This study aimed at preparing and studying the properties of nanoparticles of calcium phosphate (nCaP) with Ca/P ratios ranging from 1.0 to 1.67 using a spray-drying technique. Micro-structural analyses suggested that the nCaPs with Ca/P ratios of 1.67 to 1.33 were nano-sized amorphous calcium phosphate (ACP) containing varying amounts of acid phosphate and carbonate. The nCaP with Ca/P ratio of 1 contained only nano-sized low crystalline dicalcium phosphate (DCP). BET measurements of the nCaPs showed specific surface areas of (12 ± 2 to 50 ± 1) m(2)/g, corresponding to estimated equivalent spherical diameters of (38 to 172) nm. However, dynamic light scattering measurements revealed much larger particles of (380 ± 49 to 768 ± 111) nm, owing to agglomeration of the smaller primary nano particles as revealed by Scanning Electron Microscopy (SEM). Thermodynamic solubility measurements showed that the nCaPs with Ca/P ratio of 1.33 - 1.67 all have similar solubility behavior. The materials were more soluble than the crystalline hydroxyapatite (HA) at pH greater than about 4.7, and more soluble than β-tricalcium phosphate (β-TCP), octacalcium phosphate (OCP) and DCP at pH above 5.5. Their solubility approached that of α-tricalcium phosphate (α-TCP) at about pH 7. These nCaPs, which cannot be readily prepared by other currently available methods for nanoparticle preparation, have potential biomedical applications.

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Preparation and Properties of Nanoparticles of Calcium Phosphates With Various Ca/P Ratios

A new route, based on the use of ionic calcium phosphate cements, has been developed to synthesize hydroxyapatite. Cements were prepared from tetracalcium phosphate, α–tricalcium phosphate, phosphoric acid, strontium nitrate, and water. They were then mixed and shaped. Cements with various amounts of strontium and different (Ca + Sr)/P atomic ratios were prepared. All the materials obtained were coherent and solid. When the amount of strontium was low, mixed hydroxyapatite was obtained at low temperatures. Mixed calcium strontium apatite was obtained after heating. This original method can be of interest in various fields such as biomaterials or the storage of radioactive waste.

Preparation of calcium strontium hydroxyapatites by a new route involving calcium phosphate cements

Nano-particles of calcium and phosphorous compounds are made in a highly pure generally amorphous state by spray drying a weak acid solution of said compound and evaporating the liquid from the atomized spray in a heated column followed by collection of the precipitated particles. Hydroxyapatite (HA) particles formed by such apparatus and methods are examples of particle manufacture useful in bone and dental therapies. Dual nozzle spraying techniques are utilized for generally insoluble compounds.

Nanostructured bioactive materials prepared by dual nozzle spray drying techniques

Characterizations of Biocompatible and Bioactive Hydroxyapatite Particles

Osteoporotic distal radius fractures are a public health problem that medical osteoporosis treatment is unable to check. We have described a bone substitute method to improve mechanical properties in bone. Our current study aims at improving the technique by maximising the filling of the distal radius. Cavities were created by curettage in the distal radius using a styloid process approach in ten randomly selected wrists from the sample population of ten cadavers. All radii were injected percutaneously with calcium phosphate cement. Cement quantities injected were calculated and corrected for observed cement leakage. Our results show that distal radius curettage before cementoplasty can double the amount of calcium phosphate cement injected. Prevention of osteoporotic distal radius fractures by cementoplasty seems a promising technique. Slowly absorbed micro-porous biomaterial use is preferable in long-term preventive treatment. Nevertheless, in the future, this technique should apply in specific cases, such as medical osteoporosis treatment failure with contra-lateral wrist fracture.

J.C. Heughebaert

Papers

Optimization of a Hydraulic Calcium Phosphate Cement