This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Development of nanocomposites for bone grafting

The mechanical behavior under compressive stresses of β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) scaffolds fabricated by direct-write assembly (robocasting) technique is analyzed. Concentrated colloidal inks prepared from β-TCP and HA commercial powders were used to fabricate porous structures consisting of a 3-D tetragonal mesh of interpenetrating ceramic rods. The compressive strength and elastic modulus of these model scaffolds were determined by uniaxial testing to compare the relative performance of the selected materials. The effect of a 3-week immersion in simulated body fluid (SBF) on the strength of the scaffolds was also analyzed. The results are compared with those reported in the literature for calcium phosphate scaffolds and human bone. The robocast calcium phosphate scaffolds were found to exhibit excellent mechanical performances in terms of strength, especially the HA structures after SBF immersion, indicating a great potential of this type of scaffolds for use in load-bearing bone tissue engineering applications. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008

Mechanical properties of calcium phosphate scaffolds fabricated by robocasting

Ansl:n.Lcr Unit-cell dimensions of muscovite-2M, from the Diamond mine, South Dakota, were determined to 1000'C, single-crystal X-ray structural refinements were made at 20'C and 300'C, and additional structural refinements at 20, 525. and 650'C were made on similar material from Panasqueira, Portugal. Single-crystal data showed linear expansivity of the metric dimensions to about 850"C followed by a phase change to muscovite dehydroxylate with increases in the b and c parameters and a decrease in a near 850'C. The mean atomic distances ofthe K polyhedron increased more rapidly than those for the other polyhedra as temperature increased. The result shows that (l) the K-O(2) bond is longer than KO(l) and K-O(3) at each temperature and (2) the K4(2) bond distance [2.867(3) A at 20'Cl expands with temperature more rapidly [with a mean thermal-expansion coefficient (MTEC) of 5.41 than the other two interlayer bonds tK-O(l): 2.832(3) A at 20'C, MTEC : 4.7; K-O(3): 2.844(3) A at 20'C, MTEC : 4.51. It is concluded that the proton position weakens (lengthens) the K4(2) bond relative to K-O(l) and K-O(3) and that a preferred path for dehydroxylation results. Misfit between the tetrahedral and octahedral sheets is not a factor in thermal decomposition, since the tetrahedral rotation angle is about 8.5" at 950"c. Thermal analysis (rce, orc) indicated a very broad dehydration peak, interpreted as two ovedapping and poorly resolved dehydration peaks at apparently 550 and 750'C on the basis ofcomparison to pyrophyllite. This result suggests that dehydroxylation is not a homogeneous process. A model for dehydroxylation of muscovite was developed from Pauling bond-strength summation calculations. The strength of the AI-OH bond is greatly affected by the coordination number of neighboring polyhedra. When neighboring polyhedra are in octahedral coordination, the hydroxyl group is lost at lower temperatures than when neighboring polyhedra are in fivefold coordination (after partial dehydroxylation). This efect results from the distribution ofoversaturated apical oxygens that affect also the proton position and the AI-OH bond strength. The model is applicable to pyrophyllite and similar dioctahedral 2: I layer silicates and is supported by previously reported infrared, Nun, and rnna data.

/pdf/muscovite-dehydroxylation-high-temperature-studies-mreqwxuel6.pdf

Muscovite dehydroxylation; high-temperature studies

In this review article, the state-of-the-art of calcium orthophosphate-based biocomposites and hybrid biomaterials suitable for biomedical applications is presented. This subject belongs to a rapidly expanding area of science and research, because these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. The review starts with an introduction to locate the reader. Further, general information on composites and hybrid materials including a brief description of their major constituents are presented. Various types of calcium orthophosphate-based bone-analogue biocomposites and hybrid biomaterials those are either already in use or being investigated for various biomedical applications are then extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those with nanosized calcium orthophosphates, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using calcium orthophosphate-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the review also examines the critical issues and scientific challenges that require further research and development.

