Three dimensional Liesegang spherical layers of CaHPO 4 in gelatin ball were performed by employing CaCl 2 and Na 2 HPO 4 as the inner and outer electrolyte, respectively. Effects of concentrations of inner and outer electrolyte as well as pH on the morphologies of Liesegang rings (LRs) were investigated. As a result, it was observed that the time law, spacing law and width law found in 1D/2D gel systems were obeyed in this 3D gelatin system. The interaction of Ca 2+ and HPO 4
2− with gelatin matrix played a key role to the formation of LRs due to the existence of carboxylic groups on the gelatin chains. Using Ca 2+ as the inner electrolyte, LRs were prepared. However, employing HPO 4
2− as inner electrolyte, LRs were not obtained. Moreover, pH of gelatin solution greatly impacted on the formation of LRs. The number of LRs increased with the decrease of pH, whereas the width inversely decreased. pH 4.40 was a turn point, from which the spacing coefficient abruptly increased as pH increased. All these results indicated that the network was created by the interaction of Ca 2+ and –COO − of gelatin chains, which dominated the formation of CaHPO 4 LRs in gelatin.
In this paper, the feasibility was demonstrated to turn Liesegang patterned gelatin hydrogel into the multi-pulsed drug release system. Calcium hydrogen phosphate (CaHPO 4 ) crystals were selected as the Liesegang rings (LRs) materials. The structure of CaHPO 4 /gelatin was well tailored by adding the sodium dodecyl benzene sulfonate (SDBS) micelles or SDBS/cholesterol microcapsules. As a result, the completely isometric CaHPO 4 /gelatin LRs were prepared. The enzymolysis of gelatin with isometric LRs and cholesterol/SDBS microcapsules was carried out by using typsin. A stepwise kinetic curve of enzymolysis was obtained due to the obstacles of CaHPO 4 rings. This result indicated that CaHPO 4 /gelatin LRs were potentially a versatile platform for the multi-pulsed release of various drugs.
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