Papers by Author: Kunio Ishikawa

Abstract: This study concerns the evaluation of the bioactivity and cells response of strontium (Sr) doped sol-gel derived S53P4 bioglass due to Sr induced osteoblast. Moreover it prevents in-vitro osteoclastic activity and is clinically used as osteoporosis treatment. The different amount of Sr was doped into the S53P4 bioglass formulation (53.82%SiO₂-1.72%P₂O₅-22.64%Na₂O-(21.76-x)%CaO-x%SrO) (x=0, 3 and 5 mol %) and synthesized via sol-gel method. These samples were denoted as 0Sr, 3Sr and 5Sr respectively. After soaking in Hank's balanced salt solution (HBSS) for 7 and 14 days, the apatite formation was examined using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) techniques. Proliferation and alkaline phosphatase activity were evaluated using osteoblastic cell line MC3T3-E1. The XRD and SEM findings confirmed the hydroxyapatite (HA) structure on the bioglass surface after soaking. More intense HA peaks were observed in 3Sr specimen on 7 day while in 5Sr specimen on 14 day. Meanwhile, 3Sr specimen showed the highest cells proliferation and ‌ significant difference in alkaline phosphatase (ALP) activity than 0Sr and 5Sr. As a result, this finding indicates that S53P4 bioglass with 3 mol % SrO (3Sr) is a good candidate for bone tissue engineering because it allows for optimum cell proliferation and ALP activity while also having a high bioactivity efficiency.

Abstract: Hydrophilicity of apatite cement was increased after O₃ gas treatment on apatite cement (AC) powder. It results on the improvement of the handling and mechanical properties of set AC. Behavior of osteoblastic cells to O₃-treated set AC was evaluated including initial cell attachment, morphology of the attached cells and proliferation using rat bone marrow cell (RBM). Cells’ response to the set AC was the same regardless of O₃ treatment. The cells well attached and spread with filopodial extensions even over the O₃-treated set AC specimens. The rates of cell proliferation on set AC were also the same regardless of O₃ treatment. The result indicated O₃ treatment of AC powder would not affect to the osteoblast cell response of set AC.

Abstract: The combination of tetracalcium phosphate (TTCP; Ca₄(PO₄)₂O) and dicalcium phosphate anhydrous (DCPA; CaHPO₄) which are known as one system of apatite cements already used in the medical and dental application. In spite of several advantages of apatite cements, such as self-setting ability and biocompatibility, their mechanical strengths are still low. The aim of this study is to improve the mechanical strength of the TTCP-DCPA apatite cement using the hydroxyapatite/collagen nanocomposite (HAp/Col). The apatite cement powder was prepared using an equimolar TTCP and DCPA with addition of 10% and 20% of the HAp/Col. That without the HAp/Col was used as a control group. Each group was mixed with 1 mol/L Na_1.8H_1.2PO₄ aqueous solution at powder/liquid ratio of 0.5 and hardened at 37°C and 100 % of relative humidity for 24 hours. A setting time of the cement was evaluated using Vicat needle according to ISO 1566 for dental zinc phosphate cements. Morphology of the cements set were observed by the scanning electron microscopy (SEM), and crystalline phases were identified by the powder X-Ray diffractometry (XRD). The mechanical strength of the cement set was evaluated by the diametral tensile strength (DTS). The setting times of cements were the shortest for the cement with HAp/Col and the longest for the control. XRD patterns of the cement at 24 hours after mixing revealed that all cements changed into apatite from the mixture of TTCP and DCPA. The DTSs of cements were the highest for the cement with 20% HAp/Col and the lowest for the control with significant differences between the cement with 20 % HAp/Col and respective other two cements. The scanning electron micrographs of the surface and fracture surface of the cements suggested that the cement with HAp/Col showed denser structure in comparison to the control and the HAp/Col fibers and/or sheets covered the fracture surface. The HAp/Col would act as reinforcement fibers as well as an adhesive of apatite granules formed by the reaction between TTCP and DCPA. The setting time and mechanical strength of apatite cement was statistically significant improved by adding 20% HAp/Col.

Abstract: Apatite cement (AC) is a breakthrough in biomaterials for the reconstruction of the bone defect. However, the replacement of AC to bone up to the present time is still controversial for researchers. Several researchers have reported that AC was replaced by bone while others claimed replacement was limited. The aim of this study is to investigate the transformation mechanism of AC to B-type carbonate apatite (CO₃Ap) using different atmosphere. An in vitro study mimicking the body environment was employed in order to examine the effect of setting atmosphere on the composition of set AC. An equimolar of tetracalcium phosphate (TTCP; Ca₄(PO₄)₂O) and dicalcium phosphate anhydrous (DCPA; CaHPO₄) mixed with distilled water was enabled to harden at 37°C and 100% of relative humidity under presence of 5% CO_2, 100% CO₂, and 100% N₂ atmospheres. XRD and FT-IR analyses revealed that in the presence of 100% CO₂ and 5% CO₂, B-type CO₃Ap could be determined and only small amounts of TTCP remained unreacted. On the contrary, in the presence of 100% N₂, the CO₃^2- bands could not be detected and larger amount of TTCP remained unreacted compared to 5% CO₂ and 100% CO₂ atmospheres. SEM morphology showed that the microstructure of AC was entangled and locked to each other. In addition, the small needle like crystals appeared in the surface of 100% N₂, similar to hydroxyapatite. We concluded that the CO₃^2- ions incorporated in AC during setting reaction may be one of the essential factors for CO₃Ap formation.

