Preparation and Characterization of Porous Material from Self-Organized Hydroxyapatite/Collagen Nanocomposite
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Preparation and characterization of porous material from self-organized hydroxyapatite/collagen nanocomposite Shunji Yunoki, Toshiyuk Ikoma, Akira Monkawa, Masanori Kikuchi, and Junzo Tanaka Biomaterials Center, National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki, 305-0044, Japan ABSTRACT Self-organized hydroxyapatite /collagen (HAp/Col) nanocomposite was synthesized by a co-precipitated method. The porous HAp/Col nanocomposites with unidirectional and interconnected pores with approximately 20µm in size were prepared by a facile method. The ice crystals were grown up at a cooling brass bottom in the paste which kneaded the HAp/Col nanocomposite with a sodium phosphate buffer. The freeze-drying technique produced the replica of ice structures, and the porous composites showed the anisotropic compressive strengths. The nanostructure and micropore structure are of great importance for developing the novel artificial bone filling materials; attachment and migration of cells and blood vessels, and early regeneration of bone tissues. INTRODUCTION The direct approach for developing a bioactive artificial bone is to mimic the nanostructure and chemical composition of natural bones. Many researchers have prepared hydroxyapatite/ collagen (HAp/Col) composites to improve its biocompatibility. One of the most popular methods for preparing HAp/Col composite was to mechanically mix HAp crystals with Col matrix. Mehlisch et al. [1] showed the excellent biocompatibility from in vivo experiments. Miyamoto et al. [2] prepared self-setting HAp cements with Col as reinforcement, and indicated its excellent biocompatibility and improvement of mechanical properties. TenHuisen et al. [3] prepared a HAp/Col nanocomposite using crystallization of HAp on Col fiber from the acid-based reaction with CaHPO4 as a HAp precursor. However, these methods could not reproduce the similar nanostructure to that of natural bone. Bone is highly organized tissues with HAp nanocrystals and type I Col fibers, in which the c-axes of the nanocrystals are regularly aligned along the Col fibers [4]. In the last several years, the authors have developed a novel HAp/Col composite with a similar nanostructure of bone tissue through the self-organization. The consolidated HAp/Col nanocomposite demonstrated excellent biocompatibility and biointegrative activity to bone tissues [5]. The control of micropores and interconnected pore structures is of great importance for cell migrations and neovascularization. In this study, porous HAp/Col nanocomposite with one-directionally connected micropores was prepared by the unidirectional solidification and subsequent freeze-dry
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processes. The unidirectional pore structure was observed by scanning electron microscopy and its anisotropic mechanical strength was elucidated by compressive tests. EXPERIMENTAL DETAILS HAp/Col nanocomposite (80/20 weight ratio) was synthesized by a co-precipitation method using Ca(OH)2, H3PO4, and atelo-type I Col as starting substances [6]; Ca(OH)2 suspension an
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