A history of calcium orthophosphates (CaPO4) and their biomedical applications.

The historical development of a scientific knowledge on calcium orthophosphates (CaPO4) from 1770-s till 1950 is described. Many forgotten and poorly known historical facts and approaches have been extracted from old publications and then they have been analyzed, systematized and reconsidered from the modern point of view. The chosen time scale starts with the earliest available studies of 1770-s (to the best of my findings, CaPO4 had been unknown before), passes through the entire 19th century and finishes in 1950, because since then the amount of publications on CaPO4 rapidly increases and the subject becomes too broad. Furthermore, since publications of the second half of the 20th century are easily accessible, the substantial amount of them has been already reviewed by other researchers. The reported historical findings clearly demonstrate that the substantial amount of the scientific facts and experimental approaches has been known for very many decades and, in fact, the considerable quantity of relatively recent investigations on CaPO4 is just either a further development of the earlier studies or a rediscovery of the already forgotten knowledge.

Calcium orthophosphates (CaPO4): Occurrence and properties.

The present overview is intended to point the readers' attention to the important subject of calcium orthophosphates (CaPO4). This type of materials is of the special significance for the human beings because they represent the inorganic part of major normal (bones, teeth and antlers) and pathological (those appearing due to various diseases) calcified tissues of mammals. For example, atherosclerosis results in blood vessel blockage caused by a solid composite of cholesterol with CaPO4, while dental caries (tooth decay) and osteoporosis (a low bone mass with microarchitectural changes) mean a partial decalcification of teeth and bones, respectively, that results in replacement of a less soluble and harder biological apatite by more soluble and softer calcium hydrogenorthophosphates. Due to the compositional similarities to the calcified tissues of mammals, CaPO4 are widely used as biomaterials for bone grafting purposes. In addition, CaPO4 have many other applications. Thus, there is a great significance of CaPO4 for the humankind and, in this paper, an overview on the current knowledge on this subject is provided.

Green chemical synthesis of calcium phosphate bioceramics.

A standard preparation technique of the graft relevant calcium phosphates (which includes the dissolution of watersoluble compounds containing calcium cations and phosphate anions, the slow addition of one solution into another under alkaline pH, followed by aging, suspension separation, washing off, drying and sintering at elevated temperatures) has been reconsidered from an environmental point of view. The entire process has been simplified to a single stage, and a number of intermediate stages have been excluded without influencing the quality of the final products. In this report, we launch a new environmentally friendly preparation technique of calcium phosphate bioceramics for potential use as bone grafts.

A first approach to in vitro simulation of vascular calcification by the controlled crystallization of poorly crystalline calcium phosphates onto porous cholesterol.

A first approach to in vitro simulation of vascular calcification was elaborated. Vascular calcification was simulated by a slow crystallization of a non-stoichiometric poorly crystallized carbonateapatite from Kokubo's revised simulated body fluid (rSBF) on the surface of a porous pellet made of pure cholesterol. To achieve this, the crystallization experiments were performed under strictly controlled conditions (similar to physiological ones) provided by a constant-composition double-diffusion (CCDD) device. To obtain an even closer match to in vivo conditions, rSBF was enriched by the addition of glucose and bovine serum albumin (BSA) in physiological amounts. Precipitation took place on the surface of cholesterol and the precipitates consisted of poorly crystalline non-stoichiometric, sodium- and magnesium-containing carbonateapatite.

Precipitation of carbonateapatite from a revised simulated body fluid in the presence of glucose.

Revised simulated body fluid (rSBF) was modified by the addition of glucose in a physiological amount. The influence of this compound on calcium phosphate crystallization from supersaturated solutions equal to 4 x rSBF ionic concentrations was studied under physiological conditions (solution pH=7.35-7.40, temperature 37.0 +/- 0.5 degrees C). The experiments were performed in both plastic vessels (fast-uncontrolled precipitation) and in a constant-composition double-diffusion (CCDD) device (slow precipitation under strictly controlled conditions). Solutions used had different concentrations of hydrogencarbonate ions and with or without Hepes buffer. Regardless of the experimental conditions chosen, glucose was found to have a negligible influence on calcium phosphate crystallization from rSBF, while hydrogencarbonate ions had a strong influence on the structure and chemical composition of the precipitates. (Journal of Applied Biomaterials & Biomechanics 2003; 1: 200-7).

Is there a chemical interaction between calcium phosphates and hydroxypropylmethylcellulose (HPMC) in organic/inorganic composites?

Solid composites of calcium phosphates and hydroxypropylmethylcellulose (HPMC) were prepared at temperatures of 121 degrees C. Three biologically relevant calcium phosphates were studied: CaHPO(4). 2H(2)O (DCPD), calcium deficient apatite (CDA), and biphasic calcium phosphate (BCP). Properties of the solid composites obtained were studied with FTIR, X-ray diffraction, and SEM techniques. Special attention was devoted to seeking a possible chemical interaction between calcium phosphates and HPMC. No interaction was found. Thus, HPMC was proven to have no influence on chemical properties of calcium phosphates.

Chemical transformation of some biologically relevant calcium phosphates in aqueous media during a steam sterilization.

The purpose of this study was to investigate the effect of steam sterilization on some biologically relevant calcium phosphates: CaHPO4 . 2H2O (DCPD), calcium deficient apatite (CDA) and biphasic calcium phosphate (BCP). Suspensions of 0.2 g of each calcium phosphate compound with 5.0 ml of deionized water were prepared and steam sterilized in an autoclave (20 min at 121 degrees C). After sterilization the suspensions were filtered and the dried solids characterized with scanning electron microscopy, IR-spectroscopy and X-ray diffraction. The pH and calcium concentrations of the filtrates were determined with ion selective electrodes. Similar measurements were made with the same samples which were not sterilized. The sterilization procedure was found to result in the dehydration of DCPD and hydration of calcium oxide incorporated into the BCP. Solution pH was observed to change from 7.3 to 5.5 for the solutions in equilibrium with DCPD and from 8.5 to 10.6 for those in equilibrium with BCP. Minor changes both with the solid and liquid phases were found to occur during the steam sterilization of CDA. These results indicate that steam sterilization may have different effects on different calcium phosphate suspensions: it can result in dehydration of DCPD, fast hydration for CaO in BCP, but no significant effect on CDA.