Fabrication of porous calcium phosphates

Prediction of the setting properties of calcium phosphate bone cement

Setting properties of bone substitutes are improved using an injectable system. The injectable bone graft substitutes can be molded to the shape of the bone cavity and set in situ when injected. Such system is useful for surgical operation. The powder part of the injectable bone cement is included of β-tricalcium phosphate, calcium carbonate, and dicalcium phosphate and the liquid part contains poly ethylene glycol solution with different concentrations. In this way, prediction of the mechanical properties, setting times, and injectability helps to optimize the calcium phosphate bone cement properties. The objective of this study is development of three different adaptive neurofuzzy inference systems (ANFISs) for estimation of compression strength, setting time, and injectability using the data generated based on experimental observations. The input parameters of models are polyethylene glycol percent and liquid/powder ratio. Comparison of the predicted values and measured data indicates that the ANFIS model has an acceptable performance to the estimation of calcium phosphate bone cement properties.

Improvement of porous beta-TCP scaffolds with rhBMP-2 chitosan carrier film for bone tissue application

Ceramic materials are osteoconductive matrices extensively used in bone tissue engineering approaches. The performance of these types of biomaterials can be greatly enhanced by the incorporation of bioactive agents and materials. It is previously reported that chitosan is a biocompatible, biodegradable material that enhances bone formation. In the other hand, bone morphogenetic protein-2 (BMP-2) is a well-known osteoinductive factor. In this work we coated porous beta-tricalcium phosphate (beta-TCP) scaffolds with recombinant human BMP-2 (rhBMP-2) carrier chitosan films and studied how they could modify the ceramic physicochemical properties, cellular response, and in vivo bone generation. Initial beta-TCP disks with an average diameter of 5.78 mm, 2.9 mm thickness, and 53% porosity were coated with a chitosan film. These coating properties were studied by X-ray diffraction, Fourier transform-infrared analysis, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray analysis (EDX). Treatment modified the scaffold porous distribution and increased the average hardness. The biocompatibility did not seem to be altered. In addition, adhered C2C12 cells expressed alkaline phosphatase activity, related to cell differentiation toward osteogenic lineage, due to the incorporation of rhBMP-2. On the other hand, in vivo observations showed new bone formation 3 weeks after surgery, a much shorter time than control beta-TCP ceramics. These results suggest that developed coating improved porous beta-TCP scaffold for bone tissue applications and added osteoinductive properties.

Calcium-deficient apatite synthesized by ammonia hydrolysis of dicalcium phosphate dihydrate: Influence of temperature, time, and pressure

In this work, calcium-deficient apatites (CDA) were synthesized by ammonia hydrolysis reaction of dicalcium phosphate dihydrate (DCPD; CaHPO4 x 2 H2O) to obtain biphasic calcium phosphates (BCP) without any extraionic substitution. The influence of three parameters was studied: temperature of the reaction (70 and 100 degrees C), time of the reaction (4 and 18 h), and the pressure (open and closed system). Experiments were made according to a factorial design method (FDM) allowing optimization of the number of samples as well as statistical analysis of results. Moreover, the influence of temperature (until 200 degrees C) was investigated. The crystal size of CDA was determined according to the Scherrer's formula and from Rietveld refinements taking the CDA anisotropy into account. The last method seems to be a reliable method to determine crystallite sizes of CDA, since crystallite sizes of CDA along <00l> and <hk0> directions were accessible. The results describe the hydroxyapatite % (HA%) in BCP by a first-order polynomial equation in the experimental area studied and the HA content was found to increase by raising time and temperature of the reaction. Moreover, the type of reaction system (open/closed vessel) appeared to have little influence on HA%.