumin (BSA) form these in-situ hydrogels showed that CS/GP, ACS-4-1/GP, ACS-6-1/GP had the similar release behavior. The burst release occurred in the first day, about 43.5%-49.4%. After that, the release behaviors of all gels were much smoother. BSA was released relatively more slowly from ACS/GP hydrogel than from CS/GP hydrogel.