No abstract

Apatite biomaterials have potential not only as cell vehicles for engineering bone tissue but also as regulators of calcium (Ca) concentration in situ for controlling osteoblast functions, for example, osteogenic differentiation and fate management of hematopoietic stem cells (HSCs). To design apatite materials having optimal chemical properties for the latter purpose, more detailed investigations into what effect Ca concentrations have on osteoblast functions is crucial. In this study, osteoblasts were cultured at different Ca concentrations, and the temporal alterations in osteogenic differentiation and HSC niche-related protein (angiopoietin-1, 2 [Ang1, 2]) expression were investigated. The different Ca concentrations (1.8-50 mmol/L) in the cell culture medium had no effect on the proliferation of osteoblasts, but did on the cell morphology. The higher Ca concentrations (<6 mmol/L) enhanced the mineralization as well as Ang1 expression. In addition, Ang1 expression in osteoblasts showed higher correlation with expression of connexin43, the major marker of cell-cell interactions, whereas Ang2 related to integrin beta1, the major marker of cell-matrix interactions. Thus, the local Ca concentration regulates cell morphology through the cell-cell or cell-matrix interactions, leading to the alteration of Ang1 expression in osteoblasts. Since these changes triggered by Ca are concerned with the osteogenic differentiation or reproduction of HSCs niche microenvironment, the results obtained in this study might be useful for designing apatite materials with optimal chemical properties.

Techniques developed for the in vitro reproduction of three-dimensional (3D) biomimetic tissue will be valuable for investigating changes in cell function in tissues and for fabricating cell/matrix composites for applications in tissue engineering techniques. In this study, we show that the simple application of a continuous strain to a fibrin gel facilitates the development of fibril alignment and bundle-like structures in the fibrin gel in the direction of the applied strain. Myoblasts cultured in this gel also exhibited well-aligned cell patterning in a direction parallel to the direction of the strain. Interestingly, the direction of cell proliferation was identical to that of cell alignment. Finally, the oriented cells formed linear groups that were aligned parallel to the direction of the strain and replicated the native skeletal muscle cell patterning. In addition, vein endothelial cells formed a linear, aligned vessel-like structure in this system. Thus, the system enables the in vitro reproduction of 3D aligned cell sets replicating biological tissue patterns.

To achieve the complete three-dimensional (3-D) data retrieval of the shape of dentition, dental casts were measured from four directions; occlusal, right, left, and labial sides using a line laser scanner. Reconstruction of the entire shape, including undercuts and tooth crowding area, was attempted by applying a perceptual grouping algorithm, which is one of pattern-recognition theories. In the data measured from occlusal, right and left sides, the rows of measurements were parallel to the frontal plane, and three-directionally combined data (3-DC data) was accomplished by affine transformation. While, in the labial side, transformation to the frontal plane was done since rows of the measured data were parallel to the sagittal plane. To combine the labial data with the 3-DC data and reconstruct the complete image, rearrangement of the order of the data in the file was attempted by applying the perceptual grouping. That is, the minimum total length of data combining was examined by considering the factor of proximity and continuity between the data. The most appropriate order of data combining and recognition of islands were accomplished. Using a computer graphic (CG) with a wire-frame model, complicated regions such as anterior segments showing tooth crowding and undercut area were found to be successfully reconstructed without any data defects. The accuracy of reconstruction was ascertained by comparing the characteristic distances between apexes of molars in the reconstructed model with the real cast. The difference was within 0.3 mm, and present method for dental cast reconstruction is considered to be satisfactory for the present purpose such as orthodontics.

A novel support system for implant surgery was tried out, which involves manipulating a three-dimensional (3-D) computed tomography (CT) image of a jawbone with a virtual reality force feedback haptic device. Through this virtual system, the haptic experience of bone drilling with vibration and the sound of the contra-angle handpiece could be realized. It is expected to be useful for training inexperienced dentists and educating dental students. The simulation of oral implant insertion was also focused on. A simple cylindrical implant model was inserted into a 3-D image of the jawbone by operating the haptic device, with consideration of bone condition. A rectangular solid object that served as a bone-supported surgical template was adopted, and the shapes of the bone and the implant were subtracted from the object. In this manner, the CAD of the surgical template with impressions of the bone and the implant guide holes for insertion was realized. The surgical template was milled with a computer-controlled milling machine (CAM). Surgical template accuracy was examined with an edentulous gypsum bone model having six holes for implant insertion. Simulation of the oral implant insertion and CAD/CAM of the surgical template were conducted. The milled surgical template was fitted on the gypsum bone model, and CT images were taken. Cross-sections of the guide holes in the surgical template were imaged, and misalignment between the guide holes of the surgical template and the drilled holes on the jawbone was measured. The average misalignment is less than 0.2 mm, and it indicates that the present system is potentially applicable to oral implant surgery.

No abstract

A morphologically controlled three-dimensional (3D) cell construct composed of only cells and having no scaffold material might be a valuable biologic material for tissue engineering applications, as the scaffold materials can cause delay of tissue regeneration in some conditions. To obtain such a 3D cell construct, a 3D thermoresponsive hydrogel (poly-N-isopropylacrylamide) was prepared as a mold material that changes its volume depending on the temperature. Three-dimensional osteoblast cell constructs with a variety of morphologies as well as a monolayered cell sheet were obtained by decreasing the surrounding temperature of the hydrogel designed with a predefined shape and formed by curing in a polymer mold manufactured via 3D printing. The cell sheet or 3D cell constructs detachment resulted from a simple change in the gel volume, not by the surface chemistry of the gel, because the surface hydrophilicity of the gel was maintained over a wide temperature range. These 2D/3D cell constructs have numbers of exciting applications such as cell carriers for tissue regeneration or as model tissues for the biological study.

Apatite-related calcium phosphate, the main component of biological hard tissue, has good biocompatibility and is an economical material. Methods for the synthesis of apatite materials including hydroxyapatite (HAp) have previously been established. Therefore, for many years, apatite materials have been utilized as substitute materials for bone in orthopedic and dental fields. Such types of conventional substitute materials, which are implanted in the human body, should ostensibly be chemically stable to maintain their quality over time. However, recent advances in tissue engineering have altered this concept. Physicians and researchers now seek to identify materials that alter their properties temporally and spatially to achieve ideal tissue regeneration. In order to use apatite materials for tissue engineering and as drug delivery systems, the materials require both a high affinity for cells, tissues and/or functional molecules (e.g. growth factors and genes) and controllable bioabsorbability. To achieve these properties, various physicochemical modifications of apatite materials have been attempted. In addition, fabrication desiring three-dimensional structures (e.g. size, morphology and porosity) of apatite materials for implant sites could be one of the crucial techniques used to obtain ideal prognoses. In this review, the latest research trends relating to the techniques for the fabrication and modification of apatite materials are introduced.