Materials in Clinical Applications VII

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Authors: Masanori Kikuchi, M. Tanaka
Abstract: Soft-nanotechnologies are based upon the synthesis technologies of nanomaterials and construction technologies of nanostructures by life forms. They are expected as new preparation methods for biomaterials that could be recognized as regular extracellular matrices (ECM) in our body by cells. We applied the soft-nanotechnology to synthesis of artificial bones made of HAp and collagen with bone-like nanostructure and examined their physical and biological properties. The nanocomposite obtained indicates bone-like nanostructure. Computer simulation and FT-IR suggested that the self-organization of HAp and collagen is based on chemical interaction between calcium ions on HAp surface and carboxy groups on collagen. After implantation in rats and dogs, the nanocomposites are resorbed by osteoclasts followed by osteogenesis; therefore, the nanocomposites are recognized as bone in the living body. Resorption rate can be controlled by crosslinkage. We also prepared sponge-like elastic porous body by gel-lyophilization technique using additional small amount of collagen solution. Bone tissue reactions of it are the same as the nanocomposites as prepared. The nanocomposites are now in clinical research in Japan to be commercialized in near future by Pentax Co.
Authors: G. Daculsi
Abstract: The development of calcium phosphate ceramics and other related biomaterials for bone graft involved a better control of the process of biomaterials resorption and bone substitution. The biphasic calcium phosphate ceramics (BCP) concept is determined by an optimum balance of the more stable phase of HA and more soluble TCP. The material is soluble and gradually dissolves in the body, seeding new bone formation as it releases calcium and phosphate ions into the biological medium The main attractive feature of BCP ceramic is their ability to form a direct bond with the host bone resulting in a strong interface. The formation of this dynamic interface is the result of a sequence of events involving interaction with cells; formation of carbonate hydroxyapatite CHA (similar to bone mineral) by dissolution/precipitation processes. At the present time, BCP is commercially available in blocks, particulates, customized design. The need of material for Minimal Invasive Surgery (MIS) induced the development of a concept of granules combination with polymer or calcium phosphate cement for injectable/mouldable bone substitutes. Four types of injectable/mouldable bone substitutes have been developed by INSERM Nantes University.
Authors: Egbert Brandau, Thorsten Brandau
Abstract: Clinical applications of Calcium phosphate compounds are done in most cases with powders of Calcium-tri-phosphate and/or Hydroxylapatite to enhance the surgery of orthopaedic repair. The application of microspheres of these compounds has big advantages to faster surgery and higher strength of the bone structure. The special processes to produce microspheres of narrow size distribution and high sphericity out Calcium-tri-phosphate and Hydroxylapatite are described. Properties and composition of these microspheres as calcined and as sintered are given.
Authors: Leif Hermansson, Hakan Engqvist, Jesper Lööf, Gunilla Gómez-Ortega, Kajsa Björklund
Abstract: This study deals with the microstructure and property profile of biomaterials within the Ca-aluminate system (CA). Hydrated CA materials are stable in bone tissue, and thus not resorbable as the Ca-phosphate materials are. Identified possible applications for CA-based materials are within vertebroplasty and odontology. CA with ZrO2 particles as well as CA with glass particles were examined with regard to mechanical properties, biocompatibility and bioactivity. The hydrates formed - examined by HRTEM - are in the size range of 20-50 nm. With the studied systems it is possible to obtain a combination of high and early strength, shape stability including low expansion pressure, and in vivo bioactivity.
Authors: Christian Rey, Christèle Combes, Christophe Drouet, Hocine Sfihi
Abstract: Apatites can accommodate a large number of vacancies and afford multiple ionic substitutions determining their reactivity and biological properties. Unlike other biominerals they offer a unique adaptability to various biological functions. The diversity of apatites is essentially related to their structure and to their mode of formation. Special charge compensation mechanisms allow molecular insertions and ion substitutions and determine to some extent their solubility behaviour. Apatite formation at physiological pH involves a structured surface hydrated layer nourishing the development of apatite domains. This surface layer contains relatively mobile and exchangeable ions, and is mainly responsible for the surface properties of apatite crystals from a chemical (dissolution properties, ion exchange ability, ion insertions, molecule adsorption and insertions) and a physical (surface charge, interfacial energy) point of view. These characteristics are used by living organisms and can also be exploited in material science.
Authors: Tsutomu Furuzono
Abstract: Hydroxyapatite (HAp) has unique properties for biomaterials such as hard-tissue-compatible material for bone and tooth and also soft-tissue-compatible materials for skin tissue. However, the hard and brittle nature of HAp limits spreading many medical devices. Recently, a unique composite of sintered HAp nano-crystals -- ceramics -- covalently coupled to polymer substrates was developed -- Nano-Ceramic Coating --. The development was depended on the two original technologies: (1) control of size/morphology of high-dispersed sintered nano-HAp, (2) donation of covalent bonding between nano-HAp and substrates to coat strongly on the surface. The nano-composite material holds not only the mechanical properties of the substrate but also biological properties of the ceramics coated on the surface. In this report, the method of synthesis of high-dispersed nano-HAp, the preparation of the nano-composite, the biological properties with cells or animal tissue, and especially, the development of medical devices, such as percutaneous device or blood vessel and so on, made of the composite will be presented.
Authors: Christophe Drouet, C. Largeot, G. Raimbeaux, Claude Estournès, Gérard Dechambre, Christèle Combes, Christian Rey
Abstract: Calcium phosphates (Ca-P) are major constituents of calcified tissues, and are also extensively used for the elaboration of biomaterials. However, the usual high-temperature sintering processes generally lead to strong alterations of their chemical, physical and biological properties. Spark plasma sintering (SPS) is a non-conventional sintering technique based on the use of pulsed current, enabling fast heating and cooling rates, and lower sintering temperatures are often observed. The sintering of several orthophosphates (DCPD, amorphous TCP, beta-TCP, OCP, HA and biomimetic nanocrystalline apatites) by SPS was investigated in order to track potential advantages of this technique over usual Ca-P sintering methods. Special attention was given to the SPS consolidation of highly bioactive nanocrystalline apatites.
Authors: Magdalena Szutkowska, Marcin Leonowicz, L.A. Ivanchenko
Abstract: In this study the hydroxyapatite powder was sintered together with magnetite nanopowder, which due to its low reactivity is commonly used in medicine, eg. in magnetic resonance. Two types of sintered materials, containing equal content 6 mol% of biogenic hydroxyapatite (BGHAp), reinforced with 50 wt% of different glass phases, were tested. The same technological conditions comprising two-stage sintering with T1 (1100°C) and T2 (780°C) were used for both types of materials. For selected specimens 2 wt% of 9 nm powder of Fe3O4 was added. The microhardness of the specimens varies within quite wide range from 150 to 508 HV0.025. Compressive splitting strength of the specimens (measured along the sample diameter) is within a range of 3.61 – 4.99 MPa. Young’s modulus, modulus of rigidity and Poisson’s ratio are in the ranges of: 20.81 – 24.86 GPa, 7.89 – 9.71 GPa and 0.252 – 0.307, respectively. Indentation fracture toughness KIC is within a range of 0.6-1.0 MPa m1/2. The hysteresis loops were determined in order to asses the possibility of application of this material as affecting the drug delivery carriers. The specimens exhibit magnetization of the order of 1.5 emu/g.

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