Wataru Fujitani

Synthesis of Apatite Ceramics with Preferential Crystal Orientation

Biological hard tissues show preferential alignment of the c-axis of biological apatite (BAp) crystallites depending on the shape and stress distribution in vivo, but apatite-base bioceramics developed for bone grafting have no preferential BAp orientation. Thus, the crystal orientation was controlled for developing novel bioceramics with apatite (Ap) texture similar to biological hard tissues. Since cortical portion in a bovine femur shows a one-dimensional orientation along the longitudinal direction of long bone, the effect of heat treatment on Ap orientation was investigated in the femur bone as a starting material. Heat treatment was performed first at 600°C for 1h to remove organic constituents and subsequently at each temperature between 700°C and 1300°C. Crystal orientation and texture of BAp were measured by the micro-beam X-ray diffractometer. Size of BAp crystallites increased remarkably after a heat treatment even at 600°C for 1h and a great amount of pore remained in the Ap ceramics in exchange for the organic constituents. Several Ap grains were surrounded as a group by the pores, but additional heat treatment in a temperature range up to 900°C reduced the number of Ap grains in the group, and finally became a single grain region at 1000°C. Pore density decreased with increasing annealing temperature, especially above 1000°C. One-dimensional preferential alignment of the c-axis in Ap maintained during all the heat treatment and the degree increased with increasing annealing temperature because a lot of low-energy low angle boundaries against the c-axis existed in the starting material and preferentially remained in the synthesized Ap ceramics. It was therefore concluded that adequate heat treatment of bovine femur can give the preferential crystal orientation in Ap ceramics.

Analysis of Biological Apatite Orientation in Rat Mandibles

Abstract Recently, significant progress has been made in medical techniques for regenerating bone. However, bone evaluation techniques generally assess bone quantity as opposed to bone quality. The use of c -axis crystallite orientation of biological apatite (BAp) as a bone quality index has recently generated great interest. BAp demonstrates strong crystallographic anisotropy, and preferential alignment of BAp in each bone varies depending on the shape and stress conditions in vivo . In the mandible, complicated bone shape and stress conditions in vivo might be associated with both bone quantity and quality. In this study, we aimed to elucidate changes in the bone microstructure in the mandible using crystallographic orientation of BAp as a bone quality index. Using Crj : CD (SD) IGS female rats, we observed changes in the dentulous mandible during bone growth. Measuring points on the mandible were determined based on its positional relationship with the teeth. For analysis of bone quantity, the area and bone mineral density of cortical bone were evaluated using peripheral quantitative computed tomography (pQCT), while the orientation of the BAp c -axis, as analyzed by a micro-beam X-ray diffraction system, was used to assess bone quality. The results of both bone quantity and quality assessments indicated that changes during bone growth varied depending on the presence of teeth. We concluded that the microstructure (especially the texture) of BAp crystallite changes in correlation with variations in stress distribution in vivo resulting from changes in chewing conditions designed to optimize the dynamic chewing function.

Change in Biological Apatite Orientation in Beagle Mandible

The orientation of biological apatite (BAp) is one of the bone quality parameters dominating bone mechanical function. In the mandible, the preferential orientation of the BAp c-axis changes depending on alteration of the in vivo stress condition induced by a change in the biting stress. In this study, to clarify the functional adaptation of the preferential BAp orientation and bone mineral density (BMD), all beagle mandibular molars on one side were extracted to remove the biting stress, leading to changes in both BAp orientation and BMD. The BMD exhibited discontinuous distribution around the first molar, mainly responsible for mastication, on the normal side. However, the distribution was continuous along the mesiodistal axis of the edentulous side. The preferential BAp orientation was analyzed in mandibular cross-sections at the first molar root region. Molar extraction led to a change in the BAp orientation: immediately under the root region on the lingual sides, two-dimensional preferential alignment in the mesiodistal and biting directions of the normal side changed to one-dimensional alignment along the mesiodistal axis of the edentulous side. One-dimensional alignment was also observed on the buccal sides irrespective of molar extraction. These findings clarify the close relationship between in vivo biting stress and the preferential BAp orientation, and will be useful clinically for diagnosis, implant placement, and so on.

