Swelling behavior of hydroxyapatite-filled chitosan-poly (acrylic acid) polyelectrolyte complexes

A family of hydroxyapatite (HAP)-filled chitosan (CHI)-poly(acrylic acid) (PAA) polyelectrolyte complexes was prepared for the development of a degradable biocompatible organic matrix with nascent HAP that will degrade in vivo over a period of time. The effects of complexation on the degradation profile of the composites as well as the interaction between the CHI-PAA matrix and HAP in the composite system were evaluated by studying the swelling behavior of these composites in phosphate-buffered saline (PBS) by varying their CHI-PAA ratio and HAP content. All composite systems showed a general trend of three stages of swelling with the variation in the degree of equilibrium swelling. The percentage weight gain initially decreased in a linear way with increases in the HAP weight percentages, leading to a first equilibrium swelling, represented by the plateau; further increased to a greater extent; and finally stabilized. The CHI/PAA/HAP composites were stable in PBS up to a period of more than 45 days whereas the 50/50 CHI/PAA control sample showed a single equilibrium attained after a period of 288 h. Further exposure of the specimen to the medium led to its disintegration. It was also observed that, even though CHI and PAA were capable of binding HAP, because of the lack of efficient binding, the integrity of the CHI-HAP and PAA-HAP composites were lost within 48 h. The 50/50/80 CHI/PAA/HAP composition showed the minimum amount of swelling in the series. (c) 2006 Wiley Periodicals, Inc.