Biomimetic carbonate–hydroxyapatite (HA) nanocrystals have been synthesized by using the sitting drop vapor diffusion technique, for the first time. The method consists of diffusing vapors of an aqueous solution of NH4HCO3 through drops containing an aqueous mixture of (CH3COO)2Ca and (NH4)2HPO4 in order to increase slowly their pH. This synthesis has been performed in a crystallization mushroom, a glass device developed for protein and small molecules crystallization. The concentrations of the reagents, the final pH and the crystallization time have been optimized to produce pure carbonate–HA as a single phase. X‐Ray diffraction, Fourier transformed infrared spectroscopy, and transmission electron microscopy have been utilized to characterize the synthesized carbonated substituted HA crystals which display nanometric dimensions, plate‐like morphology, and low crystallinity degree, closely resembling the inorganic phase of bones, teeth, and many pathological calcifications. This novel method may prove to be suitable for the study of the interactions and/or the co‐crystallization of hydroxyapatite with minute amounts of biomolecules, polymers, or drugs.
Synthetic calcium phosphates exhibit good properties as biomaterials, such as biocompatibility, bioactivity, and osteoconductivity, and they have important applications in the fields of bone tissue engineering and orthopedic therapies. In this work, we performed an extensive characterization of the composite calcium phosphates/silica synthesized in gel by varying the pH and density of the silica solution. As a function of the pH values, brushite, octacalcium phosphate, hydroxyapatite, and monetite crystallization have been obtained, while changing the silica solution density the crystals are covered by different amounts of silica which results differently structured as a function of the pH. These materials have been analyzed using several experimental techniques (X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and field emission scanning electron microscopy). Large brushite crystals present amorphous silica both embedded within them and deposited on the crystal surfaces. The resulting calcium phosphate-silica composite is deposited as a powder, but it can be also easily molded into monolithic forms. The results of this study could be of significance in the field of biomaterials for considerable improvements of performance of bone implants in terms of osteointegration and in possible association to set up calcium phosphates-silica biocomposites.
A new method of increasing the success rate in protein crystallization screening experiments by combining microseeding with counter-diffusion crystallization in capillaries (SCD) is presented. We have investigated the number of crystallization hits obtained with and without microseeding with 10 model proteins. For the cases studied, SCD generally increases the number of hits and is particularly useful when only relatively low protein concentration stocks are available, either because the stocks were prepared for, e.g., vapor diffusion experiments, or because the protein is poorly soluble. In either case, the addition of seeds becomes necessary to overcome the nucleation energy barrier so that crystal growth can take place even when the wave of supersaturation that passes along the capillary is insufficient to promote nucleation.
In this work we have used the sitting drop vapour diffusion technique, employing the "crystallization mushroom" to analyze the evolution of calcium phosphate crystallization in micro-droplets containing high initial concentrations of Ca 2+ and HPO 4 2-. The decomposition of NH 4 HCO 3 solution produces vapours of NH 3 and CO 2 which diffuse through the droplets containing an aqueous solution of Ca(CH 3 COO) 2 and (NH 4 ) 2 HPO 4 . The result is the increase of pH by means of the diffusion of NH 3 gas and the doping of the calcium phosphate with CO 3 2-ions by means of the diffusion of CO 2 gas. The pH of the crystallization process is monitored and the precipitates at different times are characterized by XRD, FTIR, TGA, SEM and TEM techniques. The slow increase of pH and the high concentration of Ca 2+ and HPO 4 2-in the droplets induce the crystallization of three calcium phosphate phases: dicalcium phosphate dihydrate (DCPD, brushite), octacalcium phosphate (OCP) and carbonate-hydroxyapatite (HA). The amount of HA nanocrystals with needle-like morphology and dimensions of about 100 nm, closely resembling the inorganic phase of bones, gradually increases, with the precipitation time up to 7 days, whereas the amount of DCPD, growing along the b axis, increases up to 3 days. Then, DCDP crystals start to hydrolyze yielding OCP nanoribbons and HA nanocrystals.
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