The carboxymethyl chitosan (CMC)/sodium alginate (SA) semi-interpenetrating polymeric network (semi-IPN) hydrogel was prepared by incorporating SA into cross-linked CMC using genipin (GP) as the cross-linker.The semi-IPN formation and cross-linking reaction mechanism of the genipin-cross-linked CMC/SA hydrogel were confirmed by means of the instrinsic viscosity measurement and Fourier transform infrared spectroscopy (FTIR).According to the measurements of mechanical properties

when the weight ratio of CMC and SA was 5:5

the tensile strength of the CMC/SA hydrogel in dry state reached 59 MPa

which was about 47.5% and 63.9% higher than that of pure CMC (40 MPa) and SA (36 MPa).The largest elongation at break of the CMC/SA hydrogel was 13.0% when SA content was 60%.The influences of the pH values and cross-linking agent concentration on the swelling characteristics of the semi-IPN hydrogel were investigated in detail.Experimental results show the swelling ratio of the semi-IPN hydrogel decreases with increasing pH values at pH 3.0

whereas at pH 3.0

the swelling ratio increases with increase of pH values.At pH=3.0

the swelling ratio is the lowest (186%)

while at pH=9.0

the swelling ratio is the highest (886%).It exhibits significant pH-sensitivity.In addition

the semi-IPN hydrogel exhibits reversibility and rapid response in swelling to pH changes.This type of semi-IPN hydrogel may be useful for stimuli-responsive drug delivery or as alternative sorbents in the removal or separation of dyes.