Michito Maruta

Fully-Interconnected Pore Forming Calcium Phosphate Cement

Calcium phosphate cement that foams fully-interconnected porous structure along with its gradual replacement to bone may be ideal for bone defect reconstruction. In the present study, α-tricalcium phosphate (αTCP) microspheres were exposed to acidic calcium phosphate solution. It was found that the αTCP microspheres set in approximately 10 min to form fully-interconnected porous structure. The porosity was approximately 50% and the pore size was 300µm. The surface of the porous body was dicalcium phosphate dihydrate whereas the inside was αTCP.

Fabrication of bone cement that fully transforms to carbonate apatite

The objective of this study was to fabricate a type of bone cement that could fully transform to carbonate apatite (CO3Ap) in physiological conditions. A combination of calcium carbonate (CaCO3) and dicalcium phosphate anhydrous was chosen as the powder phase and mixed with one of three kinds of sodium phosphate solutions: NaH2PO4, Na2HPO4, or Na3PO4. The cement that fully transformed to CO3Ap was fabricated using vaterite, instead of calcite, as a CaCO3 source. Their stability in aqueous solutions was different, regardless of the type of sodium phosphate solution. Rate of transformation to CO3Ap in descending order was Na3PO4>Na2HPO4>NaH2PO4. Transformation rate could be affected by the pH of solution. Results of this study showed that it was advantageous to use vaterite to fabricate CO3Ap-forming cement.

Effects of the method of apatite seed crystals addition on setting reaction of α-tricalcium phosphate based apatite cement

Appropriate setting time is an important parameter that determines the effectiveness of apatite cement (AC) for clinical application, given the issues of crystalline inflammatory response phenomena if AC fails to set. To this end, the present study analyzes the effects of the method of apatite seed crystals addition on the setting reaction of α-tricalcium phosphate (α-TCP) based AC. Two ACs, both consisting of α-TCP and calcium deficient hydroxyapatite (cdHAp), were analyzed in this study. In one AC, cdHAp was added externally to α-TCP and this AC was abbreviated as AC(EA). In the other AC, α-TCP was partially hydrolyzed to form cdHAp on the surface of α-TCP. This AC was referred to as AC(PH). Results indicate a decrease in the setting time of both ACs with the addition of cdHAp. Among them, for the given amount of added cdHAp, AC(PH) showed relatively shorter setting time than AC(EA). Besides, the mechanical strength of the set AC(PH) was also higher than that of set AC(EA). These properties of AC(PH) were attributed to the predominant crystal growth of cdHAp in the vicinity of the α-TCP particle surface. Accordingly, it can be concluded that the partial hydrolysis of α-TCP may be a better approach to add low crystalline cdHAp onto α-TCP based AC.

Basic Properties of Carbonate Apatite Cement Consisting of Vaterite and Dicalcium Phosphate Anhydrous

The aim of the present study is to fabricate bone cement that could transform to carbonate apatite (CO3Ap) completely at body temperature. The powder phase of vaterite and dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of NaH2PO4, Na2HPO4, and Na3PO4 aqueous solution, respectively, with liquid to powder ratio (L/P ratio) of 0.45, 0.55, and 0.65. The paste was packed into split stainless steel mold, covered with the glass slide and kept at 37°C and 100% relative humidity for up to 96 hours (h). XRD analysis revealed that the cement became pure CO3Ap within 24 h for Na3PO4, 72 h for Na2HPO4, and 96 h for NaH2PO4, respectively. FT-IR results showed that all of the obtained specimens could be assigned to B-type CO3Ap. CHN analysis showed the carbonate content of the specimen were 10.4 ± 0.3% for NaH2PO4, 11.3 ± 0.7% for Na2HPO4, and 11.8 ± 0.4% for Na3PO4, respectively. Diametral tensile strength of the set CO3Ap cement was 1.95 ± 0.42 MPa for NaH2PO4, 2.53 ± 0.53 MPa for Na2HPO4, and 3.45 ± 1.53 MPa for Na3PO4, respectively. The set CO3Ap cement had low crystallinity similar to bone apatite since it was synthesized at body temperature. We concluded, therefore, that CO3Ap cement prepared from the present method has higher possibility to be used as an ideal bone replacement.

