The effects of S-chitosan on the physical properties of calcium phosphate cements

Water-soluble disodium (1-->4)-2-deoxy-2-sulfoamino-beta-D-glucopyranuronan (S-chitosan) was prepared from chitin by successive N-deacetylation, specific carboxylation at C-6 and sulfonation. Its structure was characterized by IR spectra and elemental analysis. The S-chitosan was added to two easily developed calcium phosphate cements (CPCs). One cement was monocalcium phosphate monohydrate (MPCM) with calcium oxide (CaO) in a 1M phosphate buffer (pH 7.4)(CPC-I); the other cement was dicalcium. phosphate dihydrate (DCPD) with calcium hydroxide [Ca(OH)(2)] in a 1M Na2HPO4 solution (CPC-II). In vitro experiments showed that when S-chitosan where added to the liquid phases that the resulting S-chitosan containing CPCs had higher mechanical strengths and slightly prolonged setting times. The polyanion enhanced the mechanical strength of the CPCs by increasing the dissolubility of the cement start materials and binding the calcium ions strongly afterwards. An excess of the polyanion destroys the balances of the formulations of CPCs and lead to very slow setting processes or no setting at all.