Adaptation of BAp crystal orientation to stress distribution in rat mandible during bone growth

Biological apatite (BAp) c-axis orientation strongly depends on stress distribution in vivo and tends to align along the principal stress direction in bones. Dentulous mandible is subjected to a complicated stress condition in vivo during chewing but few studies have been carried out on the BAp c-axis orientation; so the adaptation of BAp crystal orientation to stress distribution was examined in rat dentulous mandible during bone growth and mastication. Female SD rats 4 to 14 weeks old were prepared, and the bone mineral density (BMD) and BAp crystal orientation were analyzed in a cross-section of mandible across the first molar focusing on two positions: separated from and just under the tooth root on the same cross-section perpendicular to the mesiodistal axis. The degree of BAp orientation was analyzed by a microbeam X-ray diffractometer using Cu-Kα radiation equipped with a detector of curved one-dimensional PSPC and two-dimensional PSPC in the reflection and transmission optics, respectively. BMD quickly increased during bone growth up to 14 weeks, although it was independent of the position from the tooth root. In contrast, BAp crystal orientation strongly depended on the age and the position from the tooth root, even in the same cross-section and direction, especially along the mesiodistal and the biting axes. With increased biting stress during bone growth, the degree of BAp orientation increased along the mesiodistal axis in a position separated from the tooth root more than that near the tooth root. In contrast, BAp preferential alignment clearly appeared along the biting axis near the tooth root. We conclude that BAp orientation rather than BMD sensitively adapts to local stress distribution, especially from the chewing stress in vivo in the mandible.

Dynamic observation of the phase transformation in Cu-Al-Ni alloys using an optical reflectivity technique

The colour change of Cu-13.8 mass% Al-4.0 mass% Ni and Cu-14.2 mass% Al-3.1 mass % Ni alloys was measured after annealing at 500 and 620°C, and quenching from 900°C by means of a recording spectrophotometer equipped with an integrating sphere. A large colour change of these alloys occurred on heat treatment, depending on the different phases of γ′, β1, (γ2+β1) and (α+γ2). The phase transformation between β1 phase with the DO3 structure, and γ′ martensite with the Cu3Ti-type structure, occurred in the alloys. The phase transformation was dynamically observed by the change in the spectral reflectivity on the surface of these alloys during heating and cooling. A great hysteresis in the phase transformation was noticed in the spectral reflectivity-temperature curves and the premonitory phenomenon of the martensitic transformation was observed in the curves.

Control of Oriented Extracellular Matrix Similar to Anisotropic Bone Microstructure

Bone microstructure is dominantly composed of anisotropic extracellular matrix (ECM) in which collagen fibers and epitaxially-oriented biological apatite (BAp) crystals are preferentially aligned depending on the bone anatomical position, resulting in exerting appropriate mechanical function. The regenerative bone in bony defects is however produced without the preferential alignment of collagen fibers and the c-axis of BAp crystals, and subsequently reproduced to recover toward intact alignment. Thus, it is necessary to produce the anisotropic bone-mimetic tissue for the quick recovery of original bone tissue and the related mechanical ability in the early stage of bone regeneration. Our group is focusing on the methodology for regulating the arrangement of bone cells, the following secretion of collagen and the self-assembled mineralization by oriented BAp crystallites. Cyclic stretching in vitro to bone cells, principal-stress loading in vivo on scaffolds, step formation by slip traces on Ti single crystal, surface modification by laser induced periodic surface structure (LIPSS), anisotropic collagen substrate with the different degree of orientation, etc. can dominate bone cell arrangement and lead to the construction of the oriented ECM similar to the bone tissue architecture. This suggests that stress/strain loading, surface topography and chemical anisotropy are useful to produce bone-like microstructure in order to promote the regeneration of anisotropic bone tissue and to understand the controlling parameters for anisotropic osteogenesis induction.

Evaluation of Bone Quality in Mandible of Young M-CSF Deficient-Induced Osteopetrotic Mouse

The preferred crystallographic orientation of the biological apatite (BAp) c-axis has been shown to be one of the important bone quality indices that sensitively reflect in vivo stress distribution and dominate bone mechanical functions. The BAp orientation is expected to be regulated by bone modeling or remodeling by osteoblasts and osteoclasts whose primary functions are bone formation and absorption, respectively. Mouse with macrophage colony-stimulating factor (M-CSF) deficiency-induced osteopetrosis (op/op mouse) is a suitable animal model to elucidate the role of osteoclasts in the development of BAp orientation. In this study, the mandibles of 5-week-old mice were used because their mandible is subjected to complicated stresses including a biting stress locally applied just around the roots of the teeth and a bending stress applied along the mesiodistal axis of the mandibular body, and the response to the stress distribution is important to the formation of BAp orientation. The normal mouse mandible (control) has a one-dimension preferred BAp orientation in the mesiodistal direction, but just near the tooth root, the direction of BAp orientation changes locally to that of the tooth root responding to a biting stress. In the op/op mouse, the preferred BAp orientation only along the mesiodistal direction is found, but the degree is quite lower than that in normal mice. Moreover, the effect of biting was not observed in op/op mice because these mice are devoid of teeth eruption and are unable to bite. This suggests that M-CSF plays a critical role in forming the optimal BAp orientation, and therefore, the op/op mouse without osteoclasts cannot fully develop the appropriate bone microstructure in response to in vivo stress distribution, although BAp orientation is very sensitive to local in vivo stresses in normal animals with normal osteoclast function.