Preparation And Properties Of Alginate-chitosan Polyion Complex Hydrogel

Alginate is naturally occurring polyanion typically obtained from brown seaweed.Due to its biocompatibility,structure similarity to extracellular matrices and mild gelation by addition of Ca²⁺,alginate hydrogel has been extensively investigated.However,used as tissue engineering scaffold,alginate hydrogels also have some disadvantages,such as,poor mechanical strength,low stability in vivo.Furthermore,alginate is difficult to be thoroughly removed by kidney.In this paper,high strength hydrogels were prepared by electrostatic interaction between alginate and chitosan.Sodium periodate was used to solve the degradation problem.Combined with 3D printing technology,the structure and size of hydrogels were designed,and its physical and chemical properties were controlled.The same content of alginate hydrogels crosslinked with Ca²⁺or chitosan were prepared.Then axial compression test was carried out on the two hydrogels.Alginate hydrogels were broken at 60%strain while alginate-chitosan polyion complex hydrogels were not broken at90%strain,the corresponding compression stress is 4MPa.With the increase concentration of alginate and chitosan,the mechanical properties of hydrogels were improved.The compression stress of hydrogels prepared with 20%w/v alginate-chitosan complex solution was 7MPa.The alginate-chitosan polyion complex hydrogels were immersed in NaIO₄ solution,hemiacetal structure was obtained due to the oxidation of alginate chains by Na IO₄,after then,hydrogels can be degraded by hydrolysis.The effect of concentration of NaIO₄ and oxidation time on the properties of hydrogels were explored,the results showed that with the increase of concentration of NaIO₄ and oxidation time,mechanical properties of hydrogels were decreased,degradation rate was accelerated.In vitro degradation experiments were carried out to 35d,the mass loss ratio of different hydrogels was 80%.Chitosan is swelling but insoluble in sodium alginate solution,addition of chitosan can improve the viscosity and yield stress of alginate solution without changing the rheological properties of shear thinning,thus,alginate-chitosan complex can be used as 3D printing ink for preparation of 3D printing alginate-chitosan polyion complex hydrogels.Alginate-chitosan polyion complex hydrogels have a higher mechanical strength,which can not easily collapse during extrusion process,thus improving the structure fidelity of 3D printing hydrogels.The internal pore size of 3D printing hydrogel is controllable and interconnected,which is helpful for cells to migrate and proliferate in the material.Results of cell biology indicate that 3D printing alginate-chitosan polyion complex hydrogel is biocompatible,cells seeded on the hydrogel adhere and proliferate well.