Three-dimensional porous carbonate apatite with sufficient mechanical strength as a bone substitute material

In this study, three - dimensional porous carbonate apatite (CO3Ap) materials with the chemical compositions and structures similar to cancellous bone were produced via phosphorization of porous calcite precursor in hydrothermal condition. In order to make porous calcite precursor, negative replication of polyurethane foam that named as inverse ceramic foam method was conducted. When the polyurethane template occupied within the ceramic solid walls disappeared due to burning at high temperature, interconnected hollow pathways were produced. Polyurethane foam was used as a porogen - template firstly was coated layer by layer with synthetic resin to modify morphology and enlarge thickness of struts so as to expand porous area for satisficing cellular bioactivities. Calcium hydroxide (Ca(OH)2) slurry was then infiltrated into resin coated-polyurethane foam. Heat treatment in atmosphere of oxygen and carbon dioxide gases was carried out to eliminate polyurethane template and induce carbonation process. Ca(OH)2 was converted to calcite with the internal porous channel architecture simulating polyurethane foam struts network. That interconnected porous calcite was subsequently transformed to CO3Ap with remaining the same macroporous structure through hydrothermal treatment in phosphate solution. The porous CO3Ap materials were implanted in the tibia of Japanese male rabbits and removed after a period of 3 months. The bone formation response of the three - dimensional porous carbonate apatite in vivo has been preliminary studied using micro-computed tomography (µ-CT) scanner. The results showed that the porous implant materials have sufficient mechanical strength to provide structural support during bone remodeling and successfully bond with host bone.

Synthesis of Carbonate Apatite Foam Using β-TCP Foams as Precursors

The present study reports the synthesis of carbonate apatite foam with fully interconnecting pores from βTCP foam by hydrothermal treatment in 1 mol·L-1 disodium carbonate solution at 200°C. The βTCP foam were prepared; 1) using 3 mol% Mg as βTCP stabilizer, 2) using αTCP foam as a precursor by heat treatment at 900°C for 100 hours. The βTCP foam containing Mg could not transform to carbonate apatite foam completely. Meanwhile, the βTCP foam heat-treated at 900°C transformed to carbonate apatite after hydrothermal treatment for 10 days without morphological change. Compressive strength measurement indicated that the value of carbonate apatite foam derived from βTCP was significantly higher than that from αTCP.

Preparation of Carbonate Apatite Cement Based on α-TCP

Carbonate apatite showed an excellent bioresorbability through the remodeling process of bone. In the present study, we prepared self-setting carbonate apatite cement based on α-TCP. We tried two types of the cement powder formulations, that is, first one (F1) is α-TCP containing given amounts (10 to 50 mass%) of synthesized carbonate apatite and second one (F2) is α-TCP treated in 0.5M NaHCO3 for various times between 90 and 360 min. The cement powder was mixed with 0.25M Na2HPO4 to allow set at 37°C and 100% of relative humidity up to 1 day. XRD and FT-IR results showed formation of B-type carbonate apatite phase after setting in both of the formulations. With the formulation, F1, the carbonate content was increased with the treatment time and the maximum content was 4.1 mass%. DTS deacreased with the amount of cabonate apatite in the formulation, F1, however, it increased up to 9 MPa with treatment time in the formulation, F2.

Calcite Bone Substitute Prepared from Calcium Hydroxide Compact Using Heat-Treatment under Carbon Dioxide Atmosphere

The purpose of this study is to investigate whether calcite blocks with high mechanical property could be obtained for a short period from calcium hydroxide (Ca(OH)2) compact using heat-treatment under carbon dioxide (CO2) atmosphere. The Ca(OH)2 disks compacted with different pressure was heated at different temperature ranging from 200°C to 800°C for an hour under CO2 atmosphere. From the X-ray diffractometry, Ca(OH)2 converted into calcite along with the rise of the heating temperature. Small amount of unreacted Ca(OH)2 remained in samples heated at 600°C whereas samples treated at 800°C converted to calcite with very small amount of calcium oxide. The diametral tensile strength (DTS) value increased with the rise of heating temperature up to 600°C then decreased down to 800°C. Meanwhile, the porosity decreased with the rise of heating temperature up to 600°C then slightly increased up to 800°C. From the scanning electron microscope observation, grains grew bigger along with the rise of heating temperature. Intergranular space between grains decreased from 200°C to 600°C. The highest DTS value (14 MPa±1.3) at 600°C could be the result of lesser intergranular space due to sintering.

Characterization and in vitro evaluation of biphasic α-tricalcium phosphate/β-tricalcium phosphate cement

Biphasic calcium phosphate consisting of hydroxyapatite (HA) and β-tricalcium phosphate(β-TCP) is an excellent bone substitute with controllable bioresorbability. Fabrication of biphasic calcium phosphate with self-setting ability is expected to enhance its potential application as bone substitute. In this study, mixtures of α-TCP and β-TCP with various compositions were prepared through α-β phase transition of α-TCP powder at 1000°C for various periods. These powders were mixed with 0.25M Na2HPO4 at a P/L ratio of 2, and then hardened at 37°C at 100% RH for up to 24h. Material properties of biphasic HA/β-TCP cement with different α-TCP/β-TCP composition were characterized. These cements were also evaluated with respect to cell response in vitro using MC3T3-E1 cell lines. In conclusion, mechanical and biological properties of HA/β-TCP cement could be controlled by changing the heat treatment time of α-TCP powder at 1000°C. In vitro results indicated that cell proliferation and ALP activity increased with increase β-TCP content.

Osteoconductivity and Bioresorption of an Interconnecting Porous Carbonate Apatite with Enhanced Mechanical Strength

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.