Abstract: We have established a processing method to fabricate three - dimensional porous carbonate apatite (CO₃Ap) with interconnected porous structure and improved mechanical strength. Briefly, porous CO₃Ap materials were produced via phosphorization of porous calcite precursor in hydrothermal condition. In order to make porous calcite precursor, negative replication of modified polyurethane foam template was conducted. In this study, an in vivo behavior of that porous CO₃Ap was evaluated. The interconnected porous CO₃Ap material was implanted in the tibia of Japanese male rabbits and removed after a period of 6 months. Micro-computed tomography (μ-CT) scanner and histological analysis were used to characterize the bone formation response of the porous CO₃Ap. The results suggest that porous CO₃Ap with enhanced mechanical strength was not only osteoconductive but also bioresorbable therefore it could be used as bone substitute material.

Abstract: The aim of this study is to evaluate a new and simple titanium surface modification by calcium treatment. The treatment was carried out by immersing titanium in CaCl₂ solution at 80°C which consider mild temperature. The XPS spectra showed that calcium has been successfully immobilized onto titanium surface. Moreover, the thickness of oxide layer increased after the treatment due to exposure of titanium surface to aqueous solution. In vitro evaluation revealed that the calcium treated titanium shows higher osteconductivity including greater cell attachment and proliferation. The results suggested that our current titanium surface modification is promising to improve osteoconductivity.

Abstract: The aim of present study was to fabricate porous a-tricalcium phosphate (a-TCP) with adequate mechanical strength and pore interconnectivity. First step, a-TCP spheres were exposed to acidic calcium phosphate solution to allow growth and interlocking of dicalcium phosphate dihydrate (DCPD) crystals precipitated on the surface of the a-TCP spheres. Then, the DCPD-coated a-TCP spheres were sintered at 1,500°C for 6h, which resulted in the fusion of spheres to form the interconnected porous block. XRD analysis showed single phase a-TCP was obtained. Mechanical strength of porous a-TCP was 6.9 ± 1.6 MPa and porosity was 53 ± 5%. The obtained porous a-TCP could be employed as potential bone substitute or precursor for other bioceramics like carbonate apatite and hydroxyapatite.

Abstract: Regulation of DCPD formation on β-TCP granules was achieved by exposing β-TCP granular with different concentration of acidic calcium phosphate solution. It was found that a higher amount of DCPD was formed when exposed β-TCP granular with the higher concentration of acidic calcium phosphate solution. Morphological observation shows that the surface of β-TCP granular was fully coated with DCPD crystals after exposed with the higher concentration of acidic calcium phosphate solution. These results demonstrated that the DCPD formation on the β-TCP granular surface could be regulated by varying the concentration of acidic calcium phosphate solution.

Abstract: The purpose of this study was to prepare biphasic granules containing gypsum and carbonated apatite at low temperatures. The biphasic granules were prepared using dissolution-precipitation technique at three different temperatures 30°C, 40°C and 50°C. Characterization of the biphasic granules was determined by multiple analytical methods such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infra-red (FTIR), and CHN Analysis. The obtained granules were determined by XRD as biphasic granules containing bone apatite and gypsum. The cross-section of biphasic granules was observed by SEM. The formed bone apatite was identified as B-Type carbonated apatite using FTIR The carbonate content in biphasic granules fabricated at 30°C, 40°C and 50°C were recorded by CHN analysis as 5.0 wt%, 6.1 wt% and 6.25 wt%, respectively.

Abstract: Calcium carbonate (CaCO₃) has been known as one of the components of carbonate apatite (CO₃Ap) cement. Calcite is one of the polymorph of CaCO₃ with big particle size and excellent stability. In contrast, vaterite has small particle size and a metastable phase. To discover the effect of particle size on the properties of CO₃Ap cement, this study investigated the different particle size of vaterite; calcite from vaterite, which has almost similar particle size and shape with vaterite; grounded calcite and ungrounded calcite. The powder phase of calcite or vaterite combined with dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of Na₂HPO₄ solution in 0.45 liquid to powder ratio. The paste was packed into a split stainless steel mold, covered with glass slide and kept at 37°C and 100% relative humidity for a period of time. XRD and FT-IR analysis revealed that CO₃Ap cement consisted of vaterite and DCPA transformed to pure B-type CO₃Ap in 72 hours while CO₃Ap cement that consisted of calcite with different particle size was not completely transformed to CO₃Ap even until 240 hours. We concluded that CO₃Ap cement consisted of vaterite with small particle size and metastable phase properties is more effective as starting material due to its fast transformation to CO₃Ap.