Akimichi Mieki

Osteoinductive activity of composites of bone morphogenetic protein and pure titanium

Titanium sponges were infused with bone morphogenetic protein (BMP-Ti), and the osteoinductivity of the resultant composite was measured. New bone formation occurred three weeks after implantation and was identified by soft x-ray analysis. Quantitative analysis showed no significant difference between BMP-Ti composites and control samples (BMP only). Consequently, pure titanium neither inhibited nor promoted BMP activity. Chondrocytes and new bone formation occurred in direct contact with the surfaces of the titanium. X-ray microanalysis demonstrated new bone formation inside the pores of the titanium sponges. The BMP-Ti composite has interesting properties as an osteoinductive implant and has potential practical clinical applications.

Proliferation of mouse fibroblast-like and osteoblast-like cells on pure titanium films manufactured by electron beam melting.

The physical characteristics and biological compatibility of surfaces produced by electron beam melting (EBM) are not well known. In particular, there are not many reports on biocompatibility qualities. In this study, pure Ti films were manufactured using EBM. While it is reported that moderately hydrophilic biomaterial surfaces display improved cell growth and biocompatibility, contact angle measurements on the EBM‐produced pure Ti films showed slight hydrophobicity. Nonetheless, we found the cell count of both fibroblast‐like cells (L929) and osteoblast‐like cells (MC3T3‐E1) increased on pure Ti films, especially the MC3T3‐E1, which increased more than that of the control. In addition, the morphology of L929 and MC3T3‐E1 was polygonal and spindle‐shaped and the cytoskeleton was well developed in the pure Ti surface groups. Upon staining with Alizarin red S, a slight calcium deposition was observed and this level gradually rose to a remarkable level. These results indicate that pure Ti films manufactured by EBM have good biocompatibility and could be widely applied as biomedical materials in the near future.

Rheological approach for determining yield stresses in flowable resin composites prior to setting

The purpose of this study is to develop a method for quantifying the fluidity of flowable resin composites using determinations of yield stress. Five commercially available composites (AliteFlo LV, Flow-it ALC, Venus flow, Tetric N-flow, Revolution Formula2) were investigated. Yield stress values were obtained by plotting shear stresses for a range of shear rates, followed by fitting of Casson fluid models to flow curve data and extrapolation to the stress axis. To confirm that yield stress reflected fluidity, apparent viscosity at the lower shear rate (0.2 s-1) was calculated from flow curves. Yield stresses ranged from 5.4 to 43.1 Pa, and were found to capture differences in the fluidity of composites that were not captured by viscosity measurement at the low shear rate. Yield stress is directly proportional to fluidity, and could serve as a simple and precise indicator for selecting flowable resin composites for use in various clinical applications.

rhBMP-2 Induces Immature Muscular Tissue to Differentiate into Bone-Like Tissue In Vitro

The aim of this study is to induce bone from immature muscular tissue in vitro using recombinant human BMP (rhBMP)-2 and expanded polytetrafluoroethylene (ePTFE) as a scaffold. Commercially available rhBMP-2 was used in this experiment. IMTs were harvested from the forelimbs of 20th Sprague-Dawley embryonic rats and placed into a homogenizer with 10ng/μl of rhBMP-2 and then homogenized. The homogenized IMT was placed on ePTFE and cultured for 2 weeks. The analyses of histological observation, electron probe micro analyzer (EPMA), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were carried out following culture. The bone-like tissue, which was made up of osteoblast-like cells and osteoids, was partially observed by H-E staining. Moreover, strong mineral deposition was observed in the extracellular matrix by von Kossa staining. Ca, P and O were detected in the extracellular matrix by EPMA and were confirmed to be at almost the same position based on the findings of synchronized images. XRD patterns and FTIR spectra of specimen were found to have typical hydroxyapatite crystal peaks and spectra, respectively. These results suggest that rhBMP-2 induced IMT differentiation into bone-like tissue in vitro.

Osteoinductive activity of biocompatible ceramic-BMP(Bone morphogenetic protein) complex. Part 2. Titania (TiO2)-BMP complex.

Bone morphogenetic protein (BMP) was combined with titania (TiO2) to develop a new biomaterial with osteogenetic properties. To evaluate titania as a base material of the titania-BMP complex, firstly the titania were implanted in the subcutaneous tissue of rats, and secondary osteoinductive activity of titania-BMP complex was examined in the heterotopie site.In the first experiment, titania particles (purity: 99.8%) were molded cylindrically, and sintered at 1, 450°C in an electric furnace. The cylindrical sintered titania were 2 mm in diameter and 6 mm in length. These titania were implanted in the dorsal subcutaneous tissue of wistar rats, and as controls titarium was implanted in the same manner. Five weeks after implantation, all the animals were sacrificed, then the tissue around the samples was excised. After fixation in 10% formalin, samples were removed, and the tissue was observed histomorphologically.In the second experiment, BMP was extracted from bovine bone by 6M Urea with 0.5 MCaCl2 using the procedure reported previously. In order tomake porous titania block, titania particles mixed with resin beads were molded spherically and sintered as described before. Five mg of BMP was hound on to porous titania by using 10μl of 10% gelatine solution. The complex was lyophilized and sterilized by EOG, then implanted in the thigh muscle pouch of ddy conventional mice which were sacrificed 4 weeks after implantation. As controls, BMP (5 mg)-gelatine pellets were implanted in the same way. In order to quantitate new bone formation, bone like deposit on soft X-ray films was analyzed by means of roentgenographic and computer image analysis. Furthermore undecalcified ground sections were examined by light microscopy.After 4 weeks of implantation, the titania were surrounded by thin fibrous tissue without inflammatory cells, as were the controls. All the titania-BMP complex induced new bone. On examining the subjects by computer image analysis, no significant differerce appeared between the implantation of titania-BMP complex and controls. In histomorphological observation, woven bone was seen around the titania and in the titania pores, where woven bonecontacted partially.These results suggest that titania has biocompatibility and does not suppress BMP activity. Moreover, titania-BMP complex could be clinically applied.