LV Xian-chen
【Abstract】In this paper， chitosan was used as a macromolecular cross-linker to prepare high-strength poly（methacrylic acid） hydrogels. The effects of chitosan content and pH on the Swelling Behavior were studied. The swelling rate and the equilibrium swelling ratio decrease with increase of chitosan. Effect of pH on the equilibrium swelling ratio indicates pH-sensitivity of the hydrogels.
【Key words】Hydrogel；Chitosan；Swelling performance；pH-sensitive
中圖分类号： TQ427.26 文献标识码： A 文章编号： 2095-2457（2018）06-0178-002
1 Introduction
Hydrogels refer to materials that have a three-dimensional network structure containing a large amount of water[1].They are made of cross-linked hydrophilic macromolecules which can remain in an aqueous solution for a long time without dissolving.The character of hydrogels is attributed to the large number of hydrophilic groups bearing in the macromolecules，such as-OH，-COOH and so on[2].Due to its good water absorption properties，hydrogels have shown promising applications in biomedical fields，e.g.，as substitutes for artificial cartilage， blood vessels and tendons，and as drug release carriers [3].However，the poor mechanical properties of conventional hydrogels hinder their practical applications.
Previously，our group reported a new approach to fabricate high-strength hydrogels exploiting chitosan as a macro-cross-linker[4].Herein，the swelling behavior of chitosan cross-linked poly（methacrylic acid） （CS-PMAA） hydrogels was investigated.The effect of the amount of CS， the solid content，the dosage of KPS and the pH of the aqueous solution is reported.
2 Experimental
2.1 Swelling Performance Test of CS-PMAA Hydrogels
The prepared hydrogels were dried to constant weight. The swelling kinetics was tested using gravimetric method. The sample was taken out and weigh at predetermined time intervals.The swelling ratio（SR） of the sample was calculated according to Eq.（1）.
where SR（%）is the swelling ratio，wt is the hydrogel mass after swelling for time t，wd is the mass of the initial hydrogel.
3 Results and Discussion
3.1 Swelling Behavior of CS-PMAA Hydrogels
It can be seen from Fig.1 that the equilibrium swelling ratios decrease with the increase of CS dosage. Because the higher content of CS as a cross-linking agent，the greater cross-linking density of the gel system， which leads to a decrease in the pore size of the hydrogel.
Fig.1 The swelling kinetic curves of CS-PMAA hydrogel with different CS dosages（solid content=20wt%，KPS/MAA=0.7wt%）
Fig.2 Effect of pH on the swelling behavior（solid content=20wt%，KPS/MAA=0.7wt%）
Fig.2can be seen from the figure that the hydrogels exhibit pH-sensitivity and the higher the CS content，the worse the sensitivity of the hydrogels.
4 Conclusions
The experimental results indicate that the higher amounts of CS result in the increasing cross- linking density，which decreases the pore size and inhibit water diffusion into the network，and the equilibrium swelling ratio and the swelling rate decrease correspondingly. The prepared hydrogels demonstrates pH-sensitivity which dependent much on the CS content.
【References】
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