Alpha-alumina is a ceramic with excellent chemical stability, mechanical property, high melting point, and insulating property; however, it shows poor workability due to its low fracture toughness. There are a lot of molding processes for α-alumina, such as press molding and extrusion methods. 3D printing is rapidly growing technology to make complex and precious moldings. However, there are still only a few descriptions on 3D ink-jet powder laminating printings for α-alumina due to no self-hydration hardening property. To achieve α-alumina moldings with the 3D ink-jet printers, powder fluidity of α-alumina powders and binders for bonding the powders should be investigated. The powders mixed with α-alumina at 20, 3.4 and 0.4 μm in sizes were adjusted to improve powder fluidity and packing density. Polyvinyl alcohol (PVA) or polyallylamine (PAA) including other additives was used as an ink. The addition of PVA on the adjusted powders made no chemical interaction of powders and no retention of shapes, but that of PAA formed the printed moldings. The relative packing density and compressive strength of the printed moldings were 40 % and 8.2 kPa, which was clearly depended on the printed directions due to the nozzle structure of printer head. Sintering the moldings at 1500°C caused near-net zero shrinkage and improved the maximum compressive strength at 3.6 MPa.

Medical products comprised of devices and drugs have been known as a combination product. The biodegradable collagen (Col) sponges impregnated with recombinant human bone morphogenetic protein can make bone formation hasten. It is expected further features by a combination of various growth factors and artificial bone materials. The binding properties of such factors to Col and hydroxyapatite (HAp) have not been elucidate to achieve a controlled release. In this study, we investigated artificial periosteum-like membranes made from tilapia fish Col and HAp composites as a drug carrying support. The Col-HAp composites with three different compositions in weight ratio of 2:8, 5:5 and 8:2 were made and crosslinked by irradiation of gamma-ray in wet condition. The tensile strengths of the membranes in wet or dry were depended on the compositions; however the strengths of the membranes in wet were apparently weaker at 1/10 or less than those in dry at a maximum 90 MPa. The adsorption ability of proteins, bovine serum albumin (BSA) or lysozyme (LSZ), on the membranes exhibited different tendency; the membranes including higher weight ratio of HAp adsorbed BSA rather than LSZ. These results indicated that the artificial Col-HAp membranes would be the suitable materials for biomedical device as combination products.

The antibacterial properties are useful to restrain inflammatory response caused by bacterial infection after implantation. The composites of hydroxyapatite (HAp) and silver nano-dots, silver oxide or silver phosphate have been investigated; however there are still some disadvantage in sintering; 1) silver nano-dots grow large, and are not homogenously distributed, 2) silver nano-dots melt and remove, and 3) silver phosphate and silver oxide formed exhibit higher solubility than metal silver. In this study, the distribution of silver nano-dots in HAp microparticles sintered was controlled at grain boundary with a modified silver mirror reaction as a novel route. HAp microparticles adsorbed formaldehyde by a vapor deposition method were soaked in an ammoniacal silver nitrate solution and were then sintered. There was a single phase of HAp including metal silver at 6.4 wt% even after sintering. The silver nano-dots were homogeneously distributed inside the microparticles. The release profiles of silver ions in phosphate buffer saline were compared with a reference; the HAp microparticles were soaked into silver nitrate solution and were then sintered. The distribution of silver in the reference was not homogeneous and large silver microparticles were grown outside the particles at 6.3wt%. The elution amount of silver ions from the microparticles at 12 hours was one-eighteenth of that from the reference. These results suggest that the HAp microparticles including silver nano-dots at grain boundary will be suitable for a long-term antibacterial material.

A reverse micro-emulsion method has been investigated to control crystal morphology in a nanometer region and to increase specific surface area for calcium phosphate. The nanocrystals with the control of its morphology is a candidate of drug delivery carriers. This study investigated the effects of mixing volume ratios of two surfactants, tween80 (T) and aliquate 336 (A) in kerosene as an oil phase, and pH values in the nano-region on crystalline phases and specific surface area of calcium phosphate synthesized by the reverse micro-emulsion method. A di-ammonium hydrogen phosphate solution including phosphoric acid at pH of 6.3 and a calcium nitrate solution at pH of 5.7 were adjusted, and both the solutions were separately added into the kerosene with the surfactants. Both the emulsions were then mixed at the same volume and the Ca/P ratio of 1.0, and stirred at room temperature for 24 hours. The crystalline phases were dependent on the T amounts; pure DCPD with the specific surface area of 6.7 to 12 m2/g was obtained at the T/A ratio of 4, the mixture of DCPD and DCPA with that of 48 to 162 m2/g was at the ratios of 5 to 8, and a low crystalline HAp with 163 m2/g was at the ratio of 9. These specific surface areas of DCPD (T/A=4) and HAp (T/A=9) were apparently higher than those prepared with a wet method, 7.8 times and 1.8 times respectively. DCPA with 43 m2/g was successfully produced to decrease the pH of phosphate solution at T/A of 9. The change of crystalline phases would be explained as follows; the increase of T amount decreased the micro-emulsion sizes to reduce bulk water to be DCPA, and increased the pH to precipitate HAp nanocrystals.

