Papers by Author: Kunio Ishikawa

Abstract: The processing of porous ceramics spheres (PCS) has been developed for biphasic calcium phosphates (BCP), hydroxyapatite (HAp) and beta tricalcium phosphate (β-TCP) in order to be used mostly as bone fillers and drug delivery systems. The importance of the PCS is due to better accommodation of them in order to fill empty spaces and also because is more friendly to cells and bone tissue growth. Also is important to obtain a surface roughness to increase the surface area in contact with the living tissue and their fluids. There are several methods used to achieve the PCS form and most of them use suspensions based on liquids immiscibility effect or additives. The aim of this work was to achieve PCS of BCP, HAp and β-TCP with rough surface and varying size without using solutions or additives. The method developed is based on a mechanical continuous movement of the particles, relying on the normal ability of the ceramic powders to aggregate themselves while rolling in a cylindrical container for long periods. The physical forces involved in the process, gravity, particle attraction, centripetal force and shocking make the ceramic rounds with golf ball appearance on its surface. With this method it was possible obtain PCS with 30% of porosity with rough surface and size between 1 to 4 mm in diameter.

Abstract: 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.

Abstract: The present study reports the synthesis of βTCP foam with fully interconnecting pores based on phase transformation of αTCP foam precursor by employing heat treatment. First, the αTCP foam precursor was fabricated by sintering the ceramics slurry-coated polyurethane foam template at 1,500°C. The resultant αTCP foam was again heated below α,β transition temperature for an extended period of times. After heating at 800°C for 150 hours, 900°C for 100 hours and 1,000°C for 300 hours, βTCP foam was obtained. The compressive strength of βTCP foam was approximately 46 kPa and the porosity was approximately 93%. The long heating period as well as heating temperature were the key to the transformation of βTCP phase. βTCP foam could be an ideal bone replacement since the invasion of bone cells into the pores provides optimum bone growth or repair.