/pdf/calcium-orthophosphate-based-biocomposites-and-hybrid-1ltrx5hb43.pdf

Calcium Orthophosphate-Based Biocomposites and Hybrid Biomaterials

The crystal structure of muscovite dehydroxylate

Effect of bone-like layer growth from culture medium on adherence of osteoblast-like cells

The structure-controlled hydroxyapatite/zirconia (HAp/ZrO 2 ) composites were fabricated. At first, cylindrical hydroxyapatite (HAp) samples were prepared by the extrusion process, and then the extruded HAp cylindrical samples were coated with 3 mol% of Y 2 O 3 partially stabilized ZrO 2 slurry, dried and aligned unidirectionally to form a composite bulk. The volume fraction of ZrO 2 in the HAp/ZrO 2 composite was estimated to be about 23 vol%. Bulk density and bending strength of the composites increased with sintering temperature. Fracture energy of HAp/ZrO 2 composite sintered at 1350 °C was approximately 1.6 times higher than that of monolithic HAp. Although the bending strength of HAp/ZrO 2 composite prepared in this study was relatively low, it exhibited high fracture energy than HAp monolithic and a non-brittle fracture behavior was obtained without using fiber as the reinforcement.

Fabrication of structure-controlled hydroxyapatite/zirconia composite

高温型コーディエライト (Mg2Al4Si5O18) の3種類の構成原子の一部を他の原子で置換し, その置換による結晶格子の熱膨張の変化を高温粉末X線回折法により研究した. 各々の置換により熱膨張特性は特徴的な変化を示し, 更に熱膨張の異方性や線膨張係数の低減も可能なことが明らかになった. 主要な結果を要約すると次のようになる.MgをFeあるいはMnで置換すると, a軸の格子定数 (a0) は大きくなるがc0は小さくなる. この置換によりa軸方向の小さな正の熱膨張は更に小さくなり, c軸方向の負の熱膨張は正の方へ移行する.AlをGaで置換すると, a0及びc0いずれも大きくなる. この置換固溶体の格子定数の再現性は非常に悪く, 合成の度ごとに大きく異なる. この置換による熱膨張特性の変化は, 前述のFeやMnの置換固溶による変化に類似している.SiをGeで置換すると, a0及びc0いずれも直線的に大きくなる. この置換によりc軸方向の負の熱膨張は負の方向に大きくなるが, a軸方向の熱膨張は固溶量により複雑に変化する.

https://www.jstage.jst.go.jp/article/jcersj1950/94/1087/94_1087_344/_pdf

Thermal Expansion of High Cordierite and Its Solid Solutions

In order to prepare an inorganic antimicrobial agent with a biocompatibility, we have attempted synthesis of beta-tricalcium phosphate( 3 -TCP) doped with silver using a solid-state reaction method, and have investigated the solubility and the bactericidal activity to Escherichia coli or Staphylococcus aureus of the obtained products. 0 TCP solid solutions were formed by reaction of the mixture of (3 -TCP and silver ion. The Cat} ion in 3 -TCP was replaced with silver ion of up to 10 mol%. It was considered that Ca2+ ion and vacancy located Ca(4) site in 3 -TCP structure were displaced by two silver ions. The products doped with silver ion showed a high bactericidal activity and their antimicrobial effects increased with increase of the amount of silver ion. In order to change the bactericidal activity of 3 -TCP doped with silver ion, further more, alkali metal ion was added to ƒÀ-TCP together with silver ion. As the result, alkali metal ion also replaced Ca2+ ion, and formed the substituted solid solution that is similar to silver ion. The bactericidal activity of 13 -TCP doped with silver and potassium ions was increased and that of ƒÀTCP doped with silver and lithium ions was decreased. This depended on the solubility of the obtained TCP solid solution. By means of ESR evaluation using a spin-trap reagent, we found that superoxide radicals was generated from 3 -TCP doped with silver ion by UV irradiation, and considered that 3 TCP doped with silver ion has both an antimicrobial effect that was generated by photo irradiation and an antimicrobial effect that was caused by the dissolved silver ion.

Shigekazu Udagawa

Papers

The crystal structure of muscovite dehydroxylate

Effect of bone-like layer growth from culture medium on adherence of osteoblast-like cells

Fabrication of structure-controlled hydroxyapatite/zirconia composite

Thermal Expansion of High Cordierite and Its Solid Solutions

Antimicrobial Properties and Synthesis of Tricalcium Phosphate Doped with Alkali Metal and Silver Ions