Papers by Author: Mitsuru Takemoto

Abstract: We are developing a new bone paste (CaNaP paste), consists of calcium sodium phosphate (CaNaPO₄), alpha-TCP, beta-TCP and citrate. It has improved handling and mechanical property with decreased setting time. For in vivo analysis using a rabbit model, four kinds of materials (Material 1: CaNaPO₄ + alpha, beta-TCP + citrate, Material 2: commercially available CaP paste, Material 3: CaNaPO₄ + alpha-TCP + citrate, and Material 4: commercially available porous beta-TCP) were prepared, and they were implanted into the rabbit femoral condyles (n=8). After 4 weeks and 12 weeks, histo-morphometrical analyses were performed, and bone-material contact index, bone area in the material, bone area ratio around the material, degree of bone penetration into the material, and material absorptivity were calculated. Results showed that Material 1 (newly developed CaNaP pasted containing beta-TCP) is more osteoconductive than Material 2 and Material 3 (CaNaP paste without beta-TCP), and can be expected as an attractive alternative for the bone substitute material.

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: In a previous study, we have reported that sodium removal by dilute hydrochloric acid (HCl) converted the sodium titanate layer on the surface of an alkali-treated porous titanium into titania with a specific structure that has better bioactivity than sodium titanate. We have shown that a porous titanium with this treatment have good osteoinductivity in soft tissue of canines. In the present study, we investigated the effect of this treatment on the osteoconductive abilities of porous bioactive titanium implant in the long term. Three types of surface treatments were applied: (a) no treatment , (b) alkali, hot water, and heat treatment ( conventional treatment: W-AH treatment), and (c) alkali, dilute HCl, hot water, and heat treatment (Na-free treatment: HCl-AH treatment). We then examined the osteoconductivity of the materials implanted in the femoral condyles of Japanese white rabbits at 6, 12, 26, and 52 weeks. The results showed that the bone ingrowth in HCl-AH porous bioactive titanium was significantly higher than in W-AH porous bioactive titanium at 52 weeks. Therefore, sodium removal has a positive effect on the osteoconductivity of the porous bioactive titanium implant in the long term.

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: The aim of this study was to optimize the surface treatment and to accelerate the osteoinductivity of porous bioactive titanium implant. Previous studies have reported that sodium removal with hot water treatment converts sodium titanate on the surface of an alkali-treated titanium plate into titania with a specific structure, which has better bioactivity than sodium titanate. We developed a dilute hydrochloric acid (HCl) treatment for porous titanium, which removed sodium from the complexly shaped porous structure more effectively than conventional hot water treatment. Three types of surface treatments were applied: (a) alkali and heat treatment, (b) alkali, hot water, and heat treatment (conventional treatment), and (c) alkali, dilute HCl, hot water, and heat treatment (Na-free treatment). The osteoinductivity of the materials implanted in the back muscles of adult beagle dogs was examined at three, six, and twelve months. Na-free porous bioactive titanium exhibited the highest osteoinductivity, and bone formation was observed within three months. This study showed that sodium removal has a significant positive effect on the osteoinductivity of the porous bioactive titanium implant.

Abstract: Generally, characterizations of pore structures of porous biomaterials are mainly based on 2-dimensional (2-D) analysis using cross sectional micrographs. However, interconnectivity of each pore may be more important factor, when tissue ingrowth into deeper pores is considered. In this paper, using micro-CT imaging with 3-D image processing software, analyses of porous material based on 3-demensional (3-D) geometrical considerations were successfully performed. Plasmasprayed porous titanium implant (PT) and four types of sintered porous titanium implants (ST50- 200, ST50-500, ST70-200, and ST70-500) that possess different porosities (50% and 70%) and pore sizes (200-500+m and 500-1500+m) were analyzed in this study. A micro focus X-ray computed tomography system was employed to acquire microstructural information from the porous implants. Using 3-D image processing software, we performed three types of 3-D analysis including detection of the dead space (% dead pore), analysis of interconnectivity by blocking the narrow pore throat with caliber less than 52 +m (% pore with narrow throat) and analysis of material construct by contracting thin strut with thickness less than 52 +m (% construct with thin strut). ST50S and ST50L possessed interconnected porous structure with thicker strut; however, pore throat was considered to be relatively narrow. On the other hand, PT implant possesses favorable interconnectivity despite its’ low porosity; however, relatively thin strut indicate the structural disadvantage for mechanical property. These results suggest that the 3-D analysis of pore and strut structure using micro focus X-ray computed tomography and 3-D image processing software will provide effective information to develop porous implant.

Abstract: The nano-composite of a ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) and alumina (Al2O3) polycrystals (Ce-TZP/Al2O3) is attractive as a load-bearing bone substitute because of its mechanical properties and phase stability. We have developed a new method of hydrofluoric acid and heat treatment (HFT) to give a microporous structure to the surface of this Ce-TZP/Al2O3 nanocomposite ceramic. Bone-bonding ability of a microporous surface and calcium phosphate coating on Ce-TZP/Al2O3 composite has been investigated through in vivo detaching model. Thin calcium phosphate coating layer was added by alternate soaking process, and thick CaP layer was produced by soaking in simulated body fluid for 5 days. HFT treated Ce-TZP/Al2O3 composite showed high bone-bonding ability compared with the control group. Thick and thin CaP coating accelerated bone-bonding ability in early post-implantation period. The submicron microporous surface was beneficial for achieving mechanical interlocking between the ceramic and surrounding bone. These results suggest the possibility of using a Ce-TZP/Al2O3 nanocomposite ceramic with microporous surface and calcium phosphate coating as the bearing material for uncemented total joint replacements.