SHENG+Nan-nan

【Abstract】Alginate sodium（ALG） and chitosan （CHI） can form fiber， films， microspheres， hydrogels and all with a wide range of biomedical applications.Few works have been done as a result of the easily flocculation of chitosan in negatively charged matrix.Complex coacervation composed of polyelectrolytes alginate and chitosan were successfully fabricated.The results showed that the lower molecular weights of the chitosan is better for the fabricated of the complex coacervation.

【Key words】alginate sodium；chitosan；Complex coacervation

0 Introduction

Sodium alginate （ALG） and chitosan （CHI） have a broad application prospect due to its solubility， stability and good biological compatibility and film-forming properties[1-2].Sodium alginate and chitosan can generate precipitation easily due to electrostatic complexation.Complex coacervation composed of polyelectrolytes alginate and lower molecular weights of the chitosan were successfully fabricated with good workability， biocompatibility， flexibility and elasticity.In this paper，by controlling the different molecular weight of chitosan to explore the conditions for fabricating the complex coacervation and the nature of the coacervation by rheology analysis.

1 Experimental Section

1.1 Materials and Instrument

Sodium alginate，different molecular weight of Chitosan，Sodium chloride，Stirrer，Centrifuge， Rheometer

1.2 Preparation of ALG/CH coacervation

We dissolved powders of alginate and different molecular weights of CHI in deionized water with a fixed concentration 0.05M and Sodium chloride 0.3M was added.We have 5 groups solution.Sodium alginate mix with the high molecular weights of the chitosan with 2%for 391mpas-1and the other 4 different molecular weight of chitosan.Take some mixture by centrifugation at 8000 rpm for 10 min at 25°C to get the the lower liquit.Explore the rheological properties of sodium alginate，chitosan polyelectrolyte complexes coacervation though the rheological steady scanning and dynamic scanning test.

2 Results and Discussion

Fig.1 shows that the left side of the macroscopic state diagram for the reaction of sodium alginate and high molecular weight chitosan and the right side of the macroscopic state diagramfor the sodium alginate and lowest molecular weight chitosan after the reaction， due to the colour of low molecular weight chitosan is brown，so the right side of the vial rendering brown.The white precipitate formed when sodium alginate mixed with a high molecular weight chitosan；while the uniform brown macroscopic state formed when sodium alginate mixed with lowest molecular weight chitosan，not large precipitates.After centrifuged，a coacervation with a certain flexibility and fluidity occurs.

Fig.2 shows，The first figure is the results of steady-state scan，the second figure is the dynamic scanning test.Polyelectrolyte complexes coacervation of sodium alginate with lowest molecular weight chitosan is a obviously shear thinning behavior.viscosity decreased with shear rate increase.From a dynamic scan，as we can seen，the storage modulus is higher than the loss modulus.It reveals that the sodium alginate chitosan polyelectrolyte complexes coacervation presents the the characteristics of gel.Sodium alginate and other lower molecular weight chitosan complexhave the similar properties.White precipitate produced immediately when sodium alginate mixed with high molecular weight chitosan，and after centrifuged，it is unable to obtain a uniform layer of coacervation.

3 Conclusion

Molecular weight of chitosan has a great influence on the generation of sodium alginate and chitosan polyelectrolyte complexes coacervation. Relatively lower molecular weight of chitosan is beneficial to produce coagulation.By excellent processability of the flocculation layer，we can preparate films，fibers and so on with high performance.It can also be used to support further research on human tissue， cell interaction.

【References】

[1]Overgaard S，Scharer JM，Moo-Young M，Bols NC.Immobilization of hybridoma cells in chitosan alginate beads.Can J Chem Eng，1991，69：439-443.

[2]Yan XL，Khor E，Lim LY.PEC films prepared from chitosan alginate coacervates.Chem Pharm Bull，2000，48：941-946.

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