A series of poly(vinyl alcohol)/water-soluble chitosan/glycerol hydrogels were prepared by irradiation followed by freeze-thawing.Yunnan Baiyao was loaded into the hydrogels by solvent sorption technique.The influences of pH

ionic strength

freeze-thawing cycles and PVA concentration on the swelling capacity and Yunnan Baiyao release behavior were investigated.The swelling capacity decreased with increasing ionic strength

and it was larger in acidic media than in neutral media.Much more amount of Yunnan Baiyao could be loaded into PVA/ws-chitosan/glycerol hydrogels than into PVA hydrogels.Yunnan Baiyao release behavior of the former hydrogel showed pH and ionic strength sensitivity due to the existence of ws-chitosan.Larger amount of Yunnan Baiyao was released in pseudo-extracellular fluid solution than in neutral media and only small amount of the drug was released in acidic media and in distilled water

which was opposite to the swelling behavior.However

it was found that the swelling capacity and Yunnan Baiyao release amount both decreased with increasing freeze-thawing cycles and PVA concentration.These results indicated that Yunnan Baiyao release amount in various release media was mainly determined by the ionic exchange capacity between the drug and the ions in the solution.However

the release amount was mainly determined by swelling capacity when the hydrogels were in the same release media for different hydrogels.The swelling rate was much larger than the drug release rate indicating that the drug release rate was mainly diffusioncontrolled.The pH sensitive drug release behavior indicated that the hydrogel had potential to be used for the oral delivery of Yunnan Baiyao.