Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells.

/pdf/calcium-orthophosphate-based-bioceramics-4c2yzraois.pdf

Calcium Orthophosphate-Based Bioceramics

In the late 1960s, much interest was raised in regard to biomedical applications of various ceramic materials. A little bit later, such materials were named bioceramics. This review is limited to bioceramics prepared from calcium orthophosphates only, which belong to the categories of bioactive and bioresorbable compounds. There have been a number of important advances in this field during the past 30–40 years. Namely, by structural and compositional control, it became possible to choose whether calcium orthophosphate bioceramics were biologically stable once incorporated within the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics—which is able to promote regeneration of bones—was developed. Presently, calcium orthophosphate bioceramics are available in the form of particulates, blocks, cements, coatings, customized designs for specific applications and as injectable composites in a polymer carrier. Current biomedical applications include artificial replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Exploratory studies demonstrate potential applications of calcium orthophosphate bioceramics as scaffolds, drug delivery systems, as well as carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

https://www.mdpi.com/2079-4983/1/1/22/pdf

Calcium Orthophosphates as Bioceramics: State of the Art

Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique.

https://oatao.univ-toulouse.fr/649/1/Vahlas_649.pdf

Principles and applications of CVD powder technology

Calcium orthophosphate bioceramics

XRD and FTIR crystallinity indices in sound human tooth enamel and synthetic hydroxyapatite.

Synthesis of fine AlN powder by a floating nitridation technique using an N2/NH3 gas mixture

Synthesis of fine AlN powder by vapour-phase reaction

Fine AIN powder was synthesized by the vapour-phase reaction of AICl3 and NH3 at 600 to 1100° C, and the particulate characteristics and the deposition features were investigated. The powder deposited near the AlCl3-feeding nozzle included radially-grown particles with columnar crystals. The powder deposited apart from the AlCl3-feeding nozzle consisted of only fine, spherical particles. Vapour-phase reaction at 1100° C produced fine powder, which was characterized by uniform and fine particle size; its distribution width was from 0.1 to 0.3μm, and median diameter was 0.18μm. Deposition area of the powder was affected by the reaction temperature and the temperature profile in the reactor.

Particulate characteristics and deposition features of fine AIN powder synthesized by vapour-phase reaction

Interfacial reaction in a multiple emulsion, which is one of methods for
producing inorganic microspheres, was applied to synthesize hydroxyapatite. The
multiple emulsion was a W/O/W emulsion, made of dipotassium hydrogen phosphate
solution as an inner aqueous phase, benzene as an oil phase, and calcium nitrate solution
as an outer aqueous phase. The reaction was carried out in the multiple emulsion for 24 hours at 
323 K. The crystalline phase was varied with an initial pH of the inner aqueous
phase, and single phase hydroxyapatite was synthesized at an initial pH of 12. The
products were composed of porous microspheres of less than 3  μ m in size. The microspheres were composed of nanospheres of less than 120 nm in size. By
considering the mass balance, it was suggested that each nanosphere was formed in an
inner aqueous phase droplet.

/pdf/synthesis-of-hydroxyapatite-by-interfacial-reaction-in-a-4j66vnyc8r.pdf

Synthesis of Hydroxyapatite by Interfacial Reaction in a Multiple Emulsion

Al 2 O 3 -TiB 2 composites containing 0–50 wt% TiB 2 were prepared by sintering at 1600–1750°C for 15–120 min in a vacuum. Relative density increased with TiB 2 addition from 97% (no TiB 2 ) to about 99% (10–40 wt% TiB 2 ) on sintering at 1750°C for 60 min. TiB 2 behaved as a sintering aid to promote densification by inhibiting rapid grain growth of Al 2 O 3 . Bending strength and microhardness increased with increasing relative density. In particular, microhardness was so improved as to exceed that of Al 2 O 3 and reach 30·1 GPa. Resistivity decreased with increasing TiB 2 content and dropped down to 3 × 10 −2 ω m with 30 wt% TiB 2 .

Isao Kimura

Papers

Synthesis of fine AlN powder by a floating nitridation technique using an N2/NH3 gas mixture

Synthesis of fine AlN powder by vapour-phase reaction

Particulate characteristics and deposition features of fine AIN powder synthesized by vapour-phase reaction

Synthesis of Hydroxyapatite by Interfacial Reaction in a Multiple Emulsion

Sintering and characterization of Al2O3-TiB2 composites