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/1m 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.

The function of biomacromolecules during biomineralization was studied by simulating the nucleation and growth of calcium carbonates in vitro. The synthetic crystals nucleated and grew on different organic (EDTA-insoluble proteins) and inorganic (silicon) matrices with EDTA-soluble proteins extracted from mollusk shells. The polymorph and morphology of the crystals were investigated using scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM) with selected area electron diffraction (SAED). It is found that different proteins have specialties to induce different crystals with special morphologies. The soluble proteins extracted from nacre can induce aragonite and the one from prism can induce calcite grown with a preferred orientation of[104]. The crystals induced by the same soluble proteins have the same polymorph and morphology. The insoluble proteins insoluence the density of nucleation sites as well as the sizes and quantities of the crystals.

A simple supersaturated calcification solution (SCS) was used to deposit calcium phosphate (Ca-P) on the surface of NaOH-treated titanium (NaOH-Ti), in order to study the corresponding deposition mechanism of calcium phosphate (Ca-P). No Ca-P coating from SCS was found on titanium without NaOH-treatment, while NaOH-Ti possessed the capability to induce a Ca-P coating on the titanium surface. Octacalcium phosphate (OCP) crystals were first grown on an NaOH-Ti surface, followed by hydroxyapatite (HA) with a[001] preferential orientation on OCP. It is found that two factors controlled the growth of Ca-P crystals on NaOH-Ti from SCS. First, the surface morphology of NaOH-Ti characterized with crevices seems to be beneficial for inducing a Ca-P coating from SCS; second, the basic hydroxyl, Ti-OH, radical has increased in NaOH-Ti with the increase of treating time and concentration, which facilitate the nucleation of Ca-P crystals.

Based on the investigations of crystal structure of nacre using SEM, TEM and XRD, it is proposed that there exists a domain structure of crystal orientation in the nacre. The orientation domain consists of continuous 3-10 tablets along the direction perpendicular to nacreous plane, and 1-5 tablets in a single lamina. The tablets in a domain are crystallographic identical in three dimensions. From the crack morphologies, it is found that the crack deflection, fibre pull-out and organic matrix bridging are the three main toughening mechanisms acting on nacre. The organic matrix plays an important role in the toughening of this biological composite. The biomimetically synthesized composite made of alumina and kevlar showed significant increase in the fracture energy compared with the single ceramics. The soluble proteins extracted from nacre can induce aragonite and the one from prism can induce calcite grown with the preferred orientation of 104. The insoluble proteins control the nucleation site and thus lead to a finer crystallization of CaCO3.