An intensity-enhanced dynamic light scattering technique revealed the presence of calcium phosphate clusters from 0.7 to 1.0 nm in size in a simulated body fluid. The clusters were also present in fluids undersaturated with respect to octacalcium and amorphous calcium phosphates and supersaturated with respect only to hydroxyapatite. These clusters are the growth unit of hydroxyapatite judging from the fact that hydroxyapatite grows by step flow 0.8 or 1.6 nm in height and that the probability of incorporation of the growth unit into the crystal is extremely low, as revealed previously. We propose a cluster growth model where hydroxyapatite grows by selective hexagonal packing of left-and right-handed chiral Ca 9 -(PO 4 ) 6 clusters 0.8 nm in size. Theoretically, stacking faults of clusters create a reflectiontwin crystal, edge dislocations with a Burgers vector of C/2 and screw dislocations. An example of the reflection-twin is the merohedry twin which is frequently found in cadmium chlorapatite. An atomic image corresponding to the edge dislocations with a Burgers vector of C/2 was actually obtained on the surface of synthetic single-crystal hydroxyapatite.

The conventional treatment of dental caries involves mechanical removal of the affected part and filling of the hole with a resin or metal alloy. But this method is not ideal for tiny early lesions because a disproportionate amount of healthy tooth must be removed to make the alloy or resin stick. Here we describe a dental paste of synthetic enamel that rapidly and seamlessly repairs early caries lesions by nanocrystalline growth, with minimal wastage of the natural enamel.

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An animal's hard tissue is mainly composed of crystalline calcium phosphate. In vitro, small changes in the reaction conditions affect the species of calcium phosphate formed, whereas, in vivo, distinct types of crystalline calcium phosphate are formed in a wellcontrolled spatiotemporal-dependent manner. A variety of proteins are involved in hard-tissue formation; however, the mechanisms by which they regulate crystal growth are not yet fully understood. Clarification of these mechanisms will not only lead to the development of new therapeutic regimens but will also provide guidance for the application of biomineralization in bionanotechnology. Here, we focused on the peptide motifs present in dentin matrix protein 1 (DMP1), which was previously shown to enhance hydroxylapatite (HAP) formation when immobilized on a glass substrate. We synthesized a set of artificial proteins composed of combinatorial arrangements of these motifs and successfully obtained clones that accelerated formation of HAP without immobilization. Time-resolved static light-scattering analyses revealed that, in the presence of the protein, amorphous calcium phosphate (ACP) particles increased their fractal dimension and molecular mass without increasing their gyration radii during a short period before precipitation. The protein thus facilitated reorganization of the internal structure of amorphous particles into ordered crystalline states, i.e., the direct transformation of ACP to HAP, thereby acting as a nucleus for precipitation of crystalline calcium phosphate. Without the protein, the fractal dimension, molecular mass, and gyration radii of ACP particles increased concurrently, indicating heterogeneous growth transformation. biomaterials ͉ biomineralization ͉ crystal growth ͉ protein engineering H ydroxylapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAP) is a major component of bone and teeth (1). Formation of HAP in vitro is readily affected by the small changes in reaction conditions (2-4), whereas, in vivo, it is formed under the robust biomineralization process. Various proteins have been proposed to be involved in the biomineralization of HAP (5-7). Dentin matrix protein1 (DMP1) is one of such biomineralization proteins, and the ablation of its gene results in bone malformation (8-11). He et al. (6) have shown that two peptide motifs identified in DMP1 [motif-A (ESQES) and motif-B (QESQSEQDS)] enhanced in vitro HAP formation when immobilized on a glass plate (6). Along with DMP1's motifs, several peptides and proteins have been shown to act as accelerators of HAP formation, and it has been suggested that these molecules mediate nucleation during crystal formation (12)(13)(14). The purpose of our experiment was to gain insight into the molecular mechanism by which the peptide motifs of DMP1 facilitate HAP formation through our synthetic approach (15). Because immobilization of a specimen poses impediments to time-resolved analyses, such as lightscattering photometry (16, 17), we first synthesized motifprogrammed artificial proteins from the t...

Simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma has been widely used for the in vitro assessment of the bioactivity of artificial materials and for the formation of bonelike apatite on various substrates. Ion concentrations of conventional SBF (c-SBF) are, however, not exactly equal to those of blood plasma, and hence the apatite formed in c-SBF is not the same as bone apatite in its composition and structure. Recently, the present authors prepared new kinds of SBFs (r-SBF, i-SBF, and m-SBF) with ion concentrations nearer to those of blood plasma. The r-SBF and i-SBF have ion concentrations equal to those of blood plasma in total and dissociated amounts, respectively. The m-SBF has ion concentrations equal to those of blood plasma in total amount except for the HCO(-) (3) concentration, which was set to the saturated level with respect to calcite. In the present study, the stabilities of c-SBF, r-SBF, i-SBF and m-SBF were examined in terms of cluster formation in the fluids by means of dynamic light scattering photometry. The c-SBF and m-SBF were found to form only calcium phosphate clusters, whose initial hydrodynamic diameter was approximately 1 nm, and this did not change with storage time at 36.5 degrees C. Besides the calcium phosphate clusters, r-SBF and i-SBF formed calcium carbonate clusters, whose initial hydrodynamic diameters were 10-30 nm, and these increased significantly with storage time. The formation and growth of calcium carbonate clusters in r-SBF and i-SBF can be attributed to their supersaturation with respect to calcite. These indicate that r-SBF and i-SBF lack long-term stability. The m-SBF is recommended for the assessment of bioactivity of artificial materials as well as the formation of bonelike apatite on various substrates from the viewpoint of stability as well as similarity to blood plasma.