Calcium phosphate cements show self-hardening reaction upon mixing with liquids to form calcium-deficient hydroxyapatite (CDHA) or dicalcium phosphate dihydrate. The effects of particle sizes, crystallinities, and natural polymers such as tilapia scale collagen (Col) and hyaluronic acid as a dispersant on the mechanical properties of alpha tricalcium phosphate (TCP) cements mixed with citric acid (CA) as an additive were investigated. Three types of alpha TCP particles were fabricated with spray-dry (SD; 14 μm), freeze-dry (FD; 45 μm), and cold isostatic press (CIP; 134 μm) methods, followed by sintering at 1300°C and ground/crushed. The amounts of Ca dissolution from these particles were in the order of SD > FD > CIP. The CA liquid was added to the powders of SD-FD or SD-CIP, and kneaded under different liquid/powder ratios. The cements containing CIP particles showed lower compressive strength at 22.9 ± 1.5 MPa than those containing FD particles at 28.3 ± 2.5 MPa, even though the apparent densities of the cements containing CIP material was higher. Although the packing density of powders is an important factor on the mechanical properties of cements, the dissolution of Ca ion has a greater impact on the mechanical properties. The addition of Col into the cements increased the mechanical properties at 33.6 ± 2.5 MPa at 1 day to enhance the re-precipitation of CDHA.

Detection of volatile organic compounds (VOCs) emitted from cancerous tumor cells in exhaled human breath allows for early diagnosis of various types of cancers. 3D graphene with a large surface area is considered a suitable material for creating novel sensitive VOCs sensors. In this study, 3D graphene and 3D graphene oxide were synthesized from graphene oxide suspension, hydroquinone and formaldehyde by employing polymerization and reduction. The capability of VOC gas sensing was evaluated by measuring the electrical current response in flowing N2 gas over a range of concentrations of acetone or 1-butanol at room temperature. It was observed that the device current correlated well with the VOC concentration. The adsorption of acetone decreased the current, but the adsorption of 1-butanol increased the current during sensing. 3D graphene oxide device was more sensitive than 3D graphene device because of the high concentration of oxygen-containing functional groups on the surface. These results indicated that 3D graphene and 3D graphene oxide may be the suitable materials for VOCs sensing devices.

B-type carbonate apatite (B-CAp) powders were prepared by a wet method using Ca(OH)2 suspension and H3PO4 solution including NaHCO3 as a carbonate source, and porous B-CAp ceramics with two different amounts of carbonate contents were fabricated by sintering freeze-dried mixtures of the powders and gelatin composite. The porous B-CAp ceramics prepared had three-dimensionally interconnected pores. The sinterability of B-CAp ceramics was dependent on the chemical composition, especially sodium content and vacancy of OH site, and the carbonate contents did not directly influence the dissolution rate of porous B-CAp ceramics.

Hydroxyapatite-chondroitin sulfate (HAp/ChS) composites were synthesized with calcium hydroxide suspension and phosphoric acid solution containing ChS through a precipitation method, and the microparticles were then fabricated by a spray dry method with the suspension of the composites. Bovine serum albumin (BSA) with negative charge or lysozyme (LYZ) with positive charge at pH7.0 was adsorbed onto the HAp/ChS microparticles. However, the HAp/ChS microparticles adsorbed LYZ more than the HAp microparticles compared with BSA due to the electrostatic interaction from negatively-charged sulfate or carboxyl group of ChS in the composites. The release property of BSA from the HAp/ChS microparticles was evaluated in Dulbecco’s phosphate buffered saline (pH7.2). The HAp/ChS microparticles released quickly 100% of the adsorbed BSA, while HAp microparticles released 45% of BSA. These results indicated that incorporation of ChS in the microparticles controls the adsorption and release properties of protein due to the electrostatic interaction. The HAp/ChS microparticles therefore are a candidate of a carrier for drugs like vaccines.

Nitinol was coated with biocompatible calcium phosphate materials by pulsed electrolytic deposition (ELD) to reduce toxic metal-ions elution. The pulse ELD for the stents was carried out with changing the current off-periods (toff) of the pulse wave. The pulse ELD suppressed the generation of H2 gas due to the electrolysis of water on a calcium phosphate layer and improved the adhesiveness of the coating layer on nitinol compared with a conventional DC-ELD. The coating layers were identified to be octacalcium phosphate (OCP) at lower toff, while they were transformed to dicalcium phosphate anhydraous (DCPA) with an increase of toff. The layers of OCP or DCPA on the nitinol surface were subjected to a NaOH treatment at 60°C for 3days to transform them into hydroxyapatite (HAp). From results of a metal-ions elution test, the deposited calcium phosphates suppressed nickel ions elution at one quarter compared with the bare nitinol stent. These results indicate that the pulse ELD of biocompatible calcium phosphate materials on the nitinol stent was one of the best techniques to create firmly attached coating on it and reduce toxic nickel ions elution.

