Protein release behavior from carbonate apatite hydrogel

Incorporation of protein in poorly crystalline carbonate apatite hydrogel, the protein release behavior from the cake and the dissolution of the cake in aqueous solution were studied. Poorly crystalline apatite was prepared by precipitation of saturated solution of calcium and phosphate in air or under N₂ atmosphere. The carbonate content and particle size of obtained hydrogel depends on the maturation period and atmospheric condition. The mixture of apatite hydrogel and protein was dried for 4 days in air at 40% of relative humidity to yield cakes. The quantity of loaded cytochrome c in apatite hydrogel formed in air was 0.490 wt.%, while that in apatite hydrogel formed under N₂ atmosphere was 0.305 wt.%. But the quantity of loaded albumin in apatite hydrogel formed in air was less than that in apatite hydrogel formed under N₂ atmosphere. For the cakes containing protein immersed in aqueous solution, the protein release was less than the decrease in weight of apatite cake, which may be associated with apatite recrystallization and protein re-incorporation. The quantity of released protein may depend on the quantity of loaded protein in apatite hydrogel.