Rheological characteristics of slurry controlling the microstructure and the compressive strength behavior of biomimetic
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K. Satou and G. Pezzotti Ceramic Physics Laboratory, Department of Materials, Kyoto Institute of Technology, Sakyo-Ku, Matsugasaki, 606-8585 Kyoto, Japan (Received 27 September 2000; accepted 27 September 2000)
The sponge impregnation of water-based suspensions of hydroxyapatite powders synthesized by the coprecipitation method was investigated. The powder characteristics and slurry properties were correlated with the porosity and mechanical properties of the porous bodies obtained. The rheological characterization in the continuous flow condition revealed a strong dependence of the rheological behavior on the solid loadings particularly with high specific surface area powder. The behavior changed from newtonian to plastic, with pronounced hysteresis effects due to time dependency, by increasing the solids loading from 10 to 18 vol%. The morphology and distribution of the macropores could be related to the starting powder crystallinity and morphology as well as to the rheological properties of the suspensions. The compressive strength of the materials was strongly influenced by the porosity, while there was almost no dependence on the crystallinity of the powder. From a statistical viewpoint, the microporosity better explained the behavior of the mechanical strength than the total porosity.
I. INTRODUCTION
The use of endogenous and exogenous bone substance has many inherent disadvantages in practical applications, and it is linked to many surgical and medical problems. 1 Accordingly, there is a growing need for fabrication of artificial bone tissue and in particular a need for developing second-generation bioactive implants that promote regeneration of the surrounding tissue. In this respect, hydroxyapatite (HA) is an elective material due to its biocompatibility and in form of a porous body it enables one to produce architectures similar to those of real bones. Permanent implants of HA ceramics have been widely tested in orthopedic and ortognatic surgery for corrections of deformities of skeleton bone. As a result, porous HA have found large-scale application as a filling material for bone defects and augmentation, and in prosthesis revision surgery. Among various processes, the impregnation of porous cellulosic substrates with HA slurry has been shown to
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Address all correspondence to this author. J. Mater. Res., Vol. 16, No. 1, Jan 2001
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be a good methodology to assure a proper pore-size distribution, as osteoconduction requires, characterized by the existence of micro/meso/macropores with a sufficient interconnection degree. 2 By varying the characteristics of the starting powders and the rheological properties of the ceramic slurries, the possibility has been demonstrated 3 of preparing HA ceramic materials with crystallinity and porosity gradients, mimicking the physicochemical features of cortical and spongy bones. The aim of this work was to develop a suitable impregnation procedure of porous cellulosic substrates and to correlate both powder mo
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