Papers by Author: Masashi Neo

Abstract: We previously found that a positively charged Ti metal has a higher apatite forming ability in vitro than a non-charged Ti metal. For in vivo analysis using a rabbit model, two types of Ti metal were examined: porous Ti metals heat-treated subsequent to a mixed acid treatment (MHs) and porous Ti metals not heat-treated subsequent to the same mixed acid treatment (MOs). Although MHs and MOs had the same macro- and micro-structure, they had different surface charges. MHs, considered positively charged, had significantly higher bone ingrowth than MOs, considered charged zero. Similarly, MHs had significantly higher percentages of bone–implant contact than MOs at 3- and 6-week. A simple heat treatment made acid-treated porous titanium implants more osteoconductive. These results suggest that a positive charge obtained by a heat treatment enhances bioactivity of acid-treated titanium implants.

Abstract: Material-induced osteoinduction has been reported in comparatively large animals such as dogs and pigs; however, it does not often occur in small animals such as rodents. In this study, we implanted the porous calcium-deficient hydroxyapatite (CDHA) in the dorsal muscles of dogs and rats, and compared cellular events occurred in 2 species with particular emphasis on the osteoclast-like multinucleated cells. In the CDHA extracted from dogs, many tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells were detected after 2 weeks, and new bone formation was observed after 4 weeks. In contrast, in rats, only a small number of TRAP-positive cells were detected and no bone formation was observed before 6 weeks. Transmission electron microscopy (TEM) revealed that multinucleated cells in the CDHA from dogs after 2 weeks showed osteoclast-like structures such as ruffled borders. However, in the CDHA from rats, there were no osteoclast-like structures observed. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that the expression of cathepsin K in dogs was higher than that in rats. These results indicate that TRAP-positive cells might be one of main factors responsible for the cross-species difference in material-induced osteoinduction.

Abstract: Several kinds of biomaterials are known to possess osteoinductive ability without bone inductive substances in ectopic implantation. β-TCP is one such material that has been reported to exhibit this ability in a canine model. In addition, prostaglandin E2 has been proved to accelerate osteogenesis in a rodent model, and one of its receptors EP4 has been considered to play a particularly important role. We examined that the EP4 agonist accelerates β-TCP-induced osteoinduction in a canine model. The results suggested that the EP4 agonist accelerated not only osteoinduction but also osteoclastogenesis prior to bone formation.

Abstract: We have developed a porous titanium implant sintered with spacer particles (porosity = 50 %, average pore size ± standard deviation = 303 ± 152 !m, yield compression strength = 100MPa). This porous titanium was successfully treated with chemical and thermal treatment that gives a bioactive micro-porous titania layer on the titanium surface, and it is expected as effective biomaterial for biological fixation on load bearing condition. In this study, ten adult female beagle dogs underwent anterior lumbar interbody fusion at L6-7 using either BT-implant or non-treated implant (NT-implant), then followed by posterior interspinous wiring and facet screw fixation. The radiographic evaluations were performed 1, 2 and 3 months postoperatively using X-ray fluoroscopy. Animals were sacrificed after 3 months postoperatively, and fusion status was evaluated by manual palpation. Histological evaluation was also performed. Both histological and radiological evaluation revealed that interbody fusion was achieved in 5 of 5 dogs (100%) in BT-group and 3 of 5 dogs (60%) in NT-group. In BT implants, we could observe a large amount of new bone formation from periphery to the center of the implant, whereas in NT implants, fibrous tissue formation was still observed even in the implants with successful fusion. The results of this study indicate that porous bioactive titanium implant will represent a new osteoconductive biomaterial with improved fusion characteristics.

Abstract: A porous structure comprises pores and pore throats with a complex three-dimensional network structure, and many investigators have described the relationship between average pore size and the amount of bone ingrowth. However, the influence of network structure or pore throats for tissue ingrowth has rarely been discussed. Bioactive porous titanium implants with 48% porosity were analyzed using specific algorithms for three-dimensional analysis of interconnectivity based on a micro focus X-ray computed tomography system. In vivo histological analysis was performed using the very same implants implanted into the femoral condyles of male rabbits for 6 weeks. This matching study revealed that more poorly differentiated pores tended to have narrow pore throats, especially in their shorter routes to the outside. Data obtained suggest that this sort of novel analysis is useful for evaluating bone and tissue ingrowth into porous biomaterials.

