Influence of Na+ on the Stoichiometry of Carbonated Hydroxyapatite Obtained by the Hydrolysis of Octacalcium Phosphate

Atomic force microscopy imaging of classical and nonclassical surface growth dynamics of calcium orthophosphates

This review highlights in situ atomic force microscopy observations of the classical and nonclassical surface growth dynamics of calcium orthophosphates.

Synthesis methods for nanosized hydroxyapatite with diverse structures

Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Isolation and Osteogenic Differentiation of Rat Periosteum-derived Cells

Selection of appropriate cultures having an osteogenic potential is a necessity if cell/biomaterial interactions are studied in long-term cultures. Osteoblastic cells derived from rat long bones or calvaria have the disadvantage of being in an advanced differentiation stage which results in terminal differentiation within 21 days. In this regard, less differentiated periosteum-derived osteoprogenitors could be more suitable.Periosteum-derived cells were isolated from the tibiae of adult Wistar rats (n = 12). The osteogenic potential with regard to alkaline phosphatase activity, morphology, nodule formation and mineralization was studied by culturing them in an osteogenic medium for up to 4 months.Seventy-five percent of the cultures (n = 9) did not show any increase in alkaline phosphatase activity nor nodule formation during long-term culture for up to 4 months. Nevertheless, in 25% of the cultures, alkaline phosphatase activity started from negligible (<5 mM pNP/mg protein) and increased towards approximately 50 mM pNP/mg protein. Three-dimensional nodule formation was observed at passages 3-5. In further passages (P5-P7), nodule formation capacity decreased and a diffuse mineralization pattern was observed.Suitable cultures with osteogenic capacity, can be selected at early passages based on the presence of cuboidal cells. These cells have the advantage of retaining their osteogenic potential even after prolonged cultivation (6-7 passages) before final differentiation occurs. Although periosteal cells are suitable for long term in vitro evaluation of biomaterials, the isolation and selection is time consuming. Hence, a more appropriate source to study cell/biomaterial interactions should be more convenient.

Continuous crystalline carbonate apatite thin films. A biomimetic approach

In contrast to extensive studies on hydroxyapatite thin films, very little has been reported on the thin films of carbonated apatite (dahllite). In this report, we describe the synthesis and characterization of a highly crystalline dahllite thin film assembled via a biomimetic pathway. A free-standing continuous precursor film of carbonated calcium phosphate in an amorphous phase was first prepared by a solution-inhibited templating method (template-inhibition) at an air-water interface. A stearic acid surface monolayer acted as the template, while a carbonate-phosphate solution composed a binary inhibition system. The precursor film formed at the air/water interface was heated at 900 degrees C and transformed into a dense crystalline film that retained the overall shape of the precursor. The crystalline phase was characterized by XRD and IR to be a single-phase carbonate apatite, with carbonate substitutions in both type A (OH-) and type B (PO4(3-)) lattice positions.

Conversion of octacalcium phosphate in calcium phosphate cements

This study investigated the in vitro conversion reaction in calcium phosphate cements (CPCs) containing octacalcium phosphate (OCP) as one of the reagents. OCP is known to be a precursor for apatite formation in vivo. The reaction products were characterized using infrared spectroscopy and X-ray diffraction. Although the conversion of OCP into hydroxyapatite is thermodynamically favorable, OCP only yields apatite formation in CPC provided it is combined with a highly soluble Ca(2+) and OH(-) releasing reaction partner. In this respect, tetracalcium phosphate is a promising compound. Adding small amounts of monocalcium phosphate monohydrate can stimulate the setting through intermediate brushite formation. The preparation method of OCP might drastically affect the performance of the cement. The reaction path of the setting of these CPC probably does not conform to the singular point principle described in the literature, and an in situ hydrolysis of OCP to apatite is conceivable. Simulation of apatite formation using OCP as the precursor and/or seed in CPC might be beneficial for some biomedical applications.