Akari Takeuchi

Heterogeneous nucleation of hydroxyapatite on protein: structural effect of silk sericin

Acidic proteins play an important role during mineral formation in biological systems, but the mechanism of mineral formation is far from understood. In this paper, we report on the relationship between the structure of a protein and hydroxyapatite deposition under biomimetic conditions. Sericin, a type of silk protein, was adopted as a suitable protein for studying structural effect on hydroxyapatite deposition, since it forms a hydroxyapatite layer on its surface in a metastable calcium phosphate solution, and its structure has been reported. Sericin effectively induced hydroxyapatite nucleation when it has high molecular weight and a β sheet structure. This indicates that the specific structure of a protein can effectively induce heterogeneous nucleation of hydroxyapatite in a biomimetic solution, i.e. a metastable calcium phosphate solution. This finding is useful in understanding biomineralization, as well as for the design of organic polymers that can effectively induce hydroxyapatite nucleation.

Fabrication of macroporous carbonate apatite foam by hydrothermal conversion of α-tricalcium phosphate in carbonate solutions

Bone consists of a mineral phase (carbonate apatite) and an organic phase (principally collagen). Cancellous bone is characterized by interconnecting porosity necessary for tissue ingrowth and nourishment of bone cells. The purpose of the present study was to fabricate macroporous carbonate apatite (CAP) blocks with interconnecting porosity as potential bone substitute biomaterials by hydrothermal conversion of alpha-TCP foam in carbonate solution. The fabrication of the macroporous CAP was accomplished in two steps: (1) preparation of alpha-TCP foams using polyurethane foams as templates, and (2) hydrothermal conversion at 200 degrees C of alpha-TCP foam in the presence of ammonium carbonate solutions of different concentrations. The maximum carbonate content of the resultant CAP foam was approximately 7.4 wt %. The mean porosity of the CAP foam was as high as 93 vol %. The macroporous CAP blocks or granules prepared in this manner has properties similar to that of bone in mineral composition and in having interconnecting macroporosity necessary for osteoconductivity and tissue ingrowth. On the basis of composition and interconnecting macroporosity, the CAP foam materials could be ideal biomaterials for bone repair and as scaffolds for tissue engineering.

Fabrication of low-crystallinity hydroxyapatite foam based on the setting reaction of α-tricalcium phosphate foam

Low-crystallinity hydroxyapatite (HAP) foam is an ideal material for bone substitutes and scaffolds for bone tissue regeneration, because its interconnected pores provide the space for cell growth and tissue penetration, and its composition induces excellent tissue response and good osteoconductivity. In this study, the feasibility of low-crystallinity HAP foam fabrication was evaluated based on the phase transformation reaction or the so-called dissolution-reprecipitation reaction of alpha-tricalcium phosphate (alpha-TCP) foam granules. When alpha-TCP foam granules were placed in water at 37 degrees C for 1 day, no reaction was observed. However, alpha-TCP foam granules set to form low-crystallinity HAP by treating it hydrothermally at 200 degrees C. The network of fully interconnected pores was retained, and porosity was as high as 82%. Pore size ranged from 50 to 300 mum with an average pore size of 160 mum. Compressive strength was 207 kPa. Although no setting reaction was observed at 37 degrees C, the setting reaction caused by the hydrothermal treatment of alpha-TCP foam granules allowed the fabrication of any shape of low-crystallinity HAP. Therefore, this method may be useful for the fabrication of bone substitutes and scaffolds in bone tissue regeneration.

Solid State MAS-NMR and FTIR Study of Barium Containing Alumino-Silicate Glasses

The glass based on a 1.5SiO2-Al2O3-0.5P2O5-CaO-0.67CaF2 composition was produced and substituted gradually by barium. The structure of the glasses was studied by multinuclear Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Fourier Transform Infrared Spectroscopy (FTIR). It was indicated by 29Si and 31P MAS-NMR spectra that silicon was present as Q4 (4Al) and Q3 (3Al) species and phosphorus was in a Q1 pyrophosphate environment. 29Al MAS-NMR spectra showed that four fold coordinated aluminum Al (IV) was the dominant species with a second peak assigned to octahedral aluminum Al (VI). The 19F spectra suggested that the barium addition caused the formation of Al-F-Ba(n) and F-Ba(n) species. Furthermore, a distribution of silicate network including Si-O-Si stretching (Q4 and Q3) and Si-O-[NBO] (Q3) per SiO4 was reflected by the FTIR study.

Apatite Foam Fabrication Based on Hydrothermal Reaction of α-Tricalcium Phosphate Foam

Apatite foam (AP foam) is an ideal material for bone substitutes and scaffolds in bone tissue regeneration. This is because its highly porous interconnected pores provide the space for cell growth and tissue penetration, and that its composition induces excellent tissue response and good osteoconductivity. In the present study, the feasibility of apatite foam fabrication was evaluated based on so-called dissolution-reprecipitation reaction of α-tricalcium phosphate (α-TCP) foam granules. When α-TCP foam granules were placed in water at 37°C for 24h, no reaction was observed. However, α-TCP foam set to form AP foam when treated hydrothermally at 200°C. The network of fully interconnected pores was retained, and porosity was as high as 82%. Pore size ranged from 50 to 300 0m with average pore size at 160 0m. Compressive strength was 207 kPa. Although no setting reaction was observed at 37°C, setting reaction caused by hydrothermal treatment of α-TCP foam granules at 200°C allows AP foam of any shape to be fabricated. Therefore, this method was suggested to be useful for the fabrication of bone substitutes and the scaffold in bone tissue regeneration.

Biodegradation of Porous Alpha-Tricalcium Phosphate Coated with Silk Sericin

Porous a-tricalcium phosphate (a-TCP) ceramics are attractive as a novel bioresorbable material for bone repair, since they can be easily fabricated through conventional sintering of b-TCP at high temperature. However, the solubility of a-TCP is too high to keep its body until the bone defect is repaired completely. Coating of the a-TCP porous body with organic polymer is a way to reduce the degradation rate. In the present study, biodegradation of a-TCP porous body coated with silk sericin was evaluated in vivo. Bone repair at the defect made in rabbit tibia was nearly completed after 4 weeks. Higher density of cortical bone was estimated for a-TCP coated with sericin than for mere a-TCP. The a-TCP porous body coated with sericin is expected as a material that show less degradation than mere a-TCP, and may result in suitable bone repair.

Effects of Hydrothermal Treatment Temperature on the Crystallinity of Cancellous Bone Type Carbonate Apatite Foam

We have previously reported that the carbonate apatite (CAP) foam that has similarities in both inorganic chemical composition and morphology to cancellous bone could be prepared from α-tricalcium phosphate (α-TCP) foam by the hydrothermal treatment with Na2CO3 at 200°C for 24 hrs. However, the crystallinity of the CAP foam was much higher than that of bone. In order to prepare CAP foam similar to cancellous bone in crystallinity as well as its inorganic composition and morphology, this study attempted to prepare CAP foam at lower temperature. Hydrothermal treatment at 100°C allowed low-crystalline CAP foam whereas longer period was imposed for complete conversion of α-TCP foam into CAP foam.

Apatite Deposition on Silk Sericin in a Solution Mimicking Extracellular Fluid: Effects of Fabrication Process of Sericin Film

An apatite-organic polymer hybrid is expected as a novel materia l for medical application, because it shows high biological affinity and high flexibility. In order to fabricate this type of hybrid, a biomimetic process was proposed, in which a bone-like apatite layer c n be coated onto organic substrates by using a simulated body fluid (SBF) at ambient conditions . P tential of induction of heterogeneous nucleation of apatite on substrate materials is an im portant parameter to achieve a successful coating of apatite. Recently, it was reported that se ricin, a protein existing on the surface of raw silk fiber, showed apatite-forming ability in 1.5SBF which has 1.5 times the ion concentrations of SBF. In the present study, the structural effect of sericin on its apatite-forming ability was investigated in 1.5SBF. Apatite was deposited on sericin with high molecular weight and β-sheet structure in 1.5SBF after 7 days. Introduction Hydroxyapatite is a kind of calcium phosphate that has high biological affinity to bone. Sintered hydroxyapatite is now widely used as bone substitute. However, the applic ation of hydroxyapatite is restricted because it does not have enough mechanical properties to bea r a large load. Therefore, a hydroxyapatite-organic polymer hybrid is expected as a novel materi al fo medical application, because it shows high biological affinity and high flexibility. Hydr oxyapatite coating on organic polymers is an attractive way to develop such hybrid materials. Kokubo and his colleagues previously proposed a biomimetic process to deposit a hydroxyapatite layer on vari ous substrates, such as organic polymers. In this process, a bone-like apatite layer can be coat d onto organic polymer substrates by either using a simulated body fluid (SBF) with ion concentrations ne arly equal to those of human blood plasma, or using a more concentrated fluid under mild conditions [1]. Potential of induction of heterogeneous nucleation of apatite on the substrate materials is an impor tant parameter to achieve a successful coating of apatite layer. Apatite crys tals can spontaneously grow in the simulated body fluid (SBF), since SBF is supersaturated with respect t o hydroxyapatite. We recently reported that sericin, a protein existing on the surface of raw si lk fiber, is able to induce apatite deposition in 1.5SBF, which has 1.5 times the ion concentrations of SBF [2]. This me an that sericin has a suitable composition and/or structure for inducing apatite nucleat ion in body environment. In this study, we have investigated the effective structure of sericin needed t o posit apatite crystals in 1.5SBF. Some sericin films were prepared from a solution containing s ericin extracted under various Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 403-406 doi:10.4028/www.scientific.net/KEM.254-256.403

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.

Synthesis and in Vitro Cell Compatibility of α-Tricalcium Phosphate-Based Apatite Cement Containing Tricalcium Silicate

The presence of silicate in artificial bone graft material is known to be effective in increasing bone formation rate. We previously reported the basic setting properties of α-tricalcium phosphate (α-Ca3PO4; α-TCP) based apatite cement (AC) with various amount of tricalcium silicate (Ca3SiO5; alite) addition using sodium dihydrogen phosphate (NaH2PO4) as the liquid phase. In this study, in vitro biological compatibility of pure α-TCP and 2.5-10.0 wt% alite added to α-TCP based AC is investigated in terms of cell attachment, proliferation and differentiation.