Preparation And Property Of The Complex Hydrogel Via Molecular Assembly

An injectable in-situ forming scaffold can be held liquid before being injected to deliver living cells or therapeutic agents. These systems can turn into gels in situ by changing conditions, such as temperature, pH, and ionic concentration. These scaffolds have many advantages, such as ease of application and localized, and prolonged drug delivery. They can be used as drug delivery systems, filler materials, tissue substitutes or temporary scaffolds. Therefore, injectable in-situ forming scaffolds are believed to have extensive use in the future.In this paper, thermo-sensitive neutral systems based on a chitosan/ glycerophosphate salt (CS/GP) complex were prepared. At physiological pH, these systems could be held liquid below room temperature and they formed monolithic gels when heated. The complex systems could be used as the injectable in-situ forming scaffolds. Various factors that affected the properties of gels were tested. The rheological properties of the complex system and the stress-strain curve of the gels were tested. Microstructure of the hydrogels and the xerogels were observed by SEM. The reversibility of the hydrogels were discussed in this paper, including thermo-reversibility and the reversibility in various medium, and the swelling degrees of the xerogels in various buffer solutions were tested. In addition, hydrogels and xerogels were characterized by DSC and FTIR spectroscopy, respectively. The results showed that an approach was provided to prepare thermo-sensitive neutral solutions based on a CS/GP complex using a mixture ofα-GP andβ-GP. The IGT, the gelation time, and the gel strength of the CS/GP complex could be controlled by adjusting the percentage ofα-GP in the GP.The effect of the additions of various substances on the properties of gels were tested in this paper, such as acid salts, base salts and neutral salts, alcohol, glucose, amino-acid and several hydrophilic polymer, etc. The results showed that the IGT,the gelation time and the gel strength could be modulated arbitrarily by adjusting the composition of the complex salts, without increasing the salt content of the system. Based on holding the properties of the gels, the salt contents of the systems could be decreased largely via adjusting the composition of the system.To study the mechanism of the sol/gel transition, the combination of chitosan and glycerophosphate salts was discussed through the test on the changes of the properties of the chitosan solution during the preparation process via chemical titration. The effect of temperature on the rheological properties and the surface tensions of the complex solution were tested. The contributions of several interactions in the complex system to the sol/gel transition were described qualitatively. The mechanism model of the sol/gel transition was put forward in this paper.Based on studies of the hydrogels mechanical characters, the mechanical model of the hydrogels were founded. Mechanical equations of the hydrogels were inferred. After mechanical characters of the hydrogels being determined, at the same time the main affecting factors and simulant errors being analyzed, reliabilities and exactness of the hydrogels mechanical model and equations were verified by experiments. Theoretical bases were established for the hydrogels studies and potential applications in the future.Several carboxymethyl chitosans (CMCS) with different degrees of substitution (DS) were prepared. A thermo-sensitive transparent hydrogels based on a CMCS/GP complex were prepared. These systems could be held liquid below room temperature and they formed monolithic gels when heated. The effect of various factors on the properties of the complex system were tested, the properties included the IGT, the rheological properties, the stress-strain curve and the transparency, etc. The results showed that the thermo-sensitive transparent hydrogels were prepared by using CMCS with DS between 0.3 and 0.6. The transparency of the solutions and the hydrogels increased with increasing DS of CMCS. In addition, a bacteria resistant hydrogels based on the CMCS/GP complex could be prepared by using CMCS with DS between 0.3 and 0.6.