Abstract: Apatite micropattern was fabricated by a combination of biomimetic process and transcription of resist pattern. We optimized some fabrication conditions such as the height of resist pattern, temperature, concentrations and pH of simulated body fluid(SBF). Consequently, we successfully obtained apatite micropattern widely and homogeneously on a substrate in a short fabrication period.

Abstract: We had investigated the biocompatibility, osteoconductivity, and biodegradability of a porous composite of hydroxyapatite (HA) and poly-DL-lactide (PDLLA) implanted into rabbit femoral condyles. It showed excellent osteoconductivity and biodegradability as a bone substitute. Newly formed bones were remodeled, and materials were resorbed almost completely at 78weeks after implantation. In consideration of its biocompatibility and degradability, we investigated its potential for use as a cellular scaffold and evaluated its osteoinductive property. On implantation to the rat dorsal subcutaneous tissue loaded with syngeneic bone marrow cells, osteogenesis with enchondral ossification was seen both on and in the material at 3 weeks after implantation. This osteogenesis in the HA/PDLLA tended to get mature and newly formed bone tissues were found in the material by 6weeks. To investigate the osteoinductive property material itself has, we attempted to implant this porous composite material to extra-osseous canine dorsal muscle. At 2months, osteogenesis was seen in the pores of the material. It indicated the material induced osteogenesis with intramembranous ossification process. Therefore, HA/PDLLA might be a desirable material for bone substitutes and cellar scaffolds with osteoconductive and osteoinductive property.

Abstract: A novel material, namely, TiO2-HDPE (TiO2/high density polyethylene) composite was developed by our research group. Its mechanical properties are similar to those of the human cortical bone; hence, we examined the possibility of using it as a bone substitute. We prepared two groups of TiO2-HDPE; one was subjected to ultraviolet irradiation for 0.1 h and the other for 9 h. In bone bonding ability test, the former indicated a lower ability than the latter, which showed approximately 7 to 8 N of failure load. The bone bonding ability of the latter group alone is not sufficient for clinical application; on the other hand, the biocompatibility test was carried out. In the biocompatibility test, the group that was irradiated for 9 h revealed neither a major inflammatory response nor formation of neoplasm. We have to further examine alternate types of polyethylene or TiO2 particles in order to improve the bone bonding ability.

Abstract: We investigated the biocompatibility, osteoconductivity, and biodegradability of porous composite of Hydroxyapatite (HA) and Poly D/L-lactide (PDLLA). At 6weeks afterimplantation to rabbit femoral condyle, HA/PDLLA was covered with bone and contacted with bone directly. The amounts of newly formed bone in the pores had increased during the examined period. By 26weeks, bone remodeling of formed bone in the pores was seen and bone marrow tissue formation was seen in the pores of HA/PDLLA. Porous HA/PDLLA was resorbed much faster than porous HA as a control. Porous HA/PDLLA was resorbed constantly through the bone formation and bone remodeling but porous HA was hardly resorbed during the period. It might be one of the desirable materials for bone substitute. To evaluate for a scaffold, disc shaped blocks loaded with rat bone marrow cell were implanted in the subcutaneous pouch of the back of syngeneic rat. At 3weeks afterimplantation, newly bone formation in the pores was observed at ectopic site. It also suggested the availability of this material as cell scaffolds.

Abstract: High resolution X-ray CT is a powerful means for analyzing comprehensive ceramic biomaterials in a living body. The benefit of this method is that morphological and volume changes of implant materials can be evaluated without retrieve of the implant in an animal body, resulting in no killing of the animals and long term evaluation even more than one year. In this study, in situ techniques for observation of calcium phosphate cement is developed. Calcium phosphate cement (CPC) was implanted into a femur and under skin of a rat. The volume and morphology change of the CPC were repeatedly measured using the same rat for more than 12 months. The 3-dimentional (3-D) structures of the CPC were imaged and reconstructed from hundreds of 2-D cross sectional CT images, which were obtained at one time by a 360 degree rotation of the sample. The structure of the CPC was visualized with 3-D, and the volume were numerically analyzed by using a 3-D structure analyzing computer software, which enabled two-value processing and estimation of the quantities of the CPC. Moreover some of the CPC samples were retrieved and were observed by SEM. In the results, the surface of the calcium phosphate cement changed from smooth to jagged with increasing implanted period. The CPC volume implanted into bone was gradually decreased with increasing implanted period. The volume loss was 8 % after 12 months. The CPC volume under skin after 1 month increased by 7 %. After that the volume gradually decreased in next 3 months. Absorption process of CPC in a rat will be discussed.