Skeletal repair in rabbits with calcium phosphate cements incorporated phosphorylated chitin

The effects of phosphorylated chitin (P-chitin) on the tissue responses to two kinds of calcium phosphate cements (CPCs) were investigated using experimental rabbits. One of them consisting of monocalcium phosphate monohydrate, calcium oxide, 1 M phosphate buffer (pH: 7.4) and different amounts of P-chitin (CPC-I or P-CPC-I) with relatively neutral initial pH was filled as paste into tibial defects of the rabbits for 1, 4, 12 and 22 weeks. The other kind of cement made from dicacium phosphate dihydrate/calcium hydroxide/1 M Na2HPO4/different amounts of P-chitin (CPC-II or P-CPC-II) with relatively higher initial pH was implanted as prehardened cylinders into the radial defects of the rabbits for the same periods. Pure CPC-I and CPC-II were used as controls. Histological and histomorphological studies were performed on thin un-decalcified and decalcified sections. Three different bone formation types in the resorption lacuna of the P-CPCs were found during this study. The biodegradation rate of the P-CPCs had a negative relationship with the P-chitin content. Most of the low P-chitin-containing samples were bioabsorbed in 16 weeks, while the high P-chitin-containing samples disappeared in 22 weeks. The newly formed bone was identified with back scattered scanning electron microscopy and X-ray energy-dispersive spectrometry. The results show that with P-chitin component in a certain range, the P-CPCs are biocompatible, bioabsorbable and osteoinductive and could be used as promising candidates of bone repair materials.