Preparation And Characterization Of Chitosan Hydrogel With Controlled Concentric Layer Structure

As the chitosan hydrogel has excellent biocompatibility, cell affinity, biodegradability and biological activity, it is widely used in drug delivery carriers, tissue engineering and biomedical materials for stopping bleeding. But now the hydrogels mostly are disordered structure, which is different with the actual natural biological material. So how to build the hydrogel with controlled structures is urgent.In this paper,based on the reaction-diffusion method, using programmatical alternating soaking technology, the method to make the concentric chitosan hydrogel with controlled structure is founded. Using environmental scanning electron microscope (ESEM) and microscope characterizes the concentric chitosan hydrogel's macro and micro structure. Using numerical simulation method to simulate the changes of the hydrogen ion's concentration to explain the mechanism of controlled structure. And the mechanical properties of chitosan hydrogel and drug release properties are characterized.ESEM results show that the method can achieve concentric structure with controlled layer thickness, layer number and layer distribution. The forecast model to predict layer thickness and layer number in the chitosan hydrogel with uniform concentric layers of the thick layer of layers. The layer number N (ranges 15-105 layers), layer thickness D (ranges 20-500 micrometers) and the reaction time T have the following relationship N = 120 / T, D = 32.50T-7.33. At the same time, some kinds of chitosan hydrogels with certain non-uniform concentric layers are prepared, such as the structure with the cycle of two thick layers and four thin layers and the structure with the cycle of one thick layer and one thin layer. the concentric chitosan hydrogel with controlled structure have anisotropic structure within the layer:in the axial direction there is multi-ring structure; in the radial layer it is arranged in parallel fibers and show different orientation angle, which is similar with the intervertebral disc.During the gelation protonated chitosan / NaOH in the reaction-diffusion system and the chitosan hydrogel shrinkage is major factors in the formation of layers, and OH- ions will lead to dramatic changes in rapid contraction of chitosan hydrogel, which lead to the separation of chitosan hydrogel layer. The results show that the morphology of every turn, it will form a layer. So we can modulate the function of the concentration of different types of wave signals, to prepare different layered structure. Through theoretical analysis and testing, There is the basic rules to make controlled structure: In one turn, the time placed in NaOH solution less than or equal placed in the water, to prevent the residual OH- ion to impact the alternation. During the process, the design for the combination of different times, different times is needed to keep each other enclosed to prevent the residual OH- ion to impact the alternation.Mechanical tests showed that the dry compression strength of chitosan gel is 27.4±5.7MPa, which is more than the compressive strength of cancellous bone .So it can be used in non-load-bearing bone repair site; Then wet chitosan hydrogel stress-strain curve is closed to the cartilage tissues. So it can be used for cartilage repair.Rifampicin is loaded on chitosan hydrogel to study the drug release behavior, with drug loading rate of 8%. In 500h it was released only 30%, which indicates that the concentric chitosan hydrogel with rifampin drug have slow release effect. Model fitting shows that the release behavior of rifampicin is controlled by diffusion in the buffer solution, and the dissolution of the matrix scaffold.