Characterization of nanoparticles of calcium sulfate in bone regeneration
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Objectives. Bone regeneration in critical-size defects occurs very slowly without the aid of osteoconductive or osteoinducing agents that fill in the defect, inducing bone tissue growth and preventing soft tissue down-growth within the defect. Nanoparticles of calcium sulfate (nCS) have tremendous potential for use as a ceramic matrix, scaffold and/or vehicle for delivering growth factors for osseous regeneration in a variety of clinical situations. The purpose of this study was to characterize the nanoparticulate calcium sulfate (nCS) obtained with a cryo-vacuum technique. Methods. The composition, structure, morphology, physical properties, and biocompatibility of the nanoparticulate calcium sulfate were examined by Scanning Electron Microscopy (SEM); Energy Dispersive X-ray Spectroscopy (EDS); transmission electron microscope (TEM); Brunauer, Emmett and Teller Method (BET); Fourier-Transform Infrared Spectroscopy (FTIR); Thermogravimetric Analysis (TGA); X-ray Diffraction (XRD); Vickers hardness test; and MTT (3-(4, 5-dimathyl-thiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) assay. Samples used for Vickers hardness and MTT tests were created in a standard size and shape so that the surface available for force loading or cell attachment and proliferation was always identical. Vickers hardness and MTT data were analyzed by descriptive statistics, one-way ANOVA, followed by the Scheffé test (α = 0.05). Results. SEM and TEM images of nCS dihydrate powder showed that the powder consisting of aggregates of closely arranged acicular crystals were linked together to form a narrow network. These acicular crystals were approximately 20-50 nm in width, 400-600 nm in length and approximately 80-100 times smaller than conventional calcium sulfate. SEM images of nCS β-hemihydrate showed that the powder contained multiple cleavage fragments of rod-shaped crystals that were approximately 30-60 nm in width and closely arranged and packed to form several aggregates. EDS spectra confirmed the presence of calcium (Ca) and Sulfur (S) within the nCS samples. FTIR and XRD analyses also confirmed the presence of nCS dihydrate, and nCS β-hemihydrate. TGA revealed that the proper temperature to make the hemihydrate form of nCS was at about 125° ∼ 145°C. BET results showed that the surface area of the nCS was about 10 times greater than that of the conventional micron-sized form. In addition, Surface microhardness testing showed that the nCS was stronger than conventional CS while the MTT results confirmed the safety and biocompatibility of nCS. Conclusions. The results showed the nCS is safe and biocompatible. They also demonstrated that nCS may have several advantages (i.e. higher surface area for osteoblast attachment and proliferation and growth factor adsorption, as well as superior mechanical strength for optimal osteoconductivity and resistance to fractures) over traditional calcium sulfate for use as an osseous grafting material. However, future research and studies are needed to evaluate the efficacy and the ability of a nano-calcium sulfate biomatrix to carry biologically active factors such as Platelet-derived Growth Factor (PDGF) or those present in Platelet-Rich Plasma (PRP).