When a biomaterial is implanted into the body, blood proteins adsorb on its surface and subsequently cells adhere via the protein adlayer. Thus, the understanding of protein adsorption and conformational change on the biomaterial surfaces is of great importance to control the biocompatibility such as antithrombotic properties and cell adhesion behaviors. In this study, we synthesized hydroxyapatite (HAp) and carbonate apatite (CAp) by a wet method. Then we successfully fabricated the HAp and CAp sensors for QCM-R by an electrophoretic deposition method. Adsorption behavior of proteins on the bone substitute material can be monitored by using these apatite sensors. Bovine serum albumin and fibrinogen were employed for the model proteins, and monitored the adsorption behavior on the HAp, CAp and reference gold (Au) sensors by the QCM-R technique. As a result, we revealed that fibrinogen and bovine serum albumin adsorbs on the gold surface by hydrophobic interaction, and adsorbs on the HAp and CAp surfaces mainly by electrostatic force. Besides, we revealed that fibrinogen adsorbs on the Au surface more rigid than on the HAp and CAp surfaces while bovine serum albumin adsorbs on the HAp and CAp surface more rigidly than on the Au surface.

Bisphosphonate (Bp) was adsorbed on the surface of crystalline calcium phosphates (CP); hydroxyapatite (HAp), octacalcium phosphate (OCP) and Dicalcium phosphate dehydrate (DCPD). The amount of Bp adsorbed was the largest for DCPD per unit surface area, while the amount was the largest for HAp per unit weight. The composites of Bp and amorphous calcium phosphate (ACP) were synthesized by titrating calcium acetate solution into phosphate buffer solution containing Bp. The amount of Bp doped in the composites was 366 μg / mg and was approximately 7 times larger than those of Bp adsorbed on the crystalline Calcium phosphates. TG-DTA measurements of a Bp-calcium and the composite indicated exothermic peaks due to Bp combustion, of which temperature were shifted to higher temperature for the composite. Bp in the composites was gradually released into phosphate buffered saline, while Bp was rapidly released into acetate buffer solution accompanied with the dissolution of ACP. This result suggests that the composite of Bp and ACP has potential for a drug-carrier releasing Bp in response to the condition of osteoclastic bone resorption.

Collagen fibril membranes (CFMs) with a high mechanical property were fabricated with a lateral face evaporation method, in which type I atelocollagen extracted from tilapia scales was used. The density and thickness of the CFM obtained were 0.51 ± 0.04 mg/cm3 and 50 ± 5 μm. The collagen fibrils in the CFM had a similar periodic stripped pattern of 67 nm with native collagen fibrils. The CFM was crosslinked in gaseous glutaraldehyde for different duration in order to increase the mechanical property. The crosslinking degrees of the CFMs analyzed by free amino groups gradually increased to 70.3 % against the exposure duration until 6 hours, and reached a plateau. The denaturation temperatures of the CFMs with the crosslinking degrees at 20.4 % to 43% were linearly increased from 49°C to 75°C. The tensile strength of the CFMs was slightly improved until the crosslinking degree at 33.3 % and then the tensile strength rapidly increased to be 68 MPa. It was suggested that a percolation phenomenon took place in the CFMs by crosslinking of collagen fibrils with polymerized GA molecules.

The mineralized structure of aligned collagen fibrils in a tilapia fish scale was investigated using transmission electron microscopy (TEM) techniques after a thin sample was prepared using aqueous techniques. Electron diffraction and electron energy loss spectroscopy data indicated that a mineralized internal layer consisting of aligned collagen fibrils contains hydroxyapatite crystals. Bright-field imaging, dark-field imaging, and energy-filtered TEM showed that the hydroxyapatite was mainly distributed in the hole zones of the aligned collagen fibrils structure, while needle-like materials composed of calcium compounds including hydroxyapatite existed in the mineralized internal layer. Dark-field imaging and three-dimensional observation using electron tomography revealed that hydroxyapatite and needle-like materials were mainly found in the matrix between the collagen fibrils. It was observed that hydroxyapatite and needle-like materials were preferentially distributed on the surface of the hole zones in the aligned collagen fibrils structure and in the matrix between the collagen fibrils in the mineralized internal layer of the scale.

Hydroxyapatite (HAp) is widely used as bioceramics for bone and dental tissue reconstructions due to its excellent biocompatibility with hard tissues and high osteoconductivity. Although it is well known that HAp has the high adsorbed ability, its ability is decreased in high ionic solution. To immobilize protein on the HAp surface, this study demonstrates that Collagen (Col) and fibronectin (Fnt) were immobilized on the surface of hydroxyapatite (HAp) sintered body with and without the silane coupling agent of aminopropyltriethoxysilane (APS). The proteins immobilized on the HAp and APS/HAp surfaces were investigated by atomic force microprobe (AFM, Simadzu; SPM 9500) analyses and Ζ potential measurements. The stability of protein/APS/HAp and protein/HAp composites was evaluated after immersion in phosphate buffer and NaCl solutions with various concentrations. AFM analyses and Ζ potential measurements revealed that proteins immobilized on the APS/HAp are more stable than those immobilized on the HAp in high